September 25, 2013
Oldest Lizard Fossil Discovered, Yields New Insights Into Reptile Evolution
Brett Smith for redOrbit.com - Your Universe Online
An international team of researchers has discovered the oldest known lizard-like fossil near Vellberg, Germany. The find offers new insights into the evolution of reptiles including lizards, snakes and tuatara, according to a newly published report in BMC Evolutionary Biology.
The ancient reptile’s fossilized jaws indicate that these reptiles were alive during the Middle Triassic period some 240 million years ago.
“The Middle Triassic represents a time when the world has recovered from the Permian mass extinction but is not yet dominated by dinosaurs,” said study author Marc Jones, an evolutionary biologist at the University College London (UCL). "This is also when familiar groups, such as frogs and lizards, may have first appeared."
The jaws’ construction indicated that the extinct reptile preyed on small insects and closely resembled that of tuatara, a lizard-like reptile native to New Zealand.
Tuatara was originally relegated to the 35 islands sitting off the coast of New Zealand but has been recently reintroduced to habitats on the mainland. The reptiles are referred to as ‘living fossils’ because they are the only survivors of a group that once inhabited ecosystems around the world. In addition to feeding on insects, tuatara occasionally prey on small lizards and the occasional sea bird.
With over 9,000 known species of lizards, snakes and tuatara around the world, knowing when their common ancestor first appeared is vital for understanding reptile diversification.
To establish the age of the newly discovered fossil, the team of evolutionary biologists used a dating technique known as a ‘molecular clock.’ This technique uses the amount of genetic divergence between living animals with a common ancestor as indicated by accumulated changes in their DNA sequences. These mutations occur at a regular pace in the same way that a clock ticks at a steady rate. For the molecular clock to translate genetic differences into geological time, it needs to be calibrated with one or more fossils of a known relationship and age.
The researchers say these new fossil jaws can be used to improve dating estimates of when reptiles began to split into snakes, lizard and tuatara, in addition to indicating when the first modern lizards arose on earth. Previous studies have varied over a range of 64 million years, but the scientists said they expect to narrow that range down.
"Some previous estimates based on molecular data suggested that lizards first evolved 290 million years ago," said co-author Cajsa Lisa Anderson, a postdoctoral researcher at the University of Gothenburg. "To a paleontologist this seems way too old and our revised molecular analysis agrees with the fossils."
The latest calculations based on the new fossils indicate that lizards began to diversify less than 150 million years ago, during the Cretaceous period.
The study researchers said the Vellberg site will probably yield yet more fossil discoveries in the future, enabling us to broaden our knowledge of vertebrate evolution.
“The fossil record of small animals such as lizards and frogs is very patchy,” said co-author Susan Evans, from the UCL Department of Cell and Developmental Biology. “Hopefully, this new fossil site in Germany will eventually give us a broader understanding of what was going on at this time."