Ornitholestes

an artistic depiction of Ornitholestes with a nasal horn

Type Species: Ornitholestes hermanni

Classification: Dinosauria – Saurischia – Theropoda – Tetanurae – Coelurosauria – Tyrannoraptora – Maniraptoromorpha  

Time Period: Late Jurassic 

Location: United States 

Diet: Carnivore

The ‘bird robber’ Ornitholestes is known from a single partial skeleton with a badly crushed skull found in Wyoming at the turn of the 20th century (making it the first theropod discovering of the 1900s). Ornitholestes was a short-bodied theropod that grew to about eight feet in length and stood three feet tall at the hips. It had a relatively short neck with a slight sigmoidal (or S-shaped) curve. Its tail was long and whip-like and accounted for half its length. Its skull was proportionally smaller than that of most theropods, but it remained heavily built with a short snout and robust lower jaw. Its front teeth were conical-shaped with few serrations whereas the back teeth were recurved and sharply serrated like those of most theropods; the teeth didn’t extend as far back as its eyes, and neither tooth row spanned more than a third of the skull length. It’s likely that Ornitholestes used its front conical-shaped teeth for tearing flesh from its prey while the recurved back teeth were used to slice through the meat before swallowing. Ornitholestes’ forelimbs were relatively long, slightly under two-thirds the length of its hind legs. The first and second fingers of its three-clawed hands were the same size, but the claw bone was likely stunted. Ornitholestes was able to bend its forearm at an angle more acute than ninety degrees, which is characteristic of maniraptors but absent in more primitive theropods such as Coelophysis and Allosaurus. When Ornitholestes bent its elbow, its arms moved inwards towards its body; this would’ve increased in grasping ability. Though Ornitholestes is often portrayed as a fast, agile runner, its lower limb bones were relatively short. Some scientists believe that its innermost toe was larger than its other toes and suggest that it may have had a sickle claw similar to those of the dromaeosaurs. Many modern reconstructions depict Ornitholestes with a covering of feathers; this isn’t because feathers for this dinosaurs have been discovered but because they are present in so many of its kin that it’s thought by many that all coelurosaurs (to which Ornitholestes belongs) had some sort of rudimentary feathery covering. These feathers would’ve have been used for flight but for display, insulation, or for brooding eggs. Early depictions of Ornitholestes show it with a nasal horn akin to a chicken’s comb. When the specimen was discovered, it had an area of broken bone near the nostril that appeared to bulge upwards. Paleontologist Gregory S. Paul interpreted this as a nasal horn, but this interpretation has been rejected; the upward flare of crushed bone was likely due to post-mortem crushing of the skull. Below is a modern depiction of Ornitholestes - covered in fur, eating an early mammal, and lacking a nasal horn:

Debate swirls around Ornitholestes’ diet. When it was first discovered, it was argued that it utilized its grasping ability and the balancing power of its tail to catch birds. Though this theory had its detractors – a simultaneous theory was that its strange tooth design indicated a ‘transitional’ stage between a carnivorous and herbivorous diet – the original theory gained steam and became the dominant theory (hence the meaning of Ornitholestes’ name, ‘Bird Robber’). Over the decades, both the ‘bird robber’ and transitional diet theories have faded out of vogue. Most modern paleontologists believe that Ornitholestes preyed upon small terrestrial vertebrates such as mammals, lizards, frogs, and even dinosaur hatchlings. Another theory is that Ornitholestes used its front conical teeth to catch fish in the many streams, rivers, and lakes of the Morrison Formation, and some scientists  believe that Ornitholestes engaged in pack hunting behavior to bring down medium-sized prey such as the ornithopod Camptosaurus. Some argue that Ornitholestes and its slightly larger contemporary Coelurus lived side-by-side by utilizing niche partitioning in which Coelurus hunted at night and Ornitholestes hunted during the day.