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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 teeth."

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...