Squamate reptiles from Kanapoi: Faunal evidence for hominin paleoenvironments

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Abstract

The squamate fossil record from Kanapoi reveals generic to higher-order similarities with modern East African herpetofaunas. The record is derived from surface collection and screen washing, and consists primarily of isolated vertebrae with a few maxillary and mandibular elements. The most abundant remains are vertebrae of large-bodied Python that are morphologically similar to extant Python sebae, and vertebrae of Varanus cf. (Varanus niloticus + Varanus exanthematicus). Additional cranial and vertebral remains indicate the presence of lygosomine skinks, indeterminate Varanus, Viperidae, cf. Atractaspididae, and multiple colubrine morphotypes in the Kanapoi ecosystem. Despite similarities with modern herpetofaunas, the Kanapoi record lacks taxa common to other East African records, including agamids, chamaeleonids, amphisbaenians, the elapid Naja, and typhlopids. The overall composition of the Kanapoi squamate record is consistent with paleoenvironments similar to modern shrub savanna habitats. There are no indicators of canopied forest environments in squamate faunal composition. The fossil record of Kanapoi suggests that assembly of squamate faunas of modern East Africa was well underway by the late Neogene.

Introduction

Documenting the paleoecological and environmental context of the primate fossil record from the Neogene of East Africa is requisite for understanding hominin evolution. Among vertebrates, the mammalian fossil record from primate-bearing localities and formations has been extensively described (e.g., Werdelin and Sanders, 2010 and references therein), however, less attention has been paid to the reptile fossil record, despite its abundance in Cenozoic sections throughout Africa. Fossil records of crocodilians and turtles have been described in variable detail for East African sections (e.g., Wood, 1976, Wood, 1979, Wood, 1983, Tchernov and van Couvering, 1978, Meylan, 1987, Meylan et al., 1990, Wood, 2003, Brochu et al., 2010, Brochu and Storrs, 2012; Conrad et al., 2013), whereas fossil squamates, though often included in faunal lists, are more rarely described in any detail (see e.g., van Couvering, 1979; Meylan, 1987, Rieppel et al., 1992, Rage and Bailon, 2011 for exceptions).

The Pliocene Kanapoi Formation consists of fluviolacustrine sedimentary sequences that crop out southwest of Lake Turkana in northwest Kenya (Feibel, 2003). Fossil-bearing sediments within the Kanapoi Formation are dated between 4.195 ± 0.033 Ma and 4.07 ± 0.02 Ma based on tuffs (see Werdelin and Manthi, 2012; Brown et al., 2013). Kanapoi localities have produced an important hominin record, including Australopithecus anamensis (Leakey et al., 1995, Leakey et al., 1998, Ward et al., 2013). In addition to hominins, a diverse Kanapoi vertebrate fossil record, including other primates, carnivorans, proboscidians, ungulates, rodents, macroscelids, chiropterans, insectivorans, turtles, crocodylians, birds, and actinopterygian fishes has been recovered and documented (Wood, 1983, Meylan and Auffenberg, 1986, Meylan et al., 1990, Winkler, 1998, Harris et al., 2003, Stewart, 2003, Storrs, 2003, Werdelin, 2003, Wood, 2003, Manthi, 2006, Werdelin and Manthi, 2012). The only major vertebrate clades present through the African Neogene fossil record not to be described from Kanapoi are Lissamphibia and Squamata.

Here we describe the fossil record of squamates from Kanapoi, including specimens recovered from surface collection and screen washing at the A. anamensis type locality (Ward et al., 2013), housed in the collections in the National Museums of Kenya, Nairobi (KNM). We place this record in the larger context of the Neogene squamate fossil record from Africa and its implications for reconstructing paleoenvironmental histories.

Section snippets

Systematic paleontology

  • Squamata Oppel, 1811.

  • Scincidae Gray, 1825.

  • cf. Lygosominae Mittleman, 1952.

  • Referred specimens: KNM-KP 59752 [collection 2003, “mandible site“, field no. 24], incomplete dentary and splenial; KNM-KP 59753 [collection 2003, “mandible site“, field no. 24], incomplete dentary and splenial.

  • Figure 1A

  • Description: Both specimens are incomplete, preserving only the midsection of the dentigerous portion of the mandible, consisting of articulated sections of the dentary and splenial (Fig. 1A). The shape

Discussion

Despite a century of multinational research developing fossil vertebrate collections in the context of understanding hominin evolution, the fossil record of African Neogene squamates is poorly documented relative to coeval North American and European records (e.g., Rage and Holman, 1984, Szyndlar, 1991a, Szyndlar, 1991b, Rage and Augé, 1993, Holman, 2000, Szyndlar, 2012), and no synthesis of the record has previously been conducted. Placing the described Afro-Arabian squamate record in a

Acknowledgements

For access to KNM collections, we thank Kyalo Manthi, Carol Ward, and Mike Plavcan. JM and JJH were funded by the Deutsche Forschungsgemeinschaft (MU 1760/4-1). JJH was additionally supported by NSF EAR-1338028. Financial support for field research is from NSF BCS-1231749, NSF BCS-1231675, Wenner Gren Foundation, University of Missouri Research Board. We thank J.-C. Rage and an anonymous reviewer for thoughtful comments on the manuscript.

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