The first amphisbaenians from Texas, with notes on other squamates from the middle Eocene Purple Bench locality

The shift to a cooler and drier climate through the Paleogene has been interpreted as the driver for changes in diversity and biogeographic distributions among mammalian taxa during the Eocene, leading to hypotheses of continued tropical climatic refugia in West Texas through the middle and late Eocene. However, the presence of ectothermic reptiles during that time has not been documented in detail and would potentially provide additional climatic indicators. We provide the first description of the herpetofauna from the Devil's Graveyard Formation (DGF), West Texas, the southernmost, well-sampled middle Eocene basin in North America. Specimens are derived from beds correlated with the Ui3 biochron of the late Uintan North American Land Mammal ‘Age’ (∼45–40 Ma). We report the first amphisbaenians known from Texas, expanding our spatial and climatic understanding of rhineurid distribution, as well as the first glyptosaurine anguimorphs and alethinophidian snakes from the Purple Bench assemblage. These new amphisbaenians preserve a jugal posteriorly enclosing the orbit and an extremely short retroarticular process and are recovered in a clade comprising †<i>Spathorhynchus</i>, †<i>Dyticonastis</i>, †<i>Ototriton</i>, and †<i>Hyporhina</i>. The documentation of the amphisbaenians and other squamates provides biogeographic range extensions of these taxa to West Texas. Despite suggestions that West Texas was a middle and late Eocene climatic refugium for mammals adapted to subtropical forested environments, rhineurid amphisbaenians show a wide range of temperature tolerances up to the beginning of the Neogene. http://zoobank.org/urn:lsid:zoobank.org:pub:3E55D6BF-0691-4220-9212-0407F454BE53 SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Stocker, M. R., and E. C. Kirk. 2016. The first amphisbaenians from Texas, with notes on other squamates from the middle Eocene Purple Bench locality. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1094081.

古近纪时期气候逐渐向冷干方向转变，被认为是始新世哺乳动物类群多样性及生物地理分布格局发生变化的驱动因素，由此衍生出“西德克萨斯在中始新世至晚始新世始终存在热带气候避难所”的假说。
然而，该时期的外温爬行动物（ectothermic reptiles）尚未得到详细记录，而这类类群本可作为补充性的气候指示物。
本研究首次对西德克萨斯魔鬼墓地组（Devil's Graveyard Formation, DGF）的两栖爬行动物区系（herpetofauna）展开描述，该地层所在的盆地是北美目前采样最为完整的最南端中始新世沉积盆地。
本次研究的化石标本采自与晚Uintan期北美陆生哺乳动物时代Ui3生物年代带对应的地层，年代约为4500万至4000万年前（Ma）。
本研究报道了德克萨斯州首个被发现的蚓蜥类（amphisbaenians）类群，拓展了我们对冷蛇蚓科（Rhineuridae）分布范围与气候适配性的认知；同时也是紫台化石组合中首次报道的雕齿蜥亚科蛇蜥类与真蛇下目蛇类。
这些新发现的蚓蜥类类群保留了后缘环绕眼眶的轭骨（jugal），以及极短的关节后突（retroarticular process），系统发育分析将其归入包含†斯帕托蚓蜥属（Spathorhynchus）、†戴克通蚓蜥属（Dyticonastis）、†奥托蚓蜥属（Ototriton）与†希波蚓蜥属（Hyporhina）的演化支（clade）。
本次对蚓蜥类与其他有鳞类（squamates）类群的记录，将这些类群的生物地理分布范围拓展至了西德克萨斯地区。
尽管有假说认为西德克萨斯是中、晚始新世适应亚热带森林环境的哺乳动物的气候避难所，但冷蛇蚓科蚓蜥类的温度耐受范围极广，直至新近纪（Neogene）早期仍有分布。

相关链接：http://zoobank.org/urn:lsid:zoobank.org:pub:3E55D6BF-0691-4220-9212-0407F454BE53
补充数据：本文的补充材料可于www.tandfonline.com/UJVP免费获取。
本文引用格式：Stocker, M. R. 与 Kirk, E. C., 2016. 《德克萨斯州首个蚓蜥类类群及中始新世紫台产地的其他有鳞类类群简述》. 《脊椎动物古生物学杂志（Journal of Vertebrate Paleontology）》. DOI: 10.1080/02724634.2016.1094081.