. A diapsid reptile from the Pennsylvanian of Kansas. Reptiles, Fossil -- Kansas; Paleontology -- Pennsylvanian; Paleontology -- Kansas. 1980 PENNSYLVANIAN DIAPSID REPTILE 29 1428 (Peabody, 1952, Figs. 2 and 4). The distal part of the tail is composed of at least twelve spool-shaped centra without neural arches. The calculated length of the caudal region based on these two immature speci- mens is about 315 mm. Cervical Vertebrae Atlas-axis complex.—The proatlas (Fig. 14) is a relatively small but robust element. The two elements of the pair do not appear to be in contact. There is a rudimentar
. A diapsid reptile from the Pennsylvanian of Kansas. Reptiles, Fossil -- Kansas; Paleontology -- Pennsylvanian; Paleontology -- Kansas. 1980 PENNSYLVANIAN DIAPSID REPTILE 29 1428 (Peabody, 1952, Figs. 2 and 4). The distal part of the tail is composed of at least twelve spool-shaped centra without neural arches. The calculated length of the caudal region based on these two immature speci- mens is about 315 mm. Cervical Vertebrae Atlas-axis complex.—The proatlas (Fig. 14) is a relatively small but robust element. The two elements of the pair do not appear to be in contact. There is a rudimentary neu- ral spine on each element and a small posterior zygapophysis that articulates with the atlas. The articulating surface of the posterior 2^'ga- pophysis faces medially so as to be aligned almost with the saggital plane. An anterior zygapophysis is also present but faces for- ward to articulate with the corresponding facet on the exoccipital. The proatlas in Petrolacosaurus is similar in outline to the proatlas in the primitive captorhinomorphs Hijlonomus and Paleothtjris; it is much short- er than the same element in the pelycosaur Ophiacodon. The atlas in Petrolacosaurus includes four elements: the intercentrum, two neural arches and the centrum. The intercentrum A ii c:::^ 1). Fic. 14.—Petrolacosaurus Jcansensis Lane. Cervical vertebrae, all x (A) Lateral view of left proatlas, KUVP 33607. (B) Ventral and anterior views of atlantal intercentrum, KUVP 33604. (C) Lateral and me- dial views of left atlantal neural arch, KUVP 33604. (D) Anterior and lateral views of atlantal centrum and fused axial intercentrum, KUVP 33604. (E) Outline of the atlas-axis complex, based on KUVP 33604 and 33607. (F) Lateral view of axis, KUVP 33604. (G) Lateral and dorsal view of third cervical vertebra, based on KUVP 9951 and 9956. (H-I) Lateral view of fourth and fiftli cervical vertebrae, KUVP 9951. (J) Lateral and dorsal views of the cervical vertebra, based on KUVP 9951 an
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