Wyoming is a beautiful place, but usually it is associated more with open range, cowboys, mountains, and skiing than it is with palm trees and alligators. What a difference 48 million years makes!
Fossils in the rocks of the Bridger Formation, spanning part of the Eocene epoch from around 49.5 to 46 million years ago, reveal a Wyoming covered by tropical forests and filled with alligators, early primates, and giant lumpy-headed herbivores. To top it off, average temperatures were probably around 9°C (16°F) warmer than today. These conditions present a tidy historical experiment to see how life responds to elevated temperatures, both in terms of evolutionary change as well as geographical distribution.
As temperatures warm in temperate zones, it is not unusual for otherwise equatorial organisms to make their home in formerly chilly climes. Thus, the newly named fossil lizard Babibasiliscus alxi is yet another example of Wyoming’s tropical connections. Babibasiliscus, which lived around 48 million years ago, is most closely related to today’s casquehead lizards. Perhaps the best known contemporary example is the basilisk lizard, also called the “Jesus Lizard” for its ability to run across the surface of standing water for short distances. The nine modern species of casquehead lizards are exclusive to the New World, ranging from Ecuador up to Mexico.
Babibasiliscus was described this week in PLOS ONE, by lizard paleontologist Jack Conrad. An analysis of the evolutionary relationships of lizards show that Babibasilicus and another extinct lizard (Geiseltaliellus, which lived around the same time in Europe) are comfortably nested well within the evolutionary branches of casquehead lizards. Not distant cousins, not some long-lost ancestor–real, genuine, bona fide casquehead lizards! This strongly suggests that the exclusively neotropical distribution of today’s lizards is an accident of history. Perhaps they even originated outside of the equatorial zone–contrary to hypotheses based solely on analysis of genetic data from modern lizards. A proud lizard empire that once spanned continents has been defeated…well, perhaps that is a bit of an exaggeration, but you get the idea.
Babibasiliscus is a wonderful example of fossils showing up in unexpected places. As the world has changed, the distributions of its animals and plants change too. The fossil record is the best tool to show this!
Conrad JL (2015) A new Eocene casquehead lizard (Reptilia, Corytophanidae) from North America. PLoS ONE 10(7): e0127900. doi:10.1371/journal.pone.0127900