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| Chaohusaurus geishanensis | |
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| Tweet Topic Started: Feb 13 2014, 12:02 PM (1,700 Views) | |
| Taipan | Feb 13 2014, 12:02 PM Post #1 |
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Chaohusaurus geishanensis![]() Temporal range: Early Triassic Scientific classification Kingdom: Animalia Phylum: Chordata Class: Reptilia Order: †Grippidia Family: †Grippiidae Genus: †Chaohusaurus Type species: †Chaohusaurus geishanensis Chaohusaurus is an extinct genus of basal ichthyopterygian, possibly ichthyosaur, from the Early Triassic of Chaohu and Yuanan, China. It has also been called Anhuisaurus and Chensaurus. It was described by Young and Dong in 1972. It was closer in form to Cymbospondylus and Mixosaurus than more advanced genera like Ichthyosaurus: it did not have the dolphin-like form of later ichthyosaurs; it had a more lizard-like appearance. It did have flippers, rather than webbed feet, but the neck is atypically long and there is no dorsal fin. The tail fin is wide-based and short. It is one of the smallest ichthyosaurs, being from 70 to 180 cm long. Its weight is estimated at 10 kg. ![]() Reproduction Chaohusaurus birthed its young viviparously, like later ichthyosaurs. However, unlike later ichthyosaurs, the young exited the birth canal head-first. Montani et al.(2014) cited this as evidence for a terrestrial evolution of viviparity in ichthyosaurs. Oldest Fossil of Reptile Live Birth Found By Becky Oskin, Staff Writer | February 12, 2014 05:04pm ET ![]() A fossil from China of an ichthyosaur mother giving birth. There are three embryos, including the one shown, which is exiting the mother headfirst. A new fossil that captures both birth and death reveals the earliest ancestors of the giant prehistoric sea predators called ichthyosaurs birthed their babies headfirst, according to a new study. The fossil of an ancient Chaohusaurus mother that likely died while in labor also suggests that reptilian live birth only evolved on land, researchers report today (Feb. 12) in the journal PLOS ONE. Ichthyosaurs were top ocean predators during the age of the dinosaurs. Sleek, streamlined swimmers that grew as long as a bus, they had teeth-filled snouts and enormous eyes for snatching prey. These air-breathing carnivores arose from land reptiles that moved into the water from land during the early Triassic period, between 251 million and 247 million years ago. (The Triassic period follows one of the biggest mass extinctions on Earth, which killed 96 percent of marine species and 70 percent of land species.) Previously found fossils of pregnant ichthyosaurs had already revealed the reptiles carried live embryos, not eggs. And one spectacular fossil of a Stenopterygius ichthyosaur in "childbirth," from the Jurassic period, between 201 million and 145 million years ago, showed at least one species had newborns come out tail-first. However, researchers didn't know whether the earliest ichthyosaurs also gave birth headfirst or tail-first. Most air-breathing marine creatures that bear live young, such as whales and dolphins, birth their babies tail-first, so the newborns don't suffocate during labor. But on land, babies tend to come out headfirst. And the earliest whales, which also evolved from land mammals, birthed their newborns headfirst. The new fossil confirms that the first ichthyosaur babies came out headfirst, the study reports. The ichthyosaur mother died with three young: one outside the mother, one half-emerged headfirst from her pelvis and one still inside, waiting to be born. Because of the burial positions, it's unlikely the babies were expelled from the mother after death, the researchers said. "The reason for this animal dying is likely difficulty in labor," said Ryosuke Motani, lead study author and a paleobiologist at the University of California, Davis. Motani believes the first baby was born dead, and the mother may have died of a labor complication from the second, which is stuck half-in, half-out of her body. "Obviously, the mother had some complications," he said. The skeleton was a lucky find. It was hidden in a rock slab with a Saurichthys fish fossil, and was only discovered when the fish fossil was prepared in the team's lab in China. (The two fossils aren't from the same time period, the researchers said.) The Chaohusaurus fossil, from one of the oldest ichthyosaur species, is about 10 million years older than other fossil embryos from reptiles found so far. The specimen is now at the Anhui Geological Museum in Hefei, China. The team recovered more than 80 new ichthyosaur skeletons during a recent field expedition to a fossil quarry in south Majiashan, China. Earliest newborns Live birth evolved independently in more than 140 different species, including about 100 reptiles. Other extinct aquatic reptiles that gave birth to live young include the plesiosaur and the mosasaur; in 2011, scientists discovered a pregnant plesiosaur, a marine reptile, which lived some 78 million years ago. The new ichthyosaur fossil pushes back the known records of live birth to the earliest appearance of marine reptiles 248 million years ago, during the beginning of the Mesozoic era. Until now, researchers thought live birth first appeared in marine reptiles after they took to the seas, Motani said. The ichthyosaur fossil counters this assumption, by providing an evolutionary link to the headfirst, terrestrial style of childbirth. "This land-style of giving birth is only possible if they inherited it from their land ancestors," Motani told Live Science. "They wouldn't do it if live birth evolved in water." And because ichthyosaurs evolved from land reptiles, the discovery suggests that land reptiles also bore live young in the earliest Mesozoic, Motani said. The oldest fossil evidence for live birth in land reptiles is no more than 125 million years old, more than 100 million years younger than the new fossil discovery. http://www.livescience.com/43344-ichthyosaur-fossil-live-birth-found.html Terrestrial Origin of Viviparity in Mesozoic Marine Reptiles Indicated by Early Triassic Embryonic Fossils Ryosuke Motani, Da-yong Jiang, Andrea Tintori, Olivier Rieppel, Guan-bao Chen Published: February 12, 2014 DOI: 10.1371/journal.pone.0088640 Abstract Viviparity in Mesozoic marine reptiles has traditionally been considered an aquatic adaptation. We report a new fossil specimen that strongly contradicts this traditional interpretation. The new specimen contains the oldest fossil embryos of Mesozoic marine reptile that are about 10 million years older than previous such records. The fossil belongs to Chaohusaurus (Reptilia, Ichthyopterygia), which is the oldest of Mesozoic marine reptiles (ca. 248 million years ago, Early Triassic). This exceptional specimen captures an articulated embryo in birth position, with its skull just emerged from the maternal pelvis. Its headfirst birth posture, which is unlikely to be a breech condition, strongly indicates a terrestrial origin of viviparity, in contrast to the traditional view. The tail-first birth posture in derived ichthyopterygians, convergent with the conditions in whales and sea cows, therefore is a secondary feature. The unequivocally marine origin of viviparity is so far not known among amniotes, a subset of vertebrate animals comprising mammals and reptiles, including birds. Therefore, obligate marine amniotes appear to have evolved almost exclusively from viviparous land ancestors. Viviparous land reptiles most likely appeared much earlier than currently thought, at least as early as the recovery phase from the end-Permian mass extinction. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0088640 |
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12:02 AM Jul 12