Stenonychosaurus

Chapter • Meet the dinosaur

Overview

Stenonychosaurus was a small, long-legged predatory dinosaur roughly two to two and a half metres long, much of that length taken up by a stiffened tail. Body mass estimates cluster between about 20 and 50 kilograms, and an adult would have stood only about knee- to hip-high to a person. It belonged to the troodontids, and like other maniraptorans it was almost certainly feathered, with down over the body and long pennaceous feathers on the arms and tail. The skull was slender and lightly built with remarkably large eye sockets, and each foot carried an enlarged, retractable second-toe claw — similar in principle to a dromaeosaur's sickle claw, but less robust. The huge sclerotic rings preserved in the eyes suggest excellent low-light vision, and studies of eye proportions point to a nocturnal or crepuscular animal. The braincase is large relative to body size, giving Stenonychosaurus one of the highest brain-to-body ratios of any non-avian dinosaur, and the ear region hints at good directional hearing rather like an owl's. That makes it one of the most bird-like dinosaurs known — though relative brain size is only a crude proxy, and calling the animal 'intelligent' in a human sense goes well beyond the evidence. Its teeth are small, laterally compressed and bear coarse, hooked serrations quite unlike the fine denticles of a committed meat-eater. Many researchers read this as evidence for an omnivorous diet of insects, lizards, small mammals, eggs and possibly plant material and fruit, rather than specialised predation on large prey. The long, slender hind limbs indicate a fast, agile runner well suited to open floodplains. The species was named in 1932 by Charles M. Sternberg on the basis of a foot, a hand and several tail vertebrae collected in 1928 from the Dinosaur Park Formation of Alberta, Canada. Dale Russell published a fuller description in 1969, and it was Stenonychosaurus that inspired his famous 1982 'dinosauroid' model, built with Ron Séguin. For decades the species was treated as a synonym of Troodon formosus, but in 2017 Aaron van der Reest and Philip Currie argued that Troodon formosus rests on inadequate material, and Stenonychosaurus inequalis was reinstated as a valid name.

Chapter • Where it lived

Habitat

Stenonychosaurus lived about 76.5–75 million years ago, during the Campanian stage of the Late Cretaceous. All secure fossils come from the Dinosaur Park Formation of southern Alberta, Canada, above all from Dinosaur Provincial Park. The setting was a humid, subtropical coastal plain on the western shore of the Western Interior Seaway, crossed by meandering rivers, swamps and patches of forest with conifers, ferns and early flowering plants. Stenonychosaurus shared this landscape with hadrosaurs such as Corythosaurus, ceratopsians such as Centrosaurus and Chasmosaurus, and large predators such as Gorgosaurus.

Chapter • Family life

Breeding

Chapter • Wild behavior

Behavior & Ecology

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Chapter • Scientific place

Taxonomy