Saturday, 12 December 2009

It is possible to draw on microsoft paint with a mouse; the life and times of Allosaurus the flesh grazer

Above: Reconstruction of Allosaurus, by the author. Done on microsoft paint.

Allosaurus has probably been the most influential dinosaur after Tyrannosaurus, appearing in movies and documentaries since its discovery in 1869. It lived 150 million years ago in the late Jurassic period. In North America it was the most abundant meat eating dinosaur; taking up 75% of the Therapod fossils in the Morrison formation.

Allosaurus on average grew up to 8.5 meters in length, and weighed about 2 tons. This predator was clearly a generalist, able to attack almost any animal in its ecosystem. Fossils of long necked dinosaurs like Camarasaurus have been found with deep scars, where the Allosaurus's claws and teeth ripped into the flesh of the animal as it fed.
Allosaurus had long gripping arms with meat hook claws to grab small prey. The jaw was relatively weak for a dinosaur of its size and probably had a bite force similar to that of a lion today. Allosaurus did have a powerful skull, that was good at withstanding pressure from the upper jaw, along with an abnormally large and powerful neck.

This suggests that even with a weak bite Allosaurus was somehow still exerting pressure on its upper jaw. Using its ability to open its jaw incredibly wide, it used its powerful neck muscles to drive the upper jaw into the flesh of its prey, dragging the teeth across the hide of the animal and tearing off huge chunks of flesh.

Perhaps Allosaurus was a flesh grazer, running up to a gigantic herbivore, gripping onto it with its meat hook claws. The Allosaurus may then have torn away a chunk of flesh, running away before the prey can defend itself. Then the chunk of meat would be taken to safety where the Allosaurus could consume it in peace.

This method leaves the prey animal badly injured, but alive, soon able to regrow and the flesh wound. By keeping the prey population alive Allosaurus could have existed in huge and dense numbers, only taking what it needed from its victim, leaving it alive for their next meeting, or to breed and provide new feeding opportunities for the predators.
Today cookie cutter sharks attack whales and dolphins hundreds and thousands of times their size. These tiny sharks do not kill their prey, but take a chunk and swim off. The advantages of this method of predation is clear when you do the math: If cookie cutter sharks were true predators, every whale they attacked would be killed and eaten.

By flesh grazing the predator keeps the prey alive and their populations steady, ensuring a constant and even supply of food that will hopefully never die out because of over hunting. In effect flesh grazing is a way that predators can exist in large numbers, but still maintain a sustainable population of prey animals in their habitat.

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