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Masiakasaurus knopfleri

Hi, folks,

Ah, _Masiakasaurus_, the mystery critter from Madagascar.  Bits and pieces
of it have shown up as SVP for the past few years, with the SUNY-Stony Brook
team asking for people's thoughts on the identity of the animal.  To me, at
first glance, the dentary looked like a spinosaurid or crocodilymorph of
some kind, while the femur was like a little _Carnotaurus_.  But you put it
all together and get...

Well, that's addressed in:
Sampson, S.D., M.T. Carrano & C.A. Forster.  2001.  A bizarre predatory
dinosaur from the Late Cretaceous of Madagascar.  Nature 409: 504-506.

It is a little critter (estimated length is 1.8 m, and fusion of the
vertebral sutures and fusion of crural and tarsal elements suggest that the
largest material is from an adult).  The skull is known from the maxilla,
dentaries, and splenial, so while the weird-ass lower jaw is real, much of
the top of the head in the reconstruction is conjecture.  I would *not* be
surprised in the least if the premaxilla (for instance) was equally weird
(maybe downswept, as in chasmatosaurs?).  Maxilla looks like _Noasaurus_'.

_Masiakasaurus_ is from the Maevarano Fm. (Maastrichtian), the unit from
which most of the Madagascan dinosaurs come.  Multiple individuals (at least
six) are known: combining all the different individuals, about 40% of the
skeleton is known.

It has some definite neocertosaur and abelisauroid features.  The authors
present a phylogram (cladogram scaled to time), but this is apparently
mostly a summary of previous work rather than a new analysis (no
supplementary data, for example).  Although they don't dismiss the
possibility that this is closer to _Noasaurus_ than to Abelisauridae (and
thus might be regarded as a noasaurid), the limited material of the Argetine
forms prevents them from stating this more conclusively: as such, they
consider _Masiakasaurus_, _Noasaurus_, and Abelisauridae as a trichotomy.

Metatarsal II in this critter is extremely slender: reminiscent of another
fragmentary Argentine theropod, _Velocisaurus_.  Indeed the tibiae of
_Masiakasaurus_ and _Velocisaurus_ are very similar in the shape of the
cnemial process and the astragalocalcameum: I would not be surprised if
these forms and _Noasaurus_ might all be related (heck, _Velocisaurus_ and
_Noasaurus_ might be cogeneric).  All three forms seem to demonstrate what I
have informally (and jokingly) called the "antarctometatarsalian" condition:
elongate metatarsi with a more robust mtIII and extremely slender mtII (and
mtIV, at least in _Velocisaurus_).

A very cool critter: hope that more of it is found soon.

P.S. One problem on the phylogram: the bar for Tetanurae only extends down
into the beginning of the Upper Jurassic (or maybe its the end of the Middle
Jurassic), but _Megalosaurus_, _Piatnitzkysaurus_, and _Proceratosaurus_ are
all definitely Middle Jurassic, _Cryolophyosaurus_ (and the possible Lufen
therizinosauroid) are Early Jurassic, and there is a specimen of a
tetanurine now known from the Late Triassic.

                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