The 366 daily episodes in 2014 were chronological snapshots of earth history, beginning with the Precambrian in January and on to the Cenozoic in December. You can find them all in the index in the right sidebar. In 2015, the daily episodes for each month were assembled into monthly packages, and a few new episodes were posted. Now, the blog/podcast is on a weekly schedule with diverse topics, and the Facebook Page showcases photos on Mineral Monday and Fossil Friday. Thanks for your interest!

Friday, September 12, 2014

September 12. Reptiles return to the sea

The Permian extinction and the dramatic changes in environment in the early Triassic certainly stressed many animal groups. Reptiles, which had become the first fully terrestrial animals back in the Carboniferous Period, about 305 million years ago, returned to the sea and a largely aquatic life during the early Triassic soon after the start of the period, about 245 million years ago. The oldest known aquatic reptiles come from early Triassic rocks in China.  

Triassic nothosaur drawing by Nobu Tamura under GFDL

The sauropterigians, whose name means “lizard flippers,” were reptiles somewhat like seals. Nothosaurs, a Triassic group, grew up to 3 meters or 10 feet long and had webbed, paddle-like feet. The long neck supported a head full of teeth, and they probably ate fish and squid.

It isn’t completely clear whether the sauropterigians were more closely related to turtles or the crocodile branch of early reptiles, partly because their aquatic lifestyle resulted in changes that obscure their taxonomic connections. It looks like all the sauropterigians died out in the extinction at the end of the Triassic, except for one lineage, the plesiosaurs. Plesiosaurs had just gotten started in the very late Triassic, survived the extinction event, and went on to proliferate and dominate the seas during Jurassic time.

Plesiosaurs were among the first fossil reptiles recognized as reptiles. Fossils found in the 1600s were thought to be fish vertebrae, but by the early 1700s they were identified as reptiles. Numerous specimens were found in Great Britain, increasingly complete in their preservation. One specimen was described in 1832 as "a sea serpent run through a turtle," a reference to the long neck and tail and broader central body.

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Today is James Hall’s birthday, September 12, 1811, in Hingham, Massachusetts. Hall studied the geology of much of the northeastern United States as well as the Midwest, but he’s probably most closely identified with New York, where he was the state geologist and author of the 4500-page Paleontology of New York, in 13 volumes. He helped found the National Academy of Sciences and was the first president of the Geological Society of America. There’s a residence hall at the Rensselaer Polytechnic Institute named for him. It’s called Hall Hall. 

—Richard I. Gibson

Triassic nothosaur drawing by Nobu Tamura under GFDL

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