Hesperonychus: small carnivorous dinosaur

Hesperonychus (lat.: Hesperonychus; “Western claw”) a genus of small feathered predatory dinosaurs from the family Dromaeosaurids (lat.: Dromaeosauridae), lived in the territory of modern Western Canada.

This genus is represented by one described species, Hesperonychus elizabethae (“Hesperonychus of Elizabeth”). This type species of Hesperonychus was named after the researcher who found its fossilized remains in 1982. Dinosaur bones were found in the lowest stratum of the Dinosaur Park Formation.: Dinosaur Park Formation), located in the Canadian province of Alberta (Eng.: Alberta). They date from the Upper Cretaceous (Campanian) and are about 76.5 million years old.

The genus Hesperonychus is known from a partially preserved pelvic girdle (holotype no. UALVP 48778) discovered by Dr. Elizabeth Nicholls.: Elizabeth Nicholls) at Dinosaur Provincial Park in Alberta, Canada.

However, the fossil remains remained undescribed until the publication in 2009 of their description by paleontologist Nick Longrich.: Nick Longrich) and Philip Currie (Philip Currie). At the same time, some very small bones of the toes contained in the collection of the Royal Tyrrell Paleontological Museum (Eng.: Royal Tyrrell Museum of Palaeontology) in the town of Drumheller (Drumheller), including sickle-shaped claws, may also belong to Hesperonychus.

Despite the small size of the pubic bones of the holotype, they were fused, which is a characteristic feature of an adult dinosaur and indicates that this specimen was not a juvenile of the species Hesperonychus elizabethae.

Although Hesperonychus is known to science only from fragmentary remains, Longrich and Carrie estimate that the dinosaur’s total length was less than 1 meter and weighed about 1.9 kilograms, making it the smallest known carnivorous dinosaur in North America. True, the representative of the Alvaresavrides family (lat.: Alvarezsauridae) Albertonykus was smaller than gesperoniki, but was rather an insecteater than a predatory dinosaur.

The phylogenetic analysis carried out by Longrich and Carrie revealed the belonging of Hesperonich to the treasure of microraptorins (lat.: Microraptorinae), uniting small droomeosaurides, which, as it was believed earlier, lived only in the lower chalk period and only in the territory of modern Asia.

The authors of the study described this find as “outstanding”, since the youngest of the previously known microorptorines was the microenemy itself (lat.: Microratraptor) related to the Assetian tier of the lower chalk period. Thus, the detection of Hesperonich in the campan tier of the upper chalk shifted the previously assumed range of the time of the existence of microreeptorins for 45 million years in advance.

While the North American bambiraptor (lat.: Bambiraptor), dating back to the Upper Cretaceous, is sometimes classified as a microraptorine, more recent studies (including those by Longrich and Carrie) have shown that Bambiraptor was more closely related to Saurornitholestes (Saurornitholestes).

Microraptorines are well known for their small size and, in some cases, their ability to fly or glide. Longrich and Carrie concluded that it was unlikely that Hesperonychus also had 4 wings, and, like the Microraptor, it was common to fly or glide, and suggested that the first of these most likely was similar to Sinornithosaurus (lat.: Sinornithosaurus), given its greater resemblance in size to Sinornithosaurus compared to Microraptor.

However, the size of Hesperonychus seems to indicate that the variation in body size between different microraptorines was not very large, and members of this clade remained very small compared to other dromaeosaurids throughout their history.

The discovery of Hesperonychus not only expanded the composition of the Microraptorina clade known to science, but also filled the existing gap in information on the biological environment of the Upper Cretaceous in the territory of modern North America. The biological environment of North America, in contrast to Europe and Asia of approximately the same era, seems to have been characterized by an insufficient number of small species of predatory dinosaurs.

In modern biosystems dominated by warm-blooded mammals, small animal species, on the contrary, outnumber larger ones. Since many scientists assume that dinosaurs were also warm-blooded animals, the existence of an insufficient number of small and at the same time a large number of large dinosaurs known to science in the territory of modern North America was not normal.

Hesperonychus helped to fill this numerical gap between small and large dinosaur species given, in particular, the number of fragmentary remains and claws collected (belonging to at least ten individual specimens of this dinosaur compared to the remains of three dozen sauroornitholes of the same era and two dromaeosaurus), one can suggest that such a ratio of the abundance of small and large species was characteristic of the entire biosystem of the Dinosaur Park Formation.

The next even smaller predator in this biological system was the mammal eodelphis (lat.: Eodelphis), whose body weight was only 600 grams. These biosystems do not appear to have contained the smallest dinosaurs and largest mammals of the same size, which Longrich and Carrie explained by suggesting that either competition with dinosaurs prevented mammals from increasing (the traditional view) or competition with mammals prevented dinosaurs from shrinking. in size, or both affected.

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