The oldest known bat skeletons and their implications for Eocene chiropteran diversification

Area of Science:

• Paleontology
• Vertebrate Paleontology
• Mammalogy

Background:

• The Green River Formation in Wyoming is a significant early Eocene Lagerstätte, yielding numerous bat fossils.
• Previous discoveries were limited to only two species of bats, suggesting low diversity.
• Nearly 30 bat fossils have been recovered from Fossil Lake over the past 50 years.

Purpose of the Study:

• To describe a new species of Icaronycteris based on two recently discovered articulated skeletons.
• To determine the phylogenetic placement of the new species within Chiroptera.
• To investigate the evolutionary relationships of early Eocene bats from North America and their divergence from Old World lineages.

Main Methods:

• Excavation and analysis of two articulated bat skeletons from the American Fossil Quarry.
• Stratigraphic analysis to establish the relative age and significance of the fossils.
• Phylogenetic analysis incorporating Eocene fossil bats and extant bat taxa.

Main Results:

• Description of a new species of Icaronycteris, representing the oldest bat skeletons discovered globally.
• Phylogenetic analysis places the new species within Icaronycteridae, closely related to Icaronycteris index.
• The two Green River archaic bat families form a distinct clade, separate from Old World bat lineages.
• Exclusion of Icaronycteris? menui and I. sigei from the Icaronycteridae family.

Conclusions:

• Green River bats represent a unique chiropteran radiation of basal bats in North America.
• The findings support the hypothesis of a rapid, multi-continental radiation of bats during the early Eocene.
• This study significantly enhances our understanding of early bat evolution and paleobiogeography.