Hesperonychus Temporal range: Late Cretaceous, | |
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UALVP 48778, holotype pelvis | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Saurischia |
Clade: | Theropoda |
Clade: | Pennaraptora |
Clade: | Paraves |
Genus: | † Hesperonychus Longrich & Currie, 2009 |
Species: | †H. elizabethae |
Binomial name | |
†Hesperonychus elizabethae Longrich & Currie, 2009 | |
Hesperonychus (meaning "western claw") is a genus of small paravian theropod dinosaur. It may be a dromaeosaurid or an avialan. 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. [1] It is known from fossils recovered from the Dinosaur Park Formation and possibly from the uppermost strata of the Oldman Formation of Alberta, dating to the Campanian stage of the Late Cretaceous around 75 million years ago. [2]
Hesperonychus is mainly 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 discovered from the Dinosaur Park Formation and Oldman Formation, including "sickle claws", in the collection of the Royal Tyrrell Museum have been tentatively referred to as cf. Hesperonychus. [2]
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. [2] Though known from partial remains, researchers have estimated that it was a small dinosaur measuring about 1 metre (3.3 ft) long and weighing between 1.5 and 2 kilograms (3.3 and 4.4 lb), making it one of the smallest non-avian dinosaurs known from North America. [2] [3]
A phylogenetic analysis performed by Longrich and Currie found Hesperonychus to be a member of the Microraptorinae, [4] 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. [2] While the Late Cretaceous, North American Bambiraptor had sometimes been classified as a microraptorine, other researchers (including Longrich and Currie) have found that it is more closely related to Saurornitholestes . [2]
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. [2]
Cladogram (2012): [5]
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 eudromaeosaurian. [6] In 2013, microraptorines were considered as averaptorans outside dromaeosaurids. [7] 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. [8] Other studies have also followed this exclusion of Hesperonychus. [9] [10] [11] [12]
In 2019, Hartman and colleagues suggested that Hesperonychus is actually an avialan close to modern birds like Balaur bondoc based on phylogenetic analyses, though they disagreed with microraptorines being avialans. [13] In the same year, Rauhut and colleagues considered various genera of theropods including Hesperonychus as 'problematic taxa' due to their unstable phylogenetic position. [14] In 2020, Hesperonychus was recovered as a dromaeosaurid and a sister taxon, but not a member, of the polytomic microraptorines. [15]
Microraptorines are well known for their small size and, in some cases, ability to fly or glide. Longrich and Currie concluded that it was unlikely for Hesperonychus to exhibit four wings or gliding behavior as in Microraptor, and speculated that it was more likely to be similar to Sinornithosaurus given their closer similarity in size. Nevertheless, Hesperonychus seems to show that microraptorines did not vary much in size, remaining very small relative to other dromaeosaurids throughout their history, [2] though it is questionable whether it was indeed a microraptorine or a dromaeosaurid. [13]
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 endothermic 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. [2] 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. [2]
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. [2]
Troodontidae is a clade of bird-like theropod dinosaurs from the Late Jurassic to Late Cretaceous. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages. More recent fossil discoveries of complete and articulated specimens, have helped to increase understanding about this group. Anatomical studies, particularly studies of the most primitive troodontids, like Sinovenator, demonstrate striking anatomical similarities with Archaeopteryx and primitive dromaeosaurids, and demonstrate that they are relatives comprising a clade called Paraves.
Deinonychosauria is a clade of paravian dinosaurs which lived from the Late Jurassic to the Late Cretaceous periods. Fossils have been found across the globe in North America, Europe, Africa, Asia, South America, and Antarctica, with fossilized teeth giving credence to the possibility that they inhabited Australia as well. This group of dinosaurs are known for their sickle-shaped toe claws and features in the shoulder bones.
Dromaeosauridae is a family of feathered coelurosaurian theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek δρομαῖος (dromaîos), meaning 'running at full speed', 'swift', and σαῦρος (saûros), meaning 'lizard'. In informal usage, they are often called raptors, a term popularized by the film Jurassic Park; several genera include the term "raptor" directly in their name, and popular culture has come to emphasize their bird-like appearance and speculated bird-like behavior.
Sinornithosaurus is a genus of feathered dromaeosaurid dinosaur from the early Cretaceous Period of the Yixian Formation in what is now China. It was the fifth non–avian feathered dinosaur genus discovered by 1999. The original specimen was collected from the Sihetun locality of western Liaoning. It was found in the Jianshangou beds of the Yixian Formation, dated to 124.5 million years ago. Additional specimens have been found in the younger Dawangzhangzi bed, dating to around 122 million years ago.
Bambiraptor is a Late Cretaceous, 72-million-year-old, bird-like dromaeosaurid theropod dinosaur described by scientists at the University of Kansas, Yale University, and the University of New Orleans.
Adasaurus is a genus of dromaeosaurid dinosaur that lived in Asia during the Late Cretaceous period about 70 million years ago. The genus is known from two partial specimens found in the Nemegt Formation of Mongolia that were partially described in 1983 by the paleontologist Rinchen Barsbold.
Jinfengopteryx is a genus of maniraptoran dinosaur. It was found in the Qiaotou Member of the Huajiying Formation of Hebei Province, China, and is therefore of uncertain age. The Qiaotou Member may correlate with the more well-known Early Cretaceous Yixian Formation, and so probably dates to around 122 Ma ago.
Microraptoria is a clade of basal dromaeosaurid theropod dinosaurs. Definitive microraptorians lived during the Barremian to Aptian stages of the Early Cretaceous in China. Many are known for long feathers on their legs and may have been semiarboreal powered fliers, some of which were even capable of launching from the ground. Most microraptorians were relatively small; adult specimens of Microraptor range between 77–90 centimetres long (2.53–2.95 ft) and weigh up to 1 kg (2.2 lb), making them some of the smallest known non-avialan dinosaurs.
Elopteryx is a genus of paravian theropod dinosaur based on fragmentary fossils found in Late Cretaceous rocks of Romania. The single species, Elopteryx nopcsai, was known only from very incomplete material until new specimens were reported in the 21st century. Balaur bondoc might represent a junior synonym of this taxon.
Velociraptorinae is a subfamily of the theropod group Dromaeosauridae. The earliest velociraptorines are probably Nuthetes from the United Kingdom, and possibly Deinonychus from North America. However, several indeterminate velociraptorines have also been discovered, dating to the Kimmeridgian stage, in the Late Jurassic Period. These fossils were discovered in the Langenberg quarry, Oker near Goslar, Germany. Dromaeosaurid teeth that resemble velociraptorines are also known from the Middle Jurassic of the Kota Formation in India.
Shanag is a genus of paravian theropod dinosaur from the Early Cretaceous Period of Mongolia. It may be a dromaeosaurid, but some researchers are skeptical of this classification. The type species is S. ashile.
Paraves are a widespread group of theropod dinosaurs that originated in the Middle Jurassic period. In addition to the extinct dromaeosaurids, troodontids, anchiornithids, and possibly the scansoriopterygids, the group also contains the avialans, which include diverse extinct taxa as well as the over 10,000 species of living birds. Basal members of Paraves are well known for the possession of an enlarged claw on the second digit of the foot, which was held off the ground when walking in some species. A number of differing scientific interpretations of the relationships between paravian taxa exist. New fossil discoveries and analyses make the classification of Paraves an active subject of research.
Mahakala is a genus of halszkaraptorine theropod dinosaur from the Campanian-age Upper Cretaceous Djadokhta Formation of Ömnögovi, Mongolia. It is based on a partial skeleton found in the Gobi Desert. Mahakala was a small dromaeosaurid, and its skeleton shows features that are also found in early troodontids and avialans. Despite its late appearance, it is among the most basal dromaeosaurids. Its small size, and the small size of other basal deinonychosaurians, suggests that small size appeared before flight capability in birds. The genus is named for Mahakala, one of eight protector deities (dharmapalas) in Tibetan Buddhism.
Saurornitholestinae is a subfamily of the theropod group Dromaeosauridae. The saurornitholestines currently include monotypic genera Atrociraptor marshalli, Saurornitholestes langstoni, and possibly Bambiraptor feinbergi and Acheroraptor temertyorum. All are medium-sized dromaeosaurs from the Late Cretaceous of western North America. The group was originally recognized by Longrich and Currie as the sister taxon to a clade formed by the Dromaeosaurinae and Velociraptorinae. However, not all phylogenetic analyses recover this group and/or with the same proposed genera.
Eudromaeosauria is a subgroup of terrestrial dromaeosaurid theropod dinosaurs. They were small to large-sized, feathered hypercarnivores that flourished in the Cretaceous Period.
Balaur is a genus of theropod dinosaur from the late Cretaceous period, in what is now Romania. It is the type species of the monotypic genus Balaur, after the balaur, a dragon of Romanian folklore. The specific name bondoc means "stocky", so Balaur bondoc means "stocky dragon" in Romanian. This name refers to the greater musculature that Balaur had compared to its relatives. The genus, which was first described by scientists in August 2010, is known from two partial skeletons. Some researchers suggest that the taxon might represent a junior synonym of Elopteryx.
Acheroraptor is an extinct genus of dromaeosaurid theropod dinosaur known from the latest Maastrichtian Hell Creek Formation of Montana, United States. It contains a single species, Acheroraptor temertyorum. A. temertyorum is one of the two geologically youngest known species of dromaeosaurids, the other being Dakotaraptor, which is also known from Hell Creek. A basal cousin of Velociraptor, Acheroraptor is known from upper and lower jaw material.
This timeline of dromaeosaurid research is a chronological listing of events in the history of paleontology focused on the dromaeosaurids, a group of sickle-clawed, bird-like theropod dinosaurs including animals like Velociraptor. Since the Native Americans of Montana used the sediments of the Cloverly Formation to produce pigments, they may have encountered remains of the dromaeosaurid Deinonychus hundreds of years before these fossils came to the attention of formally trained scientists.
Anchiornithidae is a family of small paravian dinosaurs. Anchiornithids have been classified at varying positions in the paravian tree, with some scientists classifying them as a distinct family, a basal subfamily of Troodontidae, members of Archaeopterygidae, or an assemblage of dinosaurs that are an evolutionary grade within Avialae or Paraves.