|3/3 - this, ladies and gentlemen, is the end. At least, until the inevitable prequels where I'll ignore the canon of the expanded universe and do my best to tarnish everything you liked about the original trilogy.|
This most recently identified Wealden crocodyliform is among the most sophisticated and unusual of all Wealden crocs. Named Koumpiodontosuchus aprosdokitii, it is known from a well-preserved skull which was recovered in circumstances owing much to chance and good fortune (Sweetman et al. 2014). This animal is currently only known for certain from the Wessex Formation of the Isle of Wight, specifically from fossil-rich cliffs next to the seaside village of Yaverland, and the only known skull of it is broken in half. The posterior half was discovered in March 2011 by holidaying fossil hunters, who took it to the local dinosaur museum (Dinosaur Isle, of Sandown) to have it identified. Another family, on a fossil-hunting holiday three months later, then found the front half of the skull. They took this to the same museum where, by chance, the same museum staff who’d handled the first piece were on hand. It was realised that each piece belonged to the same specimen, and the first half was rapidly brought back to the museum to check the degree of articulation. Remarkably, the join between the broken pieces was near perfect – clearly neither chunk had been exposed to weathering effects very long before being discovered – and the entire skull could be seen. Each piece was then donated to the museum to allow its study. Given the chain of events and people involved in the discovery of Koumpiodontosuchus, it’s easy to imagine how only single halves of the skull might be known to science, or even neither. This is clearly yet another story which stresses the importance of amateur fossil hunters to Wealden fossil discoveries, and the benefits of responsible collecting.
|Holotype skull and mandible of the button-toothed crocodyliform, Koumpiodontosuchus aprosdokitii. From Sweetman et al. 2014.|
Button-toothed crocodiles in contextKoumpiodontosuchus is a member of Bernissartidae, a group named by Sweetman et al. (2014) which only contains two species: Koumpiodontosuchus and Bernissartia fagesii. The latter is a famous, small Jurassic and Cretaceous crocodyliform known from France, Denmark, Spain, Portugal and particularly Belgium, where a spectacular complete skeleton has been unearthed. Indeterminate species of Bernissartia also seem to occur in the Ashdown Formation of Hastings (Salisbury and Naish 2011), but this identification may eventually warrant reappraisal now that Koumpiodontosuchus has been discovered. Bernissartid remains are not new, some of the first material of these animals being documented in the 1850s and Bernissartia itself being named from Belgian fossils in the 1880s. Isolated teeth, likely referable to Koumpiodontosuchus, have been found in Wealden deposits since at least the 1970s (Buffetaut and Ford 1979), so were clearly present across the entire geographic and stratigraphic range of the Wealden Supergroup.
Bernissartia has long been a bit of an oddball among Crocodyliformes, possessing some unusual anatomy and being of uncertain placement in crocodyliform systematics. The discovery of Koumpiodontosuchus provided a bit of light on this front, suggesting that Bernissartia was part of a group containing at least one other similar species, and that they occupy an evolutionary place between atoposaurids and the goniopholidid + Eusuchia radiation. This position isn’t too surprising, as there are a number of features in bernissartids which link them to Eusuchia – see below. Bernissartidae is primarily defined by dental characteristics, with the most obvious one also being the namesake of Koumpiodontosuchus: “button-toothed crocodile” (if anyone wants a common name for these Crocodyliformes, this is the one to use). The posterior teeth of bernissartids are rather globose – wide, short and blunt – and distinctive compared to the dentitions of most other Crocodyliformes. It’s these teeth which, even in isolation, betrayed the presence of bernissartids in the Wealden well before the more substantial Koumpiodontosuchus fossil was discovered. Their other teeth are quite different to this, however. The mid-region dentition is rather conical in shape; ‘pseudocanines’ erupt about 25 % of the jaw length from the jaw tip, and conical teeth emerge procumbently from the jaw tips themselves. Koumpiodontosuchus has two large pseudocanines on its lower jaw, which erupt so close to each other that they share a single, enlarged tooth socket. Bernissartia, by contrast, only possesses one.
|The new Wealden bernissartid Koumpiodontosuchus aprosdokitii foraging for molluscs. It's eating a mud snail, Viviparus cariniferus, while tiny (6 mm long) physid gastropods Prophysa crawl over pond scum in the lower left of the image. Dragonflies provide scale, while unnamed tetanurans (based on findings of Benson et al. 2009) prowl around the background. An earlier version of this reconstruction was featured in Sweetman et al. (2014). Prints of this image are available here.|
The bit on palaeoecologyEcologically, it seems that bernissartids had a preference for hard shelled prey. Their blunt posterior dentition has been labelled as ‘tribodont’ – literally meaning ‘crushing teeth’ – and, like slamming a couple of anvils together, are ideally shaped to crunch hard shells. Some confirmation of this idea is seen in the wear facets often seen on tribodont bernissartid teeth. Classically, their prey was largely considered to comprise molluscs such as the freshwater snails and clams populating Wealden streams and lakes (Buffetaut and Ford 1979). Recently, a broader diet has been postulated for bernissartids however, the logic being that hard shells are hardly restricted to molluscs even in freshwater settings (Sweetman et al. 2014). Insects and crayfish probably formed as much of their diet as molluscs, all of which were likely procured or extracted from soft-substrates with the procumbent anterior teeth. We should not forget the savage-looking pseudocanines of these animals however: these would be of little use against hard prey items, but may have allowed for spearing relatively soft-animals. Perhaps bernissartids are best viewed as rather opportunistic feeders, primarily taking hard-shelled prey but not turning their noses to other types of food when the opportunity arose.
|If gastropods like this Wealden mud snail, Viviparus cariniferus, had nightmares, they contained bernissartids.|
It’s worth pointing out that bernissartids may not be the only Wealden Crocodyliformes adapted for hard-shelled prey. The poorly known, 1.5 m long Wealden eusuchian Hylaeochampsa vectiana also has large posterior teeth ideal for smashing shelled prey (Clark and Norell 1992), although the dentitions of other hylaeochampsids are complex and it’s possible Hylaeochampsa had a very varied diet. As discussed for other Wealden Crocodyliformes, it’s likely that the size difference between the bernissartids and Hylaeochampsa would prevent too much overlap in prey preference: the latter may have been capable of eating large molluscs or even small armoured vertebrates, which were probably unavailable to bernissartids. There's lots more we could say here, but I'd best not - maybe Hylaeochampsa will warrant dedicated discussion at a later date.
And I guess that's where we'll leave the Wealden Crocodyliformes for now. As alluded to above, there are other crocodyliform species and groups we could discuss, but they're generally less well known than the taxa we've covered across these posts and it would be difficult to discuss them in comparative depth. I hope you've enjoyed this series of themed posts and, if artwork of ancient Wealden animals is your thing, come back soon for a big announcement about an event related to just that.
- Benson, R. B., Brusatte, S. L., Hutt, S., & Naish, D. (2009). A new large basal tetanuran (Dinosauria: Theropoda) from the Wessex Formation (Barremian) of the Isle of Wight, England. Journal of vertebrate Paleontology, 29(2), 612-615.
- Buffetaut, E., & Ford, R. L. E. (1979). The crocodilian Bernissartia in the Wealden of the Isle of Wight. Palaeontology, 22(4), 905-912.
- Clark, J. M., & Norell, M. (1992). The Early Cretaceous crocodylomorph Hylaeochampsa vectiana from the wealden of the Isle of Wight. American Museum novitates; no. 3032.
- Salisbury, S. W. & Naish, D. (2011). Crocodilians. In Batten, D. J. (ed.) English Wealden Fossils. The Palaeontological Association (London), pp. 305-369.
- Salisbury, S. W. & Frey, E. 2000. A biomechanical transformation model for the evolution of semi-spheroidal articulations between adjoining vertebral bodies in crocodilians. In Grigg, G. C., Seebacher, F. & Franklin, C. E. (eds) Crocodilian Biology and Evolution. Surry Beatty & Sons (Chipping Norton, Aus.), pp. 85-134.
- Sweetman, S.C., Pedreira-Segade, U., & Vidovic, S. (2014) A new bernissartiid crocodyliform from the Lower Cretaceous Wessex Formation (Wealden Group, Barremian) of the Isle of Wight, southern England. Acta Palaeontologica Polonica (in press)