Paraves

Last updated

Paravians
Temporal range:
Middle Jurassic–Present, 165–0  Ma [1]
Dromaeo-avemorphs.png
Examples of basal paravian dinosaurs
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Pennaraptora
Clade: Paraves
Sereno, 1997
Subgroups
Synonyms
Birds, members of the paraves, are the only living dinosaurs. Melopsittacus undulatus -Atlanta Zoo, Georgia, USA-8a-2c.jpg
Birds, members of the paraves, are the only living dinosaurs.

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. [2] 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. [3] 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. [4]

Contents

Description

Like other theropods, all paravians are bipedal, walking on their two hind legs. [5]

The teeth of basal paravians were curved and serrated, but not blade-like except in some specialized species such as Dromaeosaurus albertensis . The serrations on the front edge of dromaeosaurid and troodontid teeth were very small and fine, while the back edge had serrations which were very large and hooked. [6]

Most of the earliest paravian groups were carnivorous, though some smaller species (especially among the troodontids and early avialans) are known to have been omnivores, and it has been suggested that an omnivorous diet was the ancestral state for this group, with strict carnivory evolving in some specialized lineages. [7] [6] Fossils also suggest that legs and feet covered with feathers was an ancestral condition, possibly having originated in the Coelurosauria, even if this trait was later lost in more advanced birds. [8]

Wings

Paravians generally have long, winged forelimbs, though these have become smaller in many flightless species and some extinct lineages that evolved before flight. The wings usually bore three large, flexible, clawed fingers in early forms. [6] The fingers became fused and stiffened and the claws highly reduced or lost in some advanced lineages. An increasingly asymmetric wrist joint, a trend that can be traced back to primitive coelurosaurs, allowed the forelimbs to elongate and an elaboration of their plumage, traits that made the evolution of flapping flight possible. [9]

Many early members of Paraves had both well-developed wings and long feathers on the hind legs, which in some cases, formed a second set of airfoils. These species, most famously represented by Microraptor gui , have often been referred to as "four winged dinosaurs". [10] [11] [12] Though it has been suggested that these hind wings would have prevented some paravians from getting around on the ground, and that they must have lived in trees, there is very little evidence that any of the earliest paravians were capable of climbing. This apparent paradox was addressed by later studies which showed that early paravians like Microraptor were capable of flapping flight and powered launching from the ground into the air without relying on climbing. Microraptor in particular also seems to represent a case of flight evolving independently of the bird lineage within Paraves. [13]

Feet and sickle claw

Most theropods walked with three toes contacting the ground, but fossilized footprint tracks confirm that many basal paravians, including dromaeosaurids, troodontids, and some early avialans, held the second toe off the ground in a hyperextended position, with only the third and fourth toes bearing the weight of the animal. This is called functional didactyly. [3] The enlarged second toe bore an unusually large, curved sickle-shaped claw (held off the ground or 'retracted' when walking). This claw was especially large and flattened from side to side in the large-bodied predatory eudromaeosaurs. [14] In these early species, the first toe (hallux) was usually small and angled inward toward the center of the body, but only became fully reversed in more specialized members of the bird lineage. [6] One species, Balaur bondoc , possessed a first toe which was highly modified in parallel with the second. Both the first and second toes on each foot of B. bondoc were held retracted and bore enlarged, sickle-shaped claws. [15]

Deinonychus "sickle claw" Deinonychus patte arriere gauche.jpg
Deinonychus "sickle claw"

One of the best-known features of paravians is the presence of an enlarged and strongly curved "sickle claw" on a hyper-extendible second toe, modified to hold the sickle claw clear of the ground when walking, most notably developed in the dromaeosaurids and troodontids. While this characteristic claw and its associated modifications to the anatomy of the foot (such as a shortened metatarsus in eudromaeosaurs) had been known since the mid-20th century, their possible functions were the subject mainly of speculation, and few actual studies were published. Initial speculation regarded the claws as slashing implements used to disembowel large prey. In this scenario, the shortened upper foot would serve as an anchor point for powerful tendons to improve kicking ability. However, subsequent studies of the actual claw shape showed that the underside of the claw was only weakly keeled and would not have been an effective cutting instrument. Instead, it appeared to be more of a hooking implement. Manning et al. suggested in 2006 that the claws were similar to crampons and were used for climbing, and in the case of larger species or individuals, climbing up the flanks of very large prey. [16]

A larger study of sickle-claw function, published in 2011 by Fowler and colleagues, concluded that the earlier study by Manning and colleagues was correct and that the "sickle claws" would have been ineffective as cutting weapons. They compared the claw and overall foot anatomy of various primitive species with modern birds to shed light on their actual function. Fowler and colleagues showed that many modern predatory birds also have enlarged claws on the second toes. In modern raptors, these claws are used to help grip and hold prey of sizes smaller than or equal to the predator, while the birds use their body weight to pin their prey to the ground and eat it alive. [6] Fowler and colleagues suggested that this behavior is entirely consistent with the anatomy of advanced dromaeosaurids like Deinonychus , which had slightly opposing first toes and strong tendons in the toes and foot. This makes it likely that advanced dromaeosaurids also used their claws to puncture and grip their prey to aid in pinning it to the ground, while using shallow wing beats and tail movements to stabilize themselves. [6] Other lines of evidence for this behavior include teeth which had large, hooked serrations only on the back edge (useful in pulling flesh upward rather than slicing it) and large claws on the wings (for greater maneuvering of prey while mantling it with the wings). [6]

In more primitive dromaeosaurids and in troodontids, the feet were not as specialized and the claws were not as large or as hooked. Additionally, the toe joints allowed more range of motion than the simple up-down movements of advanced dromaeosaurids. This makes it likely that these species specialized in smaller prey that could be pinned using only the inner toes, not requiring the feet to be as strong or sturdy. [6]

Dichotomy in body sizes

Extreme examples of miniaturization and progenesis are found in Paraves. [17] The ancestors of Paraves first started to shrink in size in the early Jurassic 200 million years ago, and fossil evidence shows that this theropod line evolved new adaptations four times faster than other groups of dinosaurs, [18] and was shrinking 160 times faster than other dinosaur lineages were growing. [19] Turner et al. (2007) suggested that extreme miniaturization was ancestral for the clade, whose common ancestor has been estimated to have been around 65 centimetres (26 in) long and 600–700 grams (21–25 oz) in mass. In Eumaniraptora, both Dromaeosauridae and Troodontidae went later through four independent events of gigantism, three times in dromaeosaurids and once in troodontids, while the body mass continued to decrease in many forms within Avialae. [20] Fossils show that all the earliest members of Paraves found to date started out as small, while Troodontidae and Dromaeosauridae gradually increased in size during the Cretaceous period. [20]

Evolution

Relationships

Pennaraptora

†Oviraptorosauria

Paraves

†Scansoriopterygidae

† Xiaotingia

† Yixianosaurus

† Pedopenna

† Aurornis

† Serikornis

† Eosinopteryx

† Anchiornis

Eumaniraptora

†Troodontidae

†Dromaeosauridae

Avialae

Cladogram following the results of a phylogenetic study by Lefèvre, Cau, Cincotta, et al. (2017) [21]
Pennaraptora

† Oviraptorosauria

Paraves

† Dromaeosauridae

Averaptora

† Troodontidae

† Anchiornithinae

Avialae

† Archaeopteryx

† Scansoriopterygidae

† Rahonavis

Pygostylia

Cladogram following the results of a phylogenetic study by Cau, Beyrand, Voeten et al. (2017) [22]

Paraves is a branch-based clade defined to include all dinosaurs which are more closely related to birds than to oviraptorosaurs. The ancestral paravian is the earliest common ancestor of birds, dromaeosaurids, and troodontids which was not also ancestral to oviraptorosaurs. Paraves often comprises three major sub-groups: Avialae, including Archaeopteryx and modern birds, as well as the dromaeosaurids and troodontids, which may or may not form a natural group.

The name 'Paraves' (Greek pará, par' 'beside, near' + Latin aves, plural of avis 'bird') was coined by Sereno in 1997. [23] The clade was defined by Sereno in 1998 as a branch-based clade containing all Maniraptora closer to Neornithes (which includes all the birds living in the world today) than to Oviraptor . [24]

A node-based clade called Eumaniraptora ("true maniraptorans") was named by Padian, Hutchinson, & Holtz (1997).[ full citation needed ] They defined their clade to include only avialans and deinonychosaurs. Paraves and Eumaniraptora are generally considered to be synonyms, though some phylogenetic studies suggest that the two groups have a similar but not identical content; Agnolín and Novas (2011) [25] recovered scansoriopterygids and alvarezsaurids as paravians that were not eumaniraptorans, while Turner, Makovicky, and Norell (2012) [2] recovered Epidexipteryx as the only known non-eumaniraptoran paravian. [25] [2]

Since the 1960s, the dromaeosaurids and troodontids have often been classified together in a group or clade named the Deinonychosauria, initially based primarily on the presence of a retractable second toe with sickle-claw (now also known to be present in some avialans). The name Deinonychosauria was coined by Ned Colbert and Dale Russell in 1969, and defined as a clade (all theropods closer to dromaeosaurids than to birds) by Jacques Gauthier in 1986.

However, several more recent studies have cast doubt on the hypothesis that dromaeosaurids and troodontids were more closely related to each other than either was to birds, instead finding that troodontids were more closely related to birds than to dromaeosaurids. [4] [26] [27] Because Deinonychosauria was originally defined as all animals closer to dromaeosaurids than to birds without specific reference to troodontids, this would render Deinonychosauria a synonym of Dromaeosauridae. [27] The clade containing avialans, microraptorians, unenlagiids, Anchiornis, and Xiaotingia to the exclusion of Eudromaeosauria was named Averaptora by Agnolín and Novas (2013), defined as all animals closer to Passer than to Dromaeosaurus . [28] Most studies use a similar definition for Avialae, [29] which Agnolín and Novas redefine as the least inclusive clade including Archaeopteryx and modern birds. [28] Averaptora additionally contains troodontids according to Cau, Beyrand, Voeten et al. (2017) [22] and other phylogenies in which find Eudromaeosauria to be an outgroup to a clade including Troodontidae and Avialae. [22]

In 2015 Chatterjee created Tetrapterygidae in the second edition of his book The Rise of Birds: 225 Million Years of Evolution, where he included Microraptor , Xiaotingia , Aurornis , and Anchiornis ; together they were proposed to be the sister group of the Avialae. [30] Paraves, Eumaniraptora, and Averaptora are often considered to be synonyms, depending on the interpretation of paravian systematics. Deinonychosauria will become a synonym of Dromaeosauridae when troodontids are found to form a clade with Avialae, to the exclusion of Dromaeosauridae. Tetrapterygidae is a polyphyletic grouping of four-winged basal paravian genera.

Origin and early evolution

Paravians diverged from other maniraptorans around 165  Mya. Then, around 110–90 Mya, the ancestors of Neornithes (modern birds) split from the other paravians. [31]

Other than the crown group of modern birds, which are direct descendants in the stem lineage of Paraves, there are no extant survivors or genetic material, so their entire phylogeny is inferred only from the fossil record. [32] The prototypical fossil is Archaeopteryx, of which 11 specimens have been found, both complete and partial. [33]

See also

Related Research Articles

<span class="mw-page-title-main">Troodontidae</span> Extinct family of bird-like dinosaurs

Troodontidae is a clade of bird-like theropod dinosaurs. 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.

<span class="mw-page-title-main">Deinonychosauria</span> Extinct clade of dinosaurs

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.

<span class="mw-page-title-main">Dromaeosauridae</span> Family of theropod dinosaurs

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.

<span class="mw-page-title-main">Maniraptora</span> Clade of dinosaurs

Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Dromaeosauridae, Troodontidae, Oviraptorosauria, and Therizinosauria. Ornitholestes and the Alvarezsauroidea are also often included. Together with the next closest sister group, the Ornithomimosauria, Maniraptora comprises the more inclusive clade Maniraptoriformes. Maniraptorans first appear in the fossil record during the Jurassic Period, and survive today as living birds.

<i>Rahonavis</i> Extinct genus of dinosaurs

Rahonavis is a genus of bird-like theropods from the Late Cretaceous of what is now northwestern Madagascar. It is known from a partial skeleton found by Catherine Forster and colleagues in Maevarano Formation rocks at a quarry near Berivotra, Mahajanga Province. Rahonavis was a small predator, at about 70 centimetres (2.3 ft) long and 0.45-2.27 kg, with the typical Velociraptor-like raised sickle claw on the second toe. It was originally the first African coelurosaur until the discovery of Nqwebasaurus in 2000.

<span class="mw-page-title-main">Scansoriopterygidae</span> Extinct family of dinosaurs

Scansoriopterygidae is an extinct family of climbing and gliding maniraptoran dinosaurs. Scansoriopterygids are known from five well-preserved fossils, representing four species, unearthed in the Tiaojishan Formation fossil beds of Liaoning and Hebei, China.

<span class="mw-page-title-main">Archaeopterygidae</span> Family of dinosaurs

Archaeopterygidae is a group of maniraptoran dinosaurs, known from the latest Jurassic and earliest Cretaceous of Europe. In most current classifications, it contains only the genera Archaeopteryx and Wellnhoferia. As its name suggests, Protarchaeopteryx was also once referred to this group, but most paleontologists now consider it an oviraptorosaur. Other referred genera, like Jurapteryx, Wellnhoferia, and "Proornis", are probably synonymous with Archaeopteryx or do not belong into this group. Jinfengopteryx was originally described as an archaeopterygid, though it was later shown to be a troodontid. A few studies have recovered Anchiornis and Xiaotingia to also be members of the Archaeopterygidae, though most subsequent analyses have failed to arrive at the same result. Uncertainties still exist, however, and it may not be possible to confidently state whether archaeopterygids are more closely related to modern birds or to deinonychosaurs barring new and better specimens of relevant species. Teeth attributable to archaeopterygids are known from the earliest Cretaceous (Berriasian) Cherves-de-Cognac locality and the Angeac-Charente bonebed of France.

<i>Yandangornis</i> Extinct genus of birds

Yandangornis is a genus of theropods from the Late Cretaceous Tangshang Formation of China. It lived 81.5 million years ago in what is now China. The type species, Y. longicaudus, was formally described by Cai and Zhou in 1999.

<span class="mw-page-title-main">Avialae</span> Clade including all birds and their ancestors

Avialae is a clade containing the only living dinosaurs, the birds. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally used.

<span class="mw-page-title-main">Mahakala omnogovae</span> Extinct species of dinosaur

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.

<i>Epidexipteryx</i> Extinct genus of dinosaurs

Epidexipteryx is a genus of small paravian dinosaurs, known from one fossil specimen in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing. Epidexipteryx represents the earliest known example of ornamental feathers in the fossil record.

<i>Anchiornis</i> Extinct genus of dinosaurs

Anchiornis is a genus of small, four-winged paravian dinosaurs, with only one known species, the type species Anchiornis huxleyi, named for its similarity to modern birds. The Latin name Anchiornis derives from a Greek word meaning "near bird", and huxleyi refers to Thomas Henry Huxley, a contemporary of Charles Darwin.

<i>Balaur bondoc</i> Extinct specie of dinosaurs

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.

<i>Xiaotingia</i> Extinct genus of dinosaurs

Xiaotingia is a genus of anchiornithid theropod dinosaur from Middle Jurassic or early Late Jurassic deposits of western Liaoning, China, containing a single species, Xiaotingia zhengi.

<span class="mw-page-title-main">Jinfengopteryginae</span> Extinct subfamily of dinosaurs

Jinfengopteryginae is a subfamily of bird-like theropod dinosaurs known from the Cretaceous of Eurasia. This group includes relatively few genera, with members discovered in 2005 but the name erected in 2012. Like other troodontids, this group of dinosaurs resided in the Paraves potentially close to the Avialae.

<i>Eosinopteryx</i> Extinct genus of dinosaurs

Eosinopteryx is an extinct genus of theropod dinosaurs known to the Late Jurassic epoch of China. It contains a single species, Eosinopteryx brevipenna.

<span class="mw-page-title-main">Timeline of dromaeosaurid research</span>

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.

<span class="mw-page-title-main">Anchiornithidae</span> Extinct family of reptiles

Anchiornithidae is a family of eumaniraptorans which could be the basalmost family of birds in the clade Avialae. Anchiornithids have been classified at varying positions in the maniraptoran 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.

<span class="mw-page-title-main">Biogeography of paravian dinosaurs</span> Geographic distribution of paravian dinosaurs

The biogeography of Paravian dinosaurs is the study of the global distribution of Paraves through geological history. Paraves is a clade that includes all of the Theropoda that are more closely related to birds than to oviraptorosaurs. These include Dromaeosauridae and Troodontidae and Avialae. The distribution of paraves is closely related to the evolution of the clade. Understanding the changes in their distributions may shed light on problems like how and why paraves evolve, eventually gaining the ability to fly.

<i>Overoraptor</i> Extinct genus of theropod dinosaurs

Overoraptor is an extinct genus of paravian theropod of uncertain affinities from the Late Cretaceous Huincul Formation of Argentinian Patagonia. The genus contains a single species, O. chimentoi, known from several bones of the hands, feet, and hips alongside some vertebrae.

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