Jumping the gun: Similicaudipteryx

Hagfish from www.itsnature.org

Hi folks, Yes its been quiet here on Dracovenator. School is back on, and I have a hectic 16 hours of teaching a week which coupled with a newborn in the house is leaving me kind of exhausted. In anycase I'm going to give voice to a few thoughts that flashed through my mind when I read the abstract for the latest dinosaur taxon to be named from the Jehol Group of Liaoning. I haven't seen the paper yet, someone want to forward the pdf?, So this should all be read as speculative thoughts and nothing more. Firstly I'm sure you are are wondering why the hell I've put up a picture of a hagfish, of all things, to illustrate a post about a dinosaur, well read on....
Similicaudipteryx yixianensis He et al. 2008 is described as a caudipterygiid oviraptorosaur in the latest Vertebrata Palasiatica. For those who may need reminding, Caudipteryx was one of the first non-avian theropods discovered with a plumage of undeniable pennaceous feathers. As one could have expected the 'BAND' didn't take to kindly to the idea of fully plumed non-avian theropod dinosaur and they fairly quickly responded with claims that Caudipteryx was actually a true bird that had become secondarily flightless and ground-dwelling. Indeed there is something terribly birdy about the incredibly stump-tailed Caudipteryx and its wing-like hand with a highly reduced third digit.

A very nice model skeleton of Caudipteryx. From www.dinocasts.com

These observations have occurred to many and even Stephen Gould wrote an essay about how blurry the bird-dino distinction had become and in this case he thought us dino palaeontologists had got it wrong. In anycase it didn't take long for people to see that Caudipteryx shared much with the mid to late Cretaceous Oviraptorosaurs. It has always been puzzling how many bird-like features Oviraptorosaurs display that are not present in the Deinonychosauria which is the currently accepted sister group of birds. These have been largely thought of as convergences because comprehensive cladistic analyses routinely place them outside the clade of Deinonychosauria + Birds. Why is this? Well for all their birdiness oviraptorosaurs have a suite of plesiomorphies including (but not limited to) a straight(versus bowed) metacarpal three , a deep ilium with a post-acetabular process that exceeds in length the pre-acetabular process, and a forwardly directed pubis with an anteriorly and posteriorly expanded boot. Now along comes Similicaudipteryx and adds a couple more bird-like features that are not seen in deinonychosaurs. One is the presence of deep hypapophyses on the anterior dorsal vertebrae and a pygostyle on the end of the tail. The latter had been previously reported in the oviraptorosaur Nomingia but had been dissmissed as convergence since other oviraptorosaurs apparently didn't have one. Similicaudipteryx raises the spectre that pygostyles may have been primitive for oviraptorosaurs and lost in later taxa (or simply not present because the material was not mature enough in the case of Caudipteryx). One more little observation before we can finally get to slime-hags: The undoubted volant pygostylian bird, Sapeornis, also from Liaoning, has a remarkably caudipterygiid-like skull as noted by Stephen Czerkas when he briefly described a specimen (under the name Omnivoropteryx).
Now to hagfish. Although the dust (slime?) hasn't settled on the controversy over their systematic position, it seems that the evidence for cyclostome monophyly (that is lampreys + hagfish) is growing. Now that is deeply uncomfortable to those used to working with morphology, since everything about hagfish seems to shout that they are basal to lampreys + jawed vertebrates. For instance they lack extrinsic eye muscles, innervation of the heart, vertebrae of any sort and muscles in the caudal fin. Nonetheless it looks like hagfish really are an example of pervasive, wholesale reversion to a more primitive condition. There are other less extreme examples of this phenomenon. For instance gavials are now firmly placed as the sister-group to tomistomines (false gavials) within Crocodylidae (based on combined, morphological and molecular analyses, including fossils) they have a suite of plesiomorphies throughout the skeleton that initially confounded morphological cladistic analyses by place gavials at the base of modern Crocodylia.

Wholesale taxic atavism in gavials. A graphic representation of morphological characters that place gavials on a more basal branch of crocodylian phylogeny. From Gatesy et al. 2003.

Gatesy et al. 2003 called this pervasive reversal 'wholesale taxic atavism'. Note that it does not appear to be the result of sustained selection for any particular ecophenotype. False gavials are also longirostrine fish-eaters but lack the wholesale atavism seen in gavials. This to my mind is a very interesting and understudied aspect of evolution.
Whatever its cause I'd like to suggest that Oviraptorosauria might end up being yet another example. If this is so I will predict that as we get a better fossil record of maniraptorans from the latest Jurassic and the Earliest Cretaceous we will find earlier and earlier oviraptorosaurs that get more and more like pygostylians. Maybe we will find a volant or recently ex-volant sapeornithid-caudipterygiid intermediate. Of course I could just be jumping the gun....

references

Gatesy J, Amato G, Norell M, DeSalle R and Hayashi C (2003) Combined Support for Wholesale Taxic Atavism in Gavialine Crocodylians. Systematic Biology, 52(3): 403 — 422

He T, Wang X-L, and Zhou Z-H (2008). A new genus and species of
caudipterid dinosaur from the Lower Cretaceous Jiufotang Formation of
western Liaoning, China. Vertebrata PalAsiatica 46(3):178-189.

Email glitch

Hi to all colleagues who read this. It seems that the last weeks worth of emails that I sent from my wits account have failed to be mailed and I didn't notice. I've only just started sorting through the blizzard of messages that have swollen my inbox since Anwen was born. I dislike using my university email account for several reasons (limited space, strange inability to download most attachments, excessive spam, can only be accessed by Outlook on the Web) and much prefer to use my gmail account. If you recently sent me a reprint request on my wits account please resent your request to yatesam at the site I just mentioned above.

What was it?

Wouldn't you know it?, I went to take a photo of the now-prepared mystery skull, and the thing is away on exhibition, arrgh. Nonetheless I do have a snout photo of the skull lurking in my research folder, which should make its identity rather obvious.

Yes, I'm afraid it was nothing so unusual. Just another Massospondylus skull. Nonetheless it was one I collected so I'm quite proud of it. It also came from quite a beautiful site from the Clarens Formation making it one the youngest known specimens.

Beatrix Farm in the Free State, where the skull was found.

Recently I've tallied up the number of Massospondylus skulls known (not including the Kayenta and South American specimens which, although related, are something else). There are 14 more-or-less complete skulls that I know of (if you include the two embryonic skulls, and 1 unprepared skull). Now I'm sure that there are more Psittacosaurus skulls floating around but they are divided between a host of species. Currently all these Massospondylus skulls are classified as one species, M. carinatus. Could this be the most numerous dinosaur species in terms of whole skulls?

Umbilia gazing

I'll do the big reveal on the puzzle fossil tomorrow. For now I want do something I've wanted to do since I started this blog. Post on Cenozoic molluscs. Please stick around they are fascinating - and beautiful as well.
The genus Umbilia is an endemic Australian genus of cypraeid (cowry shell).
Umbilia eximia from the Miocene of Victoria and South Australia.

Cowries are marine gastropods distantly related to periwinkles (littorinids). They are generally predators on sessile invertebrates and have a distinctive shell characterised by determinate growth. As maturity approaches the outer lip reflexes, closing the aperture to a narrow slit and causing the cessation of growth. Umbilia take their name from their countersunk spires, that look like a little belly-buttons. Other features of the genus include large size, the anterior and posterior canals produced into well developed ‘beaks’ (rostra) and a poorly developed to non-existent fossula. To those not steeped in the arcana of cypraeid anatomy, the fossula is a broadened, scooped-out area on the inner wall of the aperture (the columella) at its anterior end. The diagram below should help a little.


A typical cowry shell (Trona stercoraria)showing the major parts of the shell.

In terms of life-history, Umbilia is unusual amongst cypraeids in having direct development. That is to say that they forgo the usual planktonic larval stage, instead hatching directly into benthic crawling snails. This of course severely limits dispersal ability, and may be a reason why the genus has not been able to spread beyond the continental shelf of Australia. Members of this genus have produced a number of remarkable morphologies that are very unusual amongst cowries (a terribly conservative group on the whole) although the extant species are rather boring compared to those of the past. First lets survey this diversity.

The species of Umbilia
Umbilia makes its first appearance in the fossil record in the Late Oligocene of Victoria in south-eastern Australia, specifically at one location, the Bird-Rock Cliffs of Jan Juc Beach (right next door to the famous Bell’s Beach). Two quite different species are found here, indicating that the genus has a deeper, hidden history. Umbilia prosila is one of the Bird Rock species and is the smallest member of the genus, only reaching 39 mm long, with a globular shell and weakly produced rostra.
Umbilia prosila, this and all other specimen photos are from Darragh 2002.

Indeed U. prosila is one of the plainest, simplest members of the genus. Although U. prosila may not display any of the trademark weirdness of the genus, its contemporary U. platyryncha certainly does. At 95 mm is a medium-sized species with its anterior rostrum produced out into a broad, flat spatula-like process. Posteriorly some specimens have no rostrum at all, just a pair of heavy calluses on each side of the posterior canal, while others show the the weakest signs of posterior projection. The aperture bears only sparse, weak denticulations.
Umbilia platyrhyncha

The early Miocene contains but one named species, U. angustior, which is more widespread than its predecessors, being found at a number of localities in Victoria and across Bass Strait in Tasmania as well. It is clearly related to U. platyrhyncha but differs in smaller size, a narrower and less flattened anterior rostrum and a weakly developed posterior rostrum. Some specimens also show a vague pair of tubercles on the dorsal surface of the anterior rostrum.
Umbilia angustior

The species may have extended at least as far west as the Murray Basin of South Australia but the appropriate aged rocks (the Mannum Formation) only contain poorly preserved cypraeid moulds and casts that are presently inadequate for diagnosis. This is a common problem for the Cenozoic marine sediments of South Australia. It seems that here the section is dominated by porous bioclastic calcarenites that have allowed groundwater to flush away the original aragonite that made the shells of cowries and indeed most other molluscs. My pet hypothesis is that this is due to the drier climate of South Australia during the Cenozoic compared to Victoria, so that there were far fewer creeks and rivers dumping terrigenous silt and mud into the sea that would eventually settle out and protect the aragonite shells from the ravages of groundwater.
Like many other molluscan clades, Umbilia radiates drammatically in both diversity and disparity in the middle Miocene. This is when the shallow epicontental seas of southern Australia reached their maximum extent. Five species have been recorded from the middle Miocene and a sixth (described by yours truly) is in press. Commonest of these was U. eximia.
Umbilia eximia

It is a moderately large species, similar in size to the extant U. hesitata. It has a shorter anterior rostrum than either U. platyrhyncha and U. angustior but has a well-developed posterior rostrum that is usually bent toward the body wall. The anterior rostrum bears a strong pair of knob-like tubercles on its dorsal surface. These may indicate that the species is related to U. angustior or may even be a direct descendant of it. Another feature of U. eximia is that it often displays is a set of small basal flanges on each side of the rostra. U. eximia has been found in numerous localities across Victoria and into South Australia. It is a somewhat variable species (perhaps just a function of its larger sample size) and a host of synonyms have been named in the past (U. mccoyi, U. frankstonensis, U. sphaerodoma, U. brevis, U. montismarthae). Thomas Darragh (2002) has examined the holotypes of all of these and found that they differ only slightly (by no more than the normal variation seen in a single sample from a rich site), if at all from the holotype of U. eximia. To me the most intriguing feature of U. eximia is the denticulation of the inner lip. Unlike earlier species which have rather simple weak denticulations along the margins of the aperture, the columellar denticulations become strong, close-set ridges with rectangular cross-sections that extend across at least half the width of the base. The reason that this feature is interesting that another cypraeid genus, Zoila, evolved a sympatric species (Zoila platypyga) that displays the same morphology. Earlier species of both genera have normal to weak dentitions, as do all species of both genera after the middle Miocene. Why? The best hypothesis I can think of is that the middle Miocene of south-eastern Australia was home to a predator that specialised on cypraeids in the 90-100 mm size range (there are both larger and smaller sympatric cypraeids that do not show this modified dentition) and that these highly elongate ridges could have been an adaption to stop propagation of cracks when the shell was placed under stress by the predator trying to break in. What was this predator? I don’t know but some kind of teleost fish or starfish seems to be likely candidate (neither have left a good fossil record in the Miocene of south-eastern Australia). Whatever it was it either went extinct or switched prey and/or tactics by the end of the middle Miocene and the elongated columellar teeth disappeared from both Umbilia and Zoila. More to come later....

References

Darragh, TA (2002) A revision of the Australian genus Umbilia (Gastropoda: Cypraeidae). Memoirs of the Museum of Victoria 59: 355-392.

Picture of the day: What is it?

Given the great popularity of Darren Naish's guessing games and my complete immersion in paper writing right now, I'm going to do likewise. So here is a field photo from my archives. The specimen is now prepared. What do you think the fossil is?

A paper you may have missed

Images courtesy of Fernando Abdala

Today I’m showcasing a little paper on some very intriguing little teeth (shown above) from the Triassic of South Africa that appeared last year (Abdala et al. 2007). It didn’t make much of an impact partly because of its location (the local ‘South African Journal of Science’) and perhaps also because no firm conclusions could be reached. Nevertheless it deserves comment because whatever the teeth turn out to belong to they are significant, indeed they have the potential to be extremely significant.
The teeth in question were recognised when Helke Mocke, then an honours student at the BPI who was being supervised by Fernando Abdala, was attempting to find isolated cheek teeth of Bauria, a therocephalian therapsid with some striking convergences with mammals. Helke was attempting to test the hypothesis that Bauria was an herbivore by looking for dental microwear on the cheek teeth. Most of the Bauria in our collections either have the lower jaws tightly clamped against the upper jaws making it impossible to see the chewing surfaces of the teeth, or had the teeth mechanically prepared out of hard matrix with airscribes and pins, potentially adding a whole new set of scratches and microwear that had nothing to do with the diet of the animal. Bauria comes from the middle part of the Burgersdorp Formation of the Karoo Basin. This part of the formation is thought to be latest Early Triassic in age and is also the source of such well known extinct animals as Erythrosuchus, Cynognathus and Kannemeyeria. It is here that I play a very minor role in the story. I suggested to Helke that she might find good Bauria teeth in the older parts of the Burgersdorp Formation. The older parts (known informally as the ‘A zone’) are generally rich in aquatic or subaquatic taxa such as lungfish, hybodontid sharks and temnospondyl amphibians but a rich channel lag deposit found by palaeontologist/geologist John Hancox is crammed with all sorts of small vertebrate fossils, including some terrestrial creatures. Amongst them were teeth that had been identified as bauriid. These could be isolated by simple surface picking at the site, or screen washing in the lab. So Helke proceeded to look at the A zone bauriid teeth with a microscope. As it turned out this was the first time anyone had given these teeth anything more than a cursory glance. Surprisingly they weren’t bauriid teeth at all. Even more surprisingly the crowns of these teeth resembled nothing more than those of early mammals called haramiyidans. Compare the A zone teeth featured above with those of a haramiyidan below)

Haramiyavia, from Jenkins et al. 1997.

Haramiyidans themselves are an enigmatic group known only from teeth and incomplete jaws (apparently there are some postcranials of Haramiyavia but these are rather uninformative). Their cheek teeth bear double rows of small cusps, similar to those of multituberculates, which they are often grouped together with in the clade Allotheria. Multituberculates have a derived therian-like shoulder girdle, indicating that they share a more recent common ancestor with them than monotremes or other major Mesozoic mammal groups like eutriconodonts, docodonts and morganucodonts. The earliest haramiyidans are from the late Norian Stage of the Late Triassic. If they are truly early relatives of the multis then they would push back the origin of crown group mammals, and even more significantly advanced theriimorph mammals, to a time 45 million years or more before the next oldest appearance of this clade in the fossil record. If the A zone teeth are also regarded as allotherian then we have the appearance of theriimorph mammals before the appearance of probainognathians, at a time when only the earliest eucynodonts had just made their appearance. Clearly this is strongly at odds with the known fossil record. At this point I think there are three main hypotheses that can explain these teeth. I order them here from what is in my opinion the most likely to the least likely. 1) The A zone teeth are convergently similar to haramiyidans and do not belong to a mammal at all. 2) The A zone teeth are early haramiyidans but haramiyidans are themselves an early branch of cynodonts and are not mammals. 3) The A zone teeth are haramiyidans and haramiyidans are allotherian mammals. This last hypothesis implies a huge stratigraphic debt, with ghost lineages for chiniquodonts, probainoganthids, trithelodonts, tritylodonts, morganucodonts, Sinoconodon, docodonts, Hadrocodium, Kuehneotherium, australosphenidians and stem trechnotherians all extending back to the Early Triassic.
Multicusped rasping teeth have evolved multiple times in synapsid evolution with tritylodontids, multituberculates and ektopodontids all being independant examples (I am sure there are more). The A zone teeth are single rooted (like basal cynodonts but unlike almost all advanced cynodonts including mammals and haramiyidans) which supports hypothesis 1.
If they are only convergently mammal-like then what are they? We can't say now but I like the idea that maybe they are derived bauriids afterall. The answer will be forthcoming from the next field trip, I hope.
Oh, we still don't know what Bauria ate.

References

Abdala F, Mocke H, Hancox PJ (2007) Lower Triassic postcanine teeth with allotherian-like crowns. South African Journal of Science 103: 245-247.

Jenkins FA Jr, Gatesy SM, Shubin N, Amaral WW (1997) Haramiyids and Triassic mammalian evolution. Nature 385: 715-718.

picture of the day: Dicraeosaurus

Once again no time for a decent post - I'm going into hospital tomorrow for a minor procedure and will be off for a few days so the lack of activity will continue I'm afraid. Anyway this is a rough sketch from my notebook that I drew in the old dinosaur gallery of the Humboldt Museum in Berlin. Dave Unwin had given us (myself and Max Langer) after hours access to the gallery. I should have been furiously taking this once off oportunity to note and photograph as much as possible but I rapidly became exhausted (it had been a very hectic study trip) so after a short look at the Elaphrosaurus mount. I plonked myself in front of the Dicraeosaurus skeleton and drew this. I'm very happy with the way the head and neck turned out (note that the nostrils are in the pre-Witmer position).