Tyrannosaurus: My! What a big Gape you Have!

Just how bad was T. rex's bite? New research from the University of Bristol has found that the feeding style and dietary preferences of dinosaurs was closely linked to how wide they could open their jaws.

Using digital models and computer analyses, Dr Stephan Lautenschlager from Bristol's School of Earth Sciences studied the muscle strain during jaw opening of three different theropod dinosaurs with different dietary habits. Theropods (from the Greek for "beast-footed") were a diverse group of two-legged dinosaurs that included the largest carnivores ever to walk the Earth.

Dr Lautenschlager said: "Theropod dinosaurs, such a Tyrannosaurus rex or Allosaurus, are often depicted with widely-opened jaws, presumably to emphasise their carnivorous nature. Yet, up to now, no studies have actually focused on the relation between jaw musculature, feeding style and the maximal possible jaw gape."

The research looked at Tyrannosaurus rex, a large-sized meat-eating theropod with a massively built skull and up to 15cm long teeth; Allosaurus fragilis, a more lightly built but predatory and meat-eating theropod; and Erlikosaurus andrewsi, a closely related but plant-eating member of the theropod family.

Dr Lautenschlager said: "All muscles, including those used for closing and opening the jaw, can only stretch a certain amount before they tear. This considerably limits how wide an animal can open its jaws and therefore how and on what it can feed."

In order to fully understand the relation between muscle strain and jaw gape, detailed computer models were created to simulate jaw opening and closing, while measuring the length changes in the digital muscles. The dinosaur species in the study were also compared to their living relatives, crocodiles and birds, for which muscle strain and maximal jaw gape are known.

The study found that the carnivorous Tyrannosaurus and Allosaurus were capable of a wide gape (up to 90 degrees), while the herbivorous Erlikosaurus was limited to small gape (around 45 degrees).

Between the two carnivores, results show that Tyrannosaurus could produce a sustained muscle (and, therefore, bite) force for a wide range of jaw angles, which would be necessary for biting through meat and skin and crushing bone.

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Allosaurus Lifestyle Insight From Bone Pathologies

New insights into the lifestyle of Allosaurus (Dinosauria: Theropoda) based on another specimen with multiple pathologies

Authors:

Foth et al

Abstract:

Adult large-bodied theropods are often found with numerous pathologies. A large, almost complete, probably adult Allosaurus specimen from the Howe Stephens Quarry, Morrison Formation (Late Kimmeridgian–Early Tithonian), Wyoming, shows multiple pathologies. Pathologic bones include the left dentary, two cervical vertebrae, one cervical and several dorsal ribs, the left scapula, the left humerus, right ischium, and two left pedal phalanges. These pathologies can be classified as follows: the fifth cervical vertebra, the scapula, several ribs and the ischium are traumatic, and a callus on the shaft of the left pedal phalanx II-2 is traumatic-infectious. Traumatically fractured elements exposed to frequent movement (e.g. the scapula and the ribs) show a tendency to develop pseudarthroses instead of callus healing. The pathologies in the lower jaw and a reduced flexor tubercle of the left pedal phalanx II-2 are most likely traumatic or developmental in origin. The pathologies on the fourth cervical are most likely developmental in origin or idiopathic, that on the left humerus is infectious or idiopathic, whereas left pedal phalanx IV-1 is classified as idiopathic. With exception of the ischium, all traumatic / traumatic-infectious pathologic elements show unambiguous evidences of healing, indicating that the respective pathologies did not cause the death of this individual. Alignment of the scapula and rib pathologies from the left side suggests that all may have been caused by a single traumatic event. The ischial fracture may have been fatal. The occurrence of multiple traumatic pathologies again underlines that large-bodied theropods experienced frequent injuries during life, indicating an active predatory lifestyle, and their survival perhaps supports a gregarious behavior for Allosaurus. Signs of infections are scarce and locally restricted, indicating a successful prevention of the spread of pathogens, as it is the case in extant reptiles (including birds).

THAGOMIZED! Fossil Evidence a Stegosaur Killed an Allosaur

Stegosaurs might be portrayed as lumbering plant eaters, but they were lethal fighters when necessary, according to paleontologists who have uncovered new evidence of a casualty of stegosaurian combat. The evidence is a fatal stab wound in the pubis bone of a predatory allosaur. The wound – in the conical shape of a stegosaur tail spike – would have required great dexterity to inflict and shows clear signs of having cut short the allosaur's life.

"A massive infection ate away a baseball-sized sector of the bone," reports Houston Museum of Natural Science paleontologist Robert Bakker and his colleagues, who present a poster on the discovery on Tuesday at the meeting of the Geological Society of America in Vancouver, B.C. "Probably this infection spread upwards into the soft tissue attached here, the thigh muscles and adjacent intestines and reproductive organs." The lack of any signs of healing strongly suggests the allosaur died from the infection.

Similar wounds are seen in rodeo cowboys or horses when they are gored by longhorns, Bakker said. And since large herbivores – like longhorn cattle, rhinos and buffalo – today defend themselves with horns, it's reasonable to assume spiky herbivorous dinos did the same. A big difference is that stegosaurs wielded their weapon on their tails rather than their heads. Skeletal evidence from fossil stegosaurs suggests their tails were more dextrous than most dinosaur tails.

"They have no locking joints, even in the tail," Bakker explained. "Most dinosaur tails get stiffer towards the end." But stegosaurs had massive muscles at the base of the tails, flexibility and fine muscle control all the way to the tail tip. "The joints of a stegosaur tail look like a monkey's tail. They were built for 3-dimensional combat."

In order to deliver the mortal wound to the allosaur, a stegosaur would have had to sweep its tail under the allosaur and twist the tail tip, because normally the spikes point outward and backward. That would have been well within the ability of a stegosaur, Bakker said.

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Siats meekorum: The New Giant Allosauroid Rivaling T. rex From Cenomanian Cretaceous Utah

The large carnivorous dinosaurs of the Mesozoic are inevitably among the most exciting of these extinct animals, but they are also among the hardest to study as they were rare. Anyone who has been on safari will recognise the issue – you can see hundreds of wildebeest or zebra for you set eyes on a lion, and similarly there may have been only one Tyrannosaurus knocking around for every few dozen Triceratops or other big herbivores. As a result, fossil of these are few and far between and reconstructing evolutionary or ecological patterns.

Enter the new dinosaur Siats meekerorum, named today in a paper in Nature Communications. The genus name Siats is from a legendary monster from the Ute tribe of Utah (where the dinosaur was found), with the species name meekerorum a tribute to the Meeker family who support palaeontological research. The fossil is rather incomplete and there’s little more than a partial pelvis and some vertebrae and part of the lower leg, but this is enough to confidently assign this to a new animal, and to work out to which evolutionary group it belongs. Siats is part of a group called the allosauroids, one of the major lineages of large carnivorous dinosaurs with some members becoming true giants that rivaled anything the tyrannosaurs (Tyrannosaurus and its relatives) could produce.

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The genus name sounds a lot like the Russian word for rabbit.   :)