Fossils

Several specimens of dinosaurs and other reptiles have been found in Kessler’s quarry on the east side of Four Mile Creek. The fossil remains provide us with another window into the ancient Jurassic environments, which have been interpreted as rivers and streams with periods of flood and drought, and ponds or lakes.

Dinosaurs

Stegosaurus stenops

Stegosaurs are plated herbivorous dinosaurs with two rows of plates down the spine and tail, which ends with four large spikes positioned at the posterior end of the tail. Stegosaurus had 17 bony plates, but the arrangement of these plates was unknown until 1992 when Kenneth Carpenter and Bryan Small  of the Denver Museum of Nature and Science discovered another Stegosaurus skeleton located on the eastern side of Garden Park near the oil flats. The skeleton, known as “Spike” was articulated and showed the arrangement of the plates, which ran along the back and tail in two rows with the plates aligned in alternate arrangement.

Stegosaurus grew up to 24 feet long, about 7 feet tall at the hips, and weighed about 5000 pounds. Its skull was long, pointed, and narrow with a toothless beak and small cheek teeth, which they used to eat low growing plants. Its head was carried close to the ground, probably no more than 3 feet (1 m) high. Stegosaurs lived during the Late Jurassic period, and while many of the skeletons have been found in river or stream channel deposits, they may have lived in the flood plains or farther away from the water source.

Kessler’s Stegosaurus, which was found by high school students, later became the State Fossil of Colorado in 1982 at the urging of elementary school students from Denver. It is on display at the Denver Museum of Nature and Science.

Allosaurus sp.

The most common of all meat-eaters, or theropods, found in the Garden Park Fossil Area is Allosaurus. The first described Allosaurus fragilis was named by Othneil Charles Marsh in 1877 from a specimen found in the Marsh-Felch quarry . The bones and shed teeth of Allosaurus are known from almost every dinosaur quarry in Garden Park. Allosaurus grew to approximately 30 feet long, 6-8 feet tall at the hips, and weighed about three tons.

The skull of Allosaurus is about two feet long and contains very sharp teeth, which are long and blade-like with serrated edges. These teeth are useful for biting and cutting flesh, and this is how scientists know Allosaurus was a meat-eater. The skull also displays two lachrymal crests that are positioned above and in front of the eyes. It is thought that these represented some type of gland.  Other theories suggest Allosaurus also used these crests for display whether to attract mates or for species recognition. 

The arms of Allosaurus are short, about three feet long, but they were very muscular and strong. Unlike Tyrannosaurus rex, Allosaurus has three-fingered hands with raptor-like claws for grasping their prey. The feet also have sharp claws for holding and killing prey.

Other Dinosaurs 

Fragments of Ornithopoda have also been found in the quarry. Ornithopods are bipedal plant eaters, although it has been suggested by some that large Ornithopods may have been quadrapedal; that is they used their forelimbs to aid with walking or resting, and bipedal when they ran. Dryosaurus, Othnelia and Camptosaurus are just a few examples of Ornithopods.¹  Ornithopods are often found in numbers, suggesting that they were herders and therefore similar to herding animals today, such as antelope and deer. Most complete skeletons are found from Como Bluffs, Wyoming and Dinosaur National Monument.

Other Reptiles

In addition to dinosaurs, turtle and crocodile fragments are common vertebrate fossils in the Morrison Formation and these have also been found in Garden Park.

The turtle, Glyptops plicatulus has been identified from fragments. Glyptops shells have features that scientists use to determine the species, and in the case of Glyptops plicatulus those features used are raised ridges and tubercles. Like their modern counterparts, Late Jurassic Freshwater turtles lived in and near ponds, lakes, and rivers and their fossils are commonly found in wet environment quarries in the Morrison Formation. It must be noted that there are no currently known dry-land tortoises in the formation.²

The Crocodiles are represented by teeth and bone fragments of Goniopholis. Goniopholis is widely distributed and occurs throughout the Morrison Formation and two species have been named from the Garden Park area based on the discovery of different skulls.³