Abstract

Two articulated, partial vertebral columns of the Early Permian captorhinid Eocaptorkinus laticeps (Williston) exhibit the following serial changes in the axial skeleton: robust and unswollen neural arches on the First five presacrals gradually swell dorsally and laterally on presacrals 6–25; alternation of neural spine height of the presacrals with an interruption at presacral 9 is superimposed upon a gradual posterior decrease of spine height; slope of zygapophyseal articular surfaces changes from ventromedial on the first six presacrals to horizontal on the remaining presacrals; and spines for epaxial muscle attachment present on the neural arches of presacrals 6–14 decrease in size posteriorly. Midventral lips are present on the centra and intercentra of all presacrals. Fine cracks on the centra of caudal vertebrae 8–11 are evidence of caudal autotomy.The pattern of vertebral morphology suggests specializations in the cervical region for support of the massive head and in the dorsal region for increased lateral flexibility for locomotion and increased support of the rib cage and viscera.

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