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Cenomanian Dinosaurs in JVP



Two papers deserve extra comment from the new _JVP_, namely Mahler on Moroccan
abelisaurs, and Hawakaya, Manabe and Carpenter on a Japanese nodosaur.

  In the first paper by Luke Mahler ...

  Mahler, L. 2005. Record of Abelisauridae (Dinosauria: Theropoda) from the
    Cenomanian of Morocco. _Journal of Vertebrate Paleontology_ 25(1):236-239.

  ... a new maxilla collected from the Cenomanian of the Kem-Kem shows
unambiguous evidence for the presence of abelisaurids in northwestern Africa in
the Late Cretaceous. Previously, material from the middle Cretaceous
Aptian-Albian beds from the Tafilalt in the High Atlas were identified as
possibly abelisaurid, but these were dentary and had been subjected to some
criticism regarding the distribution of rectangular or subrectangular alveoli
as an abelisaurid trait (Sampson et al. 1998 and Carrano et al. 2002 are cited
as the sources of this data).

  Carrano, M. T., S. D. Sampson and C. A. Forster. 2002. The osteology of
    *Masiakasaurus knopfleri*, a small abelisauroid (Dinosauria: Theropoda)
from
    the Late Cretaceous of Madagascar. _Journal of Vertebrate Paleontology_
    22(3):510-534.

  Sampson, S. D., L. D. Witmer, C. A. Forster, D. W. Krause, P. M. O'Connor, P.

    Dodson, and F. Ravoavy. 1998. Predatory dinosaur remains from Madagascar:
    Implications for the Cretaceous biogeography of Gondwana. _Science_
    280:1048-1051.

  The material consists of UCPC 10, a partial right maxilla missing the
ascending and posterior rami, preserving the mesial six6 complete alveoli and
mesial margin of a seventh, including _in situ_ teeth (though the second crown,
fully erupted, is broken at the base). The lateral surface is highly
sculptured, the antorbital pneumatic recess is intact and not inflated or
perforated by medial maxillary foramina, the interdental plates are fused,
tall, and bear many tiny striae, and the alveoli are sub-rectangular in form,
allowing Mahler to refer this material to the Abelisauridae. Based on
comparisons, he attributes it to a basal abelisaurid position, including the
sloped mesial margin of the maxilla which shows that while the contact for the
premaxilla is high and long, it was inclined and not fully vertical as it is in
*Carnotaurus*.

  My only comment is that the paper, though extremely well written and showing
a great versatility with anatomy, describes the lamina lateralis as broken, but
preserving a portion of the margin of the external antorbital fenestra, yet
concludes a maxillary fenestra is not present; I cannot comment on the presence
or absence of such a fenestra, which based on recent phylogenies did not evolve
until the Tetanurae, but incomplete preservation of the ascending ramus and the
associated medial and lateral laminae do not permit this conclusion, and if
they did, the maxillary and promaxillary fenestrae are present rather on the
medial, not lateral laminae. It is likely this was a mistype, otherwise I'm
happy and this does fairly concretely place the Abelisauridae in the Late
Cretaceous of Morocco.

  The maxilla measures 109 mm along the preserved alveolar margin with a
maximum preserved length of 118 mm, and a maximum preserved height of 93.3 mm.
The sixth tooth is preserved completely and measures 19.8 mm basoapically at
the alveolar margin and has a mesiodistal (fore-aft basal) length of 12.6 mm,
so was a spectacularly short crown showing minimum distal recurvature, and a
sharp recurvature midway up the crown to form a distinct trapezoid rather than
gradual  triangle as in other theropod teeth. The tooth is also more than 50%
as broad as mesiodistally long at the base.

  If the maxilla were complete, I estimate it to be about 300 mm in length and
about 190 mm in height, implying a skull perhaps only 600 mm long and 240 mm
deep at the occiput. This is compared toi the estimated 1450 mm in length I
might estimate for the Moroccan skull of *Carcharodontosaurus*, which is close
to an estimated 900 mm tall, so it was roughly less than half the size, and
likely the animal was not at all a competitor (if adult).

  Mahler ends with a biogeographic analysis. He states that "UCPC 10, in
combination with recent fossil discoveries of similar age in Africa and South
America, establishes the presence of abelisauroids on Africa by the
Cenomanian." I should note that he is contradicting the idea that abelisaurids
were present only in the Campano-Maastrichtian worldwide, but uses
"abelisauroid," a term that includes noasaurids among some other abelisaurians,
and that this was written before the description of *Rugops* (which it barely
got to address, according to inside sources), so this is not a failing of the
paper. Mahler argues a great similarity of the maxilla with that of UNPSJB
PV247 (Lamanna et al. 2002) and *Rugops*, which would supoort a faunal
interchange by the Albian and Cenomanian, and thereby a link between the two
continents as late as, recently advocated by Sereno.

  Lamanna, M. C., R. D. Martinez, J. B. Smith. 2002. A definitive abelisaurid
    theropod dinosaur from the early Late Cretaceous of Patagonia. _Journal of
    Vertebrate Paleontology_ 22(1):58-69.

---

  In the second _JVP_ paper ...

  Hawakaya H., Manabe M. and K. Carpenter. 2005. Nodosaurid ankylosaur from the
    Cenomanian of Japan. _Journal of Vertebrate Paleontology_ 25(1):240-245.

  ... the partial skull of a nodosaurid (MCM A522, in the Mikasa City Museum;
Mikasa, Hokkaido Prefecture, Hokkaido, Japan) is recovered from the
Hikagenosawa Formation, along the Okami-sawa River in Hokkaido Prefecture,
Oyubari region, Hokkaido, Japan. The formation comes from the upper Middle Yezo
Group, whioch is constrained from the middle Cenomanian throughout the
Turonian; the nodosaur specimen derives from the middle of the formation, and
thus from the upper Cenomanian. The Mikasa Formation is sandstone bearing
lenticular gravels and shell-laden lags, indicating coastal shelf, and
indicating the fossil was washed out to sea.

  MCM A522 is a partial skull, loose teeth preserved in the matrix filling the
skull, articulated atlas with articulated anterior cervical armor. The skull as
preserved measures 267 mm and is complete from the occiput to the anterior rim
of the orbit formed from lachrymal, jugal, frontal, and prefrontal. The maxilla
is not present, and of the palate only the left pterygoid is preserved. The
skull is essentially split in half, with the left side missing. Thus, the
braincase is split and the endocranial chamber exposed, permitting a cast to be
taken, which compares roughly to that taken of *Sauropelta*. The dorsal surface
of the skull has also been split away, so that the dorsal end of the adductor
fossa is exposed, through which 11 teeth are visible.

  Hawakaya et al. refer MCM A255 to the Nodosauridae based on a complete
cingulum around the base of the crowns, their relatively large size, and fewer
denticles than in other ankylosaurs; an open (and wide) infratemporal fenestra;
and constriction of the occipital condyle at the base forming a "neck".

  It should be noted that the leading author, Hawakaya Hiroshi, passed away
prior to the publication of this paper.

  Cheers,

Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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