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Nature

Ancestors Of Tyrannosaurs Found

author

Stephen Luntz

Freelance Writer

clockFeb 19 2016, 03:52 UTC
1398 Ancestors Of Tyrannosaurs Found
L.J. Krumenacker shows off the dinosaur fossils he found, scattered bones, teeth and eggshells that reveal the diversity of the area 100 million years ago. MSU/Sepp Jannotta

At least three new species of theropod have been found in the Wayan Formation, Idaho. The dinosaurs are early members of the family that eventually led to terrifying monsters such as Tyrannosaurus rex, although these ancestral versions were on a smaller scale. The same exploration mission also turned up eggs from oviraptorosaurs, the so-called “chicken from hell” with distinctively odd skulls and grasping hands.

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Western North America has been an exceptionally rich source of dinosaur fossils, particularly theropods, the group of carnivorous dinosaurs that included tyrannosaurids and Velociraptors. Like neighboring Washington, Idaho has been something of an exception, but a paper in Historical Biology starts the process of changing this.

Montana State University PhD student L.J. Krumenacker examined fossils from the Wayan Formation in south-eastern Idaho. “The Wayan Formation has received little paleontological attention due to a lack of substantial and well-studied outcrops,” the paper notes.

Unfortunately, Krumenacker's explorations turned up no nearly complete specimens, but the paper notes there is “A diversity of theropod forms now recognized from various isolated teeth, vertebrae, eggs, and eggshells.” It is the diversity that has drawn the authors' attention, with a surprising number of species appearing for such a small number of fossils.

Tyrannosauroid and suspected tyrannosauroid teeth found in the Wayan Foundation, south-east Idaho. Credit: Krumenacker et al

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Identifying species from isolated bones or teeth, let alone eggshells, is challenging, but the paper reports, “Theropods recognized from isolated teeth include a large possible tyrannosauroid, a small tyrannosauroid, dromaeosaurids, and indeterminate theropods.”

Among the eggs is a pair from a large oviraptorosaur, the first evidence that these feathered dinosaurs, the largest known to have lived in Idaho, inhabited the area at this time.

The finds are from the Albian and Cenomanian stages, roughly in the middle of the Cretaceous period, 113 to 94 million years ago. At this point in time, the tyrannosauroids were nothing like their descendants 30 million years later. The “large possible” specimen referred to in the paper is suggested by Krumenacker to probably have been about the size of a horse, while its small relative would have been equivalent to a mid-sized dog.

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Unfortunately, it is difficult to learn much from such scattered fragments. The paper notes, “The fragmentary specimens described here mostly preclude precise taxonomic identifications.” Nevertheless, Krukenmacker said, “I put my best effort into it. It’s possible I could discover some identifications are wrong if we find more complete remains later. But I’d be thrilled because then we’d have an even better understanding.”

Such finds may not stir the public imagination like a monster the size of three buses, but for paleontologists they are important. “We don’t really have many dinosaurs from this time period,” said Krumenacker's supervisor Professor David J Varricchio.“This new evidence is really filling in the time, temporal and spatial gap.”

“While these remains are admittedly meager, their presence indicates that a substantial diversity of theropods existed in the Albian to Cenomanian environments of southeastern Idaho,” the paper concludes, making the region “Among the most diverse reported for this time period in North America.”


Nature
  • theropods,

  • Idaho,

  • oviraptorosaurs,

  • tyrannasaurids

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