FIGURE 1. Map showing the geographic position of UNSM locality Wt 13B from the Penny Creek Local Fauna at state (A), county (B), and local (C) scales. The locality is represented by a solid black circle.
FIGURE 2. Composite time-stratigraphic chart of the Neogene of Nebraska correlated with the number of snake genera presently identified from the Central Great Plains for each North American Land Mammal Age (NALMA) substage. Abbreviations: He (Hemingfordian), Ba (Barstovian), Cl (Clarendonian), Hh (Hemphillian). Each point on the snake richness chart is summarized for each substage at that substage’s midpoint, and is not necessarily correlated with a particular rock unit on the right.Species richness values include fossils from the entire Central Great Plains region, while localities from Nebraska specifically and discussed in this study are listed at each substage point and come from the rock units to the right. The star represents the data from this study, which updates the previous lack of data from Cl1 across North America (represented by the gray hashed line) with data from UNSM Wt-13B. NALMAs and substages are correlated with time based on data and figures from Tedford et al. (2004). Rock Units are adapted from Joeckel et al. (2017) and Tedford et al. (2004). Snake generic richness is modified and updated from Jacisin et al., 2015).
FIGURE 3. Basic units of snake trunk vertebrae. A-E are from a fossil colubrine, and F is from a fossil natricid. A: trunk vertebra in dorsal view. B: trunk vertebra in ventral view. C: trunk vertebra in left lateral view. D: trunk vertebra in anterior view. E: trunk vertebra in posterior view. F: trunk vertebrae in left lateral view. Abbreviations: C, centrum; CD, condyle; CT, cotyle; D, diapophysis; HE, hemapophysis; HK, hemal keel; HY, hypapophysis; IR interzygapophyseal ridge; LY, lymphapophyses; NA, neural arch; NC, neural canal; NS, neural spine; P, parapophysis; PCF, paracotylar foramen; PLE, pleurapophysis; PO, postzygapophysis; POA, postzygapophyseal articular facet; PR, prezygapophysis; PRA, prezygapophyseal articular facet; PRP, prezygapophyseal accessory process; SF, subcentral foramen; SG, subcentral groove; SN, synapophyses; SR, subcentral ridge; ZG, zygantrum; ZGF, zygantral articular facet; ZY, zygosphene; ZYF, zygosphenal articular facet.
FIGURE 4. Map of the 19 localities in Nebraska, USA with documented occurrences of snake fossils from the Barstovian through Blancan NALMAs.
FIGURE 5. Trunk vertebra of Charina cf. Charina prebottae 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.
FIGURE 6. Trunk vertebra of Lampropeltis similis 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.
FIGURE 7. Trunk vertebra of Pantherophis kansensis 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.
FIGURE 8. Posterior trunk vertebra of Salvadora paleolineata from the Penny Creek local fauna. From top left: dorsal, ventral, anterior, posterior, and left lateral views. Scale bar equals 1 mm.
FIGURE 9. Middle trunk vertebra of Heterodon cf. Heterodon (Paleoheterodon) tiheni 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
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.
FIGURE 11. Trunk vertebra of Neonatrix magna 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.
FIGURE 12. Posterior middle trunk vertebra of Nerodia sp., 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.
FIGURE 13. Principal coordinates analysis showing the relative similarity of snake assemblages from 19 Barstovian-Blancan localities in Nebraska based on presence-absence.
FIGURE 14. Complete-linkage hierarchical cluster analysis showing the relative similarity of snake assemblages from 19 Barstovian-Blancan localities in Nebraska based on presence-absence.. Three major clusters are visible. From the left, the first cluster contains only Bw 123, the unique Pratt Slide local fauna; the second cluster contains all Barstovian and Clarendonian faunas minus Bw 123, but with the addition of Hemphillian Cn 106b (Thamnophis + Colubrinae indet.); and the third cluster, containing all Hemphillian through Blancan sites except Cn 106b.
FIGURE 15. Climate envelope models of MAT (A) and AP (B) based on the congenerics of the snake assemblage of the Penny Creek local fauna. The gray-filled spaces signify the areas of overlap for all taxa included in the models.
