Monday, June 7, 2010

"Carnosaurus" and "Coelurosaurus" examined

Everybody knows "Carnosaurus" and "Coelurosaurus" are two names that were mistakenly used in Huene's paper to refer to unnamed theropod remains.  But just what do the remains belong to?

"Carnosaurus" Huene, 1929
Campanian-Maastrichtian, Late Cretaceous
Allen Formation, Rio Negro, Argentina
Material- (MLP CS 1240) metatarsal IV (100 mm)
Late Cretaceous
east of Colhue Huapi Lake and north of Chico River, Chubut Group(?), Chubut, Argentina
Material- (MACN coll.) tooth (23 x 12.5 x 6 mm)
Late Coniacian, Late Cretaceous
Plottier Formation of the Rio Neuquen Group, Neuquen, Argentina
Material- ?(MLP coll.) incomplete tooth (16 x 9.5 x 6.3 mm)

Comments- Carnosaurus was listed by Huene (1929) in a faunal list for three specimens- a metapodial (MLP CS 1240) from the Allen Formation, a tooth (MACN coll.) perhaps from the Chubut group, and provisionally ("Cf. Carnosaurus") a tooth from the Plottier Formation. As Olshevsky (DML, 1999) noted, the name is probably a typographical error for Carnosauria made when translating the paper from German to Spanish. This is indicated by the fact he never attaches a name to these specimens in the description or plates, and indeed states on of the specimens is taxonomically indistinguishable from another named genus. Since "Carnosaurus" was apparently not meant as a valid name when it was published (ICZN Article 11.5), it is a nomen nudum.


"Carnosaurus" A. non-theropod metatarsal MLP CS 1240 in anterior view. B. ?abelisaurid lateral tooth from the MACN in side view, section and magnification of distal serrations. C. avepod tooth from the MLP in labial, lingual, distal and sectional views. All after Huene (1929).

MLP CS 1240 is listed as metatarsals in the faunal list, but described as a ?third metacarpal similar to Allosaurus. However, it is dissimilar to theropod metacarpals in several respects. The distal articular surface is not ginglymoid, unlike metacarpals I-III of ceratosaurs and basal tetanurines or I-II of avetheropods. There is no extensor pit dorsally unlike theropod metacarpals I and II, and ceratosaur metacarpal III. The shaft is much more robust than tetanurine metacarpal IIIs except for Torvosaurus, while the proximal end is less expanded than theropod metacarpal IIs, and the shaft is far more elongate than most theropod metacarpal Is. The form is more similar to a sauropod or ankylosaur metatarsal, both groups that are known from the Allen Formation. It is here assigned to Dinosauria indet. pending further comparisons.

The Chubut tooth is merely described under the heading "tooth of a carnivorous saurischian from the Chico River". The mesial edge is slightly concave and the distal edge slightly convex. It has fine longitudinal ridges, and 30 serrations per 5 mm which are perpendicular to the edge. Huene stated there was no difference between it and teeth he referred to Loncosaurus except for the less curved mesial edge, which he felt could be explained by a different position in the jaw. It compares well with abelisaurids in all variables except the greater serration density, so may be a member of that clade.

The Plottier tooth is smaller and Huene described it under the heading "tooth of a carnivorous saurischian", stating it was not his intention to decide whether it was a coelurosaur or carnosaur. The mesial edge is more convex than the distal edge, especially basally. There are 12.5 serrations per 5 mm, stated to be on both mesial and distal carinae. The tooth seems to be from a somewhat anterior position, as it has an asymmetrical section, with one side generally more convex except for a distally placed concavity. What are described as growth lines on the labial and lingual surfaces may be enamel wrinkles, which are apically concave in the distal half of one side. This tooth is difficult to place without further study of Gondwanan small theropod dentitions and is here assigned to Avepoda.


"Coelurosaurus" Huene, 1929
Campanian-Maastrichtian, Late Cretaceous
Allen Formation, Rio Negro, Argentina
Material- (MLP CS 1478) partial ungual (~19 mm)

Comments- Coelurosaurus was listed by Huene (1929) in a faunal list for MLP CS 1478, a partial ungual from the Allen Formation. As Olshevsky (DML, 1999) noted, the name is probably a typographical error for Coelurosauria made when translating the paper from German to Spanish. This is indicated by the fact he never attaches a name to the specimen in the description or plates (it's described under the heading "coelurosaur claw"). Since "Coelurosaurus" was apparently not meant as a valid name when it was published (ICZN Article 11.5), it is a nomen nudum.


"Coelurosaurus" ungual MLP CS 1478 in a side view; b proximal section; c side view; d distal section; e dorsal view. After Huene (1929).

The ungual consists of the distal half, which exhibits an interesting combination of features. It is highly curved and transversely compressed, suggesting it is a tetanurine manual ungual or a paravian pedal ungual (though note both Mapusaurus and alvarezsaurids differ in being straighter). The cross section at midlength is triangular (expanded ventrally), unlike the roughtly oval shape of most theropod manual unguals (e.g. Noasaurus, Fukuiraptor, Deinonychus) or the blade-like shape of Megaraptor's manual unguals and paravian sickle claws. Yet the shape is not similar to most theropod pedal unguals either, as the ventral surface is concave and the ventral transverse expansion does not flare past the sides of the ungual. Notably, the ungual is quite asymmetric, with one wall of the ventral groove projecting further ventrally. This is more prominent distally, where the groove faces more to the side than downward. The asymmetry and ventral groove are characteristic of abelisaurid pedal unguals, though these are more straight and broad. Noasaurid pedal unguals (as judged by Masiakasaurus) are also straight, are only slightly asymmetrical and are keeled ventrally. Noasaurus itself possesses a controversial ungual most recently thought to be manual which is curved and compressed like "Coelurosaurus", but is not very asymmetrical and has a ventral keel. Another possibility is that "Coelurosaurus" belongs to a bird, as many birds are comparably sized with highly curved pedal unguals. Unfortunately, comparable bird unguals (e.g. Patagopteryx, Soroavisaurus, MACN PV RN 1105) are not described in enough detail to be usefully compared. Huene considered it to be a manual ungual based on its curvature and believed it was a distinct specimen. It is here referred to Avepoda incertae sedis.

References- Huene, 1929. Los saurisquios y ornitisquios del Cretacéo Argentino. Anales del Museo de La Plata (series 3). 3, 1-196.

Olshevsky, DML 1999. http://dml.cmnh.org/1999Nov/msg00507.html

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