Heloderma (Helodermatidae; Squamata) from the Apache Local Fauna, Pleistocene, Southwestern Oklahoma
Paleontological occurrences of helodermatid lizards (Helodermatidae) are relatively uncommon and scattered in the North American fossil record. A recently discovered concentration of vertebrate fossils was exposed in a karstic fissure filling in an active rock quarry in southwestern Oklahoma. Underwater screening of the ancient cave fill yielded numerous isolated and fragmentary skeletal elements of a diversity of small, and a few large, vertebrates including unexpected remains of Heloderma sp. as well as extinct large mammals (horse, peccary, Dwarf Pronghorn), indicating Pleistocene age. Radiometric dating of the locality is not possible because of the leaching, but fossils of the Prairie Vole, Microtus ochrogaster, from the locality help to constrain the age of the deposit between 1.21 Ma and 0.01 Ma. The fossils are the first of Heloderma in the Pleistocene of Oklahoma and the southern Great Plains. Based on taphonomic evidence and the relative abundance of rodent teeth, we infer that the fossils accumulated at least partly as the remains of vertebrates fed upon by Ringtails (Bassariscus; Procyonidae) and other small carnivorous mammals. The Pleistocene occurrence of Heloderma in the southern Great Plains of North American has potential implications for the paleobiogeography of the genus and begs further investigation of fossil herpetofaunas in North America.ABSTRACT
Greater North America (adapted from Beck, 2005 and Mead et al., 2015) with the Heloderma fossil locality of the Apache LF, Oklahoma. Hachured pattern is the approximate distribution of H. suspectum (H.s.); stippled pattern is the approximate distribution of the H. horridum (H.h.) complex containing H. exasperatum (H.e.), H. alvarezi (H.a.), and H. charlsbogerti (H.c.). Sierra Madre Occidental and Sierra Madre Oriental are located in relation to extant and fossil localities as discussed in text. Numbered localities containing Heloderma include: 1) Gypsum Cave, Nevada; 2) Deadman Cave, Arizona; 3) Vulture Cave, Arizona; 4) Waterman Mountains, Arizona; 5) Coyote Badlands, California; 6) 111 Ranch, Arizona; 7) Gray Fossil Site, Tennessee; 8) Thomas Farm, Florida; and 9) Castolon, Texas, with H. texana (see Mead et al., 2015 for details of localities).
Basicranium of a modern Heloderma showing the locations of fossil remains. The black-lined area in (A) denotes the location of the exoccipital (OMNH 78815) as detailed in Fig. 3B. Right lateral view with anterior to the right and dorsal to the top. The black-lined area in (B) denotes the location of the basioccipital/basipterygoid region of the braincase as detailed in Fig. 3C. Dorsal view with anterior to the right.
Heloderma remains from Apache LF, Oklahoma. (A) Osteoderm (OMNH 78800). (B) Lateral view of posterior fragment of right exoccipital (OMNH 78815). (C) Dorsal view of basioccipital at the basipterygoid region of the braincase (for reference, see Evans 2008:fig. 1.10); anterior at top of page. Abbreviations (Evans 2008): cr.se, crista sellaris; f.6, foramen for the CN6, abducens nerve; f.o, foramen ovalis (edge of); h.fs, hypophysial fossa; hym.f, foramen for the hyomandibular branch of the CN7 (edge of); lrst, lateral opening of the recessus scalae tympani; p.vc2, opening of the posterior extension of the vidian canal in the basipterygoid; re, recess; v.f, vagus foramen (edge of). Scale Bar = 1 mm.
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