TY - JOUR
T1 - Aspects of gorgonopsian paleobiology and evolution
T2 - Insights from the basicranium, occiput, osseous labyrinth, vasculature, and neuroanatomy
AU - Araújo, Ricardo
AU - Fernandez, Vincent
AU - Polcyn, Michael J.
AU - Fröbisch, Jörg
AU - Martins, Rui M.S.
N1 - This work was supported by Portuguese national funds through FCT Fundacao para a Ciencia e a Tecnologia within the framework of the project EXPL/BIA-EVF/0665/2013 (PALEOTECH) and by the European Synchrotron Radiation Facility (ESRF), Grenoble, France through experiment HG-23. Ricardo Araujo and Rui M.S. Martins were funded FCT/MEC for a postdoctoral fellowship (SFRH/BPD/96205/2013) and a contract under IF2014 Programme (IF/00036/2014/CP1214/CT0009), respectively
PY - 2017/1/1
Y1 - 2017/1/1
N2 - Synapsida, the clade including therapsids and thus also mammals, is one of the two major branches of amniotes. Organismal design, with modularity as a concept, offers insights into the evolution of therapsids, a group that experienced profound anatomical transformations throughout the past 270 Ma, eventually leading to the evolution of the mammalian bauplan. However, the anatomy of some therapsid groups remains obscure. Gorgonopsian braincase anatomy is poorly known and many anatomical aspects of the brain, cranial nerves, vasculature, and osseous labyrinth, remain unclear. We analyzed two gorgonopsian specimens, GPIT/RE/7124 and GPIT/RE/7119, using propagation phase contrast synchrotron micro-computed tomography. The lack of fusion between many basicranial and occipital bones in GPIT/RE/7124, which is an immature specimen, allowed us to reconstruct its anatomy and ontogenetic sequence, in comparison with the mature GPIT/RE/7119, in great detail. We explored the braincase and rendered various skull cavities. Notably, we found that there is a separate ossification between what was previously referred to as the ''parasphenoid'' and the basioccipital. We reinterpreted this element as a posterior ossification of the basisphenoid: the basipostsphenoid. Moreover, we show that the previously called ''parasphenoid'' is in fact the co-ossification of the dermal parasphenoid and the endochondral basipresphenoid. In line with previous descriptions, the anatomy of the osseous labyrinth is rendered in detail, revealing a unique discoid morphology of the horizontal semicircular canal, rather than toroidal, probably due to architectural constraints of the ossification of the opisthotic and supraoccipital. In addition, the orientation of the horizontal semicircular canal suggests that gorgonopsians had an anteriorly tilted alert head posture. The morphology of the brain endocast is in accordance with the more reptilian endocast shape of other non-mammaliaform neotherapsids.
AB - Synapsida, the clade including therapsids and thus also mammals, is one of the two major branches of amniotes. Organismal design, with modularity as a concept, offers insights into the evolution of therapsids, a group that experienced profound anatomical transformations throughout the past 270 Ma, eventually leading to the evolution of the mammalian bauplan. However, the anatomy of some therapsid groups remains obscure. Gorgonopsian braincase anatomy is poorly known and many anatomical aspects of the brain, cranial nerves, vasculature, and osseous labyrinth, remain unclear. We analyzed two gorgonopsian specimens, GPIT/RE/7124 and GPIT/RE/7119, using propagation phase contrast synchrotron micro-computed tomography. The lack of fusion between many basicranial and occipital bones in GPIT/RE/7124, which is an immature specimen, allowed us to reconstruct its anatomy and ontogenetic sequence, in comparison with the mature GPIT/RE/7119, in great detail. We explored the braincase and rendered various skull cavities. Notably, we found that there is a separate ossification between what was previously referred to as the ''parasphenoid'' and the basioccipital. We reinterpreted this element as a posterior ossification of the basisphenoid: the basipostsphenoid. Moreover, we show that the previously called ''parasphenoid'' is in fact the co-ossification of the dermal parasphenoid and the endochondral basipresphenoid. In line with previous descriptions, the anatomy of the osseous labyrinth is rendered in detail, revealing a unique discoid morphology of the horizontal semicircular canal, rather than toroidal, probably due to architectural constraints of the ossification of the opisthotic and supraoccipital. In addition, the orientation of the horizontal semicircular canal suggests that gorgonopsians had an anteriorly tilted alert head posture. The morphology of the brain endocast is in accordance with the more reptilian endocast shape of other non-mammaliaform neotherapsids.
KW - Brain
KW - Braincase
KW - Gorgonopsian
KW - Homology
KW - Mammals
KW - Modularity
KW - Synchrotron
KW - Therapsid
KW - Vasculature
KW - Vestibular organ
UR - http://www.scopus.com/inward/record.url?scp=85017378215&partnerID=8YFLogxK
U2 - 10.7717/peerj.3119
DO - 10.7717/peerj.3119
M3 - Article
C2 - 28413721
AN - SCOPUS:85017378215
SN - 2167-8359
VL - 2017
JO - PeerJ
JF - PeerJ
IS - 4
M1 - 3119
ER -