Keeping up with Carcharodontosaurus

Over the past two decades there has been an explosion in the number of large theropods that have been discovered (or as we shall see, rediscovered) in Africa and South America, the predatory dinosaurs of what was once Gondwana being just as large and terrifying as their more famous Northern Hemisphere counterparts. Abelisaurids (i.e. Carnotaurus, Rugops, Majungasaurus), Spinosaurids (i.e. Baryonyx, Suchomimus, Irritator, and Spinosaurus), and Carcharodontosaurids (i.e. Giganotosaurus, Tyrannotitan, Mapusaurus, and Carcharodontosaurus) have all emerged from the rock at an alarming rate, although some are more like long-lost dinosaurs than unexpected varieties. Spinosaurus is the most well-known example, but Carcharodontosaurus is another African theropod that was effectively lost for half a century before appearing again, and a new paper out in the Journal of Vertebrate Paleontology adds to the diversity of this genus.

Discovered in northern Africa in 1927, Carcharodontosaurus was originally known only from two teeth deemed to belong to a species of Megalosaurus by Charles Depéret and J. Savornin, the teeth being brought under the new name Carcharodontosaurus by German paleontologist Ernst Stromer in 1931 based upon comparison with better material that he had found. Much like the specimens Stomer collected of Spinosaurus, however, the Carcharodontosaurus material was destroyed during an Allied bombing raid during WW II, the original teeth found by Depéret and Savornin seemingly disappearing as well. This poses a bit of a problem; we know Carcharodontosaurus is a real dinosaur genus, especially given the discovery of more complete skull material by Paul Sereno in 1996, but the holotype fossils are missing and Stromer's neotype fossils were destroyed. On top of that, Dale Russell named what turned out to be Carcharodontosaurus remains "Sigilmassasaurus" in 1996, as well, so it is exceedingly important to establish a new neotype to preserve the status of the name Carcharodontosaurus. Thankfully, that's just what Stephen Brusatte and Paul Sereno have done in their new paper "A New Species of Carcharodontosaurus (Dinosauria: Theropoda) From the Cenomanian of Niger and a Revision of the Genus," the skull Sereno found becoming the new representative specimen for this genus.

The re-establishment of Carcharodontosaurus is vital for another reason as well; in the same paper Brusatte and Sereno describe a new species of Carcharodontosaurus, named Carcharodontosaurus iguidensis, named for the location in which it was discovered in the Republic of Niger (the first and more northern species described my Stromer was Carcharodontosaurus saharicus). As can be seen from the picture above, the maxilla of the new species (which represents its holotype), shares many of the features that distinguish Carcharodontosaurus and it's close relatives like the distinctive ridges and grooves, but it is clear that the maxillary fenestra is placed differently in the new species when compared to C. saharicus. More parts of the skull were recovered and described in the paper that have led to the establishment of the new species, but I didn't feel competent enough to discuss them at length here (although a reconstruction or articulation of the recovered materials in comparison with the 1996 skull would have been a welcome addition in this regard).

From an ecological perspective, though, this new species is interesting in that it seems to make up part of a faunal arrangement that was similar in northern Africa, yet perhaps isolated enough to achieve some amount of differentiation. At the locality in Niger, C. iguidensis was found near remains of the abelisaurid Rugops and teeth from a large spinosaurid dinosaur, a similar grouping of C. saharicus, Spinosaurus, and Deltadromeus occurring in North Africa. Indeed, the presence of at least three large predatory dinosaurs in the same place at the same time suggests some sort of partitioning as far as home range/territory and preferred prey. Modern mammalian carnivores in Africa (Cheetahs, Leopards, Wild Dogs, Spotted Hyena, and Lions) exist in close proximity to each other but exploit different prey animals to different degrees, some coming into greater confrontation with each other than others (i.e. cheetahs have greater hunting success but are easily run off prey by larger "brutes" like lions). Applying such a relationship to ancient predatory dinosaurs conjures up Mark Hallett's "Thunder Across the Delta" painting, Carcharodontosaurus perhaps running off smaller abelisaurids from kills but coming into conflict with large spinosaurids. Such speculation has its problems, however, as lions and hyenas are social carnivores that rely on numbers to help steal kills, and while a "pack" of Carcharodontosaurus might be a scary thought there's no evidence whatsoever that they would ever engage in such a behavior and remains little more than a figment of my own imagination. Still, the lesson of large, sympatric carnivore species is that their prey preferences differ, this partly being a consequence of avoiding confrontations that could result in injury or death.

In the closing sections of the paper, the authors also drop some hints about a forthcoming analysis of carcharodontosaurids and allosaurids in general, reinforcing that Carcharodontosaurus, Giganotosaurus, and Mapusaurus form a closely-related clade, something that (while requiring rigorous empirical analysis) is essentially apparent on sight. As ever, though, the placement of Acrocanthosaurus seems to be problematic and is bound to be contentious, and although I'm sure we'll all be looking forward to the analysis which is promised to appear elsewhere at some future date.

What interests me most about this study, however, is the possibility of distinct southern and norther ecologies made up of similar dinosaurs but that have been isolated long enough to exhibit differences between other populations. The site at which Rugops and C. iguidensis seems promising (especially since there appeared to be remains of more individuals of C. iguidensis from various stages of life), and hopefully paleontologists will team up with paleoecologists and those well-versed in biogeography to paint a fuller picture of what Africa was like during the Early Cretaceous (as well as the relationships between the South American and African carcharodontosaurids). Taxonomy and the establishment of new species is important, but dinosaurs were living animals that existed within various ecological settings. Given the sheer amount of fossils coming out of South America and Africa, then, the potentials for those who want to reconstruct the natural history of the ancient Cretaceous are becoming more and more exciting.

References;

Brusatte, S.L., and Sereno, P.C. (2007) "A New Species of Carcharodontosaurus (Dinosauria: Theropoda) From the Cenomanian of Niger and a Revision of the Genus." Journal of Vertebrate Paleontology 27(4):000-000.[JVP Contents Page]