I am a palaeontologist living and working in Alice Springs, in the red centre of Australia. I moved here with my wife and three kids from Johannesburg, South Africa. I used to focus my research on dinosaurs, and it is fair to say I am still a dino nut but these days I work on fossils from the NT, be they turtles, tassie tigers or anything else. In my spare time I like to watch birds, catch beetles, lizards and snakes and generally find out as much about the species around me as I can.
I have no time for a lengthy post, I'm in the midst of teaching three honours modules and trying to catch up on a backlog of research papers I need to write. I got a big one away just last week... Anyway this picture shows Golden Gate National Park at Rooidrai (Red Corner) where James Kitching found the Massospondylus embryos that featured in Science a few years back. The large sandstone bluffs are aeolian deposits belonging to the Clarens Formation, while the red friable rocks below are the fluvial mudstones and sandstones of the Elliot Formation. The embryos were found in the spoil heap created by blasting for the road. You can see the heap to the right of the truck ('bakkie'pronounced 'bucky' in South African) disappearing off down the gully.
A common lament amongst the vertebrate palaeontology community is the trend toward quick, brief publications in high-impact journals with long delayed to non-existant followup with detailed descriptions. The problem is a symptom of today’s ‘publish or perish’ academic climate where the cost of spending a lot of time producing a monograph that will inevitably appear in a low impact journal can actually harm an early career. I am guilty of adding to the problem myself. Five years after my publication of Antetonitrus in the Proceedings of the Royal Society the descriptive osteology is still in preparation (though not because I don’t wish to produce it, it is just that so many other projects have pushed their way to the front of my to do list). Fortunately more organised and focused researchers have not forgotten the value of a thorough descriptive osteology for the good of the science, if not the individual. One of these crossed my desk last week. “Anatomy and phylogenetic relationships of Tazoudasaurus naimi (Dinosauria, Sauropoda) from the late Early Jurassic of Morocco” does exactly what it says on the cover and how sorely was this needed! Tazoudasaurus is a relatively newly named Moroccan sauropod from the Early Jurassic. It is significant because it is rather completely represented non-eusauropod. For those only cursorially interested in dinosaurs eusauropods are the 'classic' sauopods with enormous bodies, long necks, tiny heads with large retracted nostrils, unique tubular, fingerless hands atop elephantine limbs and lightweight vertebrae constructed from thin laminae. In all the construction of the eusauropod 'bauplan' is one of the great transformations in dinosaur, if not vertebrate, evolution equal in my mind to the evolution of birds. Sadly our understanding of this evolution has been severely hampered by the extremely fragmented nature of pre-eusauropod sauropods. The usual standard basal taxon is Vulcanodon which is hopelessly fragmentary as you can see in the diagram below. There is enough of Vulcanodon to show that it is clearly outside Eusauropoda but it tells us nothing about the evolution of dorsal vertebrae (which must really bother these guys), hands or the skull. Help is now at hand: Tazoudasaurus is clearly a close relative of Vulcanodon (the monograph adds new derived character states which shores up the monophyly of Vulcanodontidae) and it preserves some skull bones along with good neck and dorsal vertebrae and a complete articulated hand. It is apparent that vulcanodontids are actually quite close to Eusauropoda and are distinctly more advanced than the fragmentary rabble of basal sauropods that has been steadily accreting to the base of Sauropoda in recent years (e.g. dinosaurs like Antetonitrus, Gongxianosaurus and Isanosaurus). For instance the dorsal vertebrae have transversely expanded laminar neural spines, unlike the transversely flattened, plate-like affairs seen in the aforementioned trio. The hand is really cool. The palm is not wrapped into the semitubular arrangement seen in eusauropods, and the fifth metacarpal is still quite a bit shorter than the others (as in prosauropods) but the fingers are reduced right down to mere clawless stumps. Given the high number of synapomorphies linking vulcanodontids and eusauropods over the more 'prosauropody' taxa like Antetonitrus, Allain and Aquesbi go ahead and erect a new higher level taxon: Gravisauria ('the heavy lizards'), an action I support. The authors also discuss faunal turnover at the end of the Early Jurassic but I want to save that for another post, not least because I had come to identical conclusions and even have the idea in press (where it will probably linger for another year). If you like sauropods get a hold of this paper (no I do not have a pdf).
Allain, R., Aquesbi, N. (2008). Anatomy and phylogenetic relationships of Tazoudasaurus naimi (Dinosauria, Sauropoda) from the late Early Jurassic of Morocco. Geodiversitas, 30(2), 345-424.
Back in the day when I was a postdoc at the University of Bristol I was involved in a project to build the first supertree for non-avian dinosaurs (Pisani et al. 2002). Now our initial efforts have been thoroughly superseded by a new supertree created by a new team, also from Bristol, headed up by Graeme Lloyd. What is a supertree? Basically its a very large phylogenetic tree stitched together from smaller trees made from standard cladistic analyses of a feasible size (known as source trees). This might, at first, sound like a trivial operation but when you have partially overlapping sets of taxa in the source trees it quickly becomes a calculatory nightmare to produce a rigorous consensus of the source trees. About the only feasible solution available then (and probably still now) was Matrix Representation using Parsimony, or MRP for short. In this technique each node in each tree was treated as a character and all of the ingroup members of that node are coded as '1' whereas all outgroup members are coded as '0'. Taxa that don't appear in that particular source tree are given a '?'. In effect the 'winning' signal from each analysis has all competing signals stripped away and then is combined with all the other 'winning' signals from the other source trees. A large matrix is thus compiled and can be analysed using standard parsimony-based techniques. Some of the early practitioners of supertrees got quite carried away with this and thought that by combining all these small sub-signals together a new signal, perhaps more closely approximating the truth than any other, was created. I lampooned this point of view at SVP with the slide: "Supertrees - a marvelous new way of generating new, more inclusive phylogenies without all that tedious mucking about with actual specimens" (Hat tip to the comic genius of Douglas Adams). No, in my view, supertrees should only be used as a consensus technique to form baseline phylogenies for other studies. It is good to see that that is how the supertree is used in the Lloyd et al. paper. So what did they use their supertree for? The supertree was used to look at the evolution of dinosaur diversity through time. Unsuprisingly they found that raw diversity was strongly affected by sampling bias. Crudely put there are a lot of Late Cretaceous Dinosaurs because there are a lot of late Cretaceous rocks and a lot of man-hours have been spent collecting from them. Perhaps a little more surprising is the find that after a initial burst of adaptive radiation, dinosaur diversification proceeded at a fairly steady pace throughout the Mesozoic and did not appear to change during the KTR (Cretaceous Terrestrial Revolution) where modern ecosystems were forged by the explosive radiation of flowering plants, insects and numerous other modern groups. David Hone is one of the authors on this new effort and he gives a much more over at archosaur musings
Lloyd, G.T., Davis, K.E., Pisani, D., Tarver, J.E., Ruta, M., Sakamoto, M., Hone, D.W., Jennings, R., Benton, M.J. (2008). Dinosaurs and the Cretaceous Terrestrial Revolution. Proceedings of the Royal Society B: Biological Sciences, -1(-1), -1--1. DOI: 10.1098/rspb.2008.0715
Pisani D, Yates AM, Langer M, Benton MJ (2002) A genus-level supertree of the Dinosauria. Proceedings of the Royal Society B 269: 915-921
One of the little charms(?) of South African life is the stuff they put on the telly. Mostly it is absolute dreck (failed American drama pilots and embarrassing action films that even Bill Bixby wouldn't be seen dead in*) and ancient shows excavated from the fossil record of television that the rest of the world has long since forgotten. Just last week I was minding the kids at home and Melanie was watching the Carebears. I've a vague recollection of these obnoxiously saccharine-flavoured bears from my childhood but it was not a craze that ever penetrated my world back then. Anyway it seems that the aforementioned bears have a nemesis, namely one Professor Coldheart. I was struck by the resemblance between Prof. Coldheart and none-other than Richard Owen himself (maybe its just me - judge for yourselves)
By all accounts Professor Coldheart would be an excellent description of Owen. I wonder if the creator(s) of the carebears were in some way palaeo aficionados.
*yes I shamelessly lifted these words from an old favourite. I doubt ANYONE reading would be able to recognise it however.
The latest issue of Palaeontology is choc-full of palaeo goodness. I might end up blogging quite a bit of it, then again time may elude me. For now I just want to say a few quick words about the paper by Gao Chunling et al. It describes yet another new bird from the Yixian Formation of Liaoning, China. Called Zhongornis haoae, Gao et al. bestow upon it a relatively high degree of importance because they believe it to be the sister group of all other short-tailed birds, a clade called Pygostylia. The image is from their paper (Gao et al. 2008). As the name would suggest pygostylians are characterised amongst other things by having a reduced number of tail vertebrae where the distal most ones are fused into a single element called the pygostyle. Although Zhongornis has various advanced pygostylian characters such as an elongate strut-like coracoid and a short tail (just 13 caudal vertebrae), it does not have a pygostyle. That is all 13 caudal vertebrae are unfused, separate bones. However, and this is a big however, it is clearly a juvenile specimen (based on small size, lack of fusion of wrist and manual elements and porous, grainy, bone texture). An therein lies the biggest problem with accepting Zhongornis to this privileged position. Other very juvenile early pygostylians also have unfused caudal vertebrae (e.g. ' Liaoxiornis'). Clearly like wrist fusion the formation of the pygostyle did not occur until quite late in ontogeny amongst early pygostylians. Gao et al try to side-step this problem by claiming the specimen was skeletally mature, or close to maturity because it had fledged, ie. it had grown long vaned feathers from its wings (remiges) and tail (retrices). This I think is the biggest fault with the authors' reasoning. Firstly fledging itself is a variable trait with variable timing of onset amongst modern birds (if I am not mistaken the modern mallee fowl, a kind of megapode, are hatched in a fully fledged state). Late fledging can be expected to be tied to altricial lifestyles. Altriciality is a derived trait in modern birds and should not be expected amongst the early pygostylians of the Cretaceous. Indeed the very same Liaxiornis I mentioned above is a very juvenile early pygostylian with well developed remiges. This more or less falsifies the argument of Gao et al. So what is Zhongornis? Hard to say. It is toothless so there aren't that many contemporary taxa it could be a juvenile of (Bolouchia is a possibility). It has an unique configuration of phalanges in the third finger which could argue for its status as a valid taxon (although I would classify it as Pygostylia incertae sedis, rather than the pygostylian sister group). However I even wonder if it is possible for the digit three to be reduced as the bird matures, much in the same way that the juvenile claws of the hoatzin are lost as it matures.
GAO, C., CHIAPPE, L.M., MENG, Q., OCONNOR, J.K., WANG, X., CHENG, X., LIU, J. (2008). A NEW BASAL LINEAGE OF EARLY CRETACEOUS BIRDS FROM CHINA AND ITS IMPLICATIONS ON THE EVOLUTION OF THE AVIAN TAIL. Palaeontology, 51(4), 775-791. DOI: 10.1111/j.1475-4983.2008.00793.x
As you could well imagine, I really haven't had time to write much blog material of late. So I'm showcasing one of my drawings. Its a Southern Ground Hornbill. Seriously if you like it the original is for sale (price negotiable). The proceeds will help me and my family get to the UK next year for SVP Bristol.
Yesterday, quantative morphologist and physical anthropologist Charles 'Charlie' Lockwood died in a motorbike accident in London. The story has been covered elsewhere but I wanted to add my voice to those sending their condolences to the Lockwood family. This is especially sad news for people from Wits for Charlie was due to take up his appointment as the first director of the newly created Institute of Human Origins at Wits University here in Johannesburg. I only met Charlie on a couple occasions as he visited Wits but I found him to be an affable and dynamic young scientist. I was looking forward to see the IHE (which has close ties to the BPI where I work)grow under Charlie's leadership. Alas it was not to be.
This is the long-delayed third instalment of my sauropodomorph trilogy. This discussion was sparked by a recent paper published in Acta Palaeontologia Polonica (Milàn et al. 2008). Laelaps has already blogged about this paper many weeks ago, but as I said it takes me a while to get around to things. One feature of Late Triassic (Norian – Rhaetian) and Early Jurassic faunas is the usual dominance of basal sauropodomorph dinosaurs. I say usual because it wasn’t a global hegemony. Basal sauropodomorphs are strangely absent from the Triassic of North America. There are some reported scraps and a few teeth but these are not very convincing (see Nesbitt et al. 2007). Otherwise the sole Triassic records of Sauropodomorpha from the continent are the Eosauropus tracks, which may represent true sauropods but this remains contentious. Basal sauropodomorphs are likewise absent from the admittedly meagre Early Jurassic record of Europe (Ohmdenosaurus, a vulcanodontid-grade sauropod is an exception). However all other rich deposits are chock full of basal sauropodomorphs. Take the Elliot Formation for example: here it would be no exaggeration to suggest that more than 90% of finds in the upper part (Early Jurassic) are basal sauropodomorphs, while this proportion very nearly reaches 100% in the lower part (Late Triassic) of the formation. I mention all of this was just to establish the point that basal sauropodomorphs are very common in the body fossil record. So one might expect an equally rich footprint record. Not so, the footprint record from the early phase of dinosaur history is heavily biased in favour of theropods, which are the rarest of body fossils. All I can think of to explain this is that theropods, especially the coelophysoid-grade theropods from the Late Triassic and Early Jurassic loved to patrol lake margins and river side point bars where their tracks were more likely to be preserved. The scarcity of non-theropod footprints is made all the more vexing by the inability of ichnologists to decide which of the remainder, if any at all, were made by basal sauropodomorphs. Perhaps the most commonly cited example is a single quadrupedal trackway in the Early Jurassic aeolian sandstone of the Navajo Formation. Called Navahopus falcipollex, interpretative drawings show a large four-toed hindfoot and a smaller, pronated (turned so the palm faces backward) forefoot with a large medially directed thumb claw (Baird 1980). The trackway was made in loose sand, as the animal travelled up a sand-dune, consequently details are not well recorded. Indeed many would suggest that the original reconstruction of the manus print goes too far. I failed to see an obvious thumb-claw print when I had a chance to look at a cast of the trackway. Indeed it seemed to me that partial infilling of the manus prints, where loose sand had spilled into the print from the leading (upslope) edge, had resulted in the transversely elongate, antero-posteriorly shortened manus prints. Hunt and Lucas (2006) also doubted that Navahopus was left by a sauropodomorph, noting that the supposed pollex print was not as robust as reconstructed by Baird and was rather thin and variable in its expression. Lockley and Hunt (1995) suggested that Navahopus was just a large, poorly preserved Brasilichnum (an ichnogenus believed to have been made by tritylodontid cynodonts). If Navahopus was left by a tritylodontid, then it would have had to have been a big one. That’s ok though, unusually large tritylodont body fossils are not unheard of, despite the common misconception that all synapsids in the age of the dinosaurs were small rat to shrew-sized creatures. Pictured here is a fox-sized tritylodont from the Early Jurassic Clarens formation of South Africa. It looks crappy because it is a cast made from a natural mould of the skeleton in coarse sandstone. So if Navahopus isn’t a basal sauropodomorph track then what is? There are two main contenders: Tetrasauropus and Otozoum. I have little doubt that the Early Jurassic Otozoum prints fit the bill nicely. Otozoum are medium to large four toed tracks of a biped. One track records a moment when an individual got down on all fours but didn’t take any steps until it got back up onto its hindlegs. The diagram on the right shows an Otozoum footprint and the one known track way with hand prints (shown in grey). Both are redrawn from Rainforth (2003). The digital proportions and apparent phalangeal formula of the feet (based on the admittedly dodgy method of using toe pads) match those of basal sauropodomorphs. Emily Rainforth’s 2003 paper sets out the evidence nicely and a convincing case is made. What really tickles me however is that the Otozoum matches very nicely the predictions made by Matt Bonnan and Phil Senter (2007) based on the skeletal anatomy of the shoulder girdle and forelimb of plateosaurian-grade basal sauropodomorphs like Plateosaurus and Massospondylus. They found that in these dinosaurs had very limited degrees of humeral abduction (that is sticking their forearms out laterally) and could not rotate their wrists either. Thus they were denied any means to bring the hand into a forward facing (pronated) position seen in the Navahopus tracks and were forced to keep their palms facing inwards, theropod style. This is exactly what is seen in the one Otozoum track where the animal briefly went down onto all fours. Some have argued that the lack of a print of a large recurved thumb-claw in this track argues against Otozoum being the track of a basal sauropodomorph. However modelling of the range of motions of the joints of the hand shows that it was perfectly possible for plateosaurian-grade sauropodomorphs to lift their large sharp thumb claw well clear of the ground when on all fours. The picture on the right is a reconstruction from Galton (1971) that shows the likely stance of the hand when it was placed on the ground.
Finally we now turn our attention to the featured paper. The Jesper Milàn and colleagues report on a new, better preserved Navahopus trackway (skipping over the theropod tracks entirely). Suprisingly (to me in any case) it more or less confirms Baird’s earlier interpretation of Navahopus. In particular the manus prints are much clearer and lo and behold there is a large medially directed thumb-claw. Sauropodomorphs are the only known four-toed tetrapods from that epoch with hyperenlarged thumb claws so I think we have to accept that Navahopus was indeed the spoor of a sauropodomorph. So what is Otozoum, and were basal sauropodomorph facultative quadrupeds after all? I think a plausible explanation is that we are dealing with two distinct kinds of basal sauropodomorph. Otozoum tracks were likely left by plateosaurian-grade basal sauropodomorphs (like Plateosaurus and Massospondylus), which probably were obligate bipeds (at least as adults). Navahopus, on the other hand was probably left by a basal sauropod, or near-sauropod sauropodomorph (like a smaller version of Antetonitrus or Melanorosaurus). These advanced near sauropods and early true sauropods do show the necessary modifications to their forelimbs, which would have allowed them to pronate their hands. Such a beast has yet to be found in the Navajo Formation but given the general paucity of vertebrate fossils in this unit I’m not unduly fussed about it. Is Navahopus unique or are there larger prints attributable to large Antetonitrus or Melanorosaurus-like creatures. Yes there are. The original Tetrasauropus unguiferus track from the Elliot Formation seems to be just such a track. It was produced by a large, quadruped with a four-toed hind foot and a smaller, pronated hand that bore a moderately large medially directed claw that made contact with the ground. Some have opined that this was left by a large crurotarsan (e.g. Rainforth 2003) largely on the grounds that it didn’t match Otozoum, which was taken to be a true basal sauropodomorph track. As I’ve suggested above it is possible that these tracks could both be sauropodomorph, and just represent different grades of basal sauropodomorph evolution.
Baird D (1980) A prosauropod dinosaur trackway from the Navajo Sandstone (Lower Jurassic). In: Jacobs LL, ed. Aspects of Vertebrate History. Essays in Honour of Edwin Harris Colbert. Flagstaff, Museum of Northern Arizona Press. pp. 219-230.
Bonnan MF, Senter P (2007) Were the basal sauropodomorph dinosaurs Plateosaurus and Massospondylus habitual quadrupeds? In: Barrett PM, Batten DJ, editors. Evolution and palaeobiology of early sauropodomorph dinosaurs, Special Papers in Palaeontology 77: 139-155.
Galton PM (1971) Manus movements of the coelurosaurian dinosaur Syntarsus and opposability of the theropod hallux. Arnoldia 5:1-8.
Hunt AP, Lucas SG (2006) The taxonomic status of Navahopus falcipollex and the ichnofauna and ichnofacies of the Navajo Lithosome (Lower Jurassic) of Western North America. New Mexico Museum of Natural History and Science Bulletin 37: 164-169.
Lockley MG, Hunt AP (1995) Dinosaur tracks and other fossil footprints of Western United States. New York, Columbia University Press. 338 pp.
Milàn J, Loope DB, Bromley RG (2008) Crouching theropod and Navahopus sauropodomorph tracks from the Early Jurassic Navajo Sandstone of USA. Acta Palaeontologia Polonica 53: 197-205.
Nesbitt SJ, Irmis RB, Parker WG (2007) A critical re-evaluation of the Late Triassic dinosaur taxa of North America. Journal of Systematic Palaeontology 5: 209-243.
Rainforth, EC (2003) Revision and re-evaluation of the early Jurassic dinosaurian ichnogenus Otozoum. Palaeontology 46: 803-838.
Remember I mentioned a medical emergency the week before last? That was our pregnancy, which was not progressing well. So bad infact that the doctors had decided that to continue it full term would have endangered both the baby and her mother. So this morning, Anwen Jordan Yates was born by C-section. Despite being just over seven weeks premature she weighed 2.5 kg and is doing well in ICU.
Every natural history buff that I know has a set of favourite taxa that captivates a disproportionate amount of their attention. For me there are the dinosaurs (of course), whales, beetles and Banksias amongst others, and the Diprotodontoidea. Diprotodontoids were large quadrupedal browsing marsupials from Australia. First appearing in the Oligocene, they ranged from dog-sized up to white rhino sized and were Australia’s largest herbivores up to their abrupt extinction in the late Pleistocene. Perhaps my interest in these megaherbivores arose because the first mounted skeleton of an extinct vertebrate I ever saw was a diprotodontoid. In fact it was the Diprotodon skeleton that used to stand near the entrance to the galleries of the South Australian Museum (shown on the right). Growing up in what is, after Antarctica, the most dinosaur-poor continent meant that this skeleton was as close to a dinosaur as I was going to get for quite a while. It was sufficiently weird enough for me. With its unusual retracted nose and my poor anatomical knowledge (I was only five or six when I first saw it) I mistakenly imagined the eyes fitting in the narial opening giving it a bizarre otherworldly appearance. Actually it vaguely resembles the giant South American rodents like Hydrochoerus and Josephoartigasia.
Giant Rodent (Josephoartigasia) on the left compared to Diprotodon on the right.
Diprotodon was one of the last diprotodontoids and the largest of all. Its species taxonomy has remained confused due to a flurry of poorly diagnosed species being named during the nineteenth century. Most palaeontologists have recognised a large and a small form, although the species name for these is uncertain (D. optatum is often used for the large form and D. minor is often used for the smaller). If we wish to know how many species perished during the late Pleistocene megafaunal extinctions and what their ecological and geographical distributions were we need to know how many Diprotodon there were and where and when they lived. Enter today’s featured article, a much needed, and long overdue, taxonomic review of Diprotodon by Gilbert Price (2008). Price looked at all type specimens and large collections from all major sites bearing multiple individuals (of these Bacchus Marsh, Darling Downs, Myall Creek and Lake Callabonna are most important). An analysis of adult tooth size indicates a bimodal size distribution at most localities. The exception was Bacchus Marsh where only the small morph was present. A look at the rest of the morphology showed that there was almost no other consistent difference between the two morphs save for the shape of the mandible. The smaller morph tends to have slightly shallower mandibles with a more rounded profile. This is most noticeable in the symphyseal region where the large morph develops a pronounced ‘chin’ with a steep anterior margin (even in juvenile specimens of the large morph). There certainly was other variation, particularly in the upper premolar, but this was inconsistent, with no apparent pattern even within samples from a single horizon at a single locality. Some had well developed parastyles, others not, some of them had a well developed buccal cingula, others not, some of those with parastyles had buccal cingula,while others didn’t and so on. Price concluded that the small premolar was less significant for Diprotodon feeding and so was open to more variation than is usual in other diprotodontian marsupials. The overall conclusion of this study was that since the large and small morphs co-occur at most localities, show no obvious trophic specialisations and are almost identical except for size and mandibular shape then they represent sexual dimorphs of a single widespread species. So why is only one morph represented at Bacchus Marsh? Price speculates that like some other dimorphic mammalian megaherbivores Diprotodon lived in segregated herds. The geology and taphonomy of the Bacchus Marsh site suggests that the Diprotodon (which show an unusual degree of articulation) represent a single mass death assemblage. The fossils of Lake Callabonna represent a chance to test these ideas. At this site numerous animals became mired in the floor of the lake (which obviously dried out intermittently in the Pleistocene – as opposed to its perennially dry state now). It seems that this happened several times over many thousands of years accumulating several spectacular Diprotodon fossils, including a mother preserved with a very young individual between her legs (presumably it was a pouch bound joey). Sadly the field records of the original digs are inadequate to sort out if the large and small morphs were preserved in segregated groups. Even more frustrating the pouch young was separated from its mother and we can no longer associate it with its correct adult skeleton, thus we cannot test the hypothesis that the small morphs were the females. I would say that this provides ample reason to re-open excavations at Lake Callabonna. Price further notes that if he is correct in his interpretations then Diprotodon was spread virtually continent wide, in all sorts of habitats from woodland to semi-arid saltbush plains. In other words it was an ecological generalist. This poses a little bit of a problem for those who would deny the hand of Homo sapiens in the late Pleistocene megafaunal extinctions of Australia. Severe climatic change may well have caused loss of suitable habitat in the dry center but surely huge swaths of suitable habitat remained around the margins of the continent? One final note. The holotype of D. optatum (the type species) has the shallow rounded mandibular symphysis of the small morph. If we eventually do decide that the large and small morphs represent two sympatric species, then D. optatum would be the valid name of the small morph (not the large morph it is commonly ascribed to) and the next available name for the large morph would be D. annextans.
Price GJ (2008) Taxonomy and palaeobiology of the largest-ever marsupial, Diprotodon Owen, 1838 (Diprotodontidae, Marsupalia). Zoological Journal of the Linnean Society 153: 369-397.
Well that took a lot longer than expected. It appears my computer is on its last legs. The guys at the shop were unable to fix it, suggesting that the logic board was at fault and this would basically be a good time to buy a new computer. In frustration I thumped the thing and wouldn't you know it started working again, but it is prone to frequent crashes. Anyway to give all three (possibly four) of my readers something to look at while I get my workload sorted out here is an old (2000)reconstruction of mine. The quality is bad because it is a scan of a photocopy of a bromide of the original. It shows the chigutisaurid temnospondyl Siderops pulling the theropod Cryolophosaurus to its death in a frigid pool in the Early Jurassic of Antarctica (Siderops is known from similar aged sediments in Australia and South Africa so it is no big deal to put it in between in Antarctica). Next week - a bunch of posts on peer reviewed science - I hope.