Ten Million Years Before Dinosaurs
Paleontologists announced the discovery of a dinosaur-like animal - one that shared many characteristics with dinosaurs but fell just
outside of the dinosaur family tree - living 10 million years earlier than the oldest known dinosaurs. The researchers conclude that
dinosaurs and other close relatives such as pterosaurs (flying reptiles) might have also lived much earlier than previously thought.
The description of the new species Asilisaurus kongwe (a-SEE-lee-SOAR-us KONG-way) appears in the March 4, 2010 issue of the journal
Nature in a paper lead-authored by Sterling Nesbitt, a postdoctoral researcher at The University of Texas at Austin's Jackson
School of Geosciences. Nesbitt conducted the research with his colleagues while a graduate student at Columbia University's Lamont-Doherty
Earth Observatory and the American Museum of Natural History.
Meat-Eaters Evolve into Plant-Eaters
The research also suggests that at least three times in the evolution of dinosaurs and their closest relatives, meat-eating animals evolved
into animals with diets that included plants. These shifts all occurred in less than 10 million years, a relatively short time by geological standards.
Relationship Between Silesaurs and Dinosaurs
Asilisaurus is part of a sister group to dinosaurs known as silesaurs. Silesaurs are considered dinosaur-like because they share many
dinosaur characteristics but still lack key characteristics all dinosaurs share. The relationship between silesaurs and dinosaurs is
analogous to the close relationship of humans and chimps. Even though the oldest dinosaurs discovered so far are only 230 million
years old, the presence of their closest relatives 10 million years earlier implies that silesaurs and the dinosaur lineage had already
diverged from common ancestors by 240 million years ago. Silesaurs continued to live side by side with early dinosaurs throughout much
of the Triassic Period (between about 250 and 200 million years ago).
This is the first dinosaur-like animal recovered from the Triassic Period in Africa.
Physical Characteristics of Asilisaurus
Fossil bones of at least 14 individuals were recovered from a single bone bed in southern Tanzania making it possible to reconstruct a nearly
entire skeleton, except portions of the skull and hand. The individuals stood about 0.5 to 1 meter (1.5 to 3 feet) tall at the hips and were 1
to 3 meters (3 to 10 feet) long. They weighed about 10 to 30 kilograms (22 to 66 pounds). Asilisaurus walked on four legs and most likely ate
plants or a combination of plants and meat. They lived about 240 million years ago.
Silesaurs have triangular teeth and a lower jaw with a beak-like tip which suggest that they were specialized for an omnivorous and/or herbivorous
diet. These same traits evolved independently in at least two dinosaur lineages. In all three cases, the features evolved in animals that were
originally meat-eaters. Although difficult to prove, it's possible that this shift conferred an evolutionary advantage. An ecosystem can support
far more plant eaters than meat eaters. So being able to eat plants might have opened up a broader range of habitats. Not counting modern birds,
dinosaurs survived for about 180 million years.
This new species is found along with a number of primitive crocodilian relatives in the same fossil bed in southern Tanzania. The presence of
these animals together at the same time and place suggests that the diversification of the relatives of crocodilians and birds was rapid and
happened earlier than previously suggested. It sheds light on a group of animals that later came to dominate the terrestrial ecosystem throughout
the Mesozoic (250 to 65 million years ago).
"Everyone loves dinosaurs," said Nesbitt. "But this new evidence suggests that they were really only one of several large and distinct groups of
animals that exploded in diversity in the Triassic, including silesaurs, pterosaurs, and several groups of crocodilian relatives."
An Explostion of Triassic Silesaur Finds
Silesaurus, the first known member of the silesaur group was discovered in 2003. In just 7 short years, specimens of 8 other members have been
unearthed from Triassic rocks across the globe.
"This goes to show that there are whole groups of animals out there that we've never even found evidence of that were very abundant during the
Triassic," said Nesbitt. "It's exciting because it means there is still so much chance for discovery."
Naming Asilisaurus kongwe
The name Asilisaurus kongwe is derived from asili (Swahili for ancestor or foundation), sauros (Greek for lizard), and kongwe (Swahili for ancient).
The Author Team and Supporters
Co-authors of the Nature paper include an international team consisting of: Christian A. Sidor (Burke Museum and University of Washington), Randall
B. Irmis (Utah Museum of Natural History and University of Utah), Kenneth D. Angielczyk (The Field Museum, Chicago), Roger M.H. Smith (Iziko: South
African Museum, South Africa), and Linda A. Tsuji (Museum für Naturkunde an der Humboldt-Universität zu Berlin, Germany).
Funding for the research was provided by The National Geographic Society, The Evolving Earth Foundation, The Grainger Foundation, and The National Science Foundation.
More about Asilisaurus...
More information about Asilisaurus and images are available online.
For more information, contact: Marc Airhart, Geology Foundation, Jackson School of Geosciences, 512 471 2241.
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|Team members doing fieldwork in the Ruhuhu Basin of southern Tanzania, searching for fossils of Permian and Triassic vertebrates. Photograph by Christian Sidor from the Ruhuhu Basin Research website.
| A large collection of fossilized Asilisaurus bones found by team members in the Ruhuhu Basin of Tanzania. Photograph by Christian Sidor from the Ruhuhu Basin Research website.
| Location map of the Tanzania study area prepared by Christian Sidor.