New research challenges the current consensus that the radiation of squamates – a key modern group of reptiles that includes lizards and snakes – happened in the Cretaceous period.
Scientists have found that a key modern group of reptiles that includes lizards and snakes – known as squamates – diverged in the JurassicThe Jurassic (from the Jura Mountains) is a geologic period and system that spanned 56 million years from the end of the Triassic Period 201.3 million years ago to the beginning of the Cretaceous Period 145 million years ago. It constitutes the middle period of the Mesozoic Era and is divided into three epochs: Early, Middle, and Late.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Jurassic period, 50 million years earlier than previously thought.
New research published on May 3, 2022, in the journal eLife by scientists from the Institut Català de Paleontologia Miquel Crusafont (ICP) and the University of BristolThe University of Bristol, a red brick research university in Bristol, England, received its royal charter in 1909. However, it can trace its history back to 1876 (as University College, Bristol) and 1595 (as Merchant Venturers School). It is organized into six academic faculties composed of multiple schools and departments running over 200 undergraduate courses.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>University of Bristol challenges the current consensus that the radiation of squamates happened in the CretaceousThe Cretaceous is a geological period that lasted from about 145 to 66 million years ago. It is the third and final period of the Mesozoic Era. It ended with the Cretaceous–Paleogene extinction event.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Cretaceous period. This was when many terrestrial tetrapod groups like mammals, lizards, and birds, apparently underwent a great diversification during the so-called Cretaceous Terrestrial Revolution, which was triggered by the rise of flowering plants.
The fossil of Jurassic lizard Eichstaettisaurus. Credit: Jorge Herrera Flores
Now, a new research study, led by Dr. Arnau Bolet, a paleontologist at the Institut Català de Paleontologia Miquel Crusafont and the University of Bristol, implies a much earlier radiation of squamates. Along with colleagues from Bristol’s School of Earth Sciences, Prof Michael Benton, Dr. Tom Stubbs, and Jorge Herrera-Flores, their research concludes that this group of reptiles probably achieved a diverse array of adaptations in the Jurassic (between 201 and 145 Myr.), long before current estimates.
“Even though Jurassic squamates are rare, reconstructed evolutionary trees show that all the main specializations of squamates evolved then, and it’s possible to distinguish adaptations of geckoes, iguanas, skinks, worm lizards, and snakes some 50 million years earlier than had been thought,” explains Michael Benton, co-author of the research. “But how could the scarce Jurassic fossils suggest an early burst in evolution? The key is in their anatomy.”
Collared lizard in Colorado. Credit: Pahcal123 (CC BY-SA 4.0)
The few Jurassic squamates do not show primitive morphologies as would be expected, but they relate directly to the diverse modern groups. “Instead of finding a suite of generalized lizards on the stem of the squamate tree, what we found in the Jurassic were the first representatives of many modern groups, showing advanced morphological features,” says Arnau Bolet, lead author of the article.
The observed times of divergence, morphospace plots, and evolutionary rates, all suggest that the Jurassic was a time of innovation in squamate evolution, during which the bases of the success of the group were established. According to these results, the apparent sudden increase in diversity observed in the Cretaceous could be related to an improved fossil record, capable of recording a larger number of species, or to a burst of origins of new species related to the new kinds of forests and insects.
The Squamata is the largest order of reptiles, including lizards, snakes, and worm lizards. Squamates are all cold-blooded, and their skins are covered by horny scales. They are key parts of modern terrestrial faunas, especially in warmer climates, with an astonishing diversity of more than 10,000 species. However, the evolutionary paths that forged their success are still poorly understood.
Establishing the timing and mode of radiation of squamates is key for not only understanding the dynamics of terrestrial ecosystems in the MesozoicThe Mesozoic Era is an interval of geological time from about 252 to 66 million years ago. It is also called the Age of Reptiles and the Age of Conifers and is subdivided into three major periods: the Triassic, Jurassic, and Cretaceous.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Mesozoic, but also for deciphering how the group achieved an astonishing diversity of more than 10,000 species, only rivaled by birds among tetrapodsTetrapods are four-limbed (with a few exceptions, such as snakes) vertebrates constituting the superclass Tetrapoda that includes living and extinct amphibians, reptiles, mammals, and birds. They evolved from a group of animals known as the Tetrapodomorpha which, in turn, evolved from ancient lobe-finned fishes (Sarcopterygii) around 390 million years ago in the middle Devonian period.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>tetrapods.
Reference: “The Jurassic rise of squamates as supported by lepidosaur disparity and evolutionary rates” by Arnau Bolet, Thomas L Stubbs, Jorge A Herrera-Flores and Michael J Benton, 3 May 2022, eLife.
DOI: 10.7554/eLife.66511
Source: SciTechDaily
