A new kind of carnivorous dinosaur is announced by the Natural History Museum of Utah, newly designated dinosaur "Allosaurus jimmadseni". Discovered in the 1990s at the Dinosaur National Monument in northeastern Utah, and it lived in the flood plains in 157-152 million years ago (MYA) during the Later Jurassic Period. This is one of the oldest allosaurids found, compared to the Allosaurus fragilis.
Most allosaurids vary from small to larger frames, walked on two legs specifically and existed in the Jurassic and Triassic periods. It has several features that were very different, one is a low-set facial crest on the face to the nose, the back of the skull is narrow with one flat surface the extends to the skull's bottom beneath the eyes. These structures made its skull less durable, the vision was not as good as the younger Allosaurus fragilis. One of the dominant carnivores that ruled in these eras, they hunted large herbivores too. As many as 12 species if Allosaur were found in the Morrison Formation of North America.
Only one allosaur species was thought to exist, but Allosaurus jimmadseni and Allosaurus fragilis were present in North America, though one evolved earlier by 5 million years earlier. The Fragilis came later with a heavier skull than the jimmadseni, which suggests different feeding patterns of the two relative allosaurids. This existence offers tantalizing speculation by scientists inferencing from clues left in the fossil record.
Finding a new allosaurid from a species studied for over a century and a half is one leap forward for scientists. The difference between the Allosaurus jimmadseni and Allosaurus fragilis highlights what is not known, and gives ideas on how earlier family members evolved. Finding more fossils in the Jurassic bedrock of the West of America.
A headless skeleton of the Allosaurus jimmadseni, was found by George Engelmann (University of Nebraska) in a dig at the Dinosaur National Monument in the 1990s. Later in 1996, the skull was discovered with a Geiger counter by Ramal Jones (University of Utah). Locating and excavating the head leads to the examination of a whole fossil.
One of the skeletons (Big Al) was an Allosaurus jimmadseni, found in Wyoming in 1991 and a part of the collections of the Museum of the Rockies in Bozeman, Montana. It was a mistake, thinking it was a to Allosaurus fragilis until corrections were confirmed with more studies. During the last 30 years, more data and information was discovered about the new allosaurid. Another one was found and called" Big Al Two" in the Saurier Museum Aathal in Switzerland.
When the Allosaurus jimmadseni was alive, its home was in the semi-arid Morrison Formation floodplains, in interior western America. Rock strata in this period of the Morrison Formation contained different fossils, from the more recent layer that had Stegosaurs and Diplodocus skeletons. Allosaurus jimmadseni resided in the locations of Wyoming, Utah, and Colorado in the USA.
Discovering the Allosaurus jimmadseni and the Allosaurus fragilis shows how evolution worked and changed their features and characteristics. A comparison of fossils shows the differences as the environment shaped these dinosaurs. When the time came, the Allosaurus fragilis became the top hunter with better eyesight. Lastly, the crests on the face were abandoned as it was not effective in giving better vision to the carnivore.
