Neonatrix elongata Holman, 1973

Jacisin Iii, John J. & Lawing, A. Michelle, 2024, Fossil snakes of the Penny Creek Local Fauna from Webster County, Nebraska, USA, and the first record of snakes from the Early Clarendonian (12.5 - 12 Ma) of North America, Palaeontologia Electronica (a 2) 27 (1), pp. 1-42 : 21

Neonatrix elongata Holman, 1973 †

Figure 10

Material. UNSM 139986 (17 pre-cloacal trunk vertebrae).

Description. The diagnosis follows that of Holman (2000) and is only modified where otherwise noted. Neonatrix elongata trunk vertebrae are longer than wide, with a neural spine that is drastically longer than tall or wide. The vertebrae possess poorly developed hypapophyses reaching only the posterior portion of the centrum, and unbeveled neural spines that end just short of the posterior end of the cotyle.

In anterior view, the neural canal is shaped like a ventrally restricted semi-cylinder, is medially convex at the sides, and is slightly narrower than the round cotyle. The zygosphene is convex dorsally. The synapophysis is developed. For the first time in this genus and species, we confirm the presence of paracotylar foramina in anterior view, adjacent to the cotyle on each side, approximately half-way down the cotyle. Previous descriptions exhibited excavated cavities on either side of the cotyle, but could not observe any foramina based on the specimens available.

In dorsal view, the centrum is longer than wide. The prezygapophyseal articular facets are ovoid in shape. This is a correction of Holman (2000), which appears to have mistakenly labeled the prezygapophyseal processes as ovoid, rather than the articular facets. The prezygapophyseal processes are long and somewhat pointed on the anterior end. The diapophyses only slightly extend out laterally. The epizygapophysel spines are absent or obsolete.

In lateral view, the vertebrae are elongate. The neural spine is over two times as long as it is high. The neural spine is rarely preserved at the ends in Penny Creek fossils and in Neonatrix throughout the fossil record, and so is difficult to observe, but a few mostly preserved neural spines from Penny Creek material allow us to determine the absence of an anterior projection, and an extremely reduced to absent – typically absent – posterior overhang. The subcentral ridge is convex dorsally. The prezygapophyses tilt somewhat dorsally. The hypapophysis is short and ends short of the posterior-most part of the condyle; we find that it is does not extend past even the anterior-most part of that articulation in these specimens.

In posterior view, we find that the condyle is near circular, but is slightly depressed and closer to an oval shape in some vertebrae. The neural arch is vaulted, steeply incised by the zygantral articular facets, and similar in size to the condyle. The hypapophysis is visible below the condyle around onehalf of the condyle’s height when undamaged. The postzygapophyses tilt slightly upward, just as in the prezygapophyses. In ventral view, the centrum is long and narrow. The subcentral grooves are shallow, and the hemal keel narrows slightly anteriorly to the robust but truncated hypapophysis.

Remarks. Like other species of North American Neonatrix , N. elongata have less well-developed hypapophyses that do not extend as far posteriorly (relative to the condyle) than found in the European species ( Rage and Holman, 1984). N. elongata occurs earlier than other North American species of Neonatrix and is known to occur more broadly in a temporal and geographic manner throughout the Miocene. In the Penny Creek specimens, the unbeveled neural spine and unbeveled hypapophysis that end just short of the posterior end of the cotyle indicate that these fossils belong to N. elongata , as opposed to other known species of Neonatrix . There is some variation on how rounded (or pointed) the posterior tips of the hypapophyses are, likely indicating a small amount of intracolumnar variation in the hypapophyseal morphology of the species ( LaDuke, 1991; McCartney, 2015). Nonetheless, we have not observed more variation within an individual taxon than between species, and the morphology is generally consistent with what is described above. Neonatrix elongata is typically smaller than Neonatrix magna and Neonatrix infera , but the taxon’s relative length and neural spine height are intermediate between the other two species, which are either more elongate with a shorter neural spine ( N. infera ) or less elongate with a taller neural spine ( N. magna ; Holman, 2000). It is noteworthy that these specimens show some measure of variation in terms of the neural spine height and the shape of the hypapophyses, some of which appear similar to some morphologies known in the other North American species. Given that N. elongata was considered to have “intermediate” morphologies by Holman (2000), it may be necessary to further study the intracolumnar variation with Neonatrix for additional definitive characters and consider potential changes to the taxonomy of the species within.

Figures

FIGURE 10. Posterior trunk vertebra of Neonatrix elongata from the Penny Creek local fauna. From top left: dorsal, ventral, anterior, posterior, and lateral views (anterior to the left). Scale bar equals 1 mm.