[dinosaur] Synapsid cranial allometry

Ben Creisler
[email protected]

A new paper:

Isaac W. Krone, Christian F. Kammerer  and Kenneth D. Angielczyk (2019)
The many faces of synapsid cranial allometry.
Paleobiology (advance online publication)
DOI: https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.1017_pab.2019.26&d=DwIBaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=YYBASSYpofiumumFzBZKffW8CCsEdI1b9LES28qKZD0&s=28gf7Xf_DLLMsL0yJXWmtFzZ6YQy1iPAxiPCZrtubvQ&e= 
https://urldefense.proofpoint.com/v2/url?u=https-3A__www.cambridge.org_core_journals_paleobiology_article_many-2Dfaces-2Dof-2Dsynapsid-2Dcranial-2Dallometry_D4DF84985CA3222FBE327AD993394E3D&d=DwIBaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=YYBASSYpofiumumFzBZKffW8CCsEdI1b9LES28qKZD0&s=TUxExgh4qphgR8VS7fmcQFtxCAJmwVDoA7vHrTFKicY&e= 


Previous studies of cranial shape have established a consistent
interspecific allometric pattern relating the relative lengths of the face
and braincase regions of the skull within multiple families of mammals. In
this interspecific allometry, the facial region of the skull is
proportionally longer than the braincase in larger species. The regularity
and broad taxonomic occurrence of this allometric pattern suggests that it
may have an origin near the base of crown Mammalia, or even deeper in the
synapsid or amniote forerunners of mammals. To investigate the possible
origins of this allometric pattern, we used geometric morphometric
techniques to analyze cranial shape in 194 species of nonmammalian
synapsids, which constitute a set of successive outgroups to Mammalia. We
recovered a much greater diversity of allometric patterns within
nonmammalian synapsids than has been observed in mammals, including several
instances similar to the mammalian pattern. However, we found no evidence
of the mammalian pattern within Therocephalia and nonmammalian Cynodontia,
the synapsids most closely related to mammals. This suggests that the
mammalian allometric pattern arose somewhere within Mammaliaformes, rather
than within nonmammalian synapsids. Further investigation using an
ontogenetic series of the anomodont Diictodon feliceps shows that the
pattern of interspecific allometry within anomodonts parallels the
ontogenetic trajectory of Diictodon. This indicates that in at least some
synapsids, allometric patterns associated with ontogeny may provide a "path
of least resistance" for interspecific variation, a mechanism that we
suggest produces the interspecific allometric pattern observed in mammals.

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