Turtles have long been the subject of one the most contentious questions in evolutionary biology: where do they fit among vertebrates in the evolutionary tree of life? Now, in a new study in the journal Evolution & Development scientists have determined that turtles are more closely related to birds and crocodilians than to lizards and snakes. The study is based on the combined data from anatomical, DNA and microRNA studies.
This study represents a first, most basic step in establishing the actual pattern of the reptile tree of life, says lead author Daniel Field, a Yale graduate student and a predoctoral fellow at the Smithsonians National Museum of Natural History. In evolutionary biology the first thing that you need to understand the evolution of anything is an accurate picture of how different groups of animals are related. Once we have an accurate evolutionary framework, then we can start to really try to understand how interesting and unique features, such as the turtles shell, came to be.
A research team from Dartmouth, Yale, the Smithsonian and other institutions looked at how the major groups of living reptiles, which number more than 20,000 species, are interrelated. The relationships of some reptile groups are well understoodbirds are most closely related to crocodilians among living reptiles, while snakes, lizards and New Zealands tuatara form a second natural group. But the question of how turtles fit into this evolutionary picture has remained unclear. Are turtles more closely related to archosaurs (birds and crocodilians) or to lepidosaurs (lizards, snakes and tuatara)? Or are these other reptiles more closely related to each other than to turtles?
A growing number of studies examining DNA sequences have suggested a close evolutionary kinship between turtles and archosaurs, but those results were contradicted by anatomical studies and a recent study of small biomolecules called microRNAs. Because microRNAs are viewed by some as excellent evolutionary markers, the conflict between the microRNA and DNA results meant the turtle-archosaur link was viewed skeptically by many.
But the teams research suggests the earlier microRNA conclusions were erroneous, and instead indicates that microRNAs and DNA sequences yield a common signalthat turtles share a more recent common ancestor with birds and crocodilians than with lizards and snakes.
That common ancestor probably didnt look anything like a modern bird or a modern crocodilian, but we know that it had to have existed, Field explains. These divergences among the major groups of reptiles likely happened in the Permian, more than 250 million years ago.
The study included researchers from Dartmouth, Yale, the Smithsonian, Mount Desert Island Biological Research Station and University of Bristol.
Article link: Toward consilience in reptile phylogeny: miRNAs support an archosaur, not lepidosaur, affinity for turtles, Evolution & Development, by Daniel Field, Jacques Gauthier, Benjamin King, Davide Pisani, Tyler Lyson and Kevin Peterson.
A recent study of microRNAs, a small biomolecule, and anatomical studies contradicted the results of a growing body of research using DNA sequences to suggest a close evolutionary kinship between turtles and archosaurs. Given that some consider microRNAs to be excellent evolutionary markers, many people were skeptical of the turtle-archosaur link due to the discrepancy between the microRNA and DNA results.
Article link: Toward consilience in reptile phylogeny: miRNAs support an archosaur, not lepidosaur, affinity for turtles, Evolution & Development, by Daniel Field, Jacques Gauthier, Benjamin King, Davide Pisani, Tyler Lyson and Kevin Peterson.
However, the team’s research indicates that microRNAs and DNA sequences yield a common signal, suggesting that the earlier conclusions about microRNAs were incorrect and that turtles share a more recent common ancestor with birds and crocodilians than with lizards and snakes.
Researchers from the Smithsonian, Dartmouth, Yale, Mount Desert Island Biological Research Station, and University of Bristol participated in the study.
A team of researchers from Dartmouth, Yale, the Smithsonian, and other universities examined the relationships between the major groups of the more than 20,000 species of living reptiles. Certain reptile groups have well-established relationships; among extant reptiles, birds are most closely related to crocodilians, while a second natural group consists of snakes, lizards, and tuatara from New Zealand. However, it is still unclear how turtles fit into this evolutionary scheme. Or are these other reptiles more closely related to each other than to turtles? Are turtles more closely related to lepidosaurs (lizards, snakes, and tuatara) or to archosaurs (birds and crocodilians)?
For instance, anatomical studies and other research involving small biomolecules called microRNAs have occasionally contradicted growing DNA sequence studies that suggest a close evolutionary kinship between turtles and archosaurs (birds, crocodilians). These studies suggest a closer evolutionary relationship between turtles and lizards and snakes.
In summary, he stated that turtles and archosaurs (birds and crocodilians) are now united by a common signal produced by microRNAs and DNA sequences.
Precise answers to these questions have long eluded scientists. However, recent research led by Yale University’s Daniel Field and the Smithsonian Institution rewrites the long-disputed evolutionary history of turtles, offering new proof that the well-known reptiles are more closely related to crocodiles and birds than to lizards and snakes.
Toward consilience in reptile phylogeny: microRNAs support an affinity for turtles within the archosaur, not the lepidosaur, is the title of the paper. .
For the first time, we obtain a consistent evolutionary signal regarding the evolutionary position of turtles from various sources of molecular data, which makes these results exciting, according to Field.