Paleontology

Scientists Identify two Ancient Reptiles that Swam in Australian Waters



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In recent years, scientists have identified two ancient reptiles that swam in Australian waters over 100 million years ago. The new finds, which were named Umoonasaurus and Opallionectes, promise to fill in some important gaps in scientists' knowledge of a group of dinosaur-like marine reptiles known as plesiosaurs.

The two discoveries were made by a single research team led by professor Benjamin Kear, a paleontologist at the University of Adelaide. The fossil specimens were found in an opal mine, and Kear's team believes the bones now in their possession actually come from several dozen separate individuals. Kear's team dated them to about 115 million years ago, during the Jurassic period, and confirmed that they were from two separate species of plesiosaur. At the time, he says, Australia was much closer to the South Pole than it currently is, and much of today's continent was submerged in the frigid Antarctic waters.

The plesiosaurs were a common marine reptile at the same time that their distant cousins, the dinosaurs, dominated life on the land. (Although plesiosaurs like Umoonasaurus and Opallionectes are sometimes referred to as "marine dinosaurs," paleontologists actually differentiate between the two types of reptile based on tell-tale differences in their skeletal structure.) The first type of new Australian reptile, Umoonasaurus, was a member of a genus of small, agile predators called the rhomaleosaurs, which Kear describes as being the "killer whales" of the Jurassic. Opallionectes was much larger, at "about 19 feet long," and probably used its smaller, more numerous teeth to feed on small fish and shellfish.

Although the new plesiosaurs are an important contribution to Australian paleontology in their own right, they are even more important because they promise to supply what might be an important missing link in paleontologists' knowledge about these mysterious marine reptiles. Kear says that until now the best collections of plesiosaur remains were English remains about 170 million years old, and other Antarctic remains dated to about 65 million years ago. Paleontologists knew, from the fossil record, that plesiosaurs must have had their start early on, during the lower Jurassic, and then probably went extinct during the Cretaceous (along, eventually, with the dinosaurs). However, there were large gaps between these dates during which plesiosaurs must have thrived in some oceans around the world, but for which few fossil remains have been located. The new Australian finds will help scientists fill in one of those gaps.

The discoveries of Umoonasaurus and Opallionectes have been published in the journals Paleontology and Biology Letters. A summary for non-experts has also been published online by the University of Adelaide. By convention, the first paleontologists to formally describe a new species can choose a scientific name for it. These researchers chose names for their newly discovered species based on the sites where the fossils were found. Opallionectes is Latin for "opal swimmer." Umoonasaurus is named after Umoona, the Aboriginal name for the Coober Pedy site where a mostly complete skeleton of the first specimen was unearthed.

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