Ornithomimidae
Fast, ostrich-like theropods with toothless beaks and feathered hides.
Ornithomimidae were theropod dinosaurs that looked a lot like ostriches. They lived mainly during the Late Cretaceous in Laurasia (modern Asia and North America). These dinosaurs were built for running and ate either plants or a mix of plants and small animals. Their heads were small, with big eyes and toothless beaks, perched on long, slender necks. The arms were long and thin, ending in strong claws, while the legs were long and powerful, with a long foot and short, sturdy toes capped by hooff-like claws—making them likely among the fastest dinosaurs. Like many coelurosaurs, they had feathers instead of scales.
Comparisons of their scleral rings with those of modern birds and reptiles suggest ornithomimids may have been cathemeral, active in short bursts throughout the day. Not much is known about their reproduction, but fossils of neonates—either embryos or hatchlings—have been found. They were preyed on by other theropods at times; one tail vertebra shows tooth drag marks from a dromaeosaurid (Saurornitholestes). A toe bone from an unidentified ornithomimid has a “mushroomed” end, a sign of disease or injury.
Most of their calories probably came from plants. Many ornithomimosaurs, including primitive species, have gastroliths in their stomachs, a trait common in herbivores. Henry Fairfield Osborn thought their long, sloth-like arms were used to pull down branches, an idea supported by later studies of their hook-like hands. They were also the most common small dinosaurs in North America, which fits the pattern of herbivores outnumbering carnivores. Still, they might have been omnivores, eating both plants and small animals.
Their diet has been debated. In 2001, Norell and colleagues reported two fossil skulls—one from Gallimimus and one from Ornithomimus—with preserved soft tissue. Both had keratinous beaks with vertical grooves on the upper mandible, similar to the lamellae in ducks that strain small food items like plants, forams, mollusks, and ostracods from water. The authors noted ornithomimids were common in wet environments and rare in dry ones, hinting they may have filter-fed. Primitive ornithomimids had teeth, but derived forms were toothless and probably couldn’t eat large animals.
Quick Facts
- Taxon
- Ornithomimidae
- Type Species
- Ornithomimus velox
- Type Species Authority
- Marsh, 1890
Facts from the source article.
Lore & Background
Ornithomimidae was named by O.C. Marsh in 1890, originally classified as ornithopods, but Marsh realized two years later they were theropods. In the 20th century, Friedrich von Huene placed them in Coelurosauria, and Rinchen Barsbold placed them in their own infraorder, Ornithomimosauria, in 1976. Today, Ornithomimosauria is regarded as a clade within Coelurosauria. Comparisons between the scleral rings of the genus Ornithomimus and modern birds and reptiles indicate they may have been cathemeral, active throughout the day at short intervals. Little is known of their reproduction, but neonate fossils have been found representing embryos or hatchlings. They appear to have been preyed upon by other theropods, as evidenced by an ornithomimid tail vertebra with tooth drag marks attributed to a dromaeosaurid (Saurornitholestes). One specimen shows a pathologic toe bone with a mushroomed end.
Reader's Guide
Ornithomimidae holds significance as a family of fast, ostrich-like theropods that were among the most common small dinosaurs in North America. Their feeding habits have been controversial: Henry Fairfield Osborn suggested their long arms were used to pull down branches, and later studies found gastroliths consistent with herbivory. In 2001, Norell et al. reported fossil skulls with keratinous beaks bearing vertical grooves reminiscent of duck lamellae, suggesting filter feeding in mesic environments. However, Barrett (2005) questioned this, noting similar ridges in herbivorous turtles and hadrosaurids, and calculated that omnivory was more likely. The family's classification evolved from ornithopods to theropods, and eventually to a distinct clade within Coelurosauria. Their abundance and adaptations highlight the diversity of theropod diets and ecologies in the Cretaceous.
Did You Know?
- Ornithomimids were probably among the fastest of all dinosaurs.
- Their hide was feathered rather than scaly, like many other coelurosaurs.
- One ornithomimid tail vertebra preserves tooth drag marks attributed to a dromaeosaurid (Saurornitholestes).
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