Fig. 6. Hesperoherpeton garnettense Peabody. Right mandible, lateral view, KU 10295, × 4. External surfaces are pitted; broken surfaces are coarsely stippled.
VERTEBRAE (Fig. [7])
The vertebrae that are visible from a lateral view are crushed and difficult to interpret. It is possible, nevertheless, to see that the trunk vertebrae resemble those of Ichthyostegalia (Jarvik, 1952, Fig. 13 A, B), except that the pleurocentra are much larger. A few parts of additional vertebrae can be seen, but they are so scattered that it is impossible to be sure of their original location. Therefore comparisons between different regions cannot yet be made.
The U-shaped intercentrum encloses the notochord and occupies an anteroventral position in the vertebra. Anteriorly, each intercentrum articulates with the pleurocentra of the next preceding vertebra by slightly concave surfaces. Dorsolaterally there is an articular surface for the capitulum of the rib.
The two pleurocentra of each vertebra are separate ventrally as well as dorsally, but form thin, broad plates of about the same height as the notochord. The lateral surface appears to be depressed, allowing, perhaps, for movement of the rib. Above each pleurocentrum, on the lateral surface of the neural arch, there is a short diapophysis for articulation with the tuberculum of the rib.
The margin of the neural spine is convex anteriorly and concave posteriorly, the tip reaching a point vertically above the postzygapophysis. The prezygapophysis of each vertebra articulates with the preceding postzygapophysis by a smooth dorsal surface. One nearly complete neural arch shows (Fig. [7 B]) a pit above the neural canal, clearly corresponding to the canal for a dorsal ligament shown by Jarvik in Ichthyostega. Indeed this view of the neural arch and intercentrum together brings out the striking resemblance between the vertebrae of Hesperoherpeton and those of the Ichthyostegids. The rounded intercentrum in both is an incomplete ring enclosing the notochordal canal.
Fig. 7. Hesperoherpeton garnettense Peabody. A, End view of incomplete vertebra, probably near anterior end of column. B, Neural arch and intercentrum in end view, showing probable association. C, Left lateral view of trunk vertebra. All figures: KU 10295, × 4.
Table 1.—Average Measurements of the Trunk Vertebrae (in mm.).
Numbers in Parentheses Indicate the Number of Pieces Available for Measuring