Carcharodontosaurus — a Bloody Tooth-Taxon

Carcharodontosaurus saharicus is a taxon many potential readers may be familiar with. Through the work of paleontologists like Ernst von Stromer and Paul Sereno, much of what we know about this taxon is possible. It would surprise you then to know that much of what we know is not based on the original material that was used to give us the name Carcharodontosaurus saharicus.

Many species today are known based on scant, crappy, or downright horrible material. Some of them are so bad that they seem to require abandonment by convention (everyone just stops using the nomenclature) just to keep the indexes clean. This doesn’t get them off the books, but it moves them to a neat little pocket where they can be looked at only by the very interested.

Carcharodontosaurus saharicus is based on a few teeth found in Algeria [1], and was originally a species (saharicus) named to the genus Megalosaurus. Years later, the Markgraff expeditions funded by von Stromer to Egypt [2] recovered the partial remains of a skeleton of a large theropod at Baharija; von Stromer, upon examining the cranial and dental remains, named the material (much of a skeleton), determined that saharicus differed substantively from other Megalosaurus species that it deserved a new name, and granted it the “bloody-toothed” monicker of Carcharodontosaurus, as these new teeth reminded him of those sharky predators of the deep [3]. Little more of Carcharodontosaurus saharicus has been recovered, although the Saharan region of Africa, from Egypt to Morocco and further south has yielded much teeth very similar to that of saharicus. They’ve also been recovered in Asia and South America, far flung from Africa even during the middle of the Cretaceous when Africa was largely isolated from the rest of the world [4].

Much of what we now base Carcharodontosaurus saharicus on now is that Egyptian skeleton; unfortunately, this material was destroyed in WWII [2], making direct comparison difficult (von Stromer left us excellent drawings and a description, but these hardly substitute for examination of the precise material). To compound this issue, the material may have been immature based on their size, and they were recovered from a site far removed from that of the holotype teeth, which we do still have. Even further troubling has been the referal of material to Carcharodontosaurus saharicus that has been accepted as characteristic if not diagnostic for the taxon from the Aptian-Albian Gadoufoua beds of Niger [4] and the Cenomanian Kem Kem beds of Morocco [5], the former being referred to a distinct species but within Carcharodontosaurus.

Material specifically referred to Carcharodontosaurus saharicus derives from the Aptian-Albian (Algeria), and the younger beds in the Cenomanian (Egypt, Niger). Despite this, theropods called “carcharodontosaurs” are also found in similarly-aged sediments in South America, and include Giganotosaurus carolinii [6] (Cenomanian), Mapusaurus roseae [7] (also Cenomanian), and Tyrannotitan chubutensis [8] (Aptian). While it is not argued (extensively) that these taxa are the same, they are supplemented by holotypes that consist of more than teeth, and this enables their skeletal material to at least distinguish them from one another. This is not the case for Carcharodontosaurus saharicus, and a review of the process of typification should be in order.

Setting a Holotype

First, a specimen that forms a name-bearing type is usually a holotype, and is presented by the original author at the time the name is proposed. Sometimes, a specimen is not designated, but is implied, and to retain contact with the name, a lectotype is the name-bearing specimen. This is also important when the type is selected from a group of specimens (individual pieces, sets of pieces, or whole animals); if the series of bones are considered together, they can be called a syntype series, and they are collectively the name-bearing specimens.

Second, the author may refer to the hypodigm of his new taxon various specimens alongside the holotype, to supplement the diagnosis available from the holotype (especially if the material forms a bonebed of disparate and uncertain individuals), but this must be done at the same time as when the original holotytpe is determined; when it is done, any of these further specimens is called a paratype; when a lectotype is determined, for example, all other specimens from the type series are called paralectotypes.

Third, if a specimen is not considered useful enough, complete enough, or has been damaged or lost, but formed a name-bearing time, an author may designate another specimen to take its place; this is called a neotype. Normally, this can be done as any paper describing the original; but sometimes it involves tricky decisions, and an appeal to the ICZN is made to formalize it in case of debate.

These rules govern simply naming types of specimens; less formal are the principles under which the material should be selected. Generally, authors are encouraged to choose as types specimens that are comparable, sufficiently preserved to allow subsequent authors to either refer further material, or comapre different taxa to the original through their types. This generally results in choosing specimens that are more or less substantively representative of the skeleton, representing portions of the skeleton bearing apomorphies that can distinguish it (especially autapomorphies), and that are less likely to be just general crap. These are suggestions, but they are taken rather seriously.

Conclusions

By original designation (and it need not be explicit, but be taken so by following authors), Deperet and Savornin [1] designated a small set of teeth from the Albian of Algeria as the type series (taken later as a holotype) onto which they gave the original name Megalosaurus saharicus; these teeth, being distinct as known at the time (bearing mesiodistal “wrinkles” across portions or most of the crown), were incomparable theropod teeth, which would at the time make sense in forming nomenclature.

Von Stromer [3] has followed this, resulting in his referal of a partial skull and postcrania to a name based on teeth, arguing the teeth (as known then) were distinct enough to permit referral. Subsequent material has produced less definitive concerns regarding theropod teeth with mesiodistal wrinkles; such a feature, in fact, now diagnoses a larger group, conventionally termed “carcharodontosaurs” or “carcharodontosaurines,” among the carnosaurian Allosauroidea. Carcharodontosaur teeth from Morocco, Japan, North America, and South America prevents these teeth (as known) from being securely diagnosable as known today. Because of this, the holotype is insufficient based on current knowledge, and should be replaced. Unfortunately, while von Stromer’s material would have served, as it became known for 60 years as the concept for Carcharodontosaurus saharicus, it is not available for modern comparison. Substantive Algerian material is unknown, as is further Egyptian material; the most substantive material remaining is from Morocco [5], and one should be tempted to regard this material as the neotype to sustain useage of the name on securely diagnosable and differentiable material.

[1] Deperet, C. & Savornin, J. 1927. Sur la decouverte d’une faune de vertebres albiens a Timimoun (Sahara occidental) [On the discovery of a vertebrate fauna from the Albian of Timimoun (western Sahara)]. Comptes Rendus, Academie du Sciences, Paris 181:1108-1111.
[2] Nothdruft, W. & Smith, J. 2002. The Lost Dinosaurs of Egypt. (Random House, New York).
[3] von Stromer, E. 1931. Wirbeltiere-Reste der Baharijestufe (unterestes Canoman). Ein Skelett-Rest von Carcharodontosaurus  nov. gen. [Vertebrate fossils from the Baharija Formation (Lower Cenomanian). A Skeleton of Carcharodontosaurus nov. gen.]. Abhandlungen der Bayerischen Akademie der Wissenschaften, Mathematisch-naturwissenschaftliche Abteilung 9(Neue Folge):1–23.
[4] Brusatte, S.L. & 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):902-916.
[5] Sereno, P. C., Dutheil, D. B., Iarochene, M., Larsson, H. C. E., Lyon, G. H., Magwene, P. M., Sidor, C. A., Varricchio D. J. & Wilson, J. A. 1996. Predatory dinosaurs from the Sahara and the Late Cretaceous faunal differentiation. Science 272:986–991.
[6] Coria, R. A. & Salgado, L. 1995. A new giant carnivorous dinosaur from the Cretaceous of Patagonia. Nature 377: 225-226.
[7] Coria, R. A. & Currie, P. J. 2006. A new carcharodontosaurid (Dinosauria, Theropoda) from the Upper Cretaceous of Argentina. Geodiversitas 28(1):71-118.
[8] Novas, F. E.; de Valais, S., Vickers-Rich, P. & Rich, T. 2005. A large Cretaceous theropod from Patagonia, Argentina, and the evolution of carcharodontosaurids. Naturwissenschaften 92(5):226–230.