Ornithomimus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Saurischia

Family: Ornithomimidae

Genus: Ornithomimus

Species: Ornithomimus velox

Introduction

Ornithomimus belonged to a small group of dinosaurs called ornithomimids that lived during the Late Cretaceous period. It was among the last of the dinosaurs. Ornithomimid means “bird mimic” or “bird imitator.” These dinosaurs looked similar to present-day ostriches and other large flightless birds. In fact, Ornithomimus and other ornithomimids are often called “ostrich dinosaurs.”

Some people are familiar with Ornithomimus because of its appearances in the television series Prehistoric Park and the motion pictures Fantasia and Planet of Dinosaurs. In Prehistoric Park, the dinosaur was portrayed as a flock animal that swept across the vast plains at great speeds. Whether Ornithomimus lived in herds had not been clearly determined by the third decade of the twenty-first century, though nesting sites of some dinosaurs containing multiple animals have been discovered. Paleontologists, however, do support the idea that Ornithomimus could run at speeds greater than 50 kilometers (30 mi) per hour, roughly the speed of a modern-day ostrich.

Other popular cultural portrayals showed Ornithomimus caring for chicks covered in fluffy feathers. Cladistic (a system used to classify dinosaurs according to their common ancestry and shared physical characteristics) studies show that the common ancestor of all coelurosaurs, of which ornithomimids are a subgroup, would have had simple protofeathers.

Classification

A member of the Ornithomimidae family, Ornithomimus was a small to medium-sized bipedal (two-legged) theropod (a largely carnivorous group) dinosaur. The fossil evidence and anatomical investigations, however, suggest to many paleontologists that Ornithomimus was omnivorous (plant and meat eating). The creature lived during the Late Cretaceous period (specifically about 99–66 million years ago). Ornithomimus possessed traits common to dinosaurs of the order Saurischia and suborder Theropoda. Fossil evidence for Ornithomimus and other ornithomimids date only from the Cretaceous period.

The Linnaean system is a rank-based system that separates animals into different hierarchical categories based on shared traits. However, scientists often disagree as to the most accurate method of classifying living organisms, including dinosaurs. In the Linnaean system, the more well-known Struthiomimus (ostrich mimic) and Ornithomimus share the same classifications but differentiate at the genus level.

Cladistic or phylogenetic classification is another system that paleontologists use to classify dinosaurs according to their common ancestry and shared physical characteristics. The cladistic method of classification seeks to draw relationships between species. Considered a somewhat fluid system, discoveries can sometimes cause differences in opinion between paleontologists based on how they read the data. In a cladistic analysis, Ornithomimus falls under the larger Coelurosauria group of dinosaurs, and then under the subgroup Maniraptoriformes, as they are generally viewed as the most recent common ancestor of modern-day birds.

After the initial discovery of Ornithomimus, many similar specimens were assigned as species within the genus. However, upon further analysis and as more was learned about ornithomimids, many of these were reassigned, in some cases to separate genera.

Anatomy

As the first ornithomimid described, Ornithomimus was the standard by which all other ornithomimids were classified. It exhibited the key anatomical features of the group, including a slim body, hollow bones, three-toed feet, long slender arms, long neck, and a birdlike skull. Unlike other ornithomimids, however, Ornithomimus had very slender, straight hand and foot claws. In addition, it had metacarpals and fingers that were the same lengths.

Paleontologists have placed Ornithomimus in an advanced group of ornithomimids (Ornithomimidae), which are characterized by long slender rear legs. These dinosaurs had longer metatarsals than contemporary dinosaurs of the same size, with one major exception—young tyrannosaurids. The legs of these advanced ostrich dinosaurs and tyrannosaurids are nearly identical. In both groups, the middle metatarsal has a special shock-absorbing shape, allowing them to run very fast on very slender feet. Additional studies of ostrich dinosaur feet suggest to many scientists that the ornithomimids may have been among the fastest dinosaurs during the Cretaceous period. Ornithomimus, with its head and neck lowered and tail raised, could form an efficient aerodynamic shape, allowing it to reach speeds approaching 65 kilometers (40 mi) per hour.

Intelligence

Ornithomimus had a relatively small, thin-boned skull that housed a large brain cavity. Compared with other dinosaurs, almost all ornithomimids had larger brain cavities relative to their body size. Although still debated, many paleontologists think that Ornithomimus supplemented its plant diet by preying on small mammals and insects. Consequently, Ornithomimus needed a sharp sense of smell and sight, quick reflexes, and highly developed hand-eye coordination. These, the scientists argue, would require a relatively large amount of gray matter.

Studies using computed tomography (CT) scans to create three-dimensional images of dinosaur brain cavities revealed that ornithomimids were at the top of dinosaur EQ ratings, with a 0.8 mark.

Reproduction and Population

Fossil evidence offers little information regarding population numbers, gender differences, and mating and reproduction habits for Ornithomimus. Paleontologists have analyzed dinosaur hip anatomy and concluded that females, regardless of species, had a wider frame for producing and hatching eggs. As such, it is likely that the female Ornithomimus had a wider hip structure than the male.

Based on the fossil evidence, scientists think that some dinosaurs laid their eggs in nests that were eventually abandoned, leaving the eggs vulnerable to predators. Some species’ nests and eggs were safely hidden or buried, while some evidence proves that other species’ eggs were covered and kept warm by parent dinosaurs. Of particular note is the discovery in 1993 of an Oviraptor (a genus of the theropod suborder to which Ornithomimus also belongs) fossil seated atop an egg clutch, which paleontologists view as the first direct evidence of parental care by dinosaurs. Scientists also have applied more detailed findings from other similar creatures in the same class to make assumptions about the reproductive system and nesting behavior of Ornithomimus. Until fossil evidence is found, these assumptions will provide some foundation for our understanding of Ornithomimus.

Diet

As with most ornithomimids, Ornithomimus did not have teeth. Its upper and lower jaws were long and thin and resembled needle-nose pliers. Paleontologists speculate that the jaws were covered in horn sheaths, which is seen on present-day birds. It is possible that this horn sheath may have formed sharp edges along the jaws allowing Ornithomimus to cut its food as well as chomp it. Consequently, there has been much speculation about precisely what and how Ornithomimus ate.

With its long arms and clawed fingers, Ornithomimus was certainly capable of hooking onto plant branches to pull toward its mouth. Using its sharp bill, Ornithomimus could then cut its food into manageable sizes. However, unlike some Mesozoic theropods, Ornithomimus did not have grasping thumbs. It would have been difficult for it to grab onto prey. Some scientists compare Ornithomimus's hands to those of modern-day tree sloths and anteaters, suggesting that it dug into burrows or insect nests to acquire food.

Because of its similarities to modern-day ostriches, Ornithomimus is often compared to them and their relatives (rheas and emus). Ostriches are omnivores, eating fruit, seeds, insects, plants, eggs, and small vertebrates. The anatomical similarities lead some paleontologists to argue that Ornithomimus was omnivorous as well, and perhaps even engaged in scavenging habits, feeding off the remains of kills from other meat-eating dinosaurs.

Behavior

A collection of evidence has suggested to some paleontologists that Ornithomimus probably lived in small groups. Scientists have unearthed ornithomimid bone beds in present-day Montana and Mongolia consisting of many individuals. The unearthed bone beds contained both adult and juvenile remains, suggesting that they lived in herds as protection from predators.

Living in a herd would have allowed the members to help one another find food and keep watch for predators. With its long neck, Ornithomimus could have held its head high, giving its large eyes a good view of the surrounding terrain. Because Ornithomimus lacked the sharp teeth of other contemporary predatory dinosaurs, it had to rely on its only defense—speed.

Habitat and Other Life Forms

The regions of North America in which Ornithomimus roamed contained a variety of dinosaurs, including theropods, ornithopods, pachycephalosaurs, ankylosaurs, and ceratopsids. Although Ornithomimus could outrun many larger predators, it would have avoided carnivores such as Albertosaurus, Tyrannosaurus, Daspletosaurus, and swift smaller predators like Chirostenotes and Troodon.

The Late Cretaceous period saw the emergence and development of flowering plants, called angiosperms, which would eventually dominate the flora. Conifers would have been abundant, along with ferns and other herbaceous plants. Angiosperms, along with gymnosperms (non-flowering, seed-bearing plants), would have offered Ornithomimus a major source of its diet. In addition, insect life rapidly diversified because of the development of angiosperms. Placental mammals, which includes most modern mammals (primates, whales, rodents), also emerged and developed in the Cretaceous period. Although not conclusive, many scientists think that Ornithomimus hunted and ate many of the small mammals that lived at the time, as well as supplemented its diet with a variety of insects.

Research

American dinosaur hunter George Cannon found the first fossils of what would later be identified as Ornithomimus. Cannon made his discovery in Jefferson County, Colorado, in 1889. At about the same time, American paleontologist John Bell Hatcher unearthed similar looking fossils in Montana. Othniel C. Marsh, a Yale University professor and leading paleontologist in the late nineteenth century, examined both sets of fossils and immediately noted unusual features. Unlike any other dinosaur known at the time, the metacarpal bones of the hand were the same length. In addition, the middle long bone of the foot (metatarsal) was pinched between the other two. This bone structure reminded Marsh of a bird's foot, so he named this new dinosaur Ornithomimus velox (swift bird mimic).

Despite strong physical and some feeding and behavioral similarities between Ornithomimus and modern ostriches, paleontologists stress that common ancestry is not the reason for the similarities. Rather, scientists point to a theory called convergent evolution as the probable cause. This theory tries to explain how two different, unrelated animals or animal groups may come to look the same because they have similar lifestyles. For instance, long necks and pointed beaks would be helpful to both ostriches and Ornithomimus in picking up small bits of food while walking. Also, slim, light bodies with long powerful legs would be needed to outrun predators across long stretches of open plains.

In 2012, Darla Zelenitsky, a paleontologist with the University of Calgary, announced that a study of three specimens of Ornithomimus that had been uncovered provided evidence for the long-held theory that the dinosaur had some extent of feathers. While one specimen had marks on its arm that were, as the result of this analysis, determined to be evidence of large, shafted feathers, the other two specimens had preserved feathers. According to the researchers, the fact that one of the specimens was a juvenile allowed them to compare age and feather development to make more hypotheses about what the changes in feather covering meant, including whether it was related to reproduction in any way. Three years later, another published paper summarized the findings of researchers regarding another Ornithomimus specimen that had feather impressions on its tail section as well as rarely preserved soft tissue.

Bibliography

Black, Riley. "Feathery Ostrich Mimics Enfluffle the Dinosaur Family Tree." Smithsonian Magazine, 25 Oct. 2012, www.smithsonianmag.com/science-nature/feathery-ostrich-mimics-enfluffle-the-dinosaur-family-tree-92942719/. Accessed 27 May 2020.

Carpenter, Kenneth. Eggs, Nests and Baby Dinosaurs: A Look at Dinosaur Reproduction. Indiana UP, 1999.

Currie, Philip J., and Kevin Padian, editors. Encyclopedia of Dinosaurs. Academic Press, 1997.

Evans, D. C. “New Evidence on Brain−Endocranial Cavity Relationships in Ornithischian Dinosaurs.” Acta Palaeontologica Polonica, vol. 50, no. 3, 2005, pp. 617–22.

Feduccia, Alan. The Origin and Evolution of Birds. 2nd ed., Yale UP, 1999.

Holtz, Thomas R. Dinosaurs. Random House, 2007.

Jerison, H. J. “Brain Evolution and Dinosaur Brains.” American Naturalist, vol. 103, 1969, pp. 575–88.

Marshall, Chris, editor. Dinosaurs of the World. Vol. 7, Marshall Cavendish, 1999. 11 vols.

Martin, Anthony J. Introduction to the Study of Dinosaurs. 2nd ed., Blackwell, 2006.

"Ornithomimus." Natural History Museum, www.nhm.ac.uk/discover/dino-directory/ornithomimus.html. Accessed 27 May 2020.

Parker, Steve. Dinosaurus: The Complete Guide to Dinosaurs. 2nd ed., Firefly Books, 2016.

Pascoe, Jennifer. "Prehistoric Plumage Patterns." Faculty of Science, University of Alberta, 28 Oct. 2015, www.ualberta.ca/science/news/2015/october/prehistoric-plumage-patterns.html. Accessed 27 May 2020.

"Siebel Dinosaur Complex." Museum of the Rockies, www.museumoftherockies.org/exhibitions/current-exhibitions/siebel-dinosaur-complex/. Accessed 27 May 2020.

Skelton, Peter W., editor. The Cretaceous World. Cambridge UP, 2003.

UC Museum of Paleontology. University of California, Berkeley, 2020, www.ucmp.berkeley.edu. Accessed 27 May 2020.