Have you ever wondered why most dinosaurs were giant, heavy-bodied animals, and not smaller? The discovery of the dinosaur that we are going to learn about helped scientists solve this question. Hesperonychus, meaning 'western claw', is considered to be quite possibly the smallest known carnivorous dinosaur found in North America. Its fossils were unearthed in 1982 in the Dinosaur Provincial Park, which is located in the province of Alberta in Canada. At the time of discovery, these fossils were thought to have belonged to the specimen of a bird or an undetermined juvenile dinosaur. About 25 years later, Nick Longrich found a single sickle-like claw in some old collections of fossils of the Royal Tyrell Museum of Paleontology in Alberta, and it had not been studied or described yet. This got Longrich thinking about the lack of small carnivorous dinosaur remains in North America. Small dinosaurs had been previously found in Europe and Asia, but none from North America before Nick Longrich studied the bones of Hesperonychus. He managed to find a partial pelvis bone whose pubic and ilium bones were fused together, which meant that the specimen belonged to an adult dinosaur. In 2009, Longrich and Currie named and described a new genus of the small carnivorous dinosaurs as Hesperonychus. It consists of a single species, Hesperonychus elizabethae. Longrich and Currie attributed this species to the clade Microraptoria within the family Dromaeosauridae.
The discovery of this genus led to the belief that it could have been the large-sized dinosaurs that preyed upon small mammals, which led to the mammals remaining small during the Mesozoic Era. However, it could also have been that because the small mammals prevailed as the small animals of the ecosystem during that time, dinosaurs mostly remained large in size.
The meaning of the name of this dinosaur's name is 'western claw', and it is phonetically pronounced as 'hesp-air-on-i-cuss'.
Studies by Longrich and Currie confirmed that this dinosaur was a dromaeosaurid theropod that belonged to the clade Microraptoria. Microraptorines are similar to dromaeosaurids, but are much smaller, feathered in some cases, and have a few differences in their bone structures. They were earlier assumed to have existed only in Asia during the Early Cretaceous period, but it has since been found that North American Microraptorines existed as well, and almost 45 million years later than initially thought, as the remains of Hesperonychus have been dated back to almost 75 million years ago during the Late Cretaceous period. They are also thought to have been able to fly or glide using their feathers but Longrich concluded that this particular dinosaur would not have had the wings that Microraptor is thought to have had. Hesperonychus is considered to be closely related to the North American dromaeosaurid Saurornitholestes.
This dinosaur would have lived during the Campanian to Maastrichtian stages of the Late Cretaceous period. It would have walked the Earth around 83.5-70.6 million years ago.
Since this dinosaur lived during the last stages of the Late Cretaceous, it would have died off along with most dinosaur species due to the Cretaceous-Paleogene mass extinction event.
This dinosaur species would have lived in the forests of modern-day North America, as its partial fossil remains were recovered from Alberta, Canada.
Studies performed by scientists on the deposits of the Dinosaur Provincial Park have described the environment of this region as a coastal plain that would have been filled with rivers, marshes, as well as forests.
Since this dinosaur was a carnivore, it is likely that it would have led a solitary lifestyle. This is because carnivorous animals are known to usually avoid living in groups. It could have coexisted with Albertonykus, a small North American theropod also named and described by Longrich and Currie. This dinosaur lived about 68.5 million years ago, which is around the same time Hesperonychus walked the Earth. Another small animal species that also lived in modern-day North America during the Late Cretaceous were a group of mammals named Eodelphis. These were carnivorous animals that had a similar body length and weight as Hesperonychus.
The lifespan of this particular dinosaur is not known. However, smaller animals, and especially those animals who have a carnivorous diet, are thought to have lived for a shorter amount of time than herbivorous animals.
These dinosaurs would have been oviparous, that is, they would have laid eggs from which their young ones emerged.
Hesperonychus, meaning 'western claw', is known from a partial pelvic bone and several other toe bones of more than one specimen. These fossil remains were initially thought to belong to a juvenile, but when they were studied by Longrich, he described that the pubis and the ilium bones were fused, which clearly meant that they were of an adult specimen. Its teeth would have been serrated, and it would have probably been covered with feathers. The toe bones revealed that it would have had sharp, sickle-shaped claws to attack its prey.
It is currently not possible to know the total number of bones that this dinosaur would have had as it is only known from some fossil remains of a partial skeleton.
This Microraptorine dinosaur could have communicated using vocalizations or forms of body language, but it is not possible to know exactly what kind of sounds or movements they would have made.
This dromaeosaurid is currently the smallest known carnivorous dinosaur found in North America with an estimated body length of 40 in (100 cm) and a height of 20 in (50 cm). Thus, its body length was even smaller than the Albertonykus.
The speed of these dinosaurs is not currently known.
These dinosaurs are thought to have had a bodyweight of 4.2 lb (2 kg).
There are no sex-specific names for the male and female dinosaurs of this genus or species.
Like all baby dinosaurs, a baby dinosaur of this species would have been called a hatchling.
This dinosaur was a carnivore and would have fed on insects, amphibians, small mammals, and maybe even baby dinosaurs.
It is likely that these dinosaurs would have been aggressive towards smaller species, but would have scurried away before larger dinosaurs. Its sickle claws would have helped it easily attack and catch its prey.
The type species, Hesperonychus elizabethae, was named after the Royal Tyrell Museum paleontologist Dr. Elizabeth Betsy Nicholls, who first discovered the fossils of this dinosaur species that Nick Longrich later found in the Royal Tyrell Museum collections.
Yes, this dinosaur was bipedal, which means that it walked or ran on its two hind legs. There is a theory that it would've been able to climb trees as well, but it has not been confirmed yet.
Though multicellular organisms have existed for billions of years on Earth, one of the very first animals is considered to be comb jellies, which are thought to have lived more than 700 million years ago, and were dependent on water for their food and oxygen. Soon after, vertebrates such as conodonts and cephalopods followed. Animals that we know today came into existence much later. For example, even the modern cats that now live in our houses, are not related to any dinosaur, but an animal named Pseudaelurus that existed about 20 million years ago, long after dinosaurs had gone extinct.
Here at Kidadl, we have carefully created lots of interesting family-friendly dinosaur facts for everyone to discover! For more relatable content, check out these Concavenator facts and Camarillasaurus facts for kids.
You can even occupy yourself at home by coloring in one of our free printable Hesperonychus coloring pages.
Main image by Nobu Tamura.
Second image by Fred Wierum.