Product Code Database
Hesperonychus (meaning "western claw") is a genus of small Dromaeosauridae dinosaur. There is one described species, Hesperonychus elizabethae. The type species was named in honor of Dr. Elizabeth Nicholls of the Royal Tyrrell Museum of Palaeontology who collected it as a student in 1982. Alberta researchers discover mini meat-eating dinosaur, a 16 March 2009 article from CBC News It is known from recovered from the Dinosaur Park Formation and possibly from the uppermost strata of the Oldman Formation of Alberta, dating to the Campanian faunal stage of the Late Cretaceous around .
The gracile appearances of these potential toe bones make it unlikely that Hesperonychus belonged to the Eudromaeosauria. 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 partial remains, researchers have estimated that it was a small dinosaur measuring about long and weighing between , making it one of the smallest non-avian dinosaurs known from North America.
Hesperonychus was assigned to Microraptoria due to having a spatulate (rounded) pubic symphysis, a strong posterior curvature of the distal shaft of the pubis, and lateral tubercules on the pubes, which are expanded into 'wing-like' structures in the case of Hesperonychus.
However, subsequent studies have questioned its identity as a microraptorine, with some researchers excluding the taxon from phylogenetic analyses due to its fragmentary remains and others classifying it in various positions within or outside dromaeosaurids. In 2012, Martyniuk considered Hesperonychus as a . (2025). 9780988596504, Pan Aves. ISBN 9780988596504 In 2013, microraptorines were considered as outside dromaeosaurids. In 2014, Brusatte and colleagues pruned five "wildcard" taxa including the paravians Pyroraptor and Hesperonychus from phylogenetic analyses, mainly due to a huge lack of data, indicating that the definitive classifications of these taxa are uncertain. Supplementary Information Other studies have also followed this exclusion of Hesperonychus.
In 2019, Hartman and colleagues suggested that Hesperonychus is actually an Avialae close to modern like Balaur bondoc based on phylogenetic analyses, though they disagreed with microraptorines being avialans. In the same year, Rauhut and colleagues considered various genera of theropods including Hesperonychus as 'problematic taxa' due to their unstable phylogenetic position. In 2020, Hesperonychus was recovered as a dromaeosaurid and a sister taxon, but not a member, of the polytomy microraptorines.
Whether it was a microraptorine or not, the discovery of Hesperonychus filled in a gap in the ecology of Late Cretaceous North America. Unlike roughly contemporary environments in Europe and Asia, North America appeared to lack very small carnivorous dinosaurs. In modern ecosystems dominated by mammals, small animal species outnumber larger ones. Since dinosaurs are also presumed to have been endotherms, the lack of small species and great number of known large species in North America was unusual. Hesperonychus helped to fill that gap, especially since, given the number of fragmentary remains and claws that have been collected (representing at least ten distinct specimens, compared to thirty of the contemporary Saurornitholestes and two of Dromaeosaurus), it appears to have been a very common feature of the Dinosaur Park Formation environment.
The next smallest carnivore in the environment was the mammal Eodelphis, which weighed only 600 grams. There does not appear to have been any overlap between the smallest dinosaurs and the largest mammals in ecosystems such as this, which Longrich and Currie explained by hypothesizing that either competition from dinosaurs kept mammals from growing larger (the traditional view), competition from mammals kept the dinosaurs from growing smaller, or both.
|
|
