New Study Proposes Allosaurus Was a Dexterous Hunter Feeding More Like an Extant Falcon
There has been a great deal of research in recent years into the feeding methodologies of big theropod dinosaurs, with much of the work centred on the Allosaurus genus. The relative abundance of good skull material associated with this genus, especially material from the Morrison Formation of the western United States, has permitted a number of detailed studies into allosaurid feeding behaviours. A team of researchers at Ohio University have published a new paper which suggests that Allosaurus (A. fragilis) had a more delicate method of de-fleshing a carcase, feeding in a similar way to a modern-day falcon.
Allosaurus fragilis was one of the apex predators of the Late Jurassic of North America. Some specimens measure over eleven metres in length and scientists have estimated that this predator may have weighed as much as 2.5 tonnes. However, studies of the skull and jaw suggest that this dinosaur had a much weaker bite than comparable sized tyrannosaurids.
Allosaurus Head Close Up
Picture credit: Everything Dinosaur
The famous “Big Al” Allosaurus skeleton, representing a sub-adult individual which was found in Wyoming back in 1991, has been extensively studied. Three-dimensional studies show that the allosaur skull was extremely good at transmitting forces along its length, although it was much lighter than the massive skull of a Tyrannosaurus rex. The Allosaurus skull was very strong, but analysis of the bite force that this carnivore could generate revealed a surprise. Tests showed that Allosaurus had a bit force not much stronger than an extant leopard, an animal just one tenth the size. Allosaurus was not capable of crushing bone, it was not able to dismember prey through sheer force generated from its jaws.
Work by the Ohio University research team builds upon this earlier evidence, one of the authors of the scientific paper published in Palaeontologia Electronica, palaeontologist Eric Snively commented:
“Apparently one size doesn’t fit all when it comes to dinosaur feeding styles. Many people think of Allosaurus as a smaller and earlier version of T. rex, but our engineering analyses show that they were very different predators.”
The research team included mechanical engineers, palaeontologists and experts in computer model analysis. Using three-dimensional CT scans of allosaur skull material and cervical vertebrae, the scientists carefully reconstructed the muscle and tissues on the head and neck of this dinosaur from the bones outwards. Using a technique known as “multibody dynamics”, from robotics, the researchers ran a number of sophisticated simulations that explored how Allosaurus may have used it head and neck to attack prey and then to feed.
The Feeding Behaviours of Allosaurus Investigated
Picture credit: Everything Dinosaur
John Cotton, one of the mechanical engineers involved with the study project stated:
“The engineering approach combines all the biological data—things like where the muscle forces attach and where the joints stop motion—into a single model. We can then simulate the physics and predict what Allosaurus was actually capable of doing.”
A key finding of this study was an unusually placed neck muscle called the longissimus capitis superficialis. In most meat-eating theorpods, for instance the tyrannosaurids, this muscle passed from the side of the neck to a bony wing on the outer back corners of the skull. In the analysis of the allosaur skull material it was discovered that the longissimus capitis superficialis was attached much lower on the skull.
This muscle acts like a jockey pulling on the reins of a horse’s bridle. If the muscle on one side contracts, it would turn the head in that direction, if the muscles on both sides pull, the head is pulled straight back. The study into the skull dynamics and the effect of this lower position in the skull of this specific muscle suggests that this dinosaur could drive its head down into prey, hold it there and then pull the head straight back by flexing its neck and body. In this way, flesh would be ripped from any carcase, especially if the hind feet could be placed on the corpse to provide more leverage.
A spokesperson for the research team, described the potential feeding mechanism of Allosaurus like the mechanics of a backhoe that rips into the ground. The same method of feeding is seen in small birds of prey such as falcons and kestrels. Alligators for example, tend to grab anything within striking distance with their mouths and have a very different feeding mechanism when compared to that of an allosaurid.
This approach using both engineering, anatomy and computer analysis also revealed that the heavy head of a tyrannosaurid would have made it difficult for this type of dinosaur to speed up or slow down its head movements or to change its course as it swung its head around. The light, highly pneumatised head of the allosaur probably meant that Allosaurus could turn its head much more rapidly than an equivalent sized tyrannosaur.
Allosaurus Feeding Compared to a Modern-day Kestrel
Picture credit: Witmer Lab (Ohio University)
A modern-day kestrel (a small falcon) is perched atop the skull of the Jurassic predatory dinosaur Allosaurus. A key finding of the new study is that Allosaurus had a feeding style similar to falcons. In both cases, tearing flesh from carcasses involved grasping meat with the jaws and tugging back and up with the neck and body.
Having a lot of mass sitting far away from the axis of head turning, as in T. rex, increases rotational inertia, whereas having a lighter head, as in Allosaurus, decreases rotational inertia, the researchers explained. An ice skater spins faster and faster as she tucks her arms and legs into her body, decreasing her rotational inertia as the mass of her limbs moves closer to the axis of spinning.
Dr Snively explained:
“Allosaurus, with its lighter head and neck, was like a skater who starts spinning with her arms tucked in. Whereas T. rex, with its massive head and neck and heavy teeth out front, was more like the skater with her arms fully extended … and holding bowling balls in her hands. She and the T. rex need a lot more muscle force to get going.”
Earlier studies (Emily Rayfield, University of Cambridge etc.), proposed that allosaurids may have used their head like an axe. Strong neck muscles to ram the upper jaw teeth into the body of its victim. Every impact on the body of the prey animal would have resulted in the allosaur’s serrated teeth tearing through muscle leading to substantial blood loss and trauma. This new research builds on the earlier data and supports the idea that the head of Allosaurus was light but strong and it could move its head and neck around quite quickly and with considerable control. It may not have had the strength of a tyrannosaur but the proposed de-fleshing feeding technique and method of dispatching prey suggests that this dinosaur was a highly successful apex predator.
It seems that not all the theropods had the same feeding styles or methodologies. This research supports the theory that Allosaurus fed by gripping with its jaws and tugging upwards and backwards with its strong neck muscles – a sort of “gripper and a tugger” feeding method.