Most evidence indicates that the transition at the end of the Triassic, 205 million years ago, was a period of widespread extinction, leading to the ascendancy of dinosaurs during the Jurassic. The new Argentinean finds tell a different story: Vertebrate animals in the Upper Triassic were apparently more diverse in this region, showing a mixture Triassic and Jurassic forms that turns the extinction model on its head.
The new finds reported by Alcober include a prosauropod dinosaur, two ancestral crocodilians, and a mammal-like cynodont the size of a mouse. The latter group was considered extinct by this time period.
"These findings give us a broader idea of the diversity of terrestrial faunas at the end of the Triassic," said Alcober, principal investigator of Earthwatch Institute's Triassic Park project. He will also report his recent findings at the Earthwatch Annual Conference in Boston, on November 6.
"We are documenting with greater detail what happened at the end of the Triassic," added Alcober. "It seems that, in the southern part of the prehistoric supercontinent Pangea anyway, the Triassic-Jurassic extinction was not as catastrophic as apparently documented in the north."
The new dinosaur was an herbivore with a long neck and four stout legs, measuring no longer than four meters long, typical of prosauropods. What makes it unique is a foreshortened skull, like many later sauropods of the Jurassic and Cretaceous.
"This specimen shows the incredible diversification of prosauropods already in the Late Triassic," said Alcober, who has documented four species now from the same Los Colorados Formation. "This group was already diversified before the Jurassic, more evidence of the consistency of the faunas through the Triassic-Jurassic boundary."
Earthwatch teams have been collaborating with Alcober to unearth the Triassic treasures of the Ischigualasto Valley since 1994, excavating many new finds and adding greatly to our understanding of the period. The site, known as "Valley of the Moon" for its dramatic rock formations, is one of the few places in the world where one can find a fossil record of the entire Triassic Period, when both the first mammals and first dinosaurs appeared.
"Earthwatch volunteers have played a fundamental role in our expeditions," said Alcober. "In addition to providing funding, some of the most important findings in this basin were made by volunteers."
The establishment of Ischigualasto-Talampaya National Park, a UNESCO World Heritage Site, allowed the access to related fossil beds in neighboring La Rioja Province, where teams made these latest finds last year. According to Alcober, the new site is "packed with fossils," and will be the focus of future Earthwatch teams.
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