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Camptonotus amplus Marsh, 1879--Camptosaurus, Sauropoda or Allosaurus?

Ben Creisler

A new paper:

Peter M.  Galton, Kenneth Carpenter  & Sebastian G. Dalman (2015)
The holotype pes of the Morrison dinosaur Camptonotus amplus Marsh,
1879 (Upper Jurassic, western USA) – is it Camptosaurus, Sauropoda or
Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 275(3): 317-335
DOI: http://dx.doi.org/10.1127/njgpa/2015/0467

The holotype of Camptonotus amplus Marsh, 1879, the right pes YPM
VP.1879 from the Morrison Formation (Upper Jurassic) of Wyoming, USA,
has long been referred to the Morrison ornithopod dinosaur
Camptosaurus Marsh, 1885. However, the pointed proximal end of Mt I
did not reach the tarsus, but was attached by ligaments to the
mid-shaft of Mt II as in neotheropod dinosaurs, and a series of
synapomorphic characters identify the pes to the Allosauroidea. The
transversely compressed deep ungual phalanx, previously used to define
the species amplus, is removed from YPM VP.1879 because it is the left
pedal ungual of a juvenile neosauropod dinosaur. A partial skull with
a few postcranial bones (YPM VP.1892) is probably part of the same
individual and the postorbital and quadrate are very similar to those
of Allosaurus. The articular condyle of Mt I of YPM VP.1879 is about
twice the length of the rest of the non-tapering part, rather than
being subequal as in the other allosaurians from the USA (Morrison
allosaurids Allosaurus, Saurophaganax; Lower Cretaceous
carcharodontosaurian Acrocanthosaurus). For distal Mt IV, the height
is greater than the transverse width in Allosaurus, the plesiomorphic
condition for Neotheropoda, whereas they are subequal in YPM VP.1879
and Saurophaganax. YPM VP.1879 is probably an allosaurid that is
referred to as ?Allosaurus amplus (Marsh, 1879) pending further
information on the range of variation in the pes of Allosaurus.