Did ichthyosaurs fly? Probably not, no

For various reasons, I haven’t had the chance lately to do any blogging. So in order to at least add something new, I’ve decided to recycle the text of a very old article, first published in 1997. I’ve made no effort whatsoever to update it, so please keep this in mind (though, because the original article didn’t include any citations or references, these have been added). Here we go.

It is often difficult to visualise the life appearance of extinct animals: quite simply because many of these animals are profoundly different from any we have living with us today. Perhaps, out of all the extinct types of Mesozoic reptile, ichthyosaurs are the easiest to visualise. Certain living marine animals - the speedy, open-water dolphins, lamnid sharks [Great white and relatives] and scombroid fishes [the tuna-mackerel group] - possess the ichthyosaur body shape and surely move in an ichthyosaur-like way. So alike are all of these groups in their shape and presumably their behaviour that is has proved irresistible for artists to depict ichthyosaurs as ‘Mesozoic dolphins’. They are shown travelling in schools, porpoising from the waves, and smoothly powering themselves beneath the surface with their forked, shark-like tails. But try and imagine now how different things might look if ichthyosaurs did not swim in this way at all, but propelled themselves with their powerful forefins instead. They did not swim by fast side-to-side movement of the tail, but flew underwater like turtles or penguins.

This idea must sound unusual to the uninitiated. In recent years, however, it has been seriously proposed and has won a fair deal of acceptance in the community*. For my third year dissertation at the Southampton Oceanography Centre (University of Southampton), I decided to investigate this suggestion and assess for myself how likely, or unlikely, it really was. Were ichthyosaurs really underwater fliers?

* That's not true, and it wasn't in 1997 either.

The suggestion that ichthyosaurs may have flown owes itself to German palaeontologist Jurgen Riess who published his ideas in a 1986 study on ichthyosaur biomechanics and phylogeny (Riess 1984, 1985, 1986, Riess & Frey 1991, Riess & Tarsitano 1989). Riess presented new, wing-like reconstructions of ichthyosaur fins. Previous discoveries, some described as long ago as 1841, had shown that the soft tissue of ichthyosaur fins extended well beyond the fin skeleton. There seem to have been rigid plate-like structures and fibres along the fin’s leading edge, creating a stiff and narrow extension along the anterior-most border. Stiffening rods apparently supported a gently tapering, flexible posterior-most border to the fin that was much wider than the leading edge. In cross-section, these fins may have been hydrofoil shaped. In order that such fins could flap up and down to enable propulsion, constricted fin bases would be required. Riess argued that this was indeed the case [the drawing at the top, depicting the Triassic ichthyosaur Shonisaurus as an underwater flier, is by Dino Frey and from Riess (1986)].

Though aspects of the fin’s internal structure may have been common to all (or nearly all) ichthyosaurs, ichthyosaur fns do vary a great deal in shape. However, one trend that might be observed in the evolution of the ichthyosaur fin is the addition both of more and more elements (hyperphalangification), and of more and more digits (hyperdactylification). A plausible advantage of both conditions might be that a limb surface would become broader if new elements were added to its sides, or longer if more elements were added to its distal-most end. Both patterns would, in theory, be advantageous to an underwater flier.

Greater broadening of a fin could provide it with more propulsive power, and an increased length could help create a more wing-like plan: by the creation, say, of a slim, pointed fin tip. Certain ichthyosaurs carried the two patterns to the extreme, Platypterygius, a cosmopolitan genus from the Cretaceous, had up to 10 digits, the longest of which contained more than 30 phalanges, per forefin. Extra bones were added also to the forearm, making that part of the fin broader too. The evolution of these wide, elongate wing-like fins may be interpreted as increasing specialisation toward the underwater flight mode of propulsion. So far so good, but to ‘fly’ animals need more than a wing - they also need a powerful, well braced pectoral girdle as well as strong muscles. Did ichthyosaurs possess such attributes?

Articulated ichthyosaurs demonstrate that the pectoral girdle was a robust construction with vertical clavicles [collar bones] and scapulae [shoulder blades], so there was a firm base for the articulation of powerful forefins and their musculature. In some ichthyosaurs, muscle attachment sites on the pectoral girdle were quite pronounced, and fin muscles may even have extended onto the ribs too. So, not only were ichthyosaur fins wing-like in shape with a sometimes broad surface area, they were connected to a robust, torque-resistant skeletal framework and were controlled by well-developed muscles. A morphological configuration that, in its basic principles, is not unlike that of underwater-flying turtles or penguins, or indeed from airborne birds, bats and pterosaurs. The case for ichthyosaur flight looks good.

Or, it would do, were there not some modern-day forms that possess many of the same features as the ichthyosaurs, but which do not fly. Part of Riess’ case for flight in ichthyosaurs was based on analogy with two living animals: the Australian lungfish (Neoceratodus) and the Amazon river dolphin (Inia). Both animals have wing-like fins strikingly similar to those of some ichthyosaurs and Riess mistakenly believed that both forms were underwater fliers. His reasons for thinking so are complex and buried deep in the labyrinthine depths of technical zoological literature, but having surveyed the literature, discussed the issue with colleagues, and spent many hours observing Inia on video, I am certain that the idea of either flying lungfishes or dolphins has been based on misinterpretation. Mary Wade, a palaeontologist who has published some of the most important work on Platypterygius, came to the same conclusion in a 1990 paper of hers (Wade 1990).

So what does this all mean? Well, if there are living animals that possess wing-like fins yet do not fly, then a direct correlation between wing-like fins and flight does not exist. Wing-like fins, big fin muscles and robust pectoral girdles can instead be explained as adaptations for manoeuverability - something very much evident in the behaviour of Inia. Lengthening and broadening of fins is not proof of flight, either. The hyperphalangic condition occurs in certain whales (it is particularly marked in the Longfin pilot whale (Globicephala melas)), animals that most definitely are not fliers. Furthermore, some underwater fliers (e.g., sealions) do not exhibit hyperphalangy. So there is no clear correlation between hyperphalangy and flight.

Hyperdactyly - the broadening of fins - could well evolve as an aid to small-scale local movements. Most types of fish use their fins extensively for this purpose, as do whales with their flippers. As an animal that spends a great deal of time making small-scale local manoeuvres in its complex, three-dimensional watery home, Inia is especially telling in that it may actually be taking part in a trend toward hyperdactyly, as it bears an extra bone in its flipper that is to all intent and purposes a sixth digit. Those ichthyosaurs with extra-wide fins were probably spending a great deal of time moving slowly, like Inia, perhaps while investigating prey on the seafloor.

Furthermore, despite Riess’ fin reconstructions, ichthyosaurs with preserved soft tissues show that the fin attachment to the body was broad, rather than narrow. Up and down movement was therefore somewhat restricted, and not suited for vigorous flapping.

One clear correlation that does appear to be true for swimming vertebrates concerns that tail. Essentially, if an animal has a propulsive surface on the end of its tail, it uses it. Riess thought that some ichthyosaurs, his example was the Lower Jurassic genus Leptonectes*, both flapped with the forefins, and used the shark-like vertical tail to steer. However, studies of ichthyosaur locomotion, notably those by Christopher McGowan and Michael A. Taylor, have demonstrated that the ichthyosaur tail was a powerful organ of propulsion. Indeed, it is hard to explain the evolution of this important and superbly hydrodynamic feature if it was used merely for steering rather than for active and constant use.

Further confirmation of tail-propelled swimming in shark-shaped ichthyosurs comes from work by Motani, You and McGowan (Motani et al. 1996). They plotted ichthyosaur fineness ratio [body length/body height] against tail height/length ratio for different kinds of ichthyosaur and shark. Not surprisingly, the advanced shark-shaped ichthyosaurs (e.g., Stenopterygius) grouped tightly with lamnid sharks - exactly what we would expect if both groups were hydrodynamically adapted for the same style of propulsion. The result would surely have been different if these ichthyosaurs were not shark-like in their style of swimming.

* This genus was still known as Leptopterygius Huene, 1922, when Riess was writing, a name now known to be preoccupied by a fish named by Troschel in 1860.

For a previous post on ichthyosaurs see Ichthyosaurs wars and marvellous mixosaurs and Life in the Oxford Clay sea.

Incidentally, given that Neoceratodus is mentioned in the above text I am morally obliged to direct you to Pharyngula’s Neoceratodus campaign. This animal (yes I know it’s not a tetrapod) is under significant environmental pressure.

Coming soon… those long-promised posts on agamas, domestic dog origins and rhinogradentians. For the latest news on Tetrapod Zoology do go here.

Refs - -

Motani, R., You, H. & McGowan, C. 1996. Eel-like swimming in the earliest ichthyosaurs. Nature 382, 347-348.

Riess, J. 1984. How to reconstruct palecology? – Outlines of a holistic view and an introduction to ichthyosaur locomotion. In Reif, W.-E. & Westphal, F. (eds) Third Symposium on Mesozoic Terrestrial Ecosystems, Short Papers. Attempto Verlag (Tübingen), pp. 201-205.

- . 1985. Biomechanics of ichthyosaurs. In Riess, J. & Frey, E. (eds) Principles of Construction in Fossil and Recent Reptiles. Konzepte SFB 230 Heft 4, pp. 199-205.

- . 1986. Locomotion, biophysics of swimming and phylogeny of the ichthyosaurs. Palaeontographica Abteilung A 192, 93-155.

- . & Frey, E. 1991. The evolution of underwater flight and the locomotion of plesiosaurs. In Rayner, J. M. V. and Wootton, R. J. (eds) Biomechanics and Evolution. Cambridge Uni. Press (Cambridge), pp. 131-144.

- . & Tarsitano, S. F. 1989. Locomotion and phylogeny of the ichthyosaurs. American Zoologist 29, 184A (abs).

Wade, M. 1990. A review of the Australian Cretaceous longipinnate ichthyosaur Platypterygius, (Ichthyosauria, Ichthyopterygia). Memoirs of the Queensland Museum 28, 115-137.

Ichthyosaur wars and marvellous mixosaurs

Another significant hurdle: today I finished making the required changes to my thesis (should have dealt with it sooner, but you know how it is). So right now I’m feeling pretty fired up about Eotyrannus and Yaverlandia, and I really should work hard on getting the manuscripts done and submitted.

Other interesting things have been happening. My good friend Bernie Dempsey phoned me on Saturday. He’s been out filming Honey buzzards Pernis apivorus and looking for European nightjars Caprimulgus europaeus recently, but the most interesting thing is that he’s been discovering lots of stag beetles, all of them with their abdomens eaten out by some large predatory tetrapod. If this sounds familiar it’s because this formed the subject of a recent blog post (go here). We’re going to compare corpses to see if all the animals were killed the same way. The reason he was phoning was to see if I knew what was killing the beetles (I didn’t answer, but merely directed him to this blog).

I also caught up recently with my good artist/writer friend Steve White (website here). After talking about British big cats, the Sultan’s elephant and all manner of other things with him I felt especially keen to complete my post on the Cupar roe deer carcass (first mentioned in the British big cats post). It’ll follow soon. But it’s something that happened during the week (on Tuesday 20th) that’s most inspired me lately, and ironically it was a talk that I gave. How arrogant is that? The talk was titled ‘Ichthyosaurs: the Mesozoic ‘fish lizards’’.

Followers of my posts might have noted that I do quite a bit of talk-giving, usually to local natural history and geology groups. I don’t know if I do more public speaking than other academics, let alone Ph.D. students, but it sure feels like it sometimes. Then again, I don’t know any academics that are in the same situation as me (devoid of all personal finance and funding). Anyway, while this stuff is fresh in my mind I feel I may as well do a post on some of the highlights.

As I’m sure I’ve said before, in talks I like to cover things that are genuinely new to the majority of the audience. And for any group of tetrapods there are always more than enough new, exciting things to cover. So in talking about ichthyosaurs I covered the basics: stuff such as, while they hung on until as late as the early part of the Late Cretaceous, they should best be regarded as animals of the Triassic and Early Jurassic as this is when their diversity was at its peak. Stuff such as the hyperphalangy and polydactyly that evolved in the limbs of some lineages, the well-known story of how soft-tissue-bearing specimens were first discovered, and all that data from Holzmaden (and other places) on ichthyosaur birth and babies.

Exploding whales, breech babies and toxic shock

On birth and babies, I contend that not all females ‘preserved in the act of giving birth’ really were giving birth when they died. Instead these individuals may have died while pregnant, with decomposition gases later pushing unborn babies out of the cloaca. Exactly this occurs in the dead bodies of beached whales today: pregnant females may have babies protruding from the birth canal, and males often have a distended penis that, similarly, has been extruded from the body cavity by gases building up inside. Of course this leads us on to the subject of exploding whales, but we won’t go there for now. I have some nice anecdotes.

Some ichthyosaurs had breech births, as their babies are preserved protruding head-first. Here again we have an analogy with cetaceans. Baby whales and dolphins ordinarily emerge tail-first, and are thus only ‘triggered’ to take their first breath when the head emerges. But if the head emerges first, the baby drowns, and its little corpse is then lodged in the mother’s birth canal. The mother then becomes slowly poisoned as the baby decomposes wedged inside her, and she dies of toxic shock. It’s not nice, but it happens, and it’s a reasonable (albeit untestable!) speculation to think that breech-birth ichthyosaur mothers sometimes died the same way too. If I remember correctly this idea was first proposed by Deeming et al. (1996), and I’ve a feeling that Naish (1997) picked up on it.

Marvellous mixosaurs

Some of the neatest new data on ichthyosaurs comes from newly appreciated taxonomic diversity. Mixosaurs are a fairly well studied and long-known group of basal Triassic ichthyosaurs, best known for little Mixosaurus (total length c. 1.5 m) named in 1887 for specimens from Middle Triassic Europe. Mixosaurs have always been depicted as rather dull and conventional (above is Zdenek Burian's famous, but very dated, life restoration of Mixosaurus). But it now seems that at least some of them were bizarre. Really really bizarre.

Middle Triassic Europe, North America and Spitsbergen was home to the mixosaur Phalarodon, named by John Campbell Merriam in 1910. At the back of its jaws are massive, rounded crushing teeth (properly known as tribodont teeth): proportionally huge, and in fact proportionally among the biggest of any ichthyosaur. The teeth at the jaw tips were slender and subconical, so Phalarodon seems to have been a generalist, perhaps picking up small soft-bodied prey with the rostral teeth, and crushing big hard-shelled prey with the tribodont teeth further back. Incidentally, a huge percentage of Triassic marine reptiles had tribodont crushing teeth like Phalarodon, and it’s a good question as to why this was so common at the time, and so much rarer afterwards. I might cover this when I produce a post on placodonts.

What also makes Phalarodon interesting is the presence of a proportionally large sagittal crest on the back of its head. Strongly compressed laterally and projecting dorsally from the skull roof to a height similar to that of the cranium itself, it must have had an important function, but we aren’t too sure what that was. A site for muscle attachment is the most popular explanation.

Like Mixosaurus, Phalarodon wasn’t particularly big, with P. major from Germany getting to perhaps 3.5 m. But the best is yet to come. The weirdest mixosaur – and, in my opinion, the weirdest ichthyosaur – is the freakish Contectopalatus atavus. Only known from the Middle Triassic of Germany, it was a giant compared to other mixosaurs, with some incomplete specimens indicating complete lengths of 5 m. Its skull was slender-jawed and, while its many subconical teeth were blunt-tipped, it lacked the huge tribodont teeth of Phalarodon. It seems not to have gone around crushing molluscs or prey like that, therefore. It also has a sagittal crest, but it’s even more prominent than that of Phalarodon. Sticking from the top of the skull like a piece of card, the sagittal crest seems to have been flanked by shallow concavities on the skull roof. Again, all of this may have been for muscle attachment, but nobody’s really sure.










A big, mysterious and bizarre ichthyosaur, Contectopalatus was originally recognised as a new species in the 1850s, but not until 1998 did Michael Maisch and Andreas Matzke name it as a new genus (Maisch & Matzke 1998). For additional data on it, see Maisch & Matzke (2000a, b, 2001). Their reconstruction of its skull is shown above. It’s at this point that I should note that not all ichthyosaur experts agree that Phalarodon and Contectopalatus are truly distinct from boring little Mixosaurus. Ryosuke Motani has strongly disagreed with this classification, and argues that all three forms should be synonymised (Motani 1999). Indeed Motani and Maisch & Matzke differ in their opinions on so many matters of ichthyosaur taxonomy and phylogeny that we talk of the ‘Ichthyosaur wars’, though it’s not as if the workers involved would ever get physically aggressive with one another (I assume). Motani is a student of Chris McGowan, or ‘god’ as those in the ichthyosaur research community sometimes call him.

Whatever its taxonomic status, there’s no denying that Contectopalatus was unusual and interesting. This begs the question as to why it’s not better known: I have yet to see a single artistic restoration of it, for example. Back when the BBC were still deciding which animals they were going to include in the Sea Monsters series (fronted by Nigel Marven) they screened in 2003, I (via Dave Martill, one of their technical consultants) strongly recommended use of Contectopalatus. But they didn’t go with it. Shame. So there it sits, in the literature, unexploited and largely unknown.

At 5 m in length, Contectopalatus is reasonable in size for a Triassic ichthyosaur, but it’s not exceptional. The more derived cymbospondylids and shastasaurs grew to larger sizes and were also far more formidable, with their stout, keeled teeth and robust jaws indicating that they were macropredators that perhaps filled the role that pliosaurs and mosasaurs did later on in the Mesozoic. And it’s among shastasaurs that we find the biggest of all ichthyosaurs, and indeed the biggest of all marine reptiles. I was going to talk about them here, but now I can’t. I was also going to talk about the swordfish that speared Alvin the DSRV and about Excalibosaurus and Eurhinosaurus and about so much else, but it will have to wait to another time.

For the latest news on Tetrapod Zoology do go here.

Refs - -

Deeming, D. S., Halstead, L. B., Manabe, M. & Unwin, D. M. 1995. An ichthyosaur embryo from the Lower Lias (Jurassic: Hettangian) of Somerset, England, with comments on the reproductive biology of ichthyosaurs. In Sarjeant, W. A. S. (ed) Vertebrate Fossils and the Evolution of Scientific Concepts. Gordon and Breach Publishers, pp. 463-482.

Maisch, M. W. & Matzke, A. T. 1998. Observations on Triassic ichthyosaurs. Part III: A crested, predatory mixosaurid from the Middle Triassic of the Germanic Basin. Neues Jahrbuch fur Geologie und Palaontologie, Abhandlungen 209, 105-134.

- . & Matzke, A. T. 2000a. The Ichthyosauria. Stuttgarter Beiträge zur Naturkunde Serie B (Geologie und Paläontologie) 298, 1-159.

- . & Matzke, A. T. 2000b. The mixosaurid ichthyosaur Contectopalatus from the Middle Triassic of the German Basin. Lethaia 33, 71-74.

- . & Matzke, A. T. 2001. The cranial osteology of the Middle Triassic ichthyosaur Contectopalatus from Germany. Palaeontology 44, 1127-1156.

Motani, R. 1999. The skull and taxonomy of Mixosaurus (Ichthyopterygia). Journal of Paleontology 73, 917-928.

Naish, D. 1997. Aspects of Ichthyosaur Evolution and Ecology With Comments on Cross-Taxon Convergence Seen Throughout Marine Tetrapods. Research Project Report 1997/97, Department of Geology, University of Southampton, pp. 80.