Struthiomimus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Saurischia

Family: Ornithomimidae

Genus: Struthiomimus

Species: Struthiomimus altus

Introduction

Struthiomimus was a medium-sized, likely omnivorous dinosaur that lived in the open plains and scrub of Late Cretaceous Canada. The discovery of the species and analysis of its “birdlike” characteristics contributed to the ongoing debate about the relationship of dinosaurs to birds.

In the Triassic and Early Jurassic periods, the continents were joined into a single landmass, known as Pangaea. The supercontinent split during the Jurassic, resulting in two supercontinents, Gondwana in the south and Laurasia in the north. By the Late Cretaceous, further tectonic activity continued to split the supercontinents, and they began to resemble modern formations.

Struthiomimus represented a successful group of dinosaurs thought to be similar to modern flightless birds, like the ostrich and emu, and was named for its anatomical similarity to these animals. Species similar to Struthiomimus were found throughout Laurasia, having evolved from an ancestor that arrived in Laurasia during the Jurassic period.

Classification

Scientists use two major classification methods to place organisms into different categories. Linnaean taxonomy creates categories based on overall physical similarity, while an alternate method, called “cladistics,” creates groups of organisms called “clades” based on the evolutionary relationships between species.

According to Linnaean taxonomy, Struthiomimus was placed into the order Saurischia, meaning “lizard hipped,” and into the suborder Theropoda, an order that includes a variety of bipedal predatory dinosaurs united by modifications of the skull, teeth, and feet (though, in the early twenty-first century, scientists debated the Saurischia and Ornithiscia classification division, which had long been in use). Within this group, Struthiomimus was placed in the family Ornithomimidae, a group of dinosaurs classified according to their superficial anatomical similarity to modern birds.

Using cladistic analysis, Struthiomimus was placed in the clade and suborder Theropoda, the members of which share modifications of the foot, and further into the Ornithomimiformes, a group of bird-like dinosaurs characterized by adaptations of the legs to increase speed and reduced teeth. Within this group, Struthiomimus was placed into the Ornithomimidae.

Struthiomimus and the closely related species Gallimimus were common species in Late Cretaceous North America. While members of the group appear closely related both through cladistic analysis and Linnaean taxonomy, further revisions are necessary to see how the ornithomimids relate to close theropod groups.

Anatomy

Struthiomimus was a long, lean dinosaur with a light build and long legs. The adult animal could reach lengths of up to 4 meters (13 ft) and stood nearly 1.5 meters (5 ft) at the hips. The adult animal could weigh more than 300 kilograms (660 lbs).

Struthiomimus had a long neck, which was almost half as long as the body itself, with a small and lightly built head. The animal had large eyes and a thin, toothless jaw. Struthiomimus had smaller forelimbs, ending in three long, clawed fingers. The inner finger was slightly longer than the other two. The feet ended in three-clawed toes, thicker and more heavily built than those of the hands. The animal also had a long tail, which may have been used as a balance while running.

Intelligence

Struthiomimus was a member of the ornithomimidae, a family of dinosaurs generally ranked in the 0.5 to 1.5 EQ range, similar to some smaller birds and large reptiles. Though the dinosaur's appearance resembled the modern ostrich, it may not have been as intelligent.

Reproduction and Population

Paleontologists believe that some related theropods in the oviraptorosaurid group laid eggs and may have brooded nests of eggs like modern ground nesting birds. Struthiomimus may also have brooded its eggs, though intact nests have not been found.

Paleontologists have insufficient evidence to estimate population size or density for Struthiomimus or for suggesting anything about its reproductive behavior. Struthiomimus is a representative of a successful group and may therefore have been common in North America. As of the beginning of the third decade of the twenty-first century, the species was known from only a few specimens.

Diet

Paleontologists have concluded that Struthiomimus was most likely an omnivore or herbivore. It possessed a flat beak that was most likely used to crop leaves and stems of plants. Some have suggested that Struthiomimus may have lived close to lakes and rivers and may have fed by filtering small animals from the water.

Though Struthiomimus did not possess an optimal beak for predation, it would probably have been able to eat small animals, fish, and insects with its beak. Paleontologists are still researching Struthiomimus fossils to learn more about its behavior.

Behavior

Some paleontologists have suggested that the body structure of Struthiomimus enhanced its speed and agility. The dinosaur's long legs suggest that it may have been capable of speeds up to 50 kilometers (30 mi ) per hour. Some paleontologists have suggested that its long legs evolved for a different purpose, such as walking among tall plants or wading in water.

There is little evidence to suggest that Struthiomimus engaged in any sort of social behavior. Some closely related fossils have been found in groups, leading some paleontologists to suggest that Struthiomimus gathered in social groups for various purposes. If Struthiomimus displayed similar behavior, it may also have occasionally gathered in groups.

Habitat and Other Life Forms

During the Cretaceous period, central North America was covered in a shallow inland sea surrounded by swamps, lakes, and scattered forests. Elsewhere there were mountains, open plains, and arid scrub. Most of the plants in the late Cretaceous were gymnosperms, seed-bearing plants such as conifers and cycads, as well as ferns. In addition, the first angiosperms, or flowering plants, were diversifying during this time.

Canada was home to a wide variety of small reptiles, amphibians, mammals, and birds in the Cretaceous, but the skies were dominated by flying reptiles called pterosaurs, which had existed since the Triassic. There were numerous dinosaur species in Cretaceous Canada, including several varieties of predatory theropods like Albertosaurus, a smaller relative of Tyrannosaurus. There were also dromaeosaurs, or “raptors,” like Dromeosaurus, which probably preyed on herbivores like Struthiomimus. The ceratopsians, or “horned dinosaurs” such as Centrosaurus and Chasmosaurus, were among the most successful lineages of herbivores in the Cretaceous, spreading across Laurasia. Another dominant herbivore group was the hadrosaurs, or “duck-billed” dinosaurs, such as Edmontosaurus and Corythosaurus, distantly related to the ceratopsians but adapted for semi-bipedal movement.

Research

Struthiomimus was discovered by pioneering paleontologist Othniel Marsh in 1892. The species was reclassified in the early 1900s after paleontologist Henry Osborn discovered specimens of the type species in a dig site near Alberta, Canada.

Since the genus was reclassified, further research has focused on trying to determine finer points about the anatomy of Struthiomimus. Researchers have conducted measurements of the legs in an effort to calculate speed and movement of the dinosaur. Other researchers have attempted to focus on its feeding apparatus to determine diet.

As fossil analysis continued, it was argued in a 2016 paper that a partial skeleton that had been recovered in the 1930s near Canada's Dinosaur Provincial Park and described as a specimen of Struthiomimus altus was different enough, based on details such as its skull, foot, and size, from the genus to be placed under a new one; it was subsequently suggested that it be renamed Rativates evadens. Additionally, because of its relation to Ornithomimus, it was believed, after it was announced in 2012 that three specimens of Ornithomimus had been found to have evidence of feathers, that other ornithomimosaurs, including Struthiomimus, likely had some feathers as well.

Bibliography

Briggs, Derek E. G., and Peter R. Crowther. Paleobiology II. Wiley-Blackwell, 2001.

Buffetaut, Eric, et al. “An Early ‘Ostrich Dinosaur’ (Theropoda: Ornithomimosauria) from the Early Cretaceous Sao Khua Formation of NE Thailand.” Geological Society, London, Special Publications, vol. 315, 2009, pp. 229–43.

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

Chinsamay-Turan, Anusuya. Microstructure of Dinosaur Bone: Deciphering Biology with Fine-Scale Techniques. Johns Hopkins UP, 2005.

Farlow, James O., et al. “Theropod Locomotion.” Integrative and Comparative Biology, vol. 40, 2000, pp. 640–63.

Fastovsky, David E., and David B. Weishampel. Dinosaurs: A Concise Natural History. 3rd ed., Cambridge UP, 2016.

"Fossil Fuzz Gives 'Ostrich Mimic' Dinosaur a New Look." National Geographic, 4 Nov. 2015, www.nationalgeographic.com/science/phenomena/2015/11/04/fossil-fuzz-gives-ostrich-mimic-dinosaur-a-new-look/. Accessed 22 May 2020.

Horner, Jack, and James Gorman. How to Build a Dinosaur: Extinction Doesn’t Have to Be Forever. Dutton, 2009.

Horner, John R., and Edwin Dobb. Dinosaur Lives: Unearthing an Evolutionary Saga. Mariner Books, 1998.

"Late Cretaceous Dinosaur Resembled Modern Ostrich." Cleveland Museum of Natural History, 21 Sept. 2016, www.cmnh.org/rativates. Accessed 22 May 2020.

Long, John. Feathered Dinosaurs: The Origin of Birds. Oxford UP, 2008.

Lucas, Spencer G. Dinosaurs: The Textbook. 6th ed., Columbia UP, 2016.

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

“Ornithomimidae.” UC Museum of Paleontology, www.ucmp.berkeley.edu/diapsids/saurischia/ornithomimidae.html. Accessed Feb. 2010.

Paul, Gregory S. Dragons of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Johns Hopkins UP, 2002.

“Theropod Dinosaurs.” UC Museum of Paleontology, University of California, Berkeley, ucmp.berkeley.edu/diapsids/saurischia/theropoda.html. Accessed Feb. 2010.

Weishampel, David B., et al., editors. The Dinosauria. 2nd ed., U of California P, 2004.