A new enigmatic fossil crocodyliforme from the Isle of Wight, UK: Koumpiodontosuchus aprosdokiti Sweetman, Pedreira-Segade and Vidovic 2014

Mesozoic Monsters: a whole heap of vertebrate palaeontology, straight from the desk of researchers in the field. This is the title and tagline of my blog. I had every intention – when I started this blog – of regularly updating my readership with little titbits of my research, but I soon learned that it is not that simple and ideas need protecting and publishing first. So this is to be the first article that is submitted in the true spirit of MM.

The newly described Koumpiodontosuchus aprosdokiti Sweetman, Pedreira-Segade and Vidovic 2014 is a small crocodyliforme, neosuchian, bernissartiid from the Isle of Wight, UK. The specimen was found a couple years ago on the foreshore of Yaverland beach, Isle of Wight. The associated sediment suggested that the material had come out of the Wessex Formation, Wealden Group. The specimen, which is the holotype (type material) and only specimen of Koumpiodontosuchus is represented by a skull which was broken in two and found by separate individuals, but they were married together by some “serendipity” (SCW in Sweetman et al. 2014). I had the good fortune of working on this specimen, and I was tasked with placing it in the crocodile evolutionary tree, which I will discuss further below.

A palaeontological reconstruction of the Wessex Fm. Biota, by Mark Witton, reproduced with his permission.

Koumpiodontosuchus is a small crocodyliforme at an estimated 66cm in total length – the skull is 11.2cm in length. The dentition is distinctive and alerted us to the natural affinities of this small croc. It has a tribodont dentition in the distal portion of the jaw (back of mouth). Tribodont teeth are bulbous, and kind of onion-shaped. Clearly these teeth are involved more in digestion rather than prey capture. The mesial teeth (front) are somewhat procumbent (forward pointing) simple cones, followed by some pseudo-canine teeth, one of which projected up from the lower jaw and sat in a notch in the side of the upper jaw, just behind the nares (nostrils). This morphology is typical of a previously monotypic family (only contained one genus), the Bernissartiidae Dollo, 1883. Thus, it would be expected that a cladistic analysis would have no problem placing Koumpiodontosuchus with the type genus of the family Bernissartia fagesii “Known from contemporaneous strata” (Sweetman et al. 2014) in Belgium and Spain. However, there are some distinguishing features of Koumpiodontoshuchus which are not only distinct from Bernissartia, but also convergent upon Eusuchia. Namely, the position of a perforation named the choana within the pterygoid bones, which is one of the defining characteristics of Eusuchia.

This image is made available by APP through the creative commons licence. Originally produced by UP-S & SCW in Sweetman et al. 2014.

The specimen was first made public at SVPCA Oxford, but at that time it became clear – in light of the above convergences – that there were some unusual features this skull possessed which required further exploration with cladistic methods, and so I was signed up – hence the one and a half year hiatus.

The presence of compound characters in cladistic analyses means that a systematist (someone who performs these analyses) may not be telling the computer what they believe they are (Brazeau, 2011). As such character conflict may be artificially high, causing some natural groups to lack support, while other tentative groups gain support. Due to this and the chimaera-like situation that Koumpiodontosuchus found itself in meant that a whole new ‘Brazeau-acceptable’ analysis had to be constructed, picking and choosing, or altering characters from published analyses. So, in order to assess the systematic position of Koumpiodontosuchus an analysis coding 36 taxa for 242 characters was run in TNT, using a NT search. The result – after running more procedures to find the maximum number of MPTs (most parsimonious [best fitting] trees) – was a strict consensus of 17 trees with a length of 862 steps. A single tree was generated using implied weighting, which is the tree we finally presented. The logic behind this is that implied weighting changes the ‘impact’ of conflicting characters whilst the analysis runs, thus diminishing the effects of homoplasy (convergence of characters due to reasons other than a natural affinity): perfect for this scenario. The result (see cladogram) was that the Bernissartiidae was found as the sister-group to Rugosuchus, goniopholidids and Eusuchia. Interestingly, Thalattosuchia – a major group of marine crocodiles (see my article on Dakosaurus) – was found within Tethysuchia, a grouping that previously contained dyrosaurs and pholidosaurs, exclusive of thalattosuchians. Worryingly, the presence of the choana within the pterygoids of Koumpiodontosuchus, and its placement outside of Eusuchia leaves the clade of ‘true crocodiles’ wanting a definition. Salisbury et al. (2006) were happy to define the clade based on Isisfordia being the most basal member of the family, but according to this analysis that would exclude a lot of traditional Eusuchians. Brochu (1999) thought that Eusuchia could be defined by the most recent common ancestor of Hylaeochampsa and Crocodylia, but this is also an unreliable solution due to the shifting position of Hylaeochampsa between many analyses.

This image is made available by APP through the creative commons licence. Originally produced by SUV in Sweetman et al. 2014.

So what do we do? Abandon Eusuchia? Pfsh... I’m sure I don’t know. Not right now anyhow. The analysis I performed was mainly based upon cranial characters, with a very small subset of specimens. So a more comprehensive analysis in the same vein (really scrutinising characters for what they will tell the computer, in the light of Brazeau’s [2011] work) is required. I am currently in two minds as to whether I should pursue this point of enquiry or whether I should leave it to more experienced/more interested individuals. Who knows, it could be one of my next big posts.

For any South Park fans.

Paper available here

References

Brazeau, M. D. 2011. Problematic character coding methods in morphology and their effects. Biological Journal of the Linnean Society. 104: 489-498.

Brochu, C. A. 1999. Phylogenetics, taxonomy, and historical biogeography of Alligatoroidea.  Journal of Vertebrate Paleontology. 19 (sup. 2), 9–100.

Dollo, L. 1883. Premiere note sur les crocodiliens de Bernissart. Bulletin de l’Institut Royal des Sciences Naturelles de Belgique 2: 309–338.Salisbury et al. (2006)

Sweetman, S. C., Pedreira-Segade, U. and Vidovic, S.U. 2014. A new bernissartiid crocodyliform from the Lower Cretaceous Wessex Formation (Wealden Group, Barremian) of the Isle of Wight, southern England. Acta Palaeontologica Polonica. Doixxx

Odontography - all about teeth

Once again I have neglected 'MM', but it is not dead just yet. I felt that a little update was necessary. Currently I am working on some taxonomic issues within Pterosauria that it seemed impossible to ignore during a project attempting to resolve the evolutionary relationships of these creatures. I have also taken part in a project on a new genus and species of crocodile, but this is in review, so it's all hush hush for now.

So, let's talk teeth again shall we.

Teeth are used for aggression, defence, prey capture, digestion, grooming, communication, fighting, digging, sensing the surroundings, child rearing, sexual selection, sex and many more things, and they have a high preservation potential, so they are important to palaeontologists.

A slide from a presentation on understanding pterosaur teeth that I gave

A slide from a presentation on understanding pterosaur teeth that I gave

Some time ago I bought the domain Odontography.com. The website and its concept are still in the development stages. It is an ambitious project for one man without funding and too little time on his hands, but one that is close to my heart.

The concept of Odontography.com is to be an all encompassing dental resource for Biologists, Palaeontologists and other interested parties. I hope to provide general educational material as well as a search based resource for as many extinct and extant animals as possible. The concept is to build upon what Sir Richard Owen started in the 1840s with his Odontography. This treatise was a seminal piece of work, giving us terminology in common use today, e.g. dentine. The work was ~750 pages long with 150 plates of figures, contained in two separate volumes. The study looked at the teeth of fishes, reptiles (including amphibians, pterosaurs, dinosaurs and mesozoic marine reptiles) and mammals. There are histological (the study of microscopic mineralised tissue structures) images as well as depictions of the entire dental arrangement, it was a truly inspired piece of anatomical work.

Take for example the tooth of Megalosaurus which is beautifully illustrated, demonstrating the pulp cavity with the dentine tubules radiating out, through 9 bells of dentine, toward the enamel, terminating at a granular layer of tomes at the enamel dentine junction.

Megalosaurus section through the crown, originally figured by Owen 1845

Modern photograph of a Carcharodontosaurus tooth, taken by Steven Vidovic, material supplied by David Martill University of Portsmouth UK - For comparison with Megalosaurus

As you can see there is more to a tooth than what is just on the surface. In overall anatomy you have the root, cervical region and crown. The crowns can also have varying morphologies within a dentition, this is called heterodonty, as opposed to homodonty (all the same, just varying in size). The crown morphology can be divided into it's four overlapping halves, labial (cheek/lip side) and lingual (tongue side) sides, and mesial (front/central) and distal (back). Within the the tooth you have further divisions of structure; various types of dentine and cements and externally, usually (one exception being my favourite, the sloth), enamel. The varying compositions of these hard parts with soft tissues change the nature of the material all together, but I may be in danger of boring you if I go into the differences between cementums and dentines. The most impotant thing to know is your tooth is alive, with a complex network of cells working to keep it healthy. These cells are located with the pulp cavity which is accessed by the apical foramen, in many cases a tiny hole which prevents infection from entering the bone or blood.

Sloth tooth sectioned along the coronal plane, originally figured by Owen 1845

A demonstration of tooth implantation, arrangement and replacement in crocodiles, originally figured by Owen 1845

The volume should continue to serve as a valuable resource to palaeontologists. The resources should be used to test modern theories, through comparative anatomy.

So... there is life in Odontography yet. I would like to try and bring it to the 21st Century.