[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: Some (basal) intramandibular joint questions

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> HPB1956@aol.com
> According to Thomas R. Holtz (2) this joint, between the tooth-bearing
> dentary and the various post-dentary bones, probably served to absorb
> stresses associated with feeding on large living prey.
> Thomas R. Holtz mentioned earlier on this list that the geometry of this
> joint is different in herrerasaurids and neotheropods. He cited
> Sereno 1993
> (3). Is this report anywhere online available or can anybody
> please explain?

Here is the text from Sereno & Novas (1993, p. 417, column 2, paragraphs 4 &
 "(18) Well-developed intra-mandibular joint between the dentary and
surangular and between the  splenial and the angular (Figs. 7A, 8A). In H.
ischigualestensis, a well-developed intra-mandibular joint separates the
lower jaw into anterior and posterior functional units. Broad sliding
articulations are present between the dentary and surangular above the
external mandibular fenestra and between the splenial and angular below.
The splenial-angular articulation is developed between a tongue-shaped
posterior process of the splenial and a hook-shaped anterior process of the
angular. The splenial process wraps aroudn the ventral margin of the
angular, sliding against its smooth, convex ventral margin. The same
articular configuration between the splenial and angular is preserved in the
right lower jaw of Staurikosaurus (MCZ 1669).
  "Kinetic dentary-surangular and splenial-angular articulations are also
present in theropods (e.g., Ceratosaurus, Fig. 10C; Carnotaurus, Bonparte et
al. 1990). In theropods, however, the articular surfaces of the
splenial-angular sliding joint are the reverse of that in Herrerasaurus and
Staurikosaurus; the tongue-shaped process of the splenial has a convex
dorsal articular surface that slides against a concave depression on the
angular. The dentary-splenial joint is also present in theropods, but the
posterodorsal process of the dentary is not elongated as in H.
ischigualastensis. The unusual intra-mandibular joint described above is
found only in herrerasaurids and theropods among dinosaurs. Dinosaurian
outgroups (pterosaurs, crurotarsal archosaurs) also lack an intra-mandibular

Incidentally, the authors distinguish "herrerasaurids" and "theropods" in
the latter paragraph.  I do not know if this was written prior to their use
of Neotheropoda (and thus "herrerasaurids" and "theropods" could be sister
taxa), or if this section was written by Novas prior to his acceptance that
herrerasaurids were closer to traditional theropods than were
sauropodomorphs and ornithischians.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796