Allosaurus fragilis pen illustration. The feathers are completely speculative; added to give it more visual interest.
When I think of the Jurassic, one of the first dinosaurs that comes to mind is Allosaurus, an apex predator that inhabited North America and Europe during the Late Jurassic period. Allosaurus sported a mouth filled with dozens of serrated teeth, powerful arms with curved claws, and a pair of impressive horns atop it's head.
The name Allosaurus was coined by American paleontologist Othniel Charles Marsh in 1877. The name means “different lizard." It was named this because its vertebrae were unlike that of any other dinosaur known at the time. Allosaurus also had five teeth in its premaxillas (the bones that make up the tip of the snout), whereas most theropod dinosaurs have four. These teeth shed constantly, continually being replaced by new teeth. The teeth of Allosaurus were serrated like knives, and would have been perfect for shredding through flesh. But the teeth weren't the only freaky feature of Allosaurus' jaws. A 2015 study regarding dinosaur jaw musculature showed that Allosaurus was likely able to open it's jaws between 79 and 92 degrees! That is more than a right angle! Ok, now THAT is scary. Of course, this was it's maximum gape, it's optimal gape was probably around 28 degrees.
Another thing that makes Allosaurus stand out from the crowd is a pair of horns that adorned its skull. These horns were likely covered in a keratin sheath. They may have served as sunshades to protect the eyes from those Jurassic rays, or possibly they were display features, or used in combat against other Allosaurus.
The genus Allosaurus contains numerous species, but only a few of these are considered to be valid, A. fragilis (the type species), A. europaeus, and A. jimmadseni. The most famous Allosaurus specimen is an A. jimmadseni, nicknamed “Big Al” that was discovered in Wyoming in 1991. The specimen was 95% complete, and offered tantalizing clues about its life, including that it probably died from a terrible infection in its foot (it appears the infection was not isolated to the foot, however). In 1996 the same team that discovered “Big Al” discovered another well-preserved A. jimmadseni specimen, which was dubbed “Big Al II”. A Walking With Dinosaurs (BBC) two-part television special called The Ballad of Big Al was aired in 2000, and depicted the life of Big Al from its birth to its death. I haven't watched The Ballad of Big Al since I was a little kid! I was probably heart broken when Big Al died. Planet Dinosaur was on the other day; the Allosaurus from that show is pretty cool.
Pencil drawing of Allosaurus jimmadseni. Based on the specimen "Big Al II", shown in a very threatening pose.