Dinosaurs under the big sky



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RAPTOR ATTACK! (Display Case)


In 1991, a Museum of the Rockies field crew explored sediments of the Cloverly Formation near the town of Bridger, MT. Dave Varricchio, a Montana State University (MSU) doctoral student at the time, discovered a very important skeleton of the plant-eater Tenontosaurus (MOR 682B). The skeleton was important because it was superbly preserved and nearly complete, but also because excavators discovered 11 teeth of the small meat-eater Deinonychus in close proximity. Previous Tenontosaurus excavations also yielded Deinonychus teeth, leading researchers to hypothesize a predator-prey relationship between the two animals.
Contents Case: Tenontosaurus tilletti skeleton (MOR 682B)

Deinonychus tooth. One of the eleven Deinonychus teeth found

with the Tenontosaurus skeleton




Discovery Opportunity: How did this Tenontosaurus die?

Previous Tenontosaurus excavations also yielded Deinonychus teeth, leading researchers to hypothesize a predator-prey relationship between the two animals. The following observations helped paleontologists develop hypotheses about how this Tenontosaurus died.
GENERAL OBSERVATIONS: Eleven teeth of the Deinonychus, a dinosaur closely

related to Velociraptor, were found in the sediments around this Tenontosaurus

skeleton.



GEOLOGIC OBSERVATIONS: The skeleton was embedded in a grey mudstone

sediment that did not contain any other fossils except for the above-mentioned



Deinonychus teeth. The mudstone was deposited on the banks of a river. The river

flood that covered the specimen with mud had not moved any of the skeleton or teeth.



SCIENTIFIC OBSERVATIONS

Most toothed reptiles replaced their teeth on a regular basis throughout their life.



Deinonychus replaced its teeth about every 300 days or so. Living toothed reptiles, like

crocodiles, often lose their teeth when vigorously feeding. Eleven teeth is too many for

one Deinonychus to lose while feeding on a carcass. Teeth replacement data suggests that

it is likely that as many as six or eight Deinonychus fed on this Tenontosaurus. The

discovery of this Tenontosaurus skeleton and affiliated Deinonychus teeth provides

evidence for the suggestion that Deinonychus was a pack-hunting predator, and

substantiates an earlier hypothesis that the repeated association of Deinonychus teeth and

Tenontosaurus remains indicates that Deinonychus may have intentionally sought

Tenontosaurus as a food preference.
SOME HYPOTHESES THAT RESULT FROM THESE OBSERVATIONS

• The Tenontosaurus died on the floodplain of a stream or river.

• The Tenontosaurus was killed by the meat-eater Deinonychus.

• A group of Deinonychus pack-hunted and killed this Tenontosaurus.

Deinonychus actively preyed on a deliberate food choice—Tenontosaurus.
SO, HOW DID THIS TENONTOSAURUS DIE?

The Tenontosaurus was killed and eaten by a group of Deinonychus!

AN AGONIZING DEATH (Display Case)

Sometimes, the initial hypotheses on dinosaur death are disproven and a new hypothesis is developed. The Tenontosaurus tilleti skeleton (MOR 2571) within the display case was collected in 1998 in Carbon County, Montana.


Many dinosaurs, including the partial Tenontosaurus MOR 2571, are found with their necks and heads curved strongly backward toward their backs. This is called opisthotonic (uh-PIS-tho-TON-ick) posture, and for many years researchers were puzzled by its occurrence. Some scientists hypothesized that the posture was caused by the drying out of the neck tendons during rigor mortis (the stiffening of the body after death), while others thought the skeleton may have been moved by water flow. Still others cited postmortem (after death) dehydration of tissue.
Former Museum of the Rockies Postdoctoral Fellow Cynthia Marshall discovered a

scientific explanation for opisthotonic posture. Most of the existing hypotheses suggested that the posture resulted from postmortem processes. Dr. Marshall tested these hypotheses and was able to disprove them with her experiments. This led her to hypothesize that the posture was premortem, or happened as the animal was dying—not after its death. Through experimentation, Dr. Marshall concluded that the pose was the result of “death throes” — severe muscle spasms that most likely occurred when the animal was experiencing asphyxiation (lack of air).


Dr. Marshall and her co-author, MOR Research Associate Kevin Padian, reasoned that

animals found with opisthotonic postures died while gasping for breath, which could happen when the animal was being attacked by predators or succumbing to a deadly illness. Any dead animal that is preserved with its head and neck curved strongly backward likely died in agony.


Interestingly, the only kinds of animals found with opisthotonic postures are pterosaurs (flying reptiles), dinosaurs (non-avian and avian), and mammals—groups of animals that are known to have high metabolisms (an indication of warm-bloodedness). These animals consume higher levels of oxygen than animals with low metabolisms, which may account for the severity with which they would gasp for air.
Dinosaur remains collected by the Museum of the Rockies that have opisthotonic

posture include the two Tenontosaurus specimens in the Hall of Giants and the Wankel Tyrannosaurus rex skeleton.


The opisthotonic posture in the “Raptor Attack” Tenontosaurus (MOR 682) suggests that the animal died in anguish, which provides additional evidence that it did not die of

natural causes, but may have been attacked and killed by a group of Deinonychus.





TENONTOSAURUS FOR DINNER (Center Island Display)

In the center island display, full-scale sculptures show the Tenontosaurus and Deinonychus as they may have looked in life. Most Early Cretaceous plants were conifers, cycads, and ferns like the ones in the display. As a herbivore, the Tenontosaurus most likely ate these types of plants.


Deinonychus likely preyed on Tenontosaurus. The discovery of eleven Deinonychus teeth (which couldn’t all have come from one animal) around the carcass of the Tenontosaurus supports the hypothesis that Deinonychus ate and may even have group-hunted Tenontosaurus.
Discovery Opportunity: What color would you make a plant-eater? What about a meat-eater?

Scientists do not know the skin texture or color of Tenontosaurus or Deinonychus.

Our hypothesis is that the skin texture was similar to that of duck-billed dinosaurs,

of which we have impressions in sandstone. Color is also unknown, but since

dinosaurs are related to other colorful reptiles and birds, it is likely that they were

somewhat colorful. Additionally, Deinonychus is very closely related to birds, and

other dinosaurs known to be closely related to birds have been found with

evidence of feathers. The Deinonychus portrayed here has feathers on the areas of

the body where feathers are found on other closely related species.


MIDDLE CRETACEOUS IN MONTANA
BACKGROUND

Originally, the Hall of Giants was basically split in half with the first half featuring Late Jurassic dinosaurs and the second half emphasizing Early Cretaceous dinosaurs. The Middle Cretaceous was represented by the impressive maritime mural and plesiosaur fossil display at the end of the hall. No dinosaur fossils were included in the display because no dinosaur remains had been found in Montana from Middle Cretaceous rock formations. However, now the first-ever Middle Cretaceous dinosaur fossils have been found in Montana and they made burrows!


The Museum of the Rockies designed the Siebel Dinosaur Complex so that displays could be updated with the latest fossil discoveries and dinosaur research. With the discovery of the Oryctodromeous cubicularis in southwestern Montana, the Museum installed its first Middle Cretaceous dinosaur display and highlighted research on this new dinosaur. The exhibit area on Burrowing Dinosaurs opened in November 2014. The new display also highlights another new discovery, fossil remains of the earliest flowering plant in Montana, as well as an array of giant dinosaur eggs found in the same formation. In addition, the Museum enhanced the Middle Cretaceous maritime display by adding a rare crocodilian fossil just above the two plesiosaur fossil skeletons.

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