Kileskus and Proceratosauridae

[Jaime Headden <qi_leong@hotmail.com>]

  Over at the Vert Paleo mailing list, Alexander Averianov has noted a recent 
paper of his has been published, this one concerning a subject on the early 
evolution of Tyrannosauroidea, specifically a new taxon and a new taxonomic 
ripple.

  A.O. Averianov, S.A. Krasnolutskii and S.V. Ivantsov. 2010. A new basal 
coelurosaur (Dinosauria: Theropoda) from the Middle Jurassic of Siberia. 
_Proceedings of the Zoological Institute_ 314(1):42-57.

  Names *Kileskus aristotocus*, and argues a peculiarity: The name 
Proceratosauridae Rauhut et al. 2010 does not satisfy ICZN Art 13.1.1, in that 
a differential diagnosis was not provided. They thus argue that the name 
Proceratosauridae is a nomen nudum, which they seek to correct by providing 
one, under the heading Proceratosauridae fam. nov. In addition, the authors 
argue that when establishing this taxon, it is provided as a monophyletic 
clade, which Averianov et al claim as a tautology, as every clade is apparently 
monophyletic. I can note now that the only reply to this is that you can define 
a clade as a paraphyletic taxon, such that "clade" and "monophyletic" are never 
synonymous in a cladistic sense, so this point seems relatively unimportant. It 
also seems curious why there was not a need to simply provide the differential 
diagnosis to an establish name, instead of attempting to name a new taxon, but 
I'll leave that argument to people better than me.

  *Kileskus aristotocus* (from a Khakas wording meaning "lizard" and the Greek 
for "of noble origin", in reference to its basal position within 
Tyrannosauroidea) is based on a series of material from the upper Itat 
Formation, in the Bathonian of the Middle Jurassic, Krasnoyarks Ter. in W. 
Siberia, Russia. It is thus the first well-founded tyrannosauroid taxon from 
Russia. The holotype maxilla, ZIN PH 5/117 (right), is joined by a referred 
left premaxilla (6/117), left surangular (7/117), left metacarpal II and mdII-1 
(8--9/117), left mtI & III (10--11/117), pdII-2 and a pedal ungual 
(12--13/117). 

  A phylogenetic analysis is performed, using Smith's 2007 analysis of 
*Cryolophosaurus* (and its 2008 extension for the Australian *Megaraptor*-like 
ulna), totalling 58 taxa and 353 characters, which includes three taxa from the 
latest incarnation: *Guanlong*, *Proceratosaurus*, and *Kileskus*. This 
analysis recovers a tree with the following content:

(Tyrannosaurus(Dilong(Kileskus(Guanlong,Proceratosaurus))))

  This analysis thus differs from that of the TWG in recovering a less basal 
*Guanlong* than *Dilong,* but moreover, it provides another interesting distin 
ction between Rauhut et al and Averianov et al.. In the former, the clade 
Proceratosauridae was defined as a stem clade of (*Proceratosaurus* <- 
*Tyrannosaurus*), while in the latter it is (*Kileskus* + *Proceratosaurus*). 
Thus, in the former, all of these taxa would be proceratosaurids; in the 
latter, however, only the last three are; the authors thus argue that *Dilong* 
is outside of Proceratosauridae. It is interesting primarily in that the 
authors defined their Family-rank taxon (despite as a clade) on node-based 
terms, while others have adopted a more flexible Tyrannosauridae vs 
Proceratosauridae approach, allowing taxa to align less strictly under one 
label than another.

  *Kileskus* is then differentiated only within Proceratosauridae: from 
*Guanlong* by absence of a step in the anterior lob of the maxilla, and a 
gentle slope posteriorly for the ascending ramus of the maxilla from the 
rostral end; from *Proceratosaurus* with subequal mesial and distal serrations, 
fewer (17 vs 22) tooth positions in the maxilla, the promaxillary fenestra is 
not surrounded and exposed laterally in the antorbital fossa on the lateral 
surface of the maxilla, and with the promaxillary fenestra lower than the 
maxillary fenestra; is more similar to *Proceratosaurus* but unlike *Guanlong* 
in that the external nares are sloped posterodorsally and the absending ramus 
of the premaxilla is inclined anterodorsally.

  The morphology of the bones as preserved are very similar to 
*Proceratosaurus*, with the premaxilla almost a dead ringer; the maxilla 
differs largely in profile, and all bones are remarkably complete. Details of 
the suite of referred material are clear, and preservation is complete with 
exception to the cranial material.

  This taxon thus adds another Despot to a growing list of pre-Tyrants.
                                          
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