Newly Discovered Fossil Helps Bridge Evolutionary Gap Of The Ichthyosaur

Chuck Bednar for – Your Universe Online
Researchers have located fossil evidence of an amphibious ichthyosaur, a discovery that for the first time links the dolphin-like ichthyosaur to its terrestrial ancestors and is reported in the November 5 advance online edition of the journal Nature.
According to lead author Ryosuke Motani, a professor in the University of California, Davis Department of Earth and Planetary Sciences, and his colleagues, the fossil was discovered in China and represents a missing stage in the evolution of these marine reptiles, which lived from the era of the dinosaurs to roughly 250 million years ago.
Previously, there were no fossils marking the ichthyosaur’s evolutionary transition from land animal to sea creature, but as Motani explained in a statement, “now we have this fossil showing the transition.” The fossil is approximately 248 million year old, roughly 1.5 feet long, and was discovered in China’s Anhui Province.
As Christine Dell’Amore of National Geographic News explained, paleontologists have long known that the up to 65-foot long ichthyosaurs evolved from land to the sea, as they have discovered fossils belonging to both the land-dwelling ancestors and the later fast-swimming marine version of the creature. While they knew there had to have been amphibious ichthyosaurs, they had never previously discovered fossil evidence of such a creature.

Image Above: Fossil remains show the first amphibious ichthyosaur found in China by a team led by a UC Davis scientist. Its amphibious characteristics include large flippers and flexible wrists, essential for crawling on the ground. Credit: Ryosuke Motani/UC Davis
Unlike the fully marine ichthyosaur, the newly discovered Cartorhynchus lenticarpus had abnormally large and flexible flippers that would have allowed it to move around on land like a seal, the researchers explained. It also possessed flexible wrists that allowed it to crawl around on the ground, thicker bones than most ichthyosaurs, and a short nose similar to those found on land-based reptiles instead of the more common longer, beak-like snouts.
Motani told Dell’Amore that the new species might have simply avoided discovery because scientists did not investigate enough early Triassic deposits. In fact, the UC-Davis researcher explained that he wasn’t even sure what he had discovered at first, but with the help of his colleagues, he was eventually able to piece the creature together.
“Cartorhynchus represents a stage of the land-to-sea transition that was somehow lacking in the fossil record of the ichthyosaur lineage, while known in most other marine reptile and mammal lineages,” the paleontologist told Reuters. “The fossil that we found is the first to fill this gap in the fossil record. This is particularly important because some creationists tried to use ichthyosaurs as a counter-example against Darwinian evolution since the group lacked this record.”
“We knew based on their bone structure that they were reptiles, and that their ancestors lived on land at some time, but they were fully adapted to life in the water. So creationists would say, well, they couldn’t have evolved from those reptiles, because where’s the link?” he added in an interview with Rachel Feltman of The Washington Post. He added that his team now plans to turn its attention to discovering the preceding evolutionary ancestor of the ichthyosaurs – one that was also amphibious, but spent more time on land.
Experts from the Peking University, Anhui Geological Museum, the Chinese Academy of Science, University of Milan and the Field Museum in Chicago were also involved in the discovery and analysis of the fossil. Their research was funded by the National Geographic Society’s Committee for Research and Exploration, Dell’Amore noted.
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