Hesperonychus
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Hesperonychus Temporal range: Late Cretaceous, 76.5 Ma |
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| Life restoration | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Order: | Saurischia |
| Suborder: | Theropoda |
| Family: | †Dromaeosauridae |
| Clade: | †Microraptoria |
| Genus: |
†Hesperonychus Longrich & Currie, 2009 |
| Species: | †H. elizabethae |
| Binomial name | |
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Hesperonychus elizabethae Longrich & Currie, 2009 |
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Hesperonychus (meaning "western claw") was a genus of small, carnivorous dromaeosaurid dinosaur. There is one described species, Hesperonychus elizabethae; the type species was named in honor of the woman who collected it in 1982. It is known from fossils recovered from the lowermost strata of the Dinosaur Park Formation of Alberta, dating to the late Cretaceous Period (Campanian stage) about 76.5 million years ago).
Hesperonychus is known from one partial pelvic girdle, holotype specimen UALVP 48778, collected by Dr. Elizabeth Nicholls in Dinosaur Provincial Park in 1982. The fossil remained undescribed, however, until Nick Longrich and Phil Currie published on it in 2009. A number of very small toe bones, including "sickle claws", in the collection of the Royal Tyrrell Museum may also belong to Hesperonychus. Despite their small size, the pubic bones were fused, a characteristic of adult dinosaurs, indicating that the specimen does not represent a juvenile of a known species.
Though known from only partial remains, Longrich and Currie estimated its total length at under one meter and weight at about 1.9 kilograms, making it one of the smallest known carnivorous dinosaurs from North America. The alvarezsaurid Albertonykus was smaller.
A phylogenetic analysis performed by Longrich and Currie found Hesperonychus to be a member of the Microraptorinae, a clade of small dromaeosaurids previously thought to be restricted to the Early Cretaceous of Asia. The authors described this find as "remarkable"; the previously youngest known microraptorine was Microraptor itself from the Aptian stage of the Early Cretaceous, so the discovery of Hesperonychus in the Late Cretaceous Campanian stage pushed the fossil range of microraptorines forward by 45 million years. While the Late Cretaceous, North American Bambiraptor had sometimes been classified as a microraptorine, more recent studies (including those by Longrich and Currie) have found that it is more closely related to Saurornitholestes.
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