September 29, 2012 | 11
In the previous article we looked at Wealden goniopholidids, focusing in particular on the new taxa named by Steve Salisbury and myself in the review of Wealden crocodyliforms we published last year (Salisbury & Naish 2011). Having gotten some of the relevant taxa out of the way, we now need to crack on and get through the remainder.
We begin with Vectisuchus leptognathus, a relatively long-snouted goniopholidid (though read on) from the Vectis Formation collected by Steve Hutt in 1977 and described by Buffetaut & Hutt (1980). The type (and only) specimen is, unfortunately, not readable available if you’re based in the UK since it was sold to the Staatliches Museum für Naturkunde (SMNS) in Stuttgart (Germany) in 1979. The original description states that some of the material discovered in the field couldn’t be collected due to cliff collapse caused by inclement weather, but material present at the SMNS shows that some of this was collected, and hence obtained by the SMNS, at some stage afterwards (Salisbury & Naish 2011).
Anyway, Vectisuchus is a slender-snouted animal where the rostrum is well demarcated from the rest of the skull. The snout and lower jaw tip are expanded, and the large, rounded eye sockets are directed rostrolaterally (meaning that they point both forwards and sideways at the same time). It wasn’t an especially large animal, with a skull just 18 cm long and a total length estimated at 1.2 m.
An especially interesting feature of the specimen (though it isn’t unique to this taxon within Goniopholididae) is that its forelimbs are more elongate than is usual for mesoeucrocodylians*: they’re actually 10-20% longer than the hindlimbs, whereas the reverse is true in eusuchians. So far as I know, nobody has suggested a specific ‘function’ for these elongate forelimbs. I don’t think goniopholidids were reaching up into vegetation, or using their elevated forequarters to keep heavy objects carried in the jaws off the ground (two behaviours that have been linked with elongate forelimbs in other tetrapods). Other possibilities are that they were especially good at ‘poling’ along with the forelimbs while moving on submerged substrates, that they needed to stand up tall, or raise the snout especially high, while feeding or displaying.
* Mesoeucrocodylia = the crocodyliform clade that includes all taxa closer to Crocodylus niloticus than to Protosuchus richardsoni.
Incidentally, while we include Vectisuchus within Goniopholididae, there are indications that this may not be correct, since Jouve et al. (2006), Jouve (2009) and De Andrande et al. (2012) find this animal to be closer to Pholidosauridae (and their kin). Pholidosaurids are long-snouted crocodyliforms often found in phylogenies to be close to the also (typically) long-snouted dyrosaurids and thalattosuchians: the gigantic Sarcosuchus is probably the most famous member of the group. However, anyone deeply immersed in crocodyliform phylogeny and systematics will know that the term Pholidosauridae is currently somewhat problematic. I have to gloss over that issue for now and promise to come back to it later.
Weird little Leiokarinosuchus
Of the three new taxa named in our review, the most poorly known is Leiokarinosuchus brookensis Salisbury & Naish, 2011. It’s based on a partial skull (lacking essentially the whole of the rostrum) and its associated cervical vertebrae and osteoderms. This specimen was found in the Brook Bay region of the Isle of Wight (and hence is presumably from the Wessex Formation), was purchased in 1855 and has been little discussed ever since.
Lydekker (1887) referred it to the German Obernkirchen Sandstone species Pholidosaurus meyeri, one of the pholidosaurids. So, thanks to this skull, Wealden workers have often listed pholidosaurids as components of Wealden faunas. Our examination showed, however, that the Brook Bay skull is no pholidosaurid – it lacks the characteristic features of this group and is, in fact, far more likely to be a long-snouted goniopholidid (Salisbury & Naish 2011).
Several features make the skull rather different from the skulls of pholidosaurids, and they also make it weird and worthy of recognition as a new taxon. While some of the preserved skull bones are covered with the bone pitting that’s fairly normal for crocodyliforms, the preserved, posterior part of the dentary is smooth (as they are in Anteophthalmosuchus), and so are the bones on the roof of the skull. What’s more, the bones around the supratemporal fenestrae smoothly slope ‘into’ the edges of these openings. The occipital condyle is proportionally small, a feature also seen in Anteophthalmosuchus (Salisbury & Naish 2011). Unusual features are also seen in the dorsal osteoderms: they lack the articular processes seen in goniopholidids, and their lateral sections are inclined relative to the medial part – a feature seen elsewhere in Bernissartia and some eusuchians, but not in goniopholidids.
Leiokarinosuchus is thus a rather odd little animal. It preserves a combination of unusual characters and can’t be convincingly slotted into any particular crocodyliform clade, though does seem goniopholidid-like in several details and might be a member of this group. The smooth roof of the skull and the weird form of the bones around the supratemporal fenestrae certainly suggest that it warrants distinct taxonomic status, and the generic name we went for means ‘smooth-headed crocodile’ (or ‘bald-headed crocodile’).
Atoposaurids in the Wealden?
Several specimens demonstrate that members of another crocodyliform clade, Atoposauridae, were also present in Wealden assemblages. Atoposaurids are all small (something like 50-100 cm long), short-snouted crocodyliforms: like goniopholidids and Bernissartia (read on), they’re stem-neosuchians – early members of the clade that also includes the living crocodyliform lineages.
The Wealden atoposaurid remains – they include teeth from the Ashdown and Wadhurst Clay formations (both part of the Hastings Group) as well as a partial braincase from the Wessex Formation – all seem referable to Theriosuchus, a geologically long-lived and apparently widespread atoposaurid that’s currently thought to have been around from the Late Jurassic to the latest Late Cretaceous (Brinkmann 1992, Schwarz & Salisbury 2005, Martin et al. 2010). These belong to at least five species (T. pusillus Owen, 1879, T. ibericus Brinkmann, 1992, T. guimarotae Schwarz & Salisbury 2005, T. sympiestodon Martin et al., 2010 and T. grandinaris Lauprasert et al., 2011). The Wealden Theriosuchus material was first identified as such by Peter Wellnhofer in 1980 and was later described by Buffetaut (1983); we agreed with Buffetaut that, while the Wessex Formation specimen looks most like T. pusillus from the Purbeck Limestone Group, it can’t be identified precisely in the absence of better material (Salisbury & Naish 2011).
Bernissartia and other ‘bernissartids’
One of the best known Lower Cretaceous European crocodyliforms has to be little Bernissartia, and I say this because most sources on these animals mention, discuss or illustrate the near-complete skeleton of B. fagesii Dollo, 1883 [shown below]. It was discovered in the same coal mine at Bernissart, Belgium, that also yielded all those Iguanodon skeletons. Thanks to this specimen and one or two others, we know that Bernissartia was small (c. 60 cm total length), with vertebral, osteoderm and palatal characters that put it close to the origin of Eusuchia (e.g., Buffetaut 1975, Norell & Clark 1990, Salisbury et al. 2006). Its posterior, so-called tribodont teeth (these have rounded cusps where the enamel on the apical half is ornamented with vertical striations) are unlike those of any contemporary crocodyliform and can be readily identified when found in isolation.
Indeed, a large number of fragmentary remains from Upper Jurassic and Lower Cretaceous localities across western Europe have been identified as those of Bernissartia or Bernissartia-like ‘bernissartids’ (see Salisbury & Naish 2011). In the Wealden, isolated teeth and a partial skeleton show that Bernissartia is present in the Hastings Group (most likely in the Ashdown Formation), the Lower Weald Clay Formation, and the Wessex Formation. In other words, ‘bernissartids’ of some sort were present in southern England for virtually the whole time that the Wealden sediments were being deposited. Better remains are needed to identify them to species level. A small, near-complete skull of Bernissartia-like crocodyliform has recently been discovered on the Isle of Wight and is currently under study by Steve Sweetman and colleagues.
Hylaeochampsids and other eusuchians
Finally, we come to the hylaeochampsids, for the Wealden also gives us Hylaeochampsa vectiana, a crocodyliform named by Richard Owen in 1874 for yet another partial skull. Hylaeochampsa is from the Wessex Formation (not the Vectis Formation, as stated by Clark & Norell (1992)) and could potentially have lived alongside Anteophthalmosuchus and Leiokarinosuchus.
The only known specimen of Hylaeochampsa is missing its rostrum as well as its teeth; furthermore, there has been a reasonable amount of disagreement about the homology of the large openings on the posterior part of its palate. A few recently discovered crocodyliforms seem to be close relatives of Hylaeochampsa, necessitating the recognition of a Hylaeochampsidae. Both Iharkutosuchus makadii, a hylaeochampsid named from the Upper Cretaceous of Hungary in 2007 (Ősi et al. 2007, Ősi 2008), and the several species of Acynodon (suggested to be part of Hylaeochampsidae by Turner & Brochu (2010)), are smallish, short-snouted forms with enlarged, multi-cusped posterior teeth, so it looks very likely that Hylaeochampsa was like this as well. Buscalioni et al. (2011) have recently regarded Pietraroiasuchus and Pachycheilosuchus as hylaeochampsids as well.
A number of skull features – most importantly the enclosure of the choana within the pterygoid bones – show that Hylaeochampsa (and its relatives) is part of Eusuchia, the clade that includes Crocodylia and several closely related lineages. This is important, since it shows that eusuchians had appeared by the Barremian at least, and that they were present in the Northern Hemisphere at this time (some other Early Cretaceous eusuchians are Gondwanan).
Several eusuchian odds and ends – mostly procoelous vertebrae – are known from various Wealden Supergroup units, including the Hastings Group. One such specimen (a string of 12 articulated vertebrae) was named Heterosuchus valdensis by Seeley (1887) and has sometimes been regarded as synonymous with Hylaeochampsa. While this isn’t impossible, the two are very different in age, there’s no overlapping evidence that might support it, and a lack of unique features means that Heterosuchus has to be regarded as a nomen dubium (Salisbury & Naish 2011).
While there’s even more that could be said about Wealden crocodyliforms – our chapter is a not-insubstantial 64 pages long – I think this article and the previous one do a reasonable job of summarising the contents of Salisbury & Naish (2011). Our review is certainly not the last word on Wealden crocodyliforms; as a review of where we’re at right now, it’s hopefully the start of a new phase in our work on the phylogeny, systematics and ecology of these animals.
For some previous Tet Zoo coverage of crocodylomorphs (wholly crocodyliforms, and mostly crocodylians), see…
Massive thanks to my co-author, Steve Salisbury, for his work in generating, and help in providing, the images used here.
Refs – -
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