The long‐term history of dispersal among lizards in the early Eocene: new evidence from a microvertebrate assemblage in the Bighorn Basin of Wyoming, USA

Abstract

Early Eocene mammal faunas of North America were transformed by intercontinental dispersal at the Paleocene-Eocene boundary, but lizard faunas from the earliest Eocene of the same area were dominated by immigrants from within the continent. A new lizard assemblage from the middle early Eocene of Wyoming sheds light on the longer-term history of dispersal in relation to climate change. The assemblage consists of three iguanid species (including two new species possibly closely related to living Anolis), Scincoideus, 'Palaeoxantusia', four anguids, two species of an undescribed new anguimorph clade, Provaranosaurus and a varanoid (cf. Saniwa). Most North American glyptosaurin glyptosaurines are now referred to Glyptosaurus, and Glyptosaurus hillsi is given a new diagnosis. Scincoideus is otherwise known only from the mid-Paleocene of Belgium, and the specimens described here are the first to document intercontinental dispersal to North America among lizards in the early Eocene. Like in mammals, some immigrant lizard lineages first appearing in the Bighorn Basin in the earliest Eocene persisted in the area long after the Paleocene-Eocene thermal maximum, but other immigrants appear to have been restricted to the PaleoceneEocene thermal maximum.

Effects of phylogenetic uncertainty on fossil identification illustrated by a new and enigmatic Eocene iguanian

“…Kopidosaurus is not known to occur in previously described faunas from earlier Eocene deposits in the Willwood Formation 40 , 43 . Regional temperatures rose in the late early Eocene around the time of deposition of the fossil 44 , but it is not clear if the evolution of Kopidosaurus is associated with climate change, or whether its appearance represents an immigration event or in situ diversification.…”

A new Late Cretaceous iguanomorph from North America and the origin of New World Pleurodonta (Squamata, Iguania)

“…The oldest definitive crown pleurodontans are the early Eocene Afairiguana avius (Polychrotidae sensu lato [42]) and Anolbanolis banalis [41], both from Wyoming, USA. Additional representatives of pleurodontan crown clades, such as the corytophanids Babibasiliscus alxi and Geiseltaliellus maarius from Wyoming, USA and Germany, respectively, occur in the middle Eocene ( [20,49]; see [41,50,51] for additional North American records). The presence of Cretaceous and Palaeogene pleurodontans in South America is also equivocal.…”

“…The Late Cretaceous iguanian fossil record from the mid-to high-latitudes of Asia and North America consists exclusively of stem taxa [20,21], including Magnuviator, and the oldest fossil crown pleurodontans are early Eocene in age [41,42,50,51]. The absence of crown taxa from the comparatively well-sampled regions of Asia and North America [19,24], combined with the high diversity and/or endemism of many extant pleurodontan clades in the Neotropics [2,3] is consistent with an origin or initial diversification of crown Pleurodonta in the rspb.royalsocietypublishing.org Proc.…”

Phylogenetic relationships of Amazonian anole lizards (Dactyloa): Taxonomic implications, new insights about phenotypic evolution and the timing of diversification

“…(Corytophanidae), from the early Eocene (Smith, 2009(Smith, , 2011, was placed at the stem of the clade defined by Corytophanes and Basiliscus, and (3) Afairiguana avius (Leiosauridae), from the early Eocene , was placed at the stem of the clade defined by Leiosaurus and Urostrophus. In the latter case, we conservatively treated A. avius as a stem leiosaurid because found the relationships between A. avius and extant leiosaurids to be unresolved.…”