Kansasiella eatoni

Kansasiella eatoni

The occipital unit is complete with only the interior dorsolateral margins of the foramen magnum incompletely recovered. All data presented in this section are from FMNH UF462, as the entire region is absent in FMNH UF464. The occipital plate of Kansasiella has more pronounced craniospinal processes (csp.p; Figs 7C, 8E, 9C, D) than Phoebeannaia and a consequently sharper concave taper. The basioccipital is dorsoventrally thicker and encloses the vestibular fontanelle to a greater extent than in Phoebeannaia . The entire occiput is smaller relative to the rest of the braincase than is depicted in Poplin (1974); the craniospinal processes are approximately 90% as wide as the post-orbital processes, and the basioccipital does not expand ventrally to the same degree as previously described.

Unlike Phoebeannaia , in Kansasiella the midline dorsal rim of the occipital plate projects anteriorly into the posterior dorsal fontanelle (pos.d.fon; Fig. 9D); thus, the fontanelle outline is bean-shaped rather than ovoid. The vestibular fontanelles ( v.fon ; Figs 7C, 8E, 9C) are smaller than in Phoebeannaia . The interior space, in Kansasiella , is bounded anteriorly by a tall dorsum sellae (d.s; Fig. 7D) which rises into the cranial cavity from the basisphenoid, continues across the midline tracking the ventral fissure and bears foramina allowing the abducens nerves (VI, Figs 7D, 10B, D) to pass through to the rear of the posterior myodome. The notochord canal (nc.c; Figs 7D, 8E) is clearly separated from the foramen magnum above and dorsal aortic canal below and terminates at approximately the same position as in Phoebeannaia contra Poplin (1974) (p 63; fig. 20) where it was shown to reach the ventral fissure. The ventral fissure (v.f; Figs 7D, 9C) and associated lateral foramina (VII.pal,o.a; Figs 7D, 9C, 10C) are curved as in Phoebeannaia but are more widely separated from the vestibular fontanelles. There is no lateral projection for the first infrapharyngobranchial. The lateral dorsal aortae diverge within a long enclosed bony canal and exit separately (lat.d.ao.c; Fig. 9A) just posterior to the ventral fissure. Paired foramina for efferent branchial arteries (e.br.a; Figs 7D, 9C) are positioned anteriorly relative to the single midline passage in Phoebeannaia . Foramina for the occipital arteries (oc.a; Fig. 7D) are located posterior to the level of the efferent branchial foramina.

OTIC