Wednesday, May 31, 2006

Last of the most 'beautifully interesting' birds (part III)

This is the third, and last, part of the 'beautiful birds' meme. If you've read the previous parts (see Part I here and Part II here), I've converted the idea from 'beautiful birds' to 'beautifully interesting' birds.

Anyway, let's get on with it.

8. African harrier-hawk Polyboroides typus*

* I’m only discussing P. typus here, but there is another extant species in the genus (Madagascan P. radiatus).

Sometimes called the Gymnogene, Polyboroides is a gracile, naked-faced raptor with grey and black plumage, but best known for the so-called double-jointedness present in its intertarsal joints. The foot can actually bend both anteriorly and posteriorly (that is, the foot can be hyperextended as well as flexed), which needless to say is (almost) unique (read on). This is easy to see in dead or anaesthetized specimens, but it’s reportedly hard to observe in action in living birds. Cooper (1980) wrote that, after five months of observing captive specimens, the notebook was still being filled with such comments as ‘I can’t really fathom what is the ‘double-jointedness’ they refer to in the books’.

However, the behaviour has now been well documented and filmed, and the birds use this incredible flexibility to extricate lizards, insects and other prey from fissures in rocks, and nestling birds from their nests. You might presume, as I did, that Polyboroides has a unique sort of intertarsal joint, perhaps with the trochlear surfaces of the distal tibiotarsus wrapping onto the posterior surface of the bone as well as the anterior surface. But according to Cooper (1980) ‘in anatomical structure there is no significant difference between [the intertarsal joints of Polyboroides] and the corresponding joints of Kestrel, Tawny eagle or Black kite’ (p. 98). Err, gosh. I haven’t yet checked to see if there are any more recent studies of harrier-hawk ankles (let me know if you know better), but I find that pretty amazing. As I like to say sometimes 'Anatomy is not destiny' (not my quote, I stole it from a paper on armadillos).

Polyboroides is ‘beautifully interesting’ for two other reasons. Firstly, it’s amazingly similar to a South American raptor, the Crane hawk Geranospiza caerulescens. Geranospiza looks pretty much the same as Polyboroides, occupies the same ecological niche, behaves in the same manner, and even has the same bizarrely mobile intertarsal joint. Understandably, the two genera have often been regarded as each other’s closest relatives (e.g. Brown 1997). But…. they’re also different in many subtle anatomical details (Burton 1978), and consequently there’s been a long-standing debate as to whether they’re related or not. While unfortunately few phylogenetic studies include both species together, a comprehensive recent DNA-based phylogeny found the two to be well apart, with Polyboroides down with Old World vultures and honey buzzards, while Geranospiza was in the buteonine clade that also includes Buteo (of course) and Leucopternus (Lerner et al. 2005). This study is pretty compelling and the phylogeny near-conclusive. Polyboroides and Geranospiza thus represent striking, amazing instances of convergent evolution, one of the best examples of this among birds.

Incidentally, there's a second raptor that also evolved striking convergence with Polyboroides, but it's a fossil form and I'll have to talk about it another time.

Secondly, Polyboroides is interesting for being one of the most basal members of Accipitridae (the hawk-eagle-Old World vulture family). As hinted at in the previous paragraph, morphological and DNA-based phylogenies of Accipitridae tend to agree that one of the most basal clades in the group is that which includes Old World vultures and honey buzzards. Recent studies agree that Polyboroides is in this clade, and within it one of the most basal members (Holdaway 1994, Lerner et al. 2005). That makes it one of the most basal members of the whole of the accipitrid radiation. So you have there a raptor that (1) does something anatomically freaky, (2) does that anatomically freaky thing employing a mechanism that no-one yet properly understands, (3) exhibits uncanny, striking convergence with an unrelated raptor on another continent, and (4) is one of the most archaic, phylogenetically basal members of its group.

9. Kakapo Strigops habroptilis

‘… [it] clambers up and down trees because it cannot fly … it purrs like a cat and smell like a posy of fragrant flowers … it allows itself to be picked up and handled without demur or apparent concern’ (Vietmeyer 1992, p. 69).

Sometimes called the Owl parrot, the Kakapo was first described by John Gray in 1845. Everything about kakapos is extraordinary. Remember that it’s a parrot while you read the following. A large nocturnal (!), cryptically-coloured (!!) terrestrial (!!!) bird, endemic to New Zealand, the kakapo is a specialized foliage-eater that seems to live on a metabolic knife-edge, rather like the Giant panda. Successful breeding is limited only to those years when mass fruitings of podocarps occur. This worked fine in a New Zealand where there were lots of podocarps and lots of kakapos (and indeed fossils show that kakapos were formerly abundant), but environmental destruction caused by humans meant that kakapos were forced into suboptimal areas where life was even harder than before. Combined with this was devastating predation from domestic cats, stoats and rats. Consequently, as is well known, kakapos have become extinct on the mainland and only survive on managed offshore islands where introduced rats and other predators have been eliminated (Vietmeyer 1992, Clout 2001). In 2001 there were 62 individuals. Worldwide.

Apparently in order to bulk-process the poor-quality vegetation it eats, the Kakapo has evolved voluminous guts, and accordingly a larger overall body size. It has hence become a giant among parrots (with big males reaching 3.6 kg), and is the largest extant species. Conventionally stated to be flightless, it is in fact capable of gliding, so this is not strictly true. Certainly it mostly walks places however, and individuals create well-worn trails in the mountainous forest where they live. Distinctively ‘chewed’, compressed fragments of vegetation hang from the plants adjacent to these trails, and kakapos leave both compact cylindrical droppings and white traces of uric acid on the trails. The uric acid streaks apparently ‘have a herb-like smell when fresh’ (Juniper & Parr 1998, p. 372).

Uniquely among parrots, kakapos are lek breeders, with males booming out loud calls from suitable topographical hollows, and these calls can be heard from about 1 km away. Cryptic plumage and nocturnal habits don’t make much sense in an environment devoid of predators, so the fact that kakapos possess these traits suggests that there were once predators able to kill them. Now we know that New Zealand did possess such predators: endemic giant eagles and large harriers (see New Zealand eagle blog).

10. Eurasian oystercatcher Haematopus ostralegus

Finally, one of my most favourite birds is the extraordinary, charismatic, beautifully interesting oystercatcher. One of ten extant haematopodid species, it sports pied plumage, pinkish legs, and has the heaviest bill of any extant wader. One of the most interesting things about oystercatchers is the fact that they exhibit resource polymorphism, with some populations exhibiting multiple different forms (Skúlason & Smith 1995). ‘Stabbers’ feed by jabbing their laterally compressed bill tips in between the valves of a mussel’s shell, while ‘hammerers’ crack open mussel shells by pounding on them. Some hammerers only break in to the shell on its dorsal side, while others only break in to the ventral side. Others attack only the left side valve, and others only the right valve. Others are worm specialists with pointed tweezer-like bill tips.

First discovered by M. Norton-Griffiths during the 1960s (and extensively studied by a great many ornithologists since then), resource polymorphism among oystercatchers was initially thought to be learnt by the birds from their parents (and not genetically determined). It now seems that things are far more flexible, with individuals switching from one behaviour to the other over the years. It’s been said that juveniles can’t really learn how to handle prey from their parents given that many of them are reared inland and are abandoned by their parents before they ever get to the coast (Sutherland 1987). However, some oystercatcher adults spend up to a year teaching their young how to exploit prey: in fact a photo in Attenborough’s The Life of Birds shows an adult opening a shell while a juvenile, at its side, watches with apparent interest.

It seems that it’s the behavioural flexibility that controls bill shape, rather than the other way round, and another remarkable thing about oystercatchers is how specialized their bills are for coping with wear. Uniquely among waders, the bill grows at a jaw-dropping 0.4 mm per day (that’s three times faster than the growth rate of human fingernails). This rapid growth means that the bill can change shape very rapidly if the feeding style is changed, and captive individuals that were forced to switch from bivalve-feeding to a diet of lugworms changed from having chisel-shaped bills to tweezer-like bills within 10 days. A-maz-ing.

Given that oystercatchers are fairly large and powerful for waders, and able to smash open bivalve shells, it follows that they are formidable and potentially dangerous to other birds. Certainly males will chase off raptors when defending nesting females. I recall reading accounts of them caving in the heads of other waders during territorial disputes, but unfortunately I can’t remember where (a common problem, despite my well organized library). Most aggressive interactions recorded between oystercatchers, and between oystercatchers and other waders, involve piracy, and in fact some birds obtain most of their food this way, ‘attacking other birds at an average of five minute intervals during low tide’ (Hammond & Pearson 1994, p. 61). As much as 60% of the food of some individuals is obtained by piracy. Finally, oystercatchers are incredibly long-lived, with the record-holder dying at age 35! Now, come on, that is a truly extraordinary bird.

Tomorrow (June 1st) is viva day. Stay tuned for the news.

PS - for the latest news on Tetrapod Zoology do go here.

Refs - -

Brown, L. H. 1997. Birds of Prey. Chancellor Press, London.

Burton, P. J. K. 1978. The intertarsal joint of the harrier-hawks Polyboroides spp. and the Crane hawk Geranospiza caerulescens. Ibis 120, 171-177.

Clout, M. 2001. Where protection is not enough: active conservation in New Zealand. Trends in Ecology & Evolution 16, 415-416.

Cooper, J. E. 1980. Additional observations on the intertarsal joint of the African harrier-hawk Polyboroides typus. Ibis 122, 94-98.

Hammond, N. & Pearson, B. 1994. Waders. Hamlyn, London.

Holdaway, R. N. 1994. An exploratory phylogenetic analysis of the genera of the Accipitridae, with notes on the biogeography of the family. In Meyburg, B.-U. & Chancellor, R. D. (eds) Raptor Conservation Today. WWGBP/The Pica Press, pp. 601-649.

Juniper, T. & Parr, M. 1998. Parrots. Pica Press, Mountfield.

Lerner, H. R. L. & Mindell, D. P. 2005. Phylogeny of eagles, Old World vultures, and other Accipitridae based on nuclear and mitochondrial DNA. Molecular Phylogenetics and Evolution 37, 327-346.

Skúlason, S. & Smith, T. B. 1995. Resource polymorphisms in vertebrates. Trends in Ecology and Evolution 10, 366-370.

Sutherland, W. J. 1987. Why do animals specialize? Nature 325, 483-484.

- . 2002. Science, sex and the kakapo. Nature 419, 265-266.

Vietmeyer, N. D. 1992. The salvation islands. In Calhoun, D. (ed) 1993 Yearbook of Science and the Future. Encyclopaedia Brittanica Inc (Chicago), pp. 60-75.

Monday, May 29, 2006

What I saw at the zoo today

This is going to be one of the most unusual posts I will ever produce. Why? Because it is going to include (comparatively) little text, and is going to consist predominantly of pictures. Today we went to Marwell Zoological Park (Hampshire, England), and I'm pretty excited about the new animals we saw. More on those in a minute. In the world of global wildlife conservation, Marwell is an important place, having played key roles in captive breeding and/or reintroduction schemes for Takhi Equus przewalskii (the equid formerly known as Przewalski's horse), Amur tiger Panthera tigris altaica (the felid formerly known as the Siberian tiger) and Scimitar-horned oryx Oryx dammah. They've also bred Okapis Okapia johnstoni, White rhinos Ceratotherium simum, and many other species. Visit the Marwell Conservation site if you're interested.

Like most people interested in animals, I don't really like animals being kept in captivity, but my philosophy on zoos is that they're an integral part of wildlife conservation. For a good recent review of why zoos are so important see Bertram (2004). Until recently we were members of Marwell Zoological Society, but financial constraints have resulted in a lapse of our membership. Anyway, it rained a lot today, and it even hailed at one point. But this isn't such a bad thing if you want to watch captive animals, as it actually means that they do things you don't normally see. Two of the Amur tigers were incredibly playful, for example, chasing around and tussling like kittens, and it isn't very often that you see that. The giraffes obviously wanted to get out of the rain, and (as you can see from this photo), all 13 individuals stood patiently next to the enclosure gate, waiting to be let into their house. I've never been able to get this many giraffes in the same photo before.

What about those new animals I mentioned? I'll start with the most amazing [images at top left and below]. Yes, it's a Takin Budorcas taxicolor, a bizarre goat-antelope from the bamboo forests of the Himalayas. I've never seen one before, and I never even expected to see one. They had two individuals (male and female: the male is shown at top, the female below). They're odd. They look somewhat like other goat-antelopes, like tahr and serow, but they have a really slow, deliberate and muscular-looking gait, plus proportionally massive, blunt dew claws. These apparently help them grip to rocks when they're climbing. The proximal parts of their limbs were way more stocky that is usual for an artiodactyl, giving them an almost bear-like shape.

Also new to me were Vicuna Vicugna vicugna, a small Andean camelid with rodent-like incisors. They somewhat resemble Guanaco Lama guanicoe but are smaller and lack callosities on the medial sides of the forelimbs (if I remember correctly). Their fur looks shorter and less woolly, and their gait and the way they hold their neck while walking is distinctive too. This now means that I've seen all extant camelid species (all in captivity, of course), though note that the species-level taxonomy of South American camelids is a little muddled (Kadwell et al. 2001). The only photo I got shows one of the animals peeking out from its house (at left).

Finally, I was amazed and delighted to discover a captive individual of one of my favourite mammals, the Giant anteater Myrmecophaga tridactyla. Everything about anteaters is fascinating: their ecology, behaviour, anatomy, functional morphology and evolution. Unfortunately the animal was asleep, and, as you can see, the only photos I have are rubbish as the flash bounced off the glass. It slept in the posture described in the books: curled up, with the tail wrapped over the limbs and snout. Cool.

Other neat animals I saw were Fossa Cryptoprocta ferox, but I've spent hours watching these during various visits and definitely don't count them as new. We got some good photos of the male individual, including of it scent-marking a tree stump. Then there were the porcupines, hyraxes, marabou storks, okapis, snow leopards, dwarf crocodiles, peccaries, pygmy hippos and rheas. Thoughts on many of these species will follow one day, perhaps. Right now I need to go do some cooking.

PS - for the latest news on Tetrapod Zoology do go here.

Refs - -

Bertram, B. 2004. Misconceptions about zoos. Biologist 51, 199-206.

Kadwell, M., Fernandez, M., Stanley, H. F., Baldi, R., Wheeler, J. C., Rosadio, R. & Bruford, M. W. 2001. Genetic analysis reveals the wild ancestors of the llama and the alpaca. Proceedings of the Royal Society of London B 268, 2575-2584.

Saturday, May 27, 2006

More 'beautifully interesting' birds (part II)

In a desperate effort to complete the list of my ten most ‘beautifully interesting’ bird species, part of the 10 bird meme (see previous blog), here are some more. I’ll reach the full ten eventually.

5. Ground tit Pseudopodoces humilis

If convergence is one of the most interesting evolutionary phenomena, then the Ground tit should become a text-book example of it, on par with thylacines vs wolves and ichthyosaurs vs dolphins. Described in 1871 by A. Hume, the Ground tit is a weak-flying brown passerine of the Tibetan plateau, often superficially likened to a wheatear. But for most of the time that we’ve known of it, it has not gone by the name Ground tit at all: rather, it has been termed Hume’s ground-jay (or Little ground-jay or Tibetan ground-jay or Hume’s ground-pecker). This is because, you see, it was always regarded as a ground-jay, that is, as a terrestrial corvid. While superficially similar to true ground-jays (the four Podoces species), it was always regarded as a highly aberrant member of Corvidae, and as the smallest member of the group. Hume in fact initially described P. humilis as a member of Podoces. Like Podoces, P. humilis possesses a slender, decurved bill, pale brown plumage and a dry, open-country habitat. However, they’re also highly different. While ground-jays run, P. humilis hops, and while ground-jays use stick nests, P. humilis nests in tunnels or burrows. Ground-jays are also much larger than P. humilis and exhibit white wing patches and dark, iridescent plumage patches. In recognition of these differences, P. humilis was given its own subgenus within Podoces in 1902, and in 1928 this was elevated to generic status.

But the allocation of P. humilis to Corvidae wasn’t really doubted until prominent osteological differences between P. humilis and ground-jays were noted by Borecky (1978). Borecky doubted the classification of P. humilis as a corvid and hinted at an affinity with starlings. In her 1989 phd study on corvid phylogeny, Sylvia Hope agreed that P. humilis was utterly unlike corvids, and most like nuthatches and tits. Despite these objections, P. humilis has remained classified as a corvid in most standard works on Corvidae (Goodwin 1986, Madge & Burn 1999) and indeed in most general works on birds. To resolve the issue once and for all, Helen James and colleagues performed a detailed analysis of the morphology and genetics of P. humilis, comparing it widely with other passerines (James et al. 2003). All the data showed, pretty conclusively, that P. humilis is not a corvid, but in fact a parid. A tit. A unique, highly novel tit to be sure, but a tit nonetheless, hence the new vernacular name. Incidentally, the paintings in James et al. (2003) were produced by my good friend Julian Hume. His office is next door to mine.

6. Blakiston’s fish owl Bubo blakistoni

If you think evolutionary convergences are cool, then you’ll love reversals. Morphological features or aspects of behaviour that have been modified during the evolution of a lineage don’t have to ‘stay’ changed – as Louis Dollo thought they did (this is where so-called Dollo’s Law come from) – they can change back to the ancestral state if this is what works. Of the four fish owl species, Blakiston’s is the biggest and most formidable, with a wingspan approaching 2 m and a total length of c. 60 cm (could it beat a Eurasian eagle owl in a fight? Perhaps). Endemic to Siberia, eastern China, Japan, Sakhalin Island and other eastern Asian islands, it inhabits cool, remote forests and can cope with harsh winters. Some have suggested that during its history it may have suffered from competition with sea eagles (Hume 1991), which are similar in size and ecological requirements. Sadly, this remarkable bird is highly endangered.

As is well known, owls in general have soft plumage and unusual fringes of tiny barbs along the leading margins of their flight feathers. These features - both specializations that permit silent flight in a group of birds that rely on sensitive hearing - are derived relative to the condition that owls inherited from their ancestors. But fish owls don’t need to be silent given that they’ve specialized to prey on animals that live under water, and they’ve consequently reversed back to the primitive condition. Fish owls also have longer legs than those of other owls, and their feet sport rough spiny scales that resemble those of fish-eating raptors like ospreys. B. blakistoni is unique among fish owls in having feathered legs. Interestingly, fish owls walk down to the water’s edge and will even wade into the shallows. They then sit motionless, waiting for prey to come within range. They don’t just eat aquatic prey, but also terrestrial birds and mammals. Fish owls are also remarkable among owls in reportedly feeding on carrion.

How does B. blakistoni fit into owl phylogeny? Until recently, the fish owls were considered to represent a distinct genus, Ketupa, and Ketupa was considered closely related to, but distinct from, the eagle owls Bubo. Recent genetic studies have found instead that the Ketupa species are nested within Bubo (as is Nyctea, the Snowy owl), and consequently both Ketupa and Nyctea have been sunk into synonomy with Bubo (Wink & Heidrich 1999). These results are supported by osteological characters, but unfortunately this data has yet to be published (it’s included in Ford’s 1967 phd thesis, and I’ve heard that a version of this is due to be published soon). I don’t have a copy of König et al. to hand, so I don’t know exactly how the fish owl species fit into Bubo. The feathered legs and other characters of B. blakistoni, however, suggest that, among fish owls, this species is the most basal. Overall, it seems like the one fish owl that is most like ‘normal’ eagle owls.

7. Shoebill Balaeniceps rex

Also called the Shoe-billed stork, She-billed stork [not a typo], Whale-bill or Whale-headed stork, B. rex is a long-legged big-billed waterbird of central Africa, and a specialist denizen of papyrus swamps. Though known to the ancient Egyptians, it wasn’t described by science until John Gould named it in 1851. Before that time it was a cryptid, as an 1840 sighting of this as-of-then-unidentified bird had been published by Ferdinand Werne in 1849 (Shuker 1991).

Standing 1.4 m tall, the Shoebill can exceed 2.6 m in wingspan and is best known for its remarkable wide bill. This can be up to 25 cm long, is larger in males than females and, like that of pelicans, cormorants and gannets, lacks external nostril openings. The birds use the bill to grab at large aquatic prey like lungfishes, catfish, tilapia, snakes, turtles and frogs. They’re reputed to eat antelope calves, but this is highly unlikely to say the least (Renson 1998), and apparently carrion. Little known is that the Shoebill is one of a handful of birds that occasionally practices quadrupedality: when Shoebills lunge forward while grabbing prey, they sometimes use their wings to help push themselves upright.

The affinities of the Shoebill have been controversial. Gould regarded it as a pelican and data from egg-shell microstructure and ear morphology was used by later authors to support this view. Unlike pelicans however, the long toes of the Shoebill are unwebbed and it is stork-like in some aspects of behaviour, practicing bill clattering and also dribbling water onto its eggs and young during the heat of the day. Based on stapedial morphology, Feduccia (1977) argued that the Shoebill really is a stork. It is also heron like in its possession of powder-down and some other features, and some workers have argued that it is really an aberrant heron. As recently shown by Gerald Mayr (2003) however, the morphological evidence best supports a position for the Shoebill close to Steganopodes, the clade that includes frigate birds, pelicans, gannets, cormorants and anhingas (traditional Pelecaniformes is not monophyletic as tropicbirds are apparently closer to procellariiforms than they are to members of Steganopodes).

More to come. For the latest news on Tetrapod Zoology do go here.

The shoebill image, taken by Doug Janson, is from here.

Refs - -

Borecky, S. R. 1978. Evidence for the removal of Pseupodoces humilis from the Corvidae. Bulletin of the British Ornithologists’s Club 98, 36-37.

Feduccia, A. 1977. The whalebill is a stork. Nature 266, 719-720.

Goodwin, D. 1986. Crows of the World. Trustees of the British Museum (Natural History) (London).

Hume, R. 1991. Owls of the World. Parkgate Books (London).

James, H. F., Ericson, P. G. P., Slikas, B., Lei, F.-M., Gill, F. B. & Olson, S. L. 2003. Pseudopodoces humilis, a misclassified terrestrial tit (Paridae) of the Tibetan Plateau: evolutionary consequences of shifting adaptive zones. Ibis 145, 185-202.

Wink, M. & Heidrich, P. 1999. Molecular evolution and systematics of the owls (Strigiformes). In König, C., Weick, F. & Becking, J.-H. Owls: a Guide to the Owls of the World. Pica Press (London), pp. 39-57.

Madge, S. & Burn, H. 1999. Crows & Jays. Christopher Helm (London).

Mayr, G. 2003. The phylogenetic affinities of the Shoebill (Balaeniceps rex). Journal of Ornithology 144, 157-175.

Renson, G. 1998. The bill. BBC Wildlife 16 (10), 10-18.

Shuker, K. P. N. 1991. Extraordinary Animals Worldwide. Robert Hale (London).

Friday, May 26, 2006

Make that ten most ‘beautifully interesting’ birds (part I)

A while back I was tagged by Coturnix to perpetuate the 10 bird meme. As you’ll know if you’ve heard of this project, it was started by John (of A DC Birding Blog) and has so far produced over 50 responses (go here to see them). To be honest I’m not that interested in or excited by the human concept of what is considered ‘beautiful’, so I’ve added my own slant to this and have decided to cover instead a selection of birds that can be considered ‘beautiful’ in terms of what they tell us about evolution. We might call them ‘beautifully interesting’ birds. Given that there are about 10,000 extant bird species to chose from, my selection is pretty much random and hardly representative. I simply sat down and wrote about the first ten ‘beautifully interesting’ species that popped into my head. Then I started writing about them… and because I ended up producing a lot of text I’m going to split it over several posts. Here we go, I hope you enjoy. I haven’t finished with late-surviving Mesozoic synapsids yet, by the way.

1. Flying steamer-duck Tachyeres patachonicus

Admittedly, all ten of my most ‘beautifully interesting’ birds could be anseriforms, as I have a special affinity for waterfowl. But I’ll limit myself to one of my favourites, the Flying steamer-duck.

The most widely distributed of the four Tachyeres species*, T. patachonicus inhabits both the fresh and marine waters of the Falklands and southern Patagonia and Tierra del Fuego. While all other steamer-ducks are flightless, T. patachonicus is (obviously) not, and in contrast to its flightless relatives it has proportionally bigger pectoral muscles and lower wing loadings. But what makes the species especially interesting is that some males within the species actually have wing loadings that are too high to permit flight, and are thus flightless (Humphrey & Livezey 1982, Livezey & Humphrey 1986). So, within a single species, there are both flighted and flightless individuals. It is almost as if the species is poised in the transition to full flightlessness, and indeed both morphological and genetic studies (Corbin et al. 1988) agree that T. patachonicus is the most basal member of its otherwise flightless genus. Flighted and flightless individuals are known to have also occurred in some recently extinct anseriform species, incidentally.

* One species, T. leucocephalus, was only described in 1981.

But there’s more. Steamer-ducks are notoriously pugnacious. Heavy-bodied and robust compared to other ducks, they have tough skin, a massive head and neck, and are equipped with keratanised orange knobs on the proximal parts of their carpometacarpi. Both sexes use these wing knobs in territorial fights and displays. Fighting males grab each other by the head or neck and then whack each other vigorously with the wing knobs, and fights can last for up to 20 minutes. Both birds sometimes submerge during the fight, and come up still fighting. This reminds me of scenes in films where super-heroes and villains (e.g. Spider-man vs Doc Oc) fall off buildings together and continue to battle even while plummeting toward the ground, but that’s just me. An aggressive steamer-duck approaches an ‘enemy’ by either adopting the so-called submerged sneak posture (only the top of the head and back and tail tip are visible), or by ‘steaming’ noisily across the surface (the ducks charge at speed, throwing their wings like the paddles of a paddle-steamer, hence the vernacular name).

Here’s where things get especially cool. Other waterbirds are shit-scared of steamer-ducks, and ‘mass spooks’ of other duck species, grebes and coots have been recorded when these birds saw or heard the local T. patachonicus. You see, they attack and kill other waterfowl. A particularly detailed steamer-duck attack on a Shoveler Anas platalea was recorded by Nuechterlein & Storer (1985a), and I here summarise the account they describe on p. 89.

A male steamer-duck caught a male shoveler by the neck and began pounding it with its wing knobs. The female steamer-duck displayed excitedly nearby. The shoveler was held beneath the water, then yanked up and beat some more. The male steamer-duck took a break and displayed with his female, then he went back to the shoveler, grabbed it again by the neck and proceeded to beat it another 15-20 times. By now the shoveler was looking pretty limp (though still alive). It was pecked at and released and both steamer-ducks displayed together again, and the male steamer-duck now began to move away from the shoveler. The shoveler now began to move (slowly) toward the shore and eventually got there. Then it died. ‘Examination of the specimen disclosed several broken bones, hemorrhages in the lower neck region and massive internal bleeding at the base of the right leg’ (p. 89). During the course of their study at Laguna de la Nevada, Santa Cruz Province, Argentina, Nuechterlein & Storer (1985a) picked up the carcasses of six ducks that had definitely been killed by steamer-ducks within a single week. Why steamer-ducks are so aggressive remains the source of debate (Murray 1985, Livezey & Humphrey 1985a, b, Nuechterlein & Storer 1985b). But don’t mess with them.

2. Shovel-billed kingfisher Clytoceyx rex

A New Guinea endemic, C. rex was named in 1880 and it’s been studied by such ornithological luminaries as Forshaw, Beehler and Diamond (see blog on the Odedi). A halcyonid kingfisher and close relative (or even member) of the kookaburra group, it’s strikingly big (c. 30 cm long) and with a fantastic broad, flattened bill. This is driven hard into the ground with a vigorous action and it’s apparently used quite literally as a shovel. As is the case in some other birds that sometimes handle hard-shelled prey, the edges of its tomia are scopate: that is, they possess tiny brush-like structures (Gosner 1993). Poorly known and rarely seen, it apparently does most of its foraging at dusk. Mostly preying on worms, the species also eats lizards, snails and insects. It’s sometimes called the Earthworm-eating kingfisher. It’s cool.

3. Wrybill Anarhynchus frontalis

Tetrapods generally have symmetrical bodies, but there are a few awesome exceptions. Among birds, the best is the Wrybill, a mid-sized charadriid wader endemic to New Zealand. Its short bill, about 25 mm long, is remarkable and unique in being curved at its tip toward the right, and always to the right. To forage, the bird tilts its head to the left and explores beneath stones and rocks, scraping off arthropods, fish eggs and other objects. It always moves clockwise around a stone. In The Life of Birds, David Attenborough suggested that this unique behaviour might only have been able to evolve in a place where terrestrial predators were absent: the Wrybill keeps watch for aerial predators while foraging, but it doesn’t need to watch for terrestrial ones.

Apart from its bill, the Wrybill isn’t much to look at. It’s grey and white with a black breast band and white forehead. Phylogenetic studies find it to be close to Charadrius (Chu 1995), and thus probably a core charadriid (traditional Charadriidae is not monophyletic (Ericson et al. 2003)). Wrybills migrate from North Island to South Island to breed. The total world population is only 4000-5000.

4. Blue-capped ifrita Ifrita kowaldi

Originally described by DeVis in 1890 as Todopsis kowaldi, Ifrita was independently ‘discovered’ by Walter Rothschild in 1898 and named by him Ifrita coronata. A passerine endemic to moist montane forests on New Guinea, Ifrita is remarkable for two reasons. Firstly, nobody really knows what it is and over the years it’s been classified in several different, disparate passerine families. It’s been allied with warblers, log-runners, and corvids. Secondly, it’s poisonous. I’ll repeat that for those people who hadn’t heard it before. It’s poisonous. While it’s nowadays reasonably well known that pitohuis (a group of six species of pachycephalid passerines, also endemic to New Guinea) produce batrachotoxin in their skin and feathers, it was shown in 2000 that Ifrita does too (Dumbacher et al. 2000). It’s thought that the poisons present in these birds are sequested from poisonous insect prey, but last I heard this was still under debate.

As for why the birds are poisonous, it’s been widely suggested that the poisons they harbour function as a chemical defence against snakes, raptors and predatory mammals. However, they may also protect the birds against parasites (Mouritsen & Madsen 1994). Incidentally, (1) it seems that not all pitohui species are poisonous (although further study is required to be absolutely sure about this), (2) that another New Guinean passerine, the Rufous shrike-thrush Colluricincla megarhyncha, also produces batrachotoxin, and (3) that multiple other non-poisonous New Guinea passerines (including some other pitohuis) may mimic poisonous pitohuis and therefore gain protection from predators too (Diamond 1992, Dumbacher & Fleischer 2001).

More ‘beautifully interesting’ birds to come soon, among other stuff.

The image above is a montage cobbled together from various images I took off the web. So far as I could tell none of them needed permission for use. For the latest news on Tetrapod Zoology do go here.

Refs - -

Chu, P. C. 1995. Phylogenetic reanalysis of Strauch’s osteological data set for the Charadriiformes. The Condor 97, 174-196.

Corbin, K. W., Livezey, B. C. & Humphrey, P. S. 1988. Genetic differentiation among steamer-ducks (Anatidae: Tachyeres): an electrophoretic analysis. The Condor 90, 773-781.

Diamond, J. M. 1992. Rubbish birds are poisonous. Nature 360, 19-20.

Dumbacher, J. P. & Fleischer, R. C. 2001. Phylogenetic evidence for colour pattern convergence in toxic pitohuis: Müllerian mimicry in birds? Proceedings of the Royal Society of London B 268, 1971-1976.

- ., Spande, T. F. & Daly, J. W. 2000. Batrachotoxin alkaloids from passerine birds: a second toxic bird genus (Ifrita kowaldi) from New Guinea. Proceedings of the National Academy of Sciences, USA 97, 12970-12975.

Ericson, P. G. P., Envall, I., Irestadt, M. & Norman, J. A. 2003. Inter-familial relationships of the shorebirds (Aves: Charadriiformes) based on nuclear DNA sequence data. BMC Evolutionary Biology 3: 16.

Gosner, K. L. 1993. Scopate tomia: an adaptation for handling hard-shelled prey? Wilson Bulletin 105, 316-324.

Humphrey, P. S. & Livezey, B. C. 1982. Flightlessness in flying steamer-ducks. The Auk 99, 368-372.

Livezey, B. C. & Humphrey, P. S. 1985a. Territoriality and interspecific aggression in steamer-ducks. The Condor 87, 154-157.

- . & Humphrey, P. S. 1985b. Interspecific aggression in steamer-ducks. The Condor 87, 567-568.

- . & Humphrey, P. S. 1986. Flightlessness in steamer-ducks (Anatidae: Tachyeres): its morphological bases and probable evolution. Evolution 40, 540-558.

Mouritsen, K. N. & Madsen, J. 1994. Toxic birds: defence against parasites? Oikos 69, 357-358.

Murray, B. G. 1985. Interspecific aggression in steamer-ducks. The Condor 87, 567.

Nuechterlein, G. L. & Storer, R. W. 1985a. Aggressive behavior and interspecific killing by Flying steamer-ducks in Argentina. The Condor 87, 87-91.

- . & Storer, R. W. 1985b. Interspecific aggression in steamer-ducks. The Condor 87, 568.

Thursday, May 25, 2006

‘Time wandering’ cynodonts and docodonts that (allegedly) didn’t die: late-surviving synapsids II

I feel as if I have too much stuff to do. The most important thing approaching on the horizon is my phd viva – it’s happening next week. I’ll post about that, whatever happens (go here to find out). Over the last few days Dave Martill and I dealt with the page proofs for in-press papers we’ve done on Kimmeridge Clay dinosaurs and azhdarchoid pterosaurs, and in between editorial work I’m writing manuscripts on new Cretaceous theropod specimens. Anguid lizards and monkeys are also high on the list of priorities, and I’m excited by the recent description of the new North American pachycephalosaur Dracorex hogwartsia, though don’t ask me what I think about the name.

For now, we go back to the subject initiated in the previous post: the amazing late survival of non-mammalian synapsids, a subject that I’ve planned to cover since... well, I don't recall, but I know I mentioned it a while back. By the way, the title I previously used ('late-surviving non-mammalian synapsids') no longer applies as some of the taxa discussed here are not non-mammalian synapsids, but are in fact basal mammals. We do begin with alleged non-mammalian taxa however.

The last non-mammalian synapsid?

The most controversial of these ‘Mesozoic survivors’ is a diminutive and enigmatic animal from Upper Palaeocene North America: Chronoperates paradoxus, described by Fox et al. (1992) for a partial mandible and some isolated teeth from the Paskapoo Formation of Alberta. With a lower jaw that (when complete) would have been less than 30 mm long, and with tooth crowns about 2 mm tall, Chronoperates would have been shrew-sized. While clearly synapsid in identity, Fox et al. (1992) noted that several features made this taxon amazingly archaic.

Firstly, the medial surface of the dentary possesses trough-like concavities that Fox et al. interpreted as areas for the articulation of post-dentary bones. Crown-group mammals lack these, but they were of course widespread in other synapsids. Secondly, the teeth are unusually tall and laterally compressed, and with an archaic multi-cusped crown morphology. Superficially, the teeth resemble those of Triassic non-mammalian cynodonts like Therioherpeton. Thirdly, the tooth enamel of Chronoperates is reportedly of pseudoprismatic type, a morphology not present in placental mammals and thus by inference expected in non-mammalian synapsids.

Among synapsids, this combination of features is reportedly only seen in non-mammalian cynodonts, and Fox et al. concluded that Chronoperates must have been one of these: the first of them (at the time) to come from post-Jurassic strata. If this is correct, then the geological range of non-mammalian cynodonts had just been extended by about 100 million years, and it’s for this reason that the name Chronoperates means ‘wanderer through time’ (since 1992, Upper Jurassic and Cretaceous non-mammalian cynodonts have been described, thereby shortening this gap, but I don’t want to cover them here: wait for next post).

All in all, the case doesn’t sound too bad and initial reports were quite positive: wow, mammals weren’t the only synapsids that survived into the Cenozoic after all, and non-mammalian synapsids had been there all along, hiding in the proverbial shadows (Novacek 1992). Fox and his colleagues have stuck to their guns, and in recent publications have continued to regard Chronoperates as a non-mammalian cynodont (Scott et al. 2002).

How was it that post-Jurassic basal cynodonts had remained undetected for so long? Fox et al. proposed that the small size of these specimens, their rarity, their possible restriction to northerly regions, and a lack of the right kind of sampling, might explain their previous absence from the fossil record.

Their proposal was soon criticized. In a rebuttal, Hans Sues (1992) argued that all of the features employed by Fox et al. (1992) to demonstrate non-mammalian status for Chronoperates were problematical. Sues argued that the teeth of non-mammalian cynodonts were actually pretty different from those of Chronoperates, that Mesozoic mammals didn’t share pseudoprismatic enamel with Chronoperates, and that the interpretation of the troughs on the dentary as probable attachment areas for post-dentary bones was unconvincing. He concluded that ‘the fossils currently available do not justify classification of Chronoperates as a non-mammalian cynodont’ (p. 278). Furthermore, while Fox et al. (1992) were careful to exclude other possible contenders (including crocodyliforms, pterosaurs, lizards, xenarthrans and mesonychians) there were a number of Palaeogene mammal groups that they didn’t exclude, and it would have been more convincing had it been shown that these taxa could also be eliminated from comparison (H.-D. Sues, pers. comm.).

But if Chronoperates isn’t what Fox et al. said it was, what is it? A few possibilities have been suggested, or hinted at, in the literature. In their Classification of Mammal: Above the Species Level, McKenna & Bell (1997) classified Chronoperates as a basal holotherian (Holotheria = kuehneotheriids, spalacotherioids, dryolestoids, therians etc.). They noted that its position is ‘dubious, even at this level, but not a nonmammalian cynodont’ (p. 43). So, while they didn’t agree with Fox et al. that Chronoperates was non-mammalian, they still thought that it was closest to taxa that were otherwise Triassic and Jurassic. Well, hey, that’s about as exciting as the possibility that Chronoperates might be non-mammalian. I mean: a relative of kuehneotheriids and gobiconodontids that survived into the Cenozoic? It would be a big deal.

This possibility (that Chronoperates is a late-surviving basal holotherian mammal) has been hinted at by some other workers. In a study on the distribution of an ossified Meckel’s cartilage in basal mammals, Meng et al. (2003) noted that the medial dentary scar seen in Chronoperates might not house post-dentary bones, as Fox et al. proposed, but instead a persisting Meckel’s cartilage. Now, if Chronoperates did possess a Meckel’s cartilage, this would be a first for a post-Mesozoic synapsid, and would further support ideas that Chronoperates is actually a late-surviving basal mammal. And as I noted above, this would be very exciting. For now, this is all we know of Chronoperates, and it remains a controversial enigma, and possibly an exciting anachronism.

Last of the docodonts?

So whatever it is, Chronoperates remains enigmatic and poorly known. Quite the opposite is true of the docodonts, a relatively successful and long-lived group of basal mammals that were long known only from the Late Jurassic North American form Docodon Marsh 1881. Docodonts had characteristically broad molars and a complex dentition that appears to have been rather like that of tribosphenic mammals, and both the homology of their tooth cusps, and their affinities to other mammals, have proved controversial. In their recent phylogenetic review of Mesozoic mammals, Luo et al. (2002) found docodonts to be way down near the base of Mammalia ‘despite their precociously specialized dentition’ (p. 16). Most other workers seem to agree with this.

Early Cretaceous docodonts weren’t described until 1928 when G. G. Simpson reported Peraiocynodon inexpectatus from the Purbeck Limestone of England. Peraiocynodon is quite similar to Docodon and a number of workers have regarded the two as congeneric. Since the 1970s, several additional docodont taxa have been described from the British Middle Jurassic (see Sigogneau-Russell 2003 for review) and Middle Jurassic forms are also known from Kyrgyzstan, China and Siberia. An Upper Jurassic form, Haldanodon, was described from Portugal in 1972, and in 1994 an Upper Jurassic Mongolian form, Tegotherium, was described. A second Early Cretaceous docodont, Sibirotherium, was named by Maschenko et al. (2002) for material from Siberia. Sibirotherium shares some characters with Tegotherium, and both taxa have been united in the clade Tegotheriidae. In its 2002 description, Sibirotherium was said to be the youngest reported member of the group.

Incidentally, I have a post planned about Jurassic docodonts, as their functional morphology and ecological diversity is interesting.

But here we come to the surprise. Were docodonts all but a distant memory by the Late Cretaceous? Well, in 2000 Rosendo Pascual et al. claimed that, no, they weren’t, but that they had actually managed to hang on until the very end of the Late Cretaceous. Pascual et al. (2000) described how the poorly known Cretaceous mammal Reigitherium bunodontum, originally described by Jose Bonaparte in 1990 as a dryolestoid, appeared in fact to be a bona fide docodont, and a very late surviving one.

Discovered in the Campanian-Maastrichtian La Colonia Formation of Patagonia, if Reigitherium were a docodont, it would show that they had survived almost to the end of the Cretaceous, and - if they’d been lucky - they might even have scraped through into the Cenozoic. Pascual et al.’s proposal would also extend the docodont record by a minimum of 30 million years given that Sibirotherium might be as young as Aptian-Albian. Alternatively, Sibirotherium might be as old as Berriasian-Valanginian, in which case Reigitherium would extend the docodont record by about 55 million years. Either way, it would be significant.

But is Reigitherium really a docodont? According to an abstract produced by Rougier et al. (2003), no it isn’t, as new material from the La Colonia Formation later showed that Reigitherium really was a dryolestoid, as originally identified by Bonaparte. Technical details of the molar cusps and roots, and the tooth count, better match those of dryolestoids more than docodonts, and in fact Reigitherium appears particularly closely related to the Palaeocene dryolestoid Peligrotherium, with both being united by Rougier et al. (2003) in the dryolestoid clade Reigitheriidae. Oh well. I confess that I had totally missed this abstract and didn’t know of it until David Marjanovic pointed it out to me (see comments, below). The scepticism that some Mesozoic mammal workers had about the alleged docodont status of Reigitherium might explain why Maschenko et al. (2002) appeared to ‘overlook’ the 2000 reidentification of Reigitherium as a late-surviving docodont, hence their claim that Sibirotherium was the youngest known docodont.

The image above (sorry again for the poor resolution) shows the holotype jaw of Chronoperates together with a life restoration of the Jurassic docodont Haldanodon (no life restorations of Reigitherium available, unfortunately). Again, both images can be pulled from various places on the web.

UPDATE (added December 2006): I can now reveal that this post was inspired by rumours of a Mesozoic-grade mammal that managed to survive on New Zealand until the Miocene. The fossils concerned were finally published late in 2006 and concern a basal form close to multituberculates and the base of Trechnotheria (the mammal clade that includes dryolestoids and therians): free pdf available here. Palaeontologists aren’t very good at keeping secrets, and the New Zealand animals have been whispered about for years. For the latest news on Tetrapod Zoology do go here.

Refs - -

Fox, R. C., Youzwyshyn, G. P. & Krause, D. W. 1992. Post-Jurassic mammal-like reptile from the Palaeocene. Nature 358, 233-235.

Luo, Z., Kielan-Jaworowska, Z. & Cifelli, R. L. 2002. In quest for a phylogeny of Mesozoic mammals. Acta Palaeontologica Polonica 47, 1-78.

Maschenko, E. N., Lopatin, A. V. & Voronkevich, A. V. 2002. A new genus of tegotheriid docodonts (Docodonta, Tegotheriidae) from the Early Cretaceous of West Siberia. Russian Journal of Theriology 1, 75-81.

McKenna, M. C. & Bell, S. K. 1997. Classification of Mammals: Above the Species Level. Columbia University Press (New York).

Meng, J., Hu, Y., Wang, Y. & Li, C. 2003. The ossified Meckel’s cartilage and internal groove in Mesozoic mammaliaforms: implications to origin of the definitive mammalian middle ear. Zoological Journal of the Linnean Society 138, 431-448.

Novacek, M. J. 1992. Wandering across time. Nature 358, 192.

Pascual, R., Goin, F. J., González, P., Ardolino, A. & Puerta, P. F. 2000. A highly derived docodont from the Patagonian Late Cretaceous: evolutionary implications for Gondwanan mammals. Geodiversitas 22, 395-414.

Rougier, G., Novacek, M. J., Ortiz-Jaureguizar, E., Pol, D. & Puerta, P. 2003. Reinterpretation of Reigitherium bunodontum as a Reigitheriidae dryolestoid and the interrelationships of the South American dryolestoids. Journal of Vertebrate Paleontology 23 (Supp. 3), 90.

Scott, C. S., Fox, R. C. & Youzwyshyn, G. P. 2002. New earliest Tiffanian (late Paleocene) mammals from Cochrane 2, southwestern Alberta, Canada. Acta Palaeontologica Polonica 47, 691-704.

Sigogneau-Russell, D. 2003. Docodonts from the British Mesozoic. Acta Palaeontologica Polonica 48, 357-374.

Sues, H.-D. 1992. No Palaeocene ‘mammal-like reptile’. Nature 359, 278.

Tuesday, May 23, 2006

Dicynodonts that didn’t die: late-surviving non-mammalian synapsids I

If you’ve read my previous posts you’ll know that - rightly or wrongly - I’ve invested an unreasonable amount of time in arguing against what’s been termed the ‘prehistoric survivor paradigm’: the notion, endorsed and propounded by some cryptozoologists, that numerous tetrapod groups known only from the fossil record might have survived to the present, yet without leaving an intervening fossil record. But the history of zoological discovery shows us that there’s nothing intrinsically wrong with the idea of either long gaps in the fossil record, or of the discovery of Lazarus taxa (that is, organisms that represent late survivors of supposedly long-extinct groups), and I’ve discussed some cases of this in previous posts (see New, obscure, and nearly extinct rodents of South America, and…. when fossils come alive).

We now know that quite a few fossil tetrapod groups really did hang on for much longer than was conventionally thought: in these cases, both long gaps in the fossil record, and the unexpected appearance of Lazarus taxa, occur. Some such cases have been big news in the palaeontological world, but mostly these instances have been largely ignored or unreported given that the animals concerned were obscure, deemed mundane, or of interest only to specialists. I personally think all the relevant cases are really interesting, and in future posts I aim to review them. Here we’re going to look at some of the more obscure and unreported of these cases – namely, the late survival of non-mammalian synapsids. If you don’t know what these are, the following paragraph is for you. If you do, skip ahead.

Mammals are the only surviving members of a far larger and more diverse tetrapod clade, Synapsida. Mammals evolved in the Triassic*, but they are but one of numerous synapsid clades, few of which made it past the mass extinctions at the end of the Triassic, and most of which evolved and diversified in the Carboniferous and Permian. Basal synapsids (things like caseids, ophiacodontids and sphenacodontids) looked superficially reptile-like, and for this reason non-mammalian synapsids have traditionally been dubbed ‘mammal-like reptiles’, and even classified within Reptilia. This obscures their affinity with mammals, and it’s nowadays agreed that Synapsida and Reptilia are different clades: basal synapsids are better regarded as ‘stem mammals’, and they aren’t reptiles. While some non-mammalian synapsids were bizarrely unique and quite different from mammals, during the Permian and Triassic a number of very mammal-like non-mammalian synapsids evolved. Some of these animals evolved small body size, and probably endothermy and body fur. So were you to travel back to the Triassic and catch an assortment of small synapsids, you might be hard pressed to work out which were the mammals.

* There are multiple different views on how the term Mammalia should be defined (Rowe & Gauthier 1992). Here (as in a previous blog on the soft tissue morphology of ears) I’ve decided to follow what seems to be the consensus view, and include all the Triassic mammal-like cynodonts (including Adelobasileus, morganucodontids and so on) within Mammalia.

In terms of taxonomic diversity, one of the most successful groups of non-mammalian synapsids were the dicynodonts, a group that first evolved in the Late Permian and then thrived in the Early and Middle Triassic. Dicynodonts were tubby-bodied, relatively short-legged synapsids, amusingly described by Mike Benton as possessing an ‘unsatisfactory tail’. Basal forms had multiple teeth, but mostly they had a strongly reduced dentition, with only large tusk-like upper canines projecting from their short, beaked jaws. Dicynodonts were probably predominantly herbivorous, but at least some may have chewed at carcasses and eaten small animals.

Sad to say, during the Late Triassic, dicynodonts dwindled in diversity until by the Norian (the penultimate stage of the Late Triassic) they were down to just three genera, and all of these were close relatives within the clade Kannemeyeriiformes (King 1990, Maisch 2001). I always liked Richard Cowen’s suggestion that these last forms were ecologically peripheralised, endangered species that hung on to existence in remote ecosystems where life was harsh. In fact Cowen compared them to Giant pandas Ailuropoda melanoleuca and Mountain gorillas Gorilla beringei if I remember correctly (Martill & Naish 2000 also covered this idea), but as for whether it’s an accurate portrayal or not I don’t know. But regardless, dwindling in numbers, and living in a world where big archosaurs were now controlling all the terrestrial ecosystems, those poor last dicynodonts gradually faded into oblivion, until they were but dust in the wind, dude. That was a Bill and Ted reference.

In June 1915 several fragmentary fossil bones were discovered near Hughenden in Queensland (Australia). Heber A. Longman (best known for his 1924 description of the giant pliosaur Kronosaurus) exhibited them at a meeting in 1915, and noted that they resembled dicynodont elements. Well, it turns out that he was right, as a 2003 reappraisal of the specimens by Tony Thulborn and Susan Turner showed that the bones could not belong to anything other than a dicynodont. One of the most telling of the specimens is a partial maxilla that still houses its slightly recurved canine tusk. In every detail – the distribution of concavities and foramina, the articulatory surfaces for other bones, the tooth shape, wear pattern and surface microstructure, the internal tooth structure (determined by CT scanning) – the specimen is indisputably dicynodont, and not matched by anything else.

But here’s the big deal: the fossils are from the late Early Cretaceous, and thus something like 100 million years younger than the previously known youngest members of the group. Thulborn & Turner (2003) noted that this ‘is so extraordinary than it demands exceptionally rigorous investigation’ (p. 987), and they carefully showed why and how other groups could be excluded from consideration. Furthermore, the Cretaceous age of the specimen is well established and there is no reason to doubt it. So dicynodonts didn’t disappear in the Late Triassic as we’d always thought. They had in fact been sneakily surviving somewhere, and as Thulborn & Turner (2003) wrote, their persistence in Australia and absence from everywhere else suggests that ‘Australia’s tetrapod fauna may have been as distinctive and anachronistic in the Mesozoic as it is at the present day’ (p. 991). That's pretty incredible.

Loads more to come on the subject, but it’ll have to come in a subsequent post. Watch this space.

The image above combines Laurie Beirne’s dicynodont life restoration, used in the press releases for Thulborn & Turner (2003), and on the front cover of the relevant issue of Proceedings of the Royal Society of London B, with a photo of the Australian fossil. Both images are widely available on the web. Sorry about the low resolution - I'll post a better picture in the near future. For the latest news on Tetrapod Zoology do go here.

Refs - -

King, G. 1990. The Dicynodonts: A Study in Palaeobiology. Chapman & Hall (London, New York).

Maisch, M. W. 2001. Observations on Karoo and Gondwana vertebrates. Part 2: A new skull-reconstruction of Stahleckeria potens von Huene, 1935 (Dicynodontia, Middle Triassic) and reconsideration of kannemeyeriiform phylogeny. Neues Jahrbuch fur Geologie und Palaontologie, Abhandlungen 220, 127-152.

Martill, D. M. & Naish, D. 2000. Walking With Dinosaurs: The Evidence. BBC Worldwide (London).

Rowe, T. & Gauthier, J. 1992. Ancestry, paleontology, and definition of the name Mammalia. Systematic Biology 41, 372-378.

Thulborn, T. & Turner, S. 2003. The last dicynodont: an Australian Cretaceous relict. Proceedings of the Royal Society of London B 270, 985-993.

Sunday, May 21, 2006

The most freaky of all mammals: rabbits

I made the point in a previous post (on gulls) that many animals which we take for granted are, when you think about them, actually very odd. And for a long time I’ve been thinking that this is oh so true of one of the mammals I see the most, the rabbit Oryctolagus cuniculus. Actually, I don’t have that species specifically in mind, but in fact all lagomorphs. Before I start on the generalizations, I’ll take this opportunity to point out (for those who might not know) that – while we have millions of bunnies here in the UK – they’re not native. The rabbit is in fact an animal of the Mediterranean region, and it’s supposed to have been introduced by the Normans after the conquest of 1066. However, there is apparently no mention of rabbits in the Domesday Book (written in 1086), and they don’t get a mention in the literature until 1176 (and even then only in a report about the Scilly Isles). It’s on the basis of this that some workers think it more likely that rabbits were actually introduced by the Crusaders in the 12th century (McBride 1988). We do have two native lagomorphs by the way, the Brown hare Lepus europeaus* and the Blue hare L. timidus*. Within Lagomorpha, rabbits and hares make up the clade Leporidae, and the less well-known pikas (aka ochotonids) form their sister-taxon.

* The correct species name for the Brown hare is controversial and the reality/monophyly of the Blue hare has recently been contested. I don’t want to cover these issues here: if you’re interested see Waltari & Cook (2005) and Ben Slimen et al. (2006).

Musings on Watership Down

It’s not in line with the rest of this post, but I’ll never forgive myself if I miss this opportunity to talk about Watership Down. I must confess to never having read Richard Adams’ 1972 book, but I really like the film and I like it more the more I see it. While not exactly zoologically accurate (the rabbits have religion, mythology, language, human emotions, team up with a friendly Black-headed gull Larus ridibundus, and learn how to use boats, among other things), some of it is not a million miles away from what we really know about rabbit society.

Two things make the film particularly memorable. Firstly, it begins with the rabbit myth of creation. In the beginning Frith, the lord of creation, made all animals alike, and they ate grass together. But El-ahrairah, the first rabbit, produced so many children that Frith became angry: control your people, or I will do something about it. El-ahrairah did nothing about it, so Frith did. He gave each of the animals a gift, and they were no longer the friends of El-ahrairah’s children – they wanted to catch them and kill them. The weasel. The stoat. The fox. The hawk. The owl. But Frith also gave El-ahrairah a gift – a bright white tail that flashed as a warning, long legs to run fast, and big ears to hear his enemies. The sequence ends as Frith tells El-ahrairah “All the world shall be your enemy, prince with a thousand enemies, and whenever they catch you, they will kill you. But first they must catch you, digger, listener, runner, prince with a swift warning. Be cunning and full of tricks and your people shall never be destroyed”. It’s a good way to start a film. The second thing that makes the film memorable is how dark and disturbing it is in places. Some of the main rabbit characters are killed by predators, caught in snares, or buried alive. Death, overall, is an important part of the story, as it is in the real lives of rabbits I suppose.

Why rabbits are just wrong

Moving on… why regard rabbits as ‘the most freaky of all mammals’? To begin with, just look at how weird they are. They’re familiar to us, but their anatomy is actually highly odd. Example? Their teeth are strange, with cusps and folds that have proved almost impossible to homologise with those of other placental mammals. The sides of their snout bones are decorated with a bizarre lattice-work of filigree bone texture (why?). Their incisive foramina (openings on the bony palate) are uniquely elongate (for what purpose?). A thin splint from their frontal bones projects down and forward, finger-like, among the snout bones. Their hindlimbs are proportionally elongate relative to their forelimbs (odd for a quadupedal mammal, when you think about it). Their ankle bones are uniquely strange, with the calcaneum housing a canal that runs diagonally through the bone (Bleefeld & Bock 2002). No other mammal has anything remotely like this. The undersides of their feet are completely covered by thick fur – that’s odd, and unique. And don’t get me started on their genitals (read on).

Many aspects of their physiology and behaviour are also odd compared to what we’re more familiar with. Get this: when baby rabbits suckle, the milk is ejected in one big squirt that only occurs after the mother has been sufficiently stimulated by the paddling action of the babies’ paws. Male rabbits also squirt, but this time the liquid is urine, and it gets squirted over potential mates. As is reasonably well known, lagomorphs practice refection – that is, they have to ‘rescue’ nutrients from their digested food by ingesting their own caecal pellets (they therefore only produce dry droppings once the food has been through the system twice). And lagomorphs are also odd in practicing so-called absentee care, with mother rabbits spending just 0.1% of their time with their young.

What, if anything, is a rabbit? (homage to Wood)

Working on the assumption that organisms should be regarded as freaky when we can’t even work out what they are, rabbits excel. Albert Wood (1957) explored this area when he wrote ‘What, if anything, is a rabbit?’. Check out the first paragraph of his paper: ‘The title of this paper is slightly modified from that of an article I encountered some years ago, which appeared to be approaching the problem of the relationships of the Lagomorpha, or rabbits and their relatives, from the most basic point of view. This paper, entitled “Gibt es Leporiden?”, seemed to be questioning the very existence of such animals. Investigation showed, however, that the question involved was not whether members of the family Leporidae existed, but whether rabbit-hare hybrids did. Since then, I have met no one who questions the existence of rabbits and hares, and I have been reluctantly forced to accept them.’ (Wood 1957, p. 417).

Originally, rabbits were included in Rodentia, and they weren’t formally separated from them until Gidley (1912) did so. What makes this decision particularly interesting is that Gidley suggested that lagomorphs had no close relationship to rodents at all, but shared some intriguing similarities with artiodactyls. While a few authors commented on this idea after Gidley, the evidence for it isn’t great. Mostly it comes down to a superficial similarity between certain Cenozoic artiodactyls (like cainotheres) and lagomorphs, and the transverse chewing style and artiodactyl-like ankle structure of lagomorphs.

It’s also been noted that lagomorphs possess similarities with the pantodonts and dinoceratans of the Palaeogene. If you know what the members of these groups looked like, you’ll understand why positing an affinity between them and lagomorphs is so radical. I’ll cover it in another post some time. Lagomorph ancestry has also been sought among the various hoofed mammals collectively termed ‘condylarths’, and in particular they’ve been tied to periptychids like Ectoconus. For reasons of time and space I don’t want to expand on this point either, but I may do so later.

Bunnies: Mesozoic relicts, or para-marsupials?

In keeping with the idea that lagomorphs have no close living relatives, it has been proposed at times that they might have descended from groups that were otherwise entirely restricted to the Mesozoic. Based on tooth cusp morphology, Gidley (1906) suggested that lagomorphs descended from triconodontids. McKenna (1982, 1994) argued that lagomorphs are part of a larger placental clade [termed Anagalida in McKenna & Bell (1997)] that includes as its most basal members the Cretaceous zalambdalestids, although the evidence for this has more recently been assessed and rejected.

Most zoologists would be surprised to hear that, in a few features, lagomorphs resemble marsupials more than they do placentals, and it’s on the basis of these features that some workers have actually suggested that lagomorphs might be close kin of marsupials (albeit not necessarily members of Marsupialia or even Metatheria). Gregory (1910) drew attention to the arterial foramen present in the last cervical vertebra, supposedly uniquely shared by lagomorphs and marsupials (but actually occurring more widely among placentals); Hartman (1925) showed that egg development in the lagomorph fallopian tube was uniquely marsupial-like; and Petrides (1950) pointed out that lagomorphs are unique among placentals in possessing a pre-penile scrotum, a character also otherwise limited to marsupials. That’s right, a pre-penile scrotum. A scrotum that is further away from the anus than the penis is. I’ve actually, err, manipulated a few rabbits to observe this remarkable configuration, thus far without success, but then the individuals in question were neutered. Hm. Anyway: so, are rabbits actually some long-lost freakish sister-group to metatherians?

The primate hypothesis, and the resurrection of Glires

Protein sequences led Graur et al. (1996) to argue that lagomorphs were closest to primates, and these authors further argued that morphological characters used to unite lagomorphs with rodents and other groups were not really indicative of affinity. This hypothesis was hailed at the time as the most likely answer to Woods’ ‘What, if anything, is a rabbit?’, but it suffers from that widespread problem of assuming that one body of evidence must somehow outweigh, or be superior to, all the other data.

The most recent assessment of the morphological and fossil data indicates that lagomorphs are, after all, most closely related to rodents, with the two forming the larger clade Glires. This is supported by the detailed morphology of Palaeocene proto-lagomorphs like Gomphos, and by a big data set with good character support across nodes (Asher et al. 2005). According to recently published phylogenetic definitions, the term Lagomorpha is best restricted to the pika-rabbit clade (viz, the crown-clade) and the old name Duplicidentata is applied to the stem-group that includes Lagomorpha. If you’re interested, both morphological and molecular data supports the inclusion of Glires within the more inclusive clade Euarchontaglires, and herein there are the primates, dermopterans and tree shrews.

So after all that, rabbits really do seem to be part of a clade that is closest to rodents. Sadly, they aren’t para-marsupials, close kin of Uintatherium, or relict survivors from a long-lost Cretaceous radiation. But I still think they’re freaky.

The photo above was borrowed from the IUCN/SSC Lagomorph Specialist Group’s site.

PS - note that I keep my promises. A post on the strangeness of rabbits was promised way back in January: see Graeme's Pleistocene megafrog.

Coming next: late-surviving Mesozoic synapsids. Yeah, really. For the latest news on Tetrapod Zoology do go here.

Refs - -

Asher, R. J., Meng, J., Wible, R. R., McKenna, M. C., Rougier, G. W., Dashzeveg, D. & Novacek, M. J. 2005. Stem Lagomorpha and the antiquity of Glires. Science 307, 1091-1094.

Ben Slimen, H., Suchentrunk, F., Memmi, A., Sert, H., Kryger, U., Alves, P. C. & Ben Ammar Elgaaied, A. 2006. Evolutionary relationships among hares from north Africa (Lepus sp. or Lepus spp.), cape hares (L. capensis) from South Africa, and brown hares (L. europaeus), as inferred from mtDNA PCR-RFLP and allozyme data. Journal of Zoological Systematics 44, 88-99.

Bleefeld, A. R. & Bock, W. J. 2002. Unique morphology of lagomorph calcaneus. Acta Palaeontologica Polonica 47, 181-183.

Gidley, J. W. 1906. Evidence bearing on tooth-cusp development. Proceedings of the Washington Academy of Science 8, 91-110.

- . 1912. The lagomorphs an independent order. Science 36, 285-286.

Graur, D., Duret, L. & Guoy, M. 1996. Phylogenetic position of the order Lagomorpha (rabbits, hares and allies). Nature 379, 333-335.

Gregory, W. K. 1910. The orders of mammals. Bulletin of the American Museum of Natural History 27, 1-524.

Hartman, C. G. 1925. On some characters of taxonomic value appertaining to the egg and ovary of rabbits. Journal of Mammalogy 6, 114-121.

McBride, A. 1988. Rabbits & Hares. Whittet Books (London).

McKenna, M. C. 1982. Lagomorph interrelationships. Geobios, mémoire spécial 6, 213-223.

- . 1994. Early relatives of Flopsy, Mopsy, and Cottontail. Natural History 103 (4), 56-58.

- . & Bell, S. K. 1997. Classification of Mammals: Above the Species Level. Columbia University Press (New York).

Petrides, G. A. 1950. A fundamental sex difference between lagomorphs and other placental mammals. Evolution 4, 99.

Waltari, E. & Cook, J. A. 2005. Hares on ice: phylogeography and historical demographics of Lepus arcticus, L. othus, and L. timidus (Mammalia: Lagomorpha). Molecular Ecology 14, 3005-3016.

Wood, A. E. 1957. What, if anything, is a rabbit? Evolution 11, 417-425.

Thursday, May 18, 2006

Snapping turtles, part III: bite, lunge, lure and snap

Pterosaurs and dinosaurs have taken up all of my research time within the last few days. The phylogeny and taxonomy of azhdarchoids, the obscure sauropods of the Kimmeridge Clay Formation, and the theropods of the Brazilian Santana Formation, among others. I will post about all of these things when the time is right. As I noted here a while back, one of the recurrent themes in my blog posts will be turtles. I still have to write up the stuff on Cuthbert and the other departmental turtles, on J-Lo the araripemydid, and on Branston the pickled Pelomedusa, and I also have posts planned on the turtles that time forgot (viz, Mesozoic-grade taxa that made it well into the Cenozoic) and on the many newly discovered geoemydids that have recently been named from China.

Forgive me if it seems like dinosaurs are the things I post about the least but, well, while I find them fascinating, I honestly don’t find them more fascinating than all the other types of tetrapods. Larks, fringe-toed lizards, tree frogs, okapis and sewer rats really are AS INTERESTING as dinosaurs, and I relish telling this to those psychologists who wonder why some of us humans are fascinated by long-extinct Mesozoic reptiles.

In two previous turtle posts I discussed chelydrids, the snapping turtles. But a third post was planned, and here it is. Those two previous posts covered, respectively, general stuff about taxonomy, evolution and body size (They bite, they grow to huge sizes, they locate human corpses: the snapping turtles, part I), and physiology and distribution (Snapping turtles, part II: hyperexcitability, supercooling and recolonisation of Europe in the Anthropocene).

What perhaps makes chelydrids most interesting is what they eat, or at least what they bite. ‘Large individuals are known to have caused injury to people unwary enough to step into or swim in the water near them, and they are quite capable of removing a toe or finger if given the opportunity’ (Alderton 1988, p. 112). Indeed, they are anecdotally credited with being able to ‘bite through a broom handle’. For his excellent TV series ‘O’Shea’s Dangerous Reptiles’, Mark O’Shea decided to test this dubious assertion. With the help of a colleague he caught the largest and nastiest alligator snappers he could, pissed them off by poking them, and then pissed them off some more by shoving a broom handle into their mouths. All the turtles bit happily, and bit hard. And as impressive as it was, sad to say not one turtle was powerful enough to cleave neatly through 25 thick mm of solid wood, which to be honest isn’t much of a surprise.

Rather more rigorous tests were applied by Herrel et al. (2002) who tested the bite force of numerous diverse turtles, including both snappers and alligator snappers. They found snappers to have bite forces of between 208 and 226 Newtons, and alligator snappers of between 158 and 176 N.

This powerful bite can have its practical uses. Zoo vet David Taylor, one of the best sources for zoological anecdotes (think tapir-eating hippos and a zebra with a tooth embedded in one of its testicles), tells the story in one of his books of how an alligator snapper in Indiana was used by its Native American owner to retrieve lost human corpses. The turtle (which was kept on a long leash) was taken to the lake where the person was missing, and released. Eventually its owner would know from the pull on the leash that the turtle was tugging around on a carcass, somewhere on the bottom. It would then be pulled slowly to the surface, and it would successfully bring the corpse with it. I couldn’t find the relevant Taylor book that relates this tale, but I did find a version of the story in Alderton (1988).

Ordinarily snapping turtles don’t feed on broom handles or human corpses of course. They are sit-and-wait predators that lunge with great speed at passing objects, but they also consume static objects like molluscs and some plants. Chelydra likes to skulk in aquatic vegetation, though it also floats near the water surface. Aquatic insects, crustaceans, worms and fish are eaten, and it also preys on a diversity of tetrapods. These include frogs and toads, salamanders, snakes, smaller turtles, birds and small mammals. As mentioned, they also eat various plants, including Canadian pondweed and parts of water lilies, and they are also reported to eat snails, clams and freshwater sponges. This interests me, as if they eat plants and clams and sponges then they obviously don’t regard moving objects only as potential prey. Do they use olfaction to determine whether or not these non-moving objects are edible? I don’t know, and I can’t find an answer in the literature. They are reported to consume more plant material during the warmer months, when plant growth is more abundant.

Macroclemys, the alligator snapper, is altogether different from Chelydra in terms of what it does and what it can do. As is reasonably well known, it possesses a lure-like organ on the floor of its mouth. This isn’t the tongue as sometimes stated but a specialised mobile organ attached to the tongue at mid-length. Grey at rest, it is red when active, and the turtles deploy it by sitting still with the mouth wide open, and by wriggling it. Some herpetologists have proposed that the lure is only used during the daytime when the turtles sit passively on the substrate (as opposed to the nightime, when the turtles actively forage for prey and don’t, in theory, deploy the lure), and while there are some observations recorded from captive individuals, it doesn’t seem that much is known about the use of the lure.

Like Chelydra, Macroclemys grabs crustaceans, worms, fish, frogs and snakes, and it also eats static prey like plants and clams. It is more dedicated to turtle-killing than Chelydra is, and well able to catch and kill turtles that are about as big as it is. Allen & Neill (1950) reported alligator snappers to eat Painted turtles Chrysemys picta, Chicken turtles Deirochelys reticularia, mud turtles Kinosternon, as well as other alligator snappers. In fact their predation on smaller turtles may be significant enough to keep populations of other species low in areas where alligator snappers are abundant. As suggested by that story about the corpse-finder alligator snapper, members of this species are also adept at carrion feeding, though how important this is in their natural diet is uncertain.

Unless you already know the answer (clever you), you might be wondering how slow, clumsy turtles are able to catch speedy, agile aquatic prey like fish. The feeding styles of aquatic turtles are pretty fascinating, and have been studied recently by Patrick Lemell and colleagues (see Lemell et al. 2000, 2002). Using expandable throats, rapidly opening jaws and streamlined skulls, aquatic turtles can dart their head forward, open their jaws, and engulf water and prey within – literally – a fraction of a second.

Along these lines, Lauder & Prendergast (1992) used high-speed video recording to study feeding behaviour in Chelydra. They showed that Chelydra lunges and engulfs fish prey within 78 ms, with ‘peak head extension velocities of 152.5 cm per second’. It doesn’t lunge as quickly when feeding on worms, darting its head forward at a sedate 54 cm per second in these cases, and engulfing worms within a leisurely 98 ms. In contrast to matamatas and other aquatic turtles that generate massive negative pressures and thereby employ suction to engulf prey, Chelydra is predominantly a ram-feeder that doesn’t generate negative pressure when it lunges.

I’d like to talk more about aquatic feeding behaviour in turtles, but it’ll have to wait for another post. It’s a story that involves plethodontid salamanders, placodonts and the evolution of filter-feeding.

The photo above, showing the lure on the floor of the mouth, is from here on Richard Butler’s excellent site on Oklahoman reptiles. And this isn’t the same Richard Butler who works on ornithischian dinosaurs. For the latest news on Tetrapod Zoology do go here.

Refs - -

Alderton, D. 1988. Turtles & Tortoises of the World. Blandford (London).

Allen, E. R. & Neill, W. T. 1950. The alligator snapping turtle, Macrochelys temminckii, in Florida. Special Publication of Ross Allen’s Reptile Institute 4, 1-15.

Herrel, A., O’Reilly, J. C. & Richmond, A. M. 2002. Evolution of bite performance in turtles. Journal of Evolutionary Biology 15, 1083-1094.

Lauder, G. V. & Prendergast, T. 1992. Kinematics of aquatic prey capture in the snapping turtle Chelydra serpentina. Journal of Experimental Biology 164, 55-78.

Lemell, P., Beisser, C. J. & Weisgram, J. 2000. Morphology and function of the feeding apparatus of Pelusios castaneus (Chelonia; Pleurodira). Journal of Morphology 244, 127-135.

- ., Lemell, C., Snelderwaard, P., Gumpenberger, M., Wochesländer, R. & Weisgram, J. 2002. Feeding patterns of Chelus fimbriatus (Pleurodira: Chelidae). The Journal of Evolutionary Biology 205, 1495-1506.

Monday, May 15, 2006

Pterosaur wings: broad-chord, narrow-chord, both, in-between, or…. all of the above?

What did pterosaurs look like when they were alive? Did they have relatively broad wing membranes [patagia from hereon] that - like those of most bats - stretched as far as their ankles, or did they have narrow patagia that attached to their hips, or perhaps to the tops of their thighs? Until the 1980s, pterosaurs were pretty much universally depicted as possessing broad-chord wings that extended to their ankles. There were exceptions: K. A. von Zittel (1882) imagined pterosaurs as possessing narrow, swallow-like wings that did not attach further distally than the knee, and Harry Seeley (1901) opined that the patagia may not have incorporated the hindlimbs at all. But, mostly, pterosaurs were regarded as bat-winged, an image that Kevin Padian (1987) argued to be primarily typological (viz, pterosaurs were initially imagined as bat-like, therefore they must have had bat-like patagia).

It’s well known that, following his studies of Dimorphodon and other pterosaurs, Padian championed the idea that pterosaurs were agile cursorial bipeds, and that their patagia were narrow and did not incorporate the hindlimbs (Padian 1983). This idea was popular for a while but, judging from the way pterosaurs are depicted today, it doesn’t seem that popular now (though this isn’t to say that there aren’t scientists and artists who are reconstructing pterosaurs in this manner).

If anything seems popular, it’s actually a sort of hybrid morphology: while the patagia are ordinarily depicted as incorporating the hindlimb, they aren’t shown as extending as far as the ankle, but to the knee or shin. This goes for all of John Sibbick’s pterosaurs (in Wellnhofer 1991 and elsewhere) as well as for many other popular life restorations. I’ll admit that my personal aesthetic sense of what is, and what is not, cool leads me to intuitively prefer the narrow-chord model, and as a teenage enthusiast self-teaching myself from the writings of Bob Bakker and Greg Paul I personally took a liking to narrow-chord wings. But being a scientist is all about going where the evidence leads, and not on what you might intuitively prefer. Where does the evidence lead: did pterosaurs have broad-chord or narrow-chord wings? Or both?

Having considered this matter in some depth (Naish & Martill 2003), and having looked at some of the pertinent specimens, I conclude that broad-chord patagia are best supported, and in fact are well supported. So, yes, the data best supports inclusion of the hindlimbs in the patagia, and extension of the patagia as far distally as the ankle. Shock horror: that’s a pretty controversial point of view in the world of pterosaur research. But quite a few specimens show this to have been the case. Let’s look at some of them.

-- The famous ‘dark wing’ Rhamphorhynchus specimen preserves intact, in-situ patagia, and the left brachiopatagium ‘curves caudomedially and attaches to the ankle of the left hindlimb’ (Frey et al. 2003, p. 243). This is clearly visible in good photos of the specimen and there is no question that the patagia are genuine, intact and preserved in-situ. I have access to an excellent cast of this three-dimensional specimen and am happy with Frey et al.’s interpretation.

-- The Eudimorphodon specimen MCSNB 8950 has patagia preserved adjacent to the ankles of both legs. Fibres preserved within the membranes appear to confirm brachiopatagia attaching as far distally as the ankle, and the presence of a cruropatagium (Bakhurina & Unwin 2003).

-- The holotype of little Sordes pilosus indisputably preserves brachiopatagia that attach to the ankles (Unwin & Bakhurina 1994). Claims that the patagial margins preserved in the fossil actually represent cracks are utterly unconvincing.

-- The Crato Formation azhdarchoid specimen SMNK Pal 3830 shows a brachiopatagium extending distally to contact the ankle (Frey et al. 2003). While this pterosaur is incomplete, the patagial edge is continuous, smoothly concave, and grades neatly into the side of the tarsus (see images above: click on them for larger versions). I’ve examined the specimen up-close in person, and was personally happy that the specimen really does preserve a partial brachiopatagium and really does preserve a brachiopatagium that attached at the ankle. In fact it was the key specimen that convinced me of the reality of broad-chord patagia. [Incidentally, the phylogenetic affinities of this specimen are uncertain. Frey et al. (2003) regarded as it a possible azhdarchid, but it possesses certain features suggesting that it might be more closely related to Tupuxuara (more news on this issue soon).]

While the interpretations given above have been challenged for some of these specimens (Peters 1995, 2001), I note the following: ALL the pterosaur specimens for which we have patagia appear to show broad-chord patagia and, while in some of these cases the broad-chord interpretation is ambiguous or arguable, there are NO specimens that unambiguously preserve narrow-chord patagia. Claims that narrow-chord membranes, unattached to the distal hindlimb or even unattached to the hindlimb altogether, are preserved in some specimens (e.g. the anurognathid Jeholopterus and the Zittel wing Rhamphorhynchus) are either based on data that is even more ambiguous than that discussed above, or are erroneous (e.g. the Zittel wing can’t be used to demonstrate lack of attachment to the hindlimb, as the caudolateral part of the membrane is missing and we don’t know how extensive the membrane was when complete).

Data from pterosaur hindlimb proportions provides support for the idea that the hindlimbs were incorporated into the patagia. By plotting the lengths of femora, tibiae and metatarsi onto ternary diagrams, Daniel Elvidge and David Unwin found that pterosaurs occupied a tight, compact group of data points within morphospace, and a ‘data cloud’ similar in size to that occupied by bats. The cloud occupied by birds was more than twice the size of the pterosaur or bat clouds (Elvidge & Unwin 2001). This data indicates that pterosaurs were constrained in hindlimb proportions in the same manner that bats are. I find the most plausible explanation for this to be the linking of the fore- and hindlimbs by patagia: because pterosaur hindlimbs were always a part of the wing apparatus, pterosaurs did not evolve the diverse hindlimb morphology that birds did.

Significantly (from the point of view of the discussion here), those pterosaur specimens preserved with patagia were distributed randomly within the pterosaur cloud. This indicates that broad-chord patagia are both widely distributed within pterosaurs, and the norm for the group. Dyke et al. (2006) have recently argued that broad-chord patagia may not have applied to all pterosaurs, but they seemed unaware that there is evidence for this morphology outside of Sordes.

I still think it’s at least possible that some pterosaurs had reduced patagia however. Morphological evidence suggests that dsungaripterids were quite terrestrial in habits (Fastnacht 2005), and it’s tempting to speculate that they were better suited for walking around on the ground than were others, and hence with less extensive patagia. But, hey, this is part of the reason why pterosaurs are so interesting: they’re unique, with no close extant analogues, and this is why they’re so controversial.

The evidence we have shows that broad-chord patagia were widespread among pterosaur clades. Maybe there were narrow-chord forms (with my money being on dsungaripterids), but we have yet to find soft-tissue evidence demonstrating their presence.

For the latest news on Tetrapod Zoology do go here.

Refs - -

Bakhurina, N. N. & Unwin, D. M. 2003. Reconstructing the flight apparatus of Eudimorphodon. Rivista del Museo Civico di Scienze Naturali “Enrico Caffi” 22, 5-8.

Dyke, G. J., Nudds, R. L. & Rayner, J. M. V. 2006. Limb disparity and wing shape in pterosaurs. Journal of Evolutionary Biology doi:10.1111/j.1420-9101.2006.01096.x

Elvidge, D. J. & Unwin, D. M. 2001. A morphometric analysis of the hind-limbs of pterosaurs. In Two Hundred Years of Pterosaurs, A Symposium on the Anatomy, Evolution, Palaeobiology and Environments of Mesozoic Flying Reptiles. Strata Série 1 11, 36.

Fastnacht, M. 2005. The first dsungaripterid pterosaur from the Kimmeridgian of Germany and the biomechanics of pterosaur long bones. Acta Palaeontologica Polonica 50, 273-288.

Frey, E., Tischlinger, H., Buchy, M.-C. & Martill, D. M. 2003. New specimens of Pterosauria (Reptilia) with soft parts with implications for pterosaurian anatomy and locomotion. In Buffetaut, E. & Mazin, J.-M. (eds) Evolution and Palaeobiology of Pterosaurs. Geological Society Special Publication 217. The Geological Society of London, pp. 233-266.

Naish, D. & Martill, D. M. 2003. Pterosaurs – a successful invasion of prehistoric skies. Biologist 50, 213-216.

Padian, K. 1983. A functional analysis of flying and walking in pterosaurs. Paleobiology 9, 218-239.

- . 1987. The case of the bat-winged pterosaur: typological taxonomy and the influence of pictorial representation on scientific perception. In Czerkas, S. J. & Olson, E. C. (eds) Dinosaurs Past and Present Vol. II. Natural History Museum of Los Angeles County/University of Washington Press (Seattle and London), pp. 64-81.

Peters, D. 1995. Wing shape in pterosaurs. Nature 374, 315-316.

- . 2002. A new model for the evolution of the pterosaur wing – with a twist. Historical Biology 15, 277-301.

Seeley, H. G. 1901. Dragons of the Air: An Account of Extinct Flying Reptiles. Methuen (London).

Unwin, D. M. & Bakhurina, N. N. 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371, 62-64.

Wellnhofer, P. 1991. The Illustrated Encyclopedia of Pterosaurs. Salamander Books (London).

Zittel, K. A. von 1882. Über Flugsaurier aus dem lithographischen Schiefer Bayerns. Paläontographica 29, 47-80.

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