On Unusual Peculiarities of Head Morphology in Therocephalian Hexacynodon purlinensis

Leonid P. Tatarinov

Abstract


A rudimentary chordal canal and pits for basicranial muscles with three pairs of openings for segmental ventral nerves were indicated on basioccipital of H. purlinensis. Up to now these nerves in land vertebrates were reported only for larvae of some amphibians. The groove on the occipital edge of squamosum, in which the external acoustic meatus is traditionally reconstructed, is connected with vascular openings on the distal part of mastoid process and with broad vascular canal trending between squamosum and quadratum. External to the medial sutural junction of basioccipital and basisphenoid the two bones are separated by fissure. Basisphenoid forms a short process here passing into the groove on the edge of basisphenoid. This articulation corresponds to the rudimentary intracranial joint in crossopterygians. In the bottom of basioccipital just anterior to the occipital condyle are deep cavities, connected by diminutive foramina in condyle with the vertebral canal. This cavity probably contained the posterior endolymphatic sac, and foramina conveyed endolymphatic ducts. The anterior endolymphatic sac was located possibly in the cavity anterior to fenestra ovalis, delimited by basioccipital, basisphenoid, and prootic. Due to the development of oblique crest on the quadrate condyle the opening of mouth was attended by lateral displacement of lower jaw. Such a displacement was possible only in condition if intramandibular mobility between dental (and splenial) and postdental block of mandibular bones.


Keywords


morphology; skull; therocephalians; Hexacynodon

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References


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