What came first, the Dino or the Lizard?
Image by Lead author Dr Marc Jones University College London 2013
The evolution of dinosaurs and lepidosaurs (predecessors of modern tuataras, lizards, and snakes) came from a reptile ancestor over 250 million years ago. Two main lineages came from that split, the archosaurs (ancestors of crocodiles, dinosaurs and birds) and the worlds’ lepidosaurs. But what evolved 1st? Fossil records show that true dinosaurs started appearing 232-234 million years ago, whereas snakes, lizards and tuataras are estimated to appear anywhere from 225 to 290 million years ago. With a new fossil discovery, this timeline has narrowed. Two new fossilized jaws were discovered in Vellberg, Germany that have predated all other known lepidosaur fossils; and beat dinos by about 12 million years.
To establish the age of the fossil remains, biologists used a technique called the “molecular clock”. This looks at the changes in the genetics code when two species or taxa diverged from a common ancestor. By tracing back things like DNA mutations, which occur fairly regularly, these change points can be used as time stamps to determine a fossil’s age.
These fossil jaws showed that lepidosaurs first appeared 240 million years ago after the end-Permian mass extinction event. This event is a turning point in earth’s history where new fauna began to recover and thrive in a more humid climate not yet dominated by dinosaurs. The fossils genetic divergence was also used to home in on when lizards diversified into modern groups, such as geckos and skinks. This fossil suggests this evolutionary milestone took place less than 150 million years ago, following continental fragmentation.
Professor Susan Evans, from the UCL Department of Cell and Developmental Biology, said: “The fossil record of small animals such as lizards and frogs is very patchy. Hopefully, this new fossil site in Germany will eventually give us a broader understanding of what was going on at this time.”
The fossils are most closely related to the tuatara and have small teeth with lightly built jaws, suggesting a diet of small insects. Modern Tuataras look like a lizard, but are not a true lizard species. They are the sole survivors of a group that once ranged throughout the world, but today the Tuatara is only found on islands lying off the coast of New Zealand, and in sanctuaries on the mainland where they have been reintroduced.
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Marc EH Jones, Cajsa Lisa Anderson, Christy A Hipsley, Johannes Müller, Susan E Evans, Rainer R Schoch. Integration of molecules and new fossils supports a Triassic origin for Lepidosauria (lizards, snakes, and tuatara). BMC Evolutionary Biology, 2013; 13 (1): 208 DOI: 10.1186/1471-2148-13-208