Saturday, March 25, 2006

New, obscure, and nearly extinct rodents of South America, and…. when fossils come alive

My phd thesis - which, may I remind you, is all about Lower Cretaceous predatory dinosaurs, focusing in particular on the basal tyrannosauroid Eotyrannus - consists of six chapters. The good news is that chapter 5 (devoted to enigmatic large theropods) is nearing completion, and chapter 6 (on Yaverlandia) is already just about done. That still leaves tidying up on the other chapters, plus various tasks like running a few analyses, inserting a few more figures here and there, and so on. But I’m getting there. Thecocoelurus, Juravenator, Calamosaurus, Becklespinax and Valdoraptor are the animals that I’ve been thinking about the most I suppose, and I’d post on them if there was enough time. But there isn’t, so here’s another post devoted to rodents. To think this was all initiated by a tea card featuring a jerboa.

Though new rodents are described from all over the place (yes, even from North America and Europe*), I had a recollection of the greatest percentage coming from South America. And indeed there are quite a few (note that some of the following don’t have common names), with a randomly-selected list of my favourites being…

-- Michoacan deer mouse Osgoodomys banderanus Hooper & Musser, 1964, a narrow-skulled Mexican murid described as a new species of Peromyscus but given its own genus (named after Osgood [see previous post: Osgood, Fuertes and mice that swim and mice that wade]) in 1980. It’s the species featured in the photo above (and, yes, I do know that Mexico isn't in South America, but let’s pretend that I've now expanded the scope to be ‘Latin America’).
-- the Candango or Brasilia burrowing mouse Juscelinomys candango Moojen, 1965, a semi-fossorial murid discovered in 1960, known from 9 specimens, last collected in 1990, and now possibly extinct (the Brazilian site where it was discovered was destroyed and built on).
-- Olrog’s chaco mouse Andalgalomys olrogi Williams & Mares, 1978, an Argentinian sigmodontine murid.
-- Abrawayaomys ruschii Cunha & Cruz, 1979, a spiny Brazilian sigmodontine known from a handful of specimens.
-- Abrocoma boliviensis Glanz & Anderson, 1990, a Bolivian chinchilla rat known from two specimens, one collected in 1926 and the other in 1955.
-- Amphinectomys savamis Malygin et al., 1994, an amphibious Peruvian murid known from a single specimen collected in 1991.
-- Pearsonomys annectans Patterson, 1992, a semi-fossorial Chilean murid.
-- Microakodontomys transitorius Hershkovitz, 1993, a Brazilian murid known from a single specimen (collected in 1986).
-- Salinomys delicatus Braun & Mares, 1995, an Argentinian phyllotine sigmodontine with proportionally long feet and large ears.
-- Roig’s Chaco mouse Andalgalomys roigi Mares & Braun, 1996, another Argentinian sigmodontine.
-- Black or Koopman’s tree porcupine Coendou koopmani Handley et al., 1992, a Brazilian tree porcupine with short, dark fur. A similar form from Ecuador, differing in being speckled with white or yellow, was reported by Emmons (1999) and may be a new, as yet unnamed, species.
-- Orces fishing mouse Chibchanomys orcesi Jenkins & Barnett, 1997, an amphibious ichthyomine murid endemic to the Ecuadorian Parque Nacional Cajas.
-- Cuscomys ashaninka Emmons, 1999, a large Peruvian chinchilla rat [see post ‘Giant furry pets of the Incas’] discovered in 1997.
-- Akodon aliquantulus Monica Díaz et al., 1999, an Argentinian sigmodontine known from two specimens collected in 1993. The smallest member of its genus.
-- Tapecomys primus Anderson & Yates, 2000, a Bolivian phyllotine sigmodontine collected in 1991.
-- Coendou ichillus Voss & da Silva, 2001, an Ecuadorian tree porcupine first collected in 1936.
-- Coendou roosmalenorum Voss & da Silva, 2001, a small tree porcupine first collected in 1996 and named for Marc van Roosmalen and his son Tomas. Van Roosmalen is well known in South American mammalogy for the multiple new monkey species he has discovered.
-- Abrocoma uspallata Braun & Mares, 2002, an Argentinian chinchilla rat with larger ears and a longer tail than related species. Known only from a single specimen collected in 1995 (incidentally, if you've read the previous post on abrocomids, go look again some time: I’ve had to update it in view of this discovery and others).
-- Thomasomys ucucha Voss, 2003, a sigmodontine (first collected in 1980) from the Cordillera Oriental of Ecuador.

There are many more. Note as usual that the discovery date of a taxon is not necessarily the same as the date as when it was first named or recognised as new. Not all new rodents are South American: other discovery hotspots include Madagascar, Australia, New Guinea, and Borneo and elsewhere in SE Asia. Because rodents are typically small and inconspicuous it follows that a steady trickle of dull little mouse-type things should be continually discovered and described as new taxa, but it wouldn’t be accurate to think that all new rodents are like this. Three of the animals listed above are tree porcupines, and these are all fairly big rodents with head and body lengths of about 30 cm. Abrocomids are also large, with head and body lengths typically exceeding 30 cm.

Discoveries of entirely new animals are very cool of course, but they’re actually mundane and entirely ordinary. If you follow the literature it is very easy to become either overwhelmed or bored by the incredible number of new species that get described, even among tetrapods. Descriptions of new rodent, frog and lizard species appear routinely within technical journals – as in, a few every month. Perhaps slightly more interesting, and certainly more unusual, are those cases where species originally described as fossils have later turned out to be still extant. Such animals are often described as ‘living fossils’, but that’s a bit silly given that virtually all extant species have a record going back many thousands of years at least, thus making their presence in the fossil record inevitable (for more on this area go see Are Sumatran rhinos really ‘living fossils’?). Anyway, classic examples of this sort of thing include the following.

-- Goosebeak or Cuvier’s beaked whale Ziphius cavirostris: described as a fossil in 1823 but realised in 1872 to be the same thing as beached specimens reported as early as 1826 but given different names.
-- Bush dog Speothos venaticus: named as a fossil in 1839 [which explains why its generic name means ‘cave wolf’], and first described in living form in 1843. The same person, Danish naturalist Peter Wilhelm Lund, described both the fossil and living animals, but failed to realise they were the same thing: he named the living animals Icticyon, and this name was for used for Speothos until well into the 20th century.
-- False killer whale Pseudorca crassidens: described as a fossil in 1846 and described from modern-day strandings in 1862.
-- Mountain pygmy possum Burramys parvus: described from Pleistocene owl pellets in 1896 but found alive in a ski lodge in the Australian Alps in 1966.
-- Chacoan peccary Catagonus wagneri: named as a fossil in 1930, and found alive in 1974.
-- Bulmer’s fruit bat Aproteles bulmerae: described as a fossil in 1977 and reported from modern-day bones in 1980, then feared extinct, but since rediscovered alive.

Relatively little known is that the generic name for white-tailed and mule deers, Odocoileus, was originally coined for a fossil (a premolar found in a Pennsylvanian cave), and later transferred to the extant species when they and the tooth were found to belong to the same genus. Among rodents, there are, similarly, a few cases where fossil species have later been discovered extant, but because the animals concerned are obscure and poorly known, the relevant cases have gone under-reported.

-- A new fossil murid from Flores was described as Floresomys naso by Musser (1981). The generic name was preoccupied by a fossil Mexican sciuravid, so Musser et al. (1986) renamed this taxon Paulamys naso. A single live individual was reported in 1991 (Kitchener et al. 1991).
-- In 1887, Herluf Winge described multiple fossil murids from the Brazilian Lagoa Santa caves, and among them was a species he called Scapteromys labiosus. In 1980 this species, now referred to the crimson-nosed rat genus Bibimys, was reported to be extant within the same region (Voss & Myers 1991).
-- Hesperomys simplex was described from the Lagoa Santa caves by Winge in 1887, but also reported by him as occurring in modern-day owl pellets, and thus still extant. A Paraguayan murid named Oryzomys wavrini was described in 1921, and was shown by Voss & Myers (1991) to be the same thing as Hesperomys simplex, the name currently used for this taxon being Pseudoryzomys simplex. It’s sometimes called the ratos-do-mato (Nowak 1999).
-- A living species from Uruguay and Brazil, described in 1955 as Holochilus magnus, was shown by Voss & Carleton (1993) to be the same thing as another Pleistocene fossil species named by Winge in 1887, Hesperomys molitor. Restudy of this murid showed that it was distinct from both Holochilus (the semiaquatic web-footed rats) and Hesperomys (nowadays synonymous with Calomys, the vesper mice) and thus deserving of its own genus, so today this species is called Lundomys molitor.

All of these ‘prehistoric survivors’ were known originally from Pleistocene or Holocene fossils, so their presence in modern times has only ever extended their geological range by a million years or so, at most (in some cases – such as that of Paulamys naso – by just a few thousand years).

Changing the subject somewhat, among modern-day mammals there are only two species whose discovery has extended the geological range of their clade by an amount of more than a few million years, and note that we’re no longer talking about members of the same species being present across a longer span of time than originally thought. One of them has lately been in the news. The first is the so-called Monito del Monte or Colocolo Dromiciops australis, described in 1894 and classified as a didelphid. In 1955 however, Reig pointed out that Dromiciops was almost identical to Microbiotherium from the Miocene, and it is now widely agreed that Dromiciops is a living representative of Microbiotheriidae, a South American marsupial clade named in 1887 and with a fossil record that doesn’t extend beyond the Lower Miocene. Dromiciops has no fossil record, so a ghost lineage of about 20 million years has to be invoked for the group. Incidentally, exactly how microbiotheriids fit into marsupial phylogeny is a hotly debated topic that would require a post all its own.

The second ‘late survivor’ brings us back to rodents: it’s the Laotian kha-nyou Laonastes aenigmamus, described last year as representing an entirely new hystricognath lineage, the Laonastidae (Jenkins et al. 2005). But - how cool is this - Dawson et al. (2006) have shown that Laonastes is in fact a living representative of Diatomyidae, a group otherwise known only as fossils, and with a fossil record that doesn’t extend beyond the Upper Miocene. So we now have to extrapolate a ghost lineage for diatomyids that extends from the Upper Miocene to the present: that’s about 7-5 million years, so not that long, but… even so. As Dawson et al. (2006) note, late survivors that represent ‘the reappearance of taxa after a lengthy hiatus in the fossil record’ are termed ‘Lazarus taxa’, and Dromiciops and Laonastes can both be described this way. As it happens I was going to post on Lazarus taxa in the near future anyway: not because of rodents but because of late-surviving Mesozoic basal synapsids. To say more would give the game away. Think also of temnospondyls, choristoderes and sphenosuchians.

And there’s more to say on Laonastes too: it’s exciting, not just in being a Lazarus taxon, but in being a specialised, highly cryptic member of a bizarre and specialised relict community. Tied to a specific unusual habitat, it is one of a suite of recently recognised species whose distribution may actually extend beyond Lao PDR. More on that soon. Err, maybe when I’ve finished the thesis. Oh yes, the thesis.

*North America recently yielded the Sonoma tree vole Arborimys pomo Johnson & George, 1991, and Europe the Bavarian pine vole Microtus bavaricus König, 1962. The latter species was thought extinct following its post-1962 disappearance, but was rediscovered in 2000.

The picture above is of Osgoodomys banderanus, and was borrowed from the Instituto de Biología site.

Refs - -

Dawson, M. R., Marivaux, L., Li, C.-k., Beard, K. C. & Metais, G. 2006. Laonastes and the “Lazarus effect” in Recent mammals. Science 311, 1456-332.

Emmons, L. H. 1999. Neotropical Rainforest Mammals: A Field Guide (Second Edition). University of Chicago Press (Chicago & London).

Jenkins, P. D., Kilpatrick, C. W., Robinson, M. F. & Timmins, R. J. 2005. Morphological and molecular investigations of a new family, genus and species of rodent (Mammalia: Rodentia: Hystricognatha) from Lao PDR. Systematics and Biodiversity 2, 419-454.

Kitchener, D. L., How, R. A. & Maharadatunkamnsi. 1991. Paulamys sp. cf. P. naso (Musser, 1981) (Rodentia: Muridae) from Flores Island, Nasu Tenggara, Indonesia – description from a modern specimen and a consideration of its phylogenetic affinities. Records of the Western Australian Museum 15, 171-189.

Musser, G. G. 1981. The giant rat of Flores and its relatives east of Borneo and Bali. Bulletin of the American Museum of Natural History 169, 67-176.

- ., van de Weerd, A. & Strasser, E. 1986. Paulamys, a replacement name for Floresomys Musser, 1981 (Muridae), and new material of that taxon from Flores, Indonesia. American Museum Novitates 2850, 1-10.

Nowak, R. M. 1999. Walker’s Mammals of the World, Sixth Edition (two volumes). The Johns Hopkins University Press (Baltimore and London).

Voss, R. S. & Carleton, M. D. 1993. A new genus for Hesperomys molitor Winge and Holochilus magnus Hershkovitz (Mammalia, Muridae): with an analysis of its phylogenetic relationships. American Museum Novitates 3085, 1-39.

- . & Myers, P. 1991. Pseudoryzomys simplex (Rodentia: Muridae) and the significance of Lund’s collections from the caves of Lagoa Santa, Brazil. Bulletin of the American Museum of Natural History 206, 414-434.


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