Darren Naish reports:
The 51st Symposium of Vertebrate Palaeontology and Comparative Anatomy was held between Wednesday 17th and Friday 19th September 2003 at the Oxford University Museum of Natural History. This is a fantastic venue as you are literally surrounded by skeletons, replicas and taxiderm specimens of numerous animals, both modern and fossil. This year the coverage of different vertebrate groups seemed fairly even, with fish, basal tetrapods, lepidosaurs and other assorted diapsids, marine reptiles, pterosaurs, dinosaurs and mammals all being reasonably well represented. I didn't attend all of the fishy talks so won't be reporting on those, nor will I have time to report all the talks, let alone the posters. But the following covers the bulk of the tetrapod presentations given at the meeting...
Per Ahlberg (et al.) revealed the increasing strangeness of Ichthyostega. The animal is now becoming so odd that basal tetrapod evolution is becoming too complex - we should ignore all of this new work and just pretend that Jarvik got it all right:) Jarvik illustrated a very odd neural spine morphology for Ichthyostega, but the same morphology is clearly not depicted in his skeletal reconstruction. In fact Ichthyostega has extremely differentiated neural spines and a reasonably well 'segmented' axial skeleton with a distinct neck, a longish lumbar region, and also a tail far shorter proportionally than that depicted by Jarvik. Superficially in fact the axial skeleton recalls that of a mammal, so Ichthyostega is now looking more suited for terrestriality than other basal tetrapods. Its scap-coracoid is proportionally bigger than conventionally shown. Elginerpeton is quite similar to Ichthyostega and the two might belong to a monophyletic ichthyostegid clade.
Hennig Blom (et al.) discussed the forelimb skeleton of Ichthyostega and also showed that reality was quite a bit different from things depicted by Jarvik. As the lower arm of Ichthyostega is extended, the wrist broadens and twists, the result being a peculiar specialised ?paddling action not particularly suited for either walking or swimming. Pronounced ontogenetic changes seem to have occurred in Ichthyostega forelimbs.
Jenny Clack discussed Silvanerpeton miripedes, a taxon originally described (by Clack) as an anthracosaur. New preparation and analysis shows that Silvanerpeton has the spike-like tabular horn seen in embolomeres and, together with Eldeceeon rolfei (which was also reanalysed), it seems to be close in the tree to basal anthracosaurs, microsaurs and stem amniotes. Casineria (published recently as the oldest tetrapod with a pentadactyl manus) grouped close to microsaurs and its removal from the tree affected the positions of Silvanerpeton and Eldeceeon.
Marcello Ruta discussed the seymouriamorph Ariekanerpeton and showed how it is sister to Discosauriscus, the two forming a Eurasiatic seymouriamorph clade of which Utegenia is the sister taxon. Seymouria is a sister to the Utegenia + Eurasiatic clade and thus it doesn't seem that Ariekanerpeton and Seymouria are close kin. Seymouriamorph monophyly is not all that secure and virtually all of the characters used to unite the group are seen elsewhere in other basal tetrapod clades.
Carol Hopkins discussed later Permian tracks that move diagonally up dune surfaces, yet have toe marks directed straight upslope. By forcing assorted living lizards to climb up little sand dunes she demonstrated how animals might produce these kinds of tracks.
Sue Evans (et al.) described new Jurassic salamander specimens from the Morrison Fm and reviewed the fossil record of Mesozoic salamanders. Laccotriton and Sinerpeton, recently described as possible stem cryptobranchoids, are Early Cretaceous and not Jurassic as claimed, and the same is probably true for the Jiulongshan Fm's Chunnerpeton (recently claimed to be a cryptobranchid). A new Morrison Fm taxon has been scanned at the Univ. Austin, Texas, and reveals loads of good character information - some of the characters are contradictory to present understanding but the specimen exhibits some salamandroid characters and may be sister to this group.
Paul Barrett spoke about new material of the procolophonoid Barasaurus and of younginiform tangasaurid material from Madagascar which show that these two taxa survived the PT event. Procolophonoid taxa have a particularly high rate of survival across the boundary.
Mark Evans discussed the new Pliensbachian plesiosaur discovered in Gloucestershire in 2000 (mentioned previously in my writeup of the SVPCA Portsmouth meeting). It comes from the 'Pliensbachian Gap', a time at which no named plesiosaur taxa are known, and represents a 3m long adult plesiosaur that combines assorted pliosauroid, elasmosaurid and other features. The neck was shortish, the caudal extensions of the premaxillae are short, and one of the strangest things is that the neural spines are D-shaped in cross section.. AND, they alternative such that the curve of the D faces left on one spine, right on the next, left on the next and so on. Very odd. When included in O'Keefe's data set the specimen was a basal polycotylid (giving the group a ghost lineage of c. 90 million yrs), but in other data sets it was variously sister to rhomaleosaurs, or a basal plesiosaur.
Richard Forrest analysed the many (c. 150) isolated plesiosaur vertebrae from the Rhaetian Bone Beds. Cervicals are better represented than other verts by a factor of three. Using assorted statistical techniques (including PAST and PCA) applied to something like 27 different vertebral measurements (Richard said he sometimes takes a break from this measuring and goes and does something more interesting, like watching paint dry), Richard showed how the vertebrae of plesiosaur taxa generally cluster neatly together, so these measurements DO provide good information. Two distinct kinds of plesiosaurs are clearly present in the Rhaetian BB (this is significant because these are the earliest records of plesiosaurs), one of which is allied to rhomaleosaurs.
Daniela Schwarz discussed the locomotor abilities of dyrosaurid crocodyliforms. Dyrosaur vertebrae look odd (compared to extant crocodylians) as they have tall neural spines throughout the column with the tallest spines being in the neck and cranial region of the tail. The resulting muscle attachments would have made a self-carrying I-beam construction (like that seen in extant crocodylians) impossible because the insertion angle of the epaxial musculature on the osteoderms would have been too high to maintain the I-beam-type construction. An inverse T-beam carrier was hypothesised and because dyrosaurs then lacked effective bracing against transverse shear loads they probably couldn't high-walk (or, at least, large individuals couldn't high-walk). Various aspects of their axial and appendicular morphology indicate that dyrosaurs were improved swimmers compared to extant crocodylians.
David Unwin discussed pteraichnites.. that's pterosaur tracks to the rest of us... and reviewed their occurrences, which clades appear to be represented (Purbeckopus might be an azhdarchoid and Haenamichnus might be an azhdarchid), and what they reveal about pterosaur behaviour. Many tracks show possible traces of feeding behaviour. The best line in Dave's talk: "How sure are we that these tracks were produced by pterosaurs? Well we're bloody sure thank you very much". However the best bit of Dave's talk :) was at the question session at the end: Paul Maderson (a Rubenite/Feducciary) stood up and said how appalled he was that Dave and his colleagues are still proclaiming that pterosaurs had body hair, whereas in fact they clearly had reticulate scales like those of rattlesnakes. Indeed (Maderson argued), Lingham-Solair has just shown that hair-like fibres can be the result of decomposition of collagenous skin layers.
Lorna Steel (accompanied by David Unwin) discussed a new toothed ornithocheirid ornithocheiroid from the Wessex Fm of the Isle of Wight. The specimen exhibits Anhanguera-like keels near its jaw tips as well as a pteranodontid-like parietal crest but it isn't the first pterosaur reported to combine teeth with a parietal crest features as another new ornithocheiroid (published in the new Buffetaut & Mazin pterosaur volume) also combines a pteranodontid-like crest with a more typical ornithocheirid toothy jaw morphology.
Eric Buffetaut spoke about a natural cast of a large pterosaur humerus discovered - unlabelled - in the old collections of the Natural History Museum at Troyes, France. The specimen appears to come from the Lower Cretaceous 'Toxaster Limestone'. At 350 mm it is big (the biggest Pteranodon humerus reported by Bennett is 316 mm long) and appears to come from an azhdarchid.
David Norman discussed new work on Heterodontosaurus, its anatomy, and preliminary work on its affinities. In reviewing other ornithischian groups, he noted that Lucas' identification of Tatisaurus as a scelidosaur was completely wrong, and new skull interpretations of Scelidosaurus and Lesothosaurus were shown. Norman showed various cladograms produced by his data, the best supported of which seemed to be (I might be wrong) that H. tucki was sister to Marginocephalia. However, it didn't take much to find a similarly supported tree in which H. tucki was sister to thyreophorans, and other combinations were possible. Interesting indeed was Norman's conclusion that new ornithischian taxa presently in the works will disturb the present, 'stable' phylogeny of the Ornithischia.
Bernd Herkner discussed the remounting of the Frankfurt Triceratops specimen. They simply couldn't get the forelimbs to match preserved trackways and had problems in getting the limbs into an anatomically reasonable pose. Don Henderson pointed out after the talk that apparently the trackways Bernd et al. were looking at are problematic: apparently they aren't a complete trackway but rather one forefoot and one hindfoot print, or something like that. However, also problematic was the fact that the Frankfurt Triceratops has its ribs (and therefore its scapulocoracoid) mounted incorrectly, so no wonder they can't get the limbs into an anatomically correct position. I pointed this out to Bernd: they are aware of this but cannot dismantle and remount the whole skeleton. So the problem isn't with the forelimbs, but with the whole skeleton. Incidentally the specimen itself is a composite of four partial skeletons.
Paul Upchurch covered the confused taxonomy and systematics of Cetiosaurus, much of which has just been sorted out by Paul and John Martin in their recent papers. They still need to petition the ICZN to propose that C. oxoniensis be designated the type of Cetiosaurus (rather than C. brevis). Paul showed the new phylogeny in press (?) for Dinosauria II and Cetiosaurus is part of a clade including Barapasaurus and Patagosaurus.. so, monophyletic Cetiosauridae after all.
Donald Henderson used computer-generated sauropod models to test for centres of mass, and to see how well these matched with narrow- and wide-gauge trackways (wgts). He found that brachiosaurs were stable when producing wgts and that diplodocoids weren't, and similarly brachiosaurs were unstable when forced to produced ngts. The conclusion was that the evolution of wide-gauge gaits resulted from huge size but this is questionable given that some diplodocoids may have exceeded the biggest brachiosaurs (and titanosaurs) in size, as Paul Barrett pointed out after the talk.
Eric Buffetaut discussed some tiny theropod eggs discovered over a couple of years at one of his team's Lower Cretaceous Thailand sites. The eggs (each of which is something like 30 mm long or less) certainly exhibit theropod-style eggshell texture, probably all belong to the same next, and contain bones. Very very small bones. A tib-fib seen in cross section was shown: surprisingly, even though the whole tibia must have been only a few mm long, a prominent cnemial crest and medial excavation on the fibula were both evident. Whatever theropod produced the eggs, it must have been very small. Possible contenders include microraptors and epidendrosaurs.
Steve Hutt discussed a few new large elements from Isle of Wight theropods, mostly manual phalanges. The elements are huge and when compared to the phalangeal lengths and proportions of large theropods with complete hands they suggest that there were some really really big theropods on the Isle of Wight in the Lower Cretaceous. Steve ended the talk by producing the hand he has made (based on Allosaurus) in which the largest of the IoW phalanges was assumed (parsimoniously) to represent the biggest phalanx in the hand. The resulting hand is obscenely large, more than 50 cm long. Naish & Hutt in prep.
Darren Naish discussed a new small theropod from the Santana Formation of Brazil, it includes a good pelvis and a near-complete tridactyl manus and has features showing that it isn't referable to SMNK 2349 Pal (the compsognathid which now has a new generic name), nor to Santanaraptor. Because the specimen combines a compsognathid-like pelvis with a rather 'basal-looking' hand, it might be evidence for compsognathid paraphyly (as argued by Longrich), but when included in assorted analyses this didn't turn out to be the case - compsognathid monophyly was upheld and the new specimen appeared further down the tree. The highlight was definitely at the end where I donned Martill's famous hat:)
Paul Maderson spoke about feather development, how ridiculously complex it is, and how no-one has even published a proper description of the whole process. He is not happy with the Prum & Brush model and was just starting to talk about Longisquama at the end when he ran out of time. Needless to say, Maderson is still insisting that Longisquama still represents the best candidate for a creature with 'proto-feathers'.
Emily Rayfield showed some fantastic animations of bite motions and the inferred kineticism of the Allosaurus skull. Different kinds of cranial deformation occurred according to bite position and bite force magnitude.
Angela Milner and Patricio Dominguez-Alonso (et al.) discussed high-resolution CT scans of the London Archaeopteryx braincase. Very very impressive and answered a lot of questions. The foramen magnum was bigger than thought previously and, while large olfactory lobes were present, Archaeopteryx appeared to have a bird-like brain with laterally displaced optic lobes, a telencephalon contacting the cerebellum, and semi-circular canal measurements overlapping with those of extant birds.
Estelle Bourdon spoke about a new genus of prophaethontid from the Palaeocene of Morocco. The taxon includes a good skull (which is good given that prophaethontids are known from so few specimens, yet already have a good skull in Prophaethon shrubsolei from the English London Clay) and, while it shares many characters with P. shrubsolei, the new taxon also differs in some aspects. Prophaethontids share with phaethontids a dorsal tympanic recess of a particular shape and position and thus might both form a clade.
Ella Hoch revealed a distal humerus from the Miocene of Denmark - it belongs to a puffin of the type now restricted to the Pacific.
Jolyon Parish gave a talk on dodo phylogeny. By combining Janoo's morphological and Shapiro et al's molecular data sets, Jo showed that dodos and solitaires (and also Natunaornis, which came out as sister to Raphus + Pezophaps) are nested within Gourinae, and that Gourinae itself is a basal columbid clade (more basal than the position proposed by Shapiro et al.). The finding of Natunaornis (from Fiji) as sister to Raphus + Pezophaps is in keeping with other lines of evidence which suggest that these Mascarene birds descend from SE Asian ancestors that migrated NW across the Indian Ocean.
Won't be discussing the synapsid talks too (have way run out of time) but the following things came up which will be of interest.. Marcelo Sanchez-Villagra (et al.) presented their new data on Phoberomys pattersoni, the giant caviomorph from Upper Miocene Venezuela. Not only is it found in an assemblage that includes Stupendemys the giant terrapin, the fauna also includes several taxa of large crocodylians, the biggest of which are something like 10 m long!
Robert Asher (et al.) showed how Necrolestes is most likely a metatherian.. what will be interest to some here however is that Asher clearly stated at the beginning of his talk that most data now indicates that insectivores/lipotyphlans are not monophyletic and he therefore seemed positive to the idea that tenrecoids are part of Afrotheria. This is significant because in some of Asher's previous papers he has noted that morphological evidence generally does not favour the placement of tenrecoids within Afrotheria.
Mesozoic mammals and near-mammals were well represented, with talks by Jose Bonaparte, Tom Kemp, William Clemens and Fuzz Crompton.
Well, I enjoyed myself and am looking forward to next year (to be held at Leicester). But the next conference on the aggenda is the British Dinosaurs Seminar, held on the Isle of Wight this November. Am preparing for that right now, so better get back to work....