An unexpected run of bad luck

Hi,

This isn't the third installment of my sauropodomorph trilogy. The latter half of last week was best with all sorts of happenings including server failures, medical emergencies, power outages and topped off with my computer crashing on Friday (this is being written from a student computer in a common room at Wits). I wasn't sufficiently backed up and I've temporarily lost all my blog related files. So there is precious little for me to bring you right now, not even a nice picture. Check back soon, I hope to be up and running again by the end of the week.

A ratty old sauropodomorph caudal

Meet BP/1/5339 another James Kitching find, this time a lone sauropodomorph caudal vertebra from the lower Elliot Formation (Late Triassic). It isn’t brilliantly preserved, nor has it been properly prepared yet but it is worthy of note because it is BIG. The anterior centrum face is 232 mm high and 194 mm wide, while in side view the centrum is 138 mm long. Granted this vertebra probably comes from the base of the tail where the caudal vertebrae are at their largest but it isn’t the first vertebra. There are chevron facets both fore and aft, indicating that this is at least the second caudal, or more probably the third. Compare its size to a comparable caudal (ca II) from NSMT-PV 20375, an Apatosaurus ajax (data from Upchurch et al. 2004). In this specimen the same measurements are 230, 240 and 134, respectively. I think you will agree that the two specimens are closely similar in size, although the apatosaur has transversely wider centra. This means that the Triassic of South Africa was harbouring a sauropodomorph whose tail base, at least, was similar in size to that of one of the larger Morrison neosauropods. I find that .....unexpected, to say the least. So what species does the caudal belong to? That’s another good question without a good answer. The basal sauropod Antetonitrus ingenipes is a plausible candidate. The holotype includes proximal caudals that are quite a bit smaller than BP/1/5339 but it is a juvenile. Most features of Antetonitrus are in agreement this specimen but this does not include any specific diagnostic characters. One difference that may be of significance is the strongly concave nature of the anterior centrum face of BP/1/5339, which is comparable to the procoelous caudals of advanced titanosaurs (the posterior face remains flat however). Maybe this could be a diagnostic character, or maybe it is the result of postmortem collapse. The answer is hopefully out there in the relatively unexplored exposures of the Elliot Formation.

reference

Upchurch P, Tomida Y, Barrett PM (2004) A new specimen of Apatosaurus ajax (Sauropoda: Diplodocidae) from the Morrison Formation (Upper Jurasic) of Wyoming, USA. National Science Museum Monographs 26: 1-107.

Antarctosaurus - a glorious sauropodomorph

So ya want sauropodomorphs do ya? Here is the first of a series of three in a mini 'sauropodofest'



The titanosaurs were quite rightly described as “the last great frontier in dinosaur phylogenetics” by Jeff Wilson. Indeed at this stage we have little idea of how the various titanosaurs are related to each other beyond a vague notion that some forms such as Andesaurus and Malawisaurus are basal to other more derived forms, of which Saltasaurus is the classic example. A big part of the problem is that although the group is diverse and many genera have been named, most are known from very incomplete remains. Skulls in particular have proved quite elusive. For a long time the best-known skull was that Antarctosaurus whichmannianus. The specimen was collected by Dr R Whichmann from the right bank of the Rio Negro, 15 km south west of General Roca, Argentina in 1912. The site was probably in the Campanian (Late Cretaceuous) Anacleto Formation. The specimen includes cranial remains and some postcranial pieces that are unquestionably that of a derived titanosaur (eg. there is a biconvex first caudal,amongst other derived titanosaurian characteristics). The skull is severely fragmented and most of the pieces are missing. Von Huene (1929) reconstructed the skull as similar to Diplodocus but with a steeper snout. This iconic reconstruction was in no small part responsible for the widespread view that titanosaurs were the derived descendants of diplodocoids. As our understanding of sauropod anatomy and evolution improved it became clear that titanosaurs were actually closer to deep-skulled sauropods (now named Macronaria) such as Camarasaurus and Brachiosaurus. Thus the Antarctosaurus skull became an anomaly. Some speculated that the skull really did belong to a diplodocoid and didn’t go with the postcranium(Jacobs et al. 1993). However there is precious little evidence of diplodocoids surviving so late in the Cretaceous. Salgado and Calvo (1997) suggested the skull had been restored incorrectly and presented a new reconstruction that presented a brachiosaurid aspect. As our knowledge of titanosaur skulls increased (thanks to skull pieces from Saltasaurus and the recognition that the so-called diplodocoids Nemegtosaurus and Quaesitosaurus were really titanosaurs) it became clear that the posterior portion of the Antarctosaurus skull was indeed that of a titanosaur. It showed several titanosaur synapomorphies such as pendant distal tips of the paroccipital processes (the braincase ‘wings’) and apparent exclusion of the squamosal from the margin of the upper temporal fenestra. However doubt about the association of the skull pieces continued. Wilson (2002) listed three derived characters of the dentary that were shared with the bizarre diplodocoid Nigersaurus (supercroc’s side-kick). It is true that jaw is remarkably diplodocoid-like, particularly with a sharp right-angled bend between the main ramus of the jaw and the toothbearing symphyseal ramus but this feature has been shown to have evolved convergently in at least one other titanosaur, Bonitasaura (Apesteguia 2004). The three characters Wilson suggested were shared specifically with Nigersaurus were 1, extension of the tooth row lateral to the main ramus of the jaw, 2, a marked increase in the number of dentary teeth and 3, restriction of the teeth to the transverse section of the jaw (= symphyseal ramus). Of these character 1 is indeed present, though only just, as you can see in the figure below.



Dentary pair of Antarctosaurus in dorsal view, created by mirroring the right dentary in photoshop. Original drawing from Huene (1929).

Character 2 is not present with three or so alveoli extending onto the main ramus, behing the symphyseal ramus, similar to the condition seen in Bonitasaura. Character 3 is not present either. There are 15 alveoli (Powell 2003), which is typical for basal macronarians, and only slightly more than in other titanosaurs (13 in Bonitasaura and Nemegtosaurus, 11 in Rapetasaurus) and a far cry from the 34 tooth columns in each dentary of Nigersaurus. Further to this the dentary lacks some diplodocoid synapomorphies that would have to have to be regarded as reversals if a special relationship with Nigersaurus is accepted. These are an increase to more than four replacement teeth per alveolus and the loss of mesial and distal carina of the tooth crowns. As in Bonitasaura there are three replacement teeth per alveolus (Apesteguia 2004) and the tooth crowns also retain mesial and distal carinae, despite their elongate diplodocoid-like shape. Elongate but carinate teeth are also present in other titanosaurs, e.g. Rinconsaurus and Ampelosaurus. Lastly the dentary displays a vertical symphyseal axis, a derived characterstic of titanosaurs. In summary there is one weak similarity with the diplodocoid, Nigersaurus, one derived characteristic of the Diplodocoidea that is convergent in some titanosaurs, the absence of two derived characters of Diplodocoidea and the presence of one derived character of titanosaurs. Following from this I think there is little reason to believe that the dentary is not that of a titanosaur. Given the scarcity of titanosaur skulls in general it seems very likely that all the cranial pieces of Antarctosaurus, which were found together at one site, belong to a single individual. Given this, I present above my own reconstruction of Antarctosaurus, using our improved knowledge of titanosaur anatomy to fill in the missing parts.



References

Apesteguia S (2004) Bonitasaura salgadoi gen. et sp. nov.: a beaked sauropod from the Late Cretaceous of Patagonia. Naturwissenschaften 91: 493-497.

Huene VF (1929) Los saurisquios y ornithisquios del Cretaceo Argentino. Annales del Museo de La Plata 3: 1-196.

Jacobs LL, Winkler DA, Downs WR, Gomani EM (1993) New material of an Early Cretaceous titanosaurid sauropod dinosaur from Malawi. Palaeontology 36: 523-534.

Powell J (2003) Revision of South American titanosaurid dinosaurs: palaeobiological, palaeobiogeographical and phylogenetic aspects. Records of the Queen Victoria Museum. 111: 1-173.

Salgado L, Calvo JO (1997) Evolution of titanosaurid sauropods. II: the cranial evidence. Ameghiniana 34: 33-48.

Wilson JA (2002) Sauropod dinosaur phylogeny: critique and cladistic analysis. Zoological Journal of the Linnean Society 136: 217-276

My dark secret

It is time for me to out a dark secret of mine. Dinosaurs are not my only subject of research these days. Just this year I’ve submitted papers on…….Cenozoic Mollusca. Yes fossil seashells are a passion of mine and have been so for most of my life. And why not? As an avid fossil hunter growing up in Adelaide, South Australia, Cenozoic marine invertebrates was about all that could be collected easily.
Why? The south-eastern corner of Australia was inundated with shallow seas several times during the Cenozoic (the two biggest transgressions happened in the late Eocene and the middle Miocene). The sediments left behind from these transgressions contain a rich record of the animals that lived in them. And what a fauna it was! Riotous diversity seems to be the watchword for the middle Miocene mollusc faunas. And not just high species diversity, morphological disparity seems way in excess of modern groups. Take the collectors favourite Cypraeidae, or cowrie shells as they are commonly known as an example. Although there are hundreds of modern species of these beautiful shells nearly all consist of simple ovoid shells with the smallest reaching no more than 7 mm and the largest 190 mm in length. However in the middle Miocene of south eastern Australia we find a size range that exceeds the modern global range, with the smallest adult sizes being 8 mm while the largest reaches a whopping 220 mm. Furthermore there is a species with its anterior and posterior canals produced into great upwardly curving siphons, another with a rectangular shell shape and yet another that is surrounded by a broad but thin, snowshoe-like flange. All in all I count 21 valid cypraeid species in the mid Miocene of south eastern Australia (compare this to the modern 14 or so species from the entire southern half of Australia). Similar extraordinary diversity can be seen most other molluscan families.
I’ll be returning to the lost Cenozoic seas of southern Australia several more times as my research gets published or as the mood strikes me. For now enjoy this picture of one such deposit from South Australia, the famed Mannum Formation of the River Murray cliffs. There are about 200km of almost continuous outcrop along the Murray. Its where I collected my first fossil – an irregular echinoid, Lovenia forbesi.





Lovenia forbesi

Burnworm

I will admit adjusting to life in South Africa has not always been easy. One small bright spot though is its wildlife. Not just the big mammalian fauna of the gameparks but the small stuff that is everywhere. Like this spectacular catepillar (a larva of the saturniid moth Bunaea alcinoe) I shot at a friend's house during the christmas holidays of 2006. Where I grew up (Adelaide) we had a diverse insect fauna but so much of it is small and drab, so much of the African fauna seems larger and brighter, and it is all new to me.

I'm slow but I get there in the end: Megaraptor in Oz

Typical! I get a really busy two weeks with a an overnight trip and a public holiday (yesterday was Youth Day in South Africa) and in come a bunch of new papers I'd like to blog about. Two of the new papers have already been covered by Laelaps here and here. What can I say? Never read this blog to get the latest info hot off the presses, I'm slow and busy, but when I do blog, I hope I can bring just a little insight that hasn't been posted elsewhere.
About two weeks ago Nate Smith and colleagues released a paper in the Proceedings of the Royal Society, that describes an Early Cretaceous theropod dinosaur ulna from Victoria, Australia that bears a close resemblance to Megaraptor, a large penecontemporaneous [edit: Megaraptor is a Late Cretaceous theropod, very far from being penecontemporaneous with the victorian specimen - oops]theropod from South America. Megaraptor is a bit of an oddity, it is clearly a large predator with a wicked manual claws. It may be related to the spinosaurids according to Smith et al. but it also shows similarities to carcharodontosaurids (Calvo et al. 2004), another group of mostly giant predators with a mostly Gondwanan distribution. Smith et al. point out a number of unusual specific resemblances not seen in other theropods and then suggest that the aussie ulna and Megaraptor are each others closest relatives. Okay, nice to get some ID on another bit of dino from Australia but isn't that rather expected? Afterall Australia is most certainly part of Gondwana and we should expect faunal ties with other Gondwanan continents. Yes but oddly the fauna that inhabited the rift system between the southern margin of Australia and Antarctica (where the ulna in question comes from) has been interpreted as largely laurasian in aspect with ornithomimosaurs, oviraptorosaurs, allosaurids, neoceratopsians and eutherian mammals. However all of these identifications are somewhat dubious, and are mostly based on single bones. So is this latest ulna, you might say, but I would counter that the difference here is that the identification is based on specific derived characteristics rather than a simple phenetic assessment (ie. 'it looks like one') that underlies most of the other identifications. So it is nice to get a solidly Gondwanan taxon in the Early Cretaceous of Australia. Or have we? For the moment lets accept that the aussie ulna and Megaraptor are closely related within Theropoda, might there be other members of this newly recognised clade? Well there is one other large theropod with huge manual claws that was found to be a close relative of the spinosaurids in a large cladistic analysis (Rauhut 2003), a poorly known creature named Chilantaisaurus tashuikouensis Hu, 1964, also of similar age to Megaraptor. However this creature is firmly Laurasian, being found in the Nei Mongol region of China.



The claw of Chilantaisaurus from Hu 1964. Scale in cm.

If Chilantaisaurus were another 'megaraptorid' then the neat biogeographic story of smith et al. is somewhat weakened. Basically these things would be part of a cosmopolitan fauna that got isolated on different continents as the continents broke apart, with differences in distribution being more to do with differential extinction than anything else. Can we tell at the moment? Hell no. Sadly the known bits of Megaraptor havealmost no overlap with known the bits of Chilantaisaurus (just the large manual claw and metatarsal 4 - neither of which are particularly usefull in this case). For all we know they may be only distantly related spinosauroids, or Megaraptor might not even be a spinosauroid at all. We won't know until more complete remains of enigmatic Megaraptor are forthcoming. I hate to end this post with the trite 'we need more fossils' message, which I usually regard as a bit of a cop-out, but in this case it seems apt.

References.

Calvo JO, Porfiri JD, Veralli C, Novas F and Poblete F (2004) Phylogenetic status of Megaraptor namunhuaiquii Novas, based on a new specimen from Neuquen, Patagonia, Argentina. Ameghiniana 41: 565-575.

Hu S-Y (1964) Carnosaur remains from Alashan, Inner Mongolia. Vertebrata PalAsiastica 8: 42-63.

Rauhut OWM (2003) The interrelationships and evolution of basal theropod dinosaurs. Special Papers in Palaeontology 69: 1-213.

Smith ND, Makovicky PJ, Agnolin FL, Ezcurra MD, Pais DF and Salisbury SW (2008) A Megaraptor -like theropod (Dinosauria: Tetanurae) in Australia: support for faunal exchange across eastern and western Gondwana in the Mid-Cretaceous. Proceedings of the Royal Society B: doi:10.1098/rspb.2008.0504

A trip to the Limpopo Province

As I was growing up no African place name seemed more exotic and remote than Limpopo. Actually the Limpopo Province lies just a few hours north of Johannesburg, yet I had never visited it until this week. This is a pity because as it turns out it is a beautifull place indeed. We were on a quick trip up to the Soutpansberg Range to check out claims of metazoan fossils in the Paleoproterozoic Soutpansberg Group (approx. 1700 million years old).


Sandstones and Conglomerates of the Soutpansberg Group

Such a fossil would exceed the next oldest metazoan fossils by about a billion years, and to say I was sceptical would be an understatement. Nevertheless one has to check these things up, just one day someone may really have found something exceedingly significant - but not this time. Nevertheless although no fossils were found (as expected) the day turned into a lovely natural history outing.
At the very start of the hike we saw a large flock of crested guinea fowl, the much rarer cousin of the ubiquitous helmeted guinea fowl, but I could not get a decent picture (although I did get a new tick for my birdlist). We found evidence for leopards in the form of scratched tree trunks (but no leopards of course!). Here are some other shots I took during our search.


It is well known that everything in Africa has thorns but check out these - you'd swear the thing was predatory!

I also snapped this cute little scarab



A story surrounding this little plant is worth relaying.



This is Khat (Catha edulis), a largely East African and Arabian plant well-known for the amphetamine-like drug it produces. Nevertheless it is growing wild all over the Soutpansberg. The place we were staying at used to be a girls school that was closed down after the students discovered this local plant and Khat-chewing became endemic in the school.
After the Soutpansberg we stopped in at Makapansgat on our way back to Jozi. This is a wonderfull little valley that is famous for its limestone caves, one of which (the Limeminer's Cave) has produced remains of the protohuman Australopithecus africanus



Although there are no obvious australopithecus fossils lying around, you can still see this string of vertebrae, left in the cave roof where an articulated sabre-toothed cat was removed (apparently the specimen is at wits but I haven't seen it).



Lastly to end with the palaeo theme, there wasn't just plio-pleistocene fossils to see. The caves themselves were etched into 2 billion year old dolomites with very nice stromatolite fossils.

Picture of the day - Massospondylus

I snapped this pic while in the South African Museum in Capetown this April. Although the individual bone preservation isn't fantastic it is one of the few symmetrical undistorted Massospondylus skulls (if a little juvenile). The whole thing is just under 11 cm long. It was found in the upper Part of the Elliot Formation (Early Jurassic) near the town of Ladybrand in the Free State, South Africa.

The story of Dracovenator - part II

James Kitching and his field assistant Regent ‘Lucas’ Huma found Dracovenator on a farm called ‘Upper Drumbo’ in the Barkly East District of the Eastern Cape Province. This district is almost entirely covered by thick lava flows of the Drakensberg Group that also make up the highlands of nearby Lesotho. Fortunately the Kraai River, and some of its tributaries have cut deep enough through the lava to get down to the underlying sediments of the Clarens and Elliot Formations. And this is where you find dinosaurs. Well a few anyway. The area can hardly be described as brimming. A recent international expedition led by Oliver Rauhut and ably assisted by yours truly, had ten or so palaeontologists crawling up and down every inch of available outcrop on Upper Drumbo. We eventually found two worthy specimens but this is quite a low haul for the Elliott (sadly neither were Dracovenator).
Anyway back to Dracovenator. I gave it the species name ‘regenti’ to honour James’ long-term field assistant and friend, Regent Huma. As Regent was a black man in apartheit South Africa he never got the recognition he deserved.
What do the bones look like? Firstly there is an odd combination of characters in the premaxilla. The snout was clearly long and low (a ‘coelophysoidy’ condition) with the external nostrils retracted posterior to the premaxillary teeth but the shape of posterior margin of the premaxilla seems to indicate a subrectangular anterior ramus of the maxilla (an advanced theropod condition). The next-most informative piece was the back end of the lower jaw, which looked just plain weird with all sorts of lumps and bumps growing out of it. However after seeing the original Dilophosaurus wetherilli specimens it became clear that Dilophosaurus also had the same morphology, only a little more subdued. Anyway desperately incomplete as the known remains are there is enough to distinguish the new species from all other known theropods.
Well almost. The known parts of Dracovenator barely overlap with the much better known dilophosaurid, Cryolophosaurus ellioti from Antarctica, and where they do overlap (just the posterior end of the maxilla and the posterior end of the dentary[edit: that should be 'mandible' not 'dentary']) they are essentially identical. So it may well be that Dracovenator is the same as Cryolophosaurus or an exteremly close relative. This isn’t so unusual as many of the species in earlier Triassic deposits of the Karoo Basin are also found in Antarctica. It does go against Nate Smith and colleagues (2007a) dilophosaurid topology. He found that the Chinese dilophosaur (‘Dilophosaurus’ sinensis) was basal to a clade consisting of Dracovenator, Dilophosaurus wetherilli and Cryolophosaurus (with D. wetherilli and Cryolophosaurus being each other’s closest relatives). This topology is strongly at odds with geography and suggests dilophosaurids were jumping all over Pangaea as they diversified (perfectly possible given that this happened before the breakup of Pangaea) (Smith et al. 2007b). Having seen both species of Dilophosaurus (the photograph is of the holotype of D. sinensis) though, I really don’t think much of the supposed differences and am impressed by strong similarities not seen in other theropods. Thus I am happy to include them in the same genus (contra some other opinions). Thus I think there may be some geographic separation of dilophosaurids after all, with a northern D. wetherilli/D. sinensis clade and a southern Crylophosaurus/Dracovenator clade. With luck permitting, new fossils should be able to test this idea.

References

Smith ND, Makovicky PJ, Hammer WR and Currie PJ. 2007a. Osteology of Cryolophosaurus ellioti (Dinosauria: Theropoda) from the Early Jurassic of Antarctica and implications for early theropod evolution. Zoological Journal of the Linnean Society 151, 377–421.

Smith ND, Makovicky PJ, Pol D, Hammer WR and Currie PJ. 2007b. The dinosaurs of the Early Jurassic Hanson Formation of the Central Transantarctic Mountains: Phylogenetic Review and Synthesis. U.S. Geological Survey and The National Academies, Short Research Paper 003; doi:10.3133/of2007-1047.srp003

Yates AM. 2006 (for 2005). A new theropod dinosaur from the Early Jurassic of South Africa and its implications for the early evolution of theropods. Palaeontologia africana 41: 105-122.

Chaoyangopterids!

It’s a good time for pterosaur enthusiasts. Recent months have seen the publication of a bunch of significant papers. We’ve had the wonderfully complete second specimen of the weird Anurognathus, Andres and Ji’s thorough cladistic analysis of pterodactyloids, tiny little Nemicolopterus, the stunning basal form Raeticodactylus, and most recently Mark Witton and Darren Naish’s paper putting ahzdarchids on the ground as predatory, ‘mega-storks’. And now we have Shenzoupterus chaoyangensis, another pterosaur from the seemingly boundless Early Cretaceous Jehol Group of Liaoning, China. The paper is accessible here: http://www.springerlink.com/content/lj46h69l5149w001/?p=797295b0e22045f780debf3a7d7e0911&pi=0
Shenzhoupterus is special, not just because it is another new, nicely preserved pterosaur but because it helps tie together a group of somewhat enigmatic and poorly-known pterosaurs. A bunch of toothless Liaoning pterosaurs have been described in recent years, starting with Chaoyangopterus and followed in short order by Jidapterus, Eopteranodon, and Eoazhdarcho. Each of these was described as a basal member of three different Late Cretaceous toothless lineages: the Nyctosauridae, Pteranodontidae and Azhdarchidae. This made a lot of sense, as we would expect earlier members of these highly derived lineages to show up in older rocks. The big phylogeny in Andres and Ji, turned this idea on its head by finding that all of these taxa were part of one large toothless radiation: the Azhdarchoidea, with all except Eopteranodon forming a clade that was the sister group to the Late Cretaceous Azhdarchidae. Now we have new Shenzhoupterus to bring them all (Eopteranodon included) and bind them. The new clade is now christened the Chaoyangopteridae. Shenzoupterus also gives us our first clear look at a chaoyangopterid skull, and what an odd skull it is. It looks at first glance like a basic azdarchid skull with the nasal aperture of a brachiosaurid sauropod (and a little pteranodontid-like occipital spine for good measure).

The posterior retraction of the naso-antorbital fenestra (the nostrils and the antorbital fenestra of all pterodactyloid pterosaurs are united into a single opening) turns out to be a feature of other chaoyangopterids and is one of their main diagnostic characters.
One may well ask what these Chaoyangopterids were doing with their giant naso-antorbital fenestrae. One obvious hypothesis is that it increased the depth of the skull for display purposes, thus achieving much the same result as the cranial crests of other azhdarchoids like tupuxuarids but in a totally different way. However I prefer the idea that the opening housed a hyperenlarged nasal vestibule that also developed in a number of other Mesozoic archosaur groups (eg. macronarian sauropods, lambeosaurine hadrosaurs and ceratopsids). What were they doing with such big noses? Good question, the short answer is we don’t know, but I wonder if it isn’t to do with heat exchange and/or water reclamation while breathing. A fertile area for future research perhaps?


Andres, B.; and Ji Q. (2008) A new pterosaur from the Liaoning Province of China, the
phylogeny of the Pterodactyloidea, and convergence in their cervical vertebrae. Palaeontology 51 (2): 453-469.

Lü J, Unwin DM, Xu L, Zhang X (2008) A new azhdarchoid pterosaur from the Lower Cretaceous of China and its implications fro pterosaur phylogeny and evolution. Naturwissenschaften DOI 10.1007/s00114-008-0397-5.