Early abelisaurs and fan-crested and stretch-jawed hadrosaurs

Continuing the theme of discussing 'things in the news', we arrive, finally, at dinosaurs. The previous 'late news' pieces looked at fossil anurans and pterosaurs, and assorted mammals. So what news has been announced recently-ish in the world of dinosaurs? Well, frankly, there are always so many newly announced dinosaurs that it's difficult to keep up. But...

... particularly cool is the recent description of the basal abelisaur Kryptops palaios and the carcharodontosaurid Eocarcharia dinops, both from the Aptian-Albian Elrhaz Formation of Niger (Sereno & Brusatte 2008) [in adjacent image, Kryptops is at the top, Eocarcharia is below. Art by Todd Marshall]. Kryptops is a basal abelisaurid, diagnosed by an unusual surface texture on the maxilla and by a bony sheet that obscures the anteroventral part of the antorbital fossa from view. The surface texture perhaps suggests that something more than skin was attached to the side of the face - perhaps a thickened, keratinous layer, as has been suggested for another basal abelisaurid from Africa, Rugops. The presence of the basal abelisaurids Kryptops and Rugops in Africa might suggest that the clade evolved here, and the presence of non-abelisaurid abelisauroids in Africa - namely Spinostropheus, Elaphrosaurus and Lower Jurassic Berberosaurus (the latter only named in 2007) - now shows that Africa was very important in the early history of this group* (Sereno et al. 2004, Allain et al. 2007, Sereno & Brusatte 2008) [life restoration of Rugops shown below - again by the Toddmeister].

* Although note that the inclusion of these three within Abelisauroidea has not been supported in all studies (thanks to Mickey Mortimer for noting this).

The carcharodontosaurid Eocarcharia, meanwhile, is characterised by particularly large pneumatic openings within the rostral part of its antorbital fossa and a large, rounded 'orbital boss' above and behind its orbit, among other characters. The orbital boss appears to have evolved for heavy-duty usage of some sort, and it may not be coincidental that a lot of additional bracing is present in the posterodorsal part of the carcharodontosaurid skull. So, Sereno & Brusatte (2008) suggest, might Eocarcharia and its relatives have engaged in lateral head-butting of some sort? Similar suggestions have been made for tyrannosaurids and other large theropods with bony bosses above and around their eyes. Phylogenetic analysis finds Eocarcharia to be one of the most basal members of Carcharodontosauridae, and the sister-taxon to North American Acrocanthosaurus. Neovenator from the Wessex Formation of the Isle of Wight appears to be more basal.

Kryptops and Eocarcharia lived alongside big spinosaurids and this is proving to be a common theme for the Cretaceous: yet again we have a fauna where three big theropods were sharing the environment, and apparently avoiding competition by occupying distinct niches. This is something I'll have to return to later, as Steve Brusatte, Roger Benson, Steve Hutt and I have just submitted a manuscript on this very subject. Incidentally, Sereno and Brusatte have also recently produced an analysis of allosauroid relationships, but I haven't yet looked at it.

A Mexican fan-crested hadrosaur

Moving now away from theropods and to something quite different: we've had a few new hadrosaurs published in recent months. Ornithopods are another one of those groups that I've not ever said much about at Tet Zoo, but that isn't because I don't like them (even though I rudely referred to them as 'the boring ones' in a recent book review), it's all down to other groups hogging the limelight. Anyway, we begin with the new Mexican lambeosaurine hadrosaur Velafrons coahuilensis from the Campanian Cerro del Pueblo Formation, recently described by Gates et al. (2007) [adjacent image shows life restoration... again by Todd Marshall. He's everywhere these days!].

Velafrons is a fan-crested lambeosaurine, closely related to Corythosaurus and Hypacrosaurus, and grouping with them and with Lambeosaurus and Asian Olorotitan in a phylogenetic analysis. It would have looked much like Corythosaurus and Hypacrosaurus, but differs from them in having an odd dorsally arched postorbital-squamosal bar. Noteworthy is that Velafrons is the first new lambeosaurine genus to be named from North America in over 70 years: like the ceratopsians Achelousaurus, Einiosaurus, Cerasinops and Eotriceratops, it demonstrates that even the North American Upper Cretaceous - one of the best understood and most-studied segments of Mesozoic time - has fresh new taxa to offer. Also neat is the fact that Velafrons reiterates the small, provincial distributions we see of Campanian lambeosaurines: no-one really knows why, but many Campanian ornithischians had very restricted distributions. They did not occur continent-wide as their extant analogues do (Lehman 2001, Gates & Evans 2005, Gates et al. 2007) [image belows shows Velafrons fossils being held by Terry Gates].

I understand that an in-press manuscript gives the fan-crested lambeosaurines a new name, Corythosaurini. And, even with Velafrons in the mix, there might be more members of this group than you think, because it now seems that some of those species previously argued to be sexual morphs of other species (Dodson 1975) deserve to be separated again. They are not contemporaneous with their alleged conspecifics, and differ from them in details that don't appear due to ontogeny or dimorphism. Look at Parasaurolophus: short-crested P. cyrtocristatus is not just a female of long-crested P. tubicen or P. walkeri (as was generally thought in the 1980s and 90s): it is, after all, an older, anatomically different animal (Sullivan & Williamson 1999, Gates et al. 2007).

Scoop-jaw and stretch-jaw: strange new Chinese hadrosaurs

And also from the world of hadrosaurs, we have two new Chinese taxa: Sahaliyania elunchunorum and Wulagasaurus dongi, both from the Maastrichtian Yuliangze Formation of Heilongjiang Province (Godefroit et al. 2008). The Yuliangze Formation has previously yielded Charonosaurus jiayinensis, a lambeosaurine closely related to Parasaurolophus. Sahaliyania is known from quite a lot of material and is identified as a lambeosaurine at the base of the parasauroloph-corythosaur clade. It is characterised by a list of skull details (among which are the unusually deep depressions it possesses on its frontal bones, dorsal to the orbits) and by a strongly expanded anterior part of the pubis. Its nasal and premaxillary bones are unknown, so we don't know what kind of crest it had, and it resembles some other basal lambeosaurines in having a massively down-turned anterior part of the lower jaw. Why some hadrosaurs had jaws like this is a good question: a rather different sort of down-turn in the jaws of Protohadros byrdi (a basal hadrosaurid outside of the Hadrosaurinae-Lambeosaurinae clade) was suggested to allow use of the mandible 'as a scoop for acquiring aquatic plants' (Head 1998, p. 734), an inferred behaviour similar to that once imagined (erroneously, as it turns out) for the shovel-tusker amebelodontid proboscideans [adjacent image shows the Sahaliyania lower jaws in both medial and lateral views, with detail of dentary teeth shown at the bottom. This image is Fig. 6 in Godefroit et al. (2008), which you can access for free here].

Until very recently, the parasauroloph-corythosaur clade was regarded as North American, and with just one Asian representative: Nipponosaurus sachalinensis, identified as the sister-taxon to Hypacrosaurus altispinus by Suzuki et al. (2004). Now that Asia has yielded Olorotitan (part of the fan-crested corythosaur clade), Charonosaurus (part of the tube-crested parasauroloph) clade, and Sahaliyania (apparently close to both the corythosaur and parasauroloph clades), it looks like different lambeosaurine lineages repeatedly invaded North America from Asia. Indeed an Asian origin for lambeosaurines as a whole is indicated by the fact that its basal members (Aralosaurus, Tsintaosaurus, Jaxartosaurus and Amurosaurus) are all Asian (Godefroit et al. 2003, 2004, 2008)

The second new Yuliangze Formation hadrosaur, Wulagasaurus dongi, is remarkable for its incredibly elongate, slender lower jaws, the most elongate and slender yet known for a hadrosaur (even exceeding those of the stretch-jawed edmontosaurs previously known as Anatotitan: shown in adjacent life restoration by Donna Braginetz). Again, what this hadrosaur was doing with jaws this long and slender is a very good question, and one we don't know the answer to. Wulagasaurus is identified as a hadrosaurine on the basis of skull and pelvic characters, and is furthermore suggested to be the most basal member of the clade (Godefroit et al. 2008). Given its late Maastrichtian age, this indicates the presence of a ghost lineage of about 13 million years, given that other basal hadrosaurines (the brachylophosaurs and gryposaurs) are known from the early Campanian. It also would hint at an Asian origin for hadrosaurines, but this is hard to be confident about because the biogeography of non-hadrosaurine hadrosaurids is still very messy: they're known from Europe, Asia and North America. It also seems odd that such a strangely aberrant hadrosaur is the most basal member of its clade, and I await future studies that further test the phylogenetic position supported for Wulagasaurus by its describers.

I said I wouldn't say it again but - we do live in exciting times. And on that note I need to get back to work. It's all big-brained theropods, dinosaur conferences and ichthyosaurs these days.

Refs - -

Allain, R., Tykoski, R., Aquesbi, N., Jalil, N.-E., Monbaron, M., Russell, D. & Taquet, P. 2007. An abelisauroid (Dinosauria: Theropoda) from the Early Jurassic of the High Atlas Mountains, Morocco, and the radiation of ceratosaurs. Journal of Vertebrate Paleontology 27, 610-624.

Dodson, P. 1975. Taxonomic implications of relative growth in lambeosaurine hadrosaurs. Systematic Zoology 24, 37-54.

Gates, T. A. & Evans, D. C. 2005. Biogeography of Campanian hadrosaurid dinosaurs of North America. In Braman, D. R., Therrien, F., Koppelhus, E. B. & Taylor, W. (eds) Dinosaur Park Symposium: Short Papers, Abstracts, and Program. The Royal Tyrrell Museum (Drumheller), pp. 33-39.

- ., Sampson, S. D., Delgado de Jesús, C. R., Zanno, L. E., Eberth, D., Hernandez-Rivera, R., Aguillón Martínez, M. C. & Kirkland, J. I. 2007. Velafrons coahuilensis, a new lambeosaurine hadrosaurid (Dinosauria: Ornithopoda) from the late Campanian Cerro del Pueblo Formation, Coahuila, Mexico. Journal of Vertebrate Paleontology 27, 917-930.

Godefroit, P., Bolotsky, Y. & Alifanov, V. 2003. A remarkable hollow-crested hadrosaur from Russia: an Asian origin for lambeosaurines. C. R. Palevol 2, 143-151.

- ., Bolotsky, Y. & Van Itterbeeck, J. 2004. The lambeosaurine dinosaur Amurosaurus riabinini, from the Maastrichtian of Far Eastern Russia. Acta Palaeontologica Polonica 49, 585-618.

- ., Hai, S., Yu, T. & Lauters, P. 2008. New hadrosaurid dinosaurs from the uppermost Cretaceous of northeastern China. Acta Palaeontologica Polonica 53, 47-74.

Head, J. J. 1998. A new species of basal hadrosaurid (Dinosauria, Ornithischia) from the Cenomanian of Texas. Journal of Vertebrate Paleontology 18, 718-738.

Lehman, T. M. 2001. Late Cretaceous dinosaur provinciality. In Tanke, D. H. & Carpenter, K. (eds) Mesozoic Vertebrate Life. Indiana University Press (Bloomington & Indianapolis), pp. 310-328.

Sereno, P. C., Wilson, J. A. & Conrad, J. L. 2004. New dinosaurs link southern landmasses in the Mid-Cretaceous. Proceedings of the Royal Society of London B 71,1325-1330.

- . & Brusatte, S. L. 2008. Basal abelisaurid and carcharodontosaurid theropod from the Lower Cretaceous Elrhaz Formation of Niger. Acta Palaeontologica Polonica 53, 15-46.

Sullivan, R. M. & Bennett, G. E. 2000. A juvenile Parasaurolophus (Ornithischia: Hadrosauridae) from the Upper Cretaceous Fruitland Formation of New Mexico. New Mexico Museum of Natural History & Science Bulletin 17, 215-220.

Suzuki, D., Weishampel, D. B. & Minoura, N. 2004. Nipponosaurus sachalinensis (Dinosauria; Ornithopoda): anatomy and systematic position within Hadrosauridae. Journal of Vertebrate Paleontology 24, 145-164.