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Re: had a thought - dimorphic tyrannosaurs? was RE New fossils provide clues to tyrannosaur/ornithomimid evolution
It's interesting how these new basal tyrannosauroids pull previously
non-tyrannosauroid taxa into the clade, as other basal tyrannosauroids.
This time, _Proceratosaurus_ comes out as a basal tyrannosauroid
(Makovicky et al., 2009).
That one is not surprising anymore:
Oliver Rauhut & Angela Milner (2008): Cranial anatomy and systematic
position of the Middle Jurassic theropod dinosaur *Proceratosaurus* from
England, supplement to JVP 28(3), 130A
"The theropod dinosaur *Proceratosaurus bradleyi* from the Middle Jurassic
(Bathonian) Forest Marble of G[l]oucestershire, England[,] is based on a
single, well-preserved skull, missing most of the dorsal skull roof.
Originally described as a new species of *Megalosaurus*, the taxon was later
thought to be closely related to *Ceratosaurus* or to *Ornitholestes*.
Recent cladistic analyses have indicated that *Proceratosaurus* might be the
oldest known coelurosaur, making it a potential key taxon for understanding
the early evolution of this group. The cranial anatomy of *Proceratosaurus*
is quite distinctive, and it can be diagnosed by a number of autapomorphies:
anterior nasal process of the premaxilla inclined slightly anterodorsally
and nasal horn core overhanging the premaxillary internarial bar anteriorly,
internarial bar of the premaxilla bifurcating posteriorly into a posteriorly
directed ramus and a dorsally directed ramus, anterior end of the maxillary
antorbital fossa placed considerably anterior and ventral to the
promaxillary foramen, and anteriormost dentary tooth curved anteriorly and
with the carinae oriented labiolingually. Other important characters of the
skull include the presence of a hollow median horn or crest on the nasals
and a very elongate external nares [sic] that extends over more than 20% of
the skull length. CT images of the skull revealed a relatively short and
high braincase, with a highly pneumatic basisphenoid, including anterior
tympanic recesses, pneumatic pockets associated with the entrance of the
internal carotids, and basipterygoid recesses. *Proceratosaurus* shows
several characters that indicate that this taxon represents the oldest known
tyrannosauroid, including a short premaxilla, a well-developed jugal recess,
a steeply sloping basisphenoid, premaxillary teeth that are considerably
smaller than the maxillary teeth, and D-shaped anteriormost premaxillary
Was a very convincing presentation.
Also, this same analysis recovers _Falcarius_ outside the
Therizinosauroidea, in a much more basal position relative to other
maniraptorans. Even though the bootstrap support would seem to be weak
(based on the cladogram), I find this position VERY interesting.
What an understatement...