Paraves

Paravians
Temporal range:
Late JurassicPresent,
Dromaeo-avemorphs.png
Examples of basal paravian dinosaurs
Scientific classification e
Kingdom:Animalia
Phylum:Chordata
Clade:Dinosauria
Clade:Saurischia
Clade:Theropoda
Clade:Pennaraptora
Clade:Paraves
Sereno, 1997
Subgroups
Birds, members of the paraves, are the only living dinosaurs

Paraves are a widespread group of theropod dinosaurs that originated in the Late Jurassic period. In addition to the extinct dromaeosaurids, troodontids, anchiornithids, and scansoriopterygids, the group also contains the avialans, among which are the over ten thousand species of living birds.[1] Early 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.[2]

Description

Like other theropods, all paravians are bipedal, walking on their two hind legs.[3]

The teeth of primitive 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.[4]

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.[5][4] 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.[6]

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.[4] 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.[7]

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".[8][9][10] 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.[11]

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.[2] 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.[12] 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.[4] 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.[13]

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.[14]

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.[4] 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.[4] 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).[4]

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.[4]

Dichotomy in body sizes

The most extreme examples of miniaturization and progenesis are found in Paraves.[15] 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,[16] and was shrinking 160 times faster than other dinosaur lineages were growing.[17] 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.[18] 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.[18]

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 Lefèvreet al., 2017[19]

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. Paravians 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 Paul Sereno in 1997.[20] 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.[21]

In 1997, a node-based clade called Eumaniraptora ("true maniraptorans") was named by Padian, Hutchinson and Holtz. They defined their clade to include only avialans and deinonychosaurs. Paraves and Eumaniraptora are generally considered to be synonyms, though a few phylogenetic studies suggest that the two groups have a similar but not identical content; Agnolín and Novas (2011) recovered scansoriopterygids and alvarezsaurids as paravians that were not eumaniraptorans,[22] while Turner, Makovicky and Norell (2012) recovered Epidexipteryx as the only known non-eumaniraptoran paravian.[1] A nearly identical definition, "the theropod group that includes all taxa closer to Passer than to Dromaeosaurus", was used by Agnolín and Novas (2013) for their clade Averaptora.[23]

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.[24][25] 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.[25]

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.[26] Paraves, Eumaniraptora and Averaptora are generally considered to be synonyms. Deinonychosauria will become a synonym of Dromaeosauridae if troodontids are closer to Avialae. Tetrapterygidae is a polyphyletic grouping of four-winged basal paravian genera.

Origin and early evolution

Paravians diverged from other maniraptorans around 165 Mya; around 110-90 Mya, the ancestors of Neornithes (modern birds) split from other paravians.[27]

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.[28] The prototypical fossil is Archaeopteryx, of which 11 whole or partial examples have been found.[29]

See also

References

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  2. ^ a b Li, Rihui; Lockley, M.G.; Makovicky, P.J.; Matsukawa, M.; Norell, M.A.; Harris, J.D.; Liu, M. (2007). "Behavioral and faunal implications of Early Cretaceous deinonychosaur trackways from China". Naturwissenschaften. 95 (3): 185–91. Bibcode:2008NW.....95..185L. doi:10.1007/s00114-007-0310-7. PMID 17952398. S2CID 16380823.
  3. ^ Mayr, G. (Oct 2016). Avian Evolution: The Fossil Record of Birds and its Paleobiological Significance (1 ed.). p. Ch. 2. ISBN 978-1119020769.
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  5. ^ Zanno, L.E.; Makovicky, P.J. (2011). "Herbivorous ecomorphology and specialization patterns in theropod dinosaur evolution". Proc Natl Acad Sci USA. 108 (1): 232–237. Bibcode:2011PNAS..108..232Z. doi:10.1073/pnas.1011924108. PMC 3017133. PMID 21173263.
  6. ^ 125-Million-Year-Old Biplanes: New Evidence Suggests the Earliest Bird Species Had Feathers on their Hind Limbs
  7. ^ The asymmetry of the carpal joint and the evolution of wing folding in maniraptoran theropod dinosaurs
  8. ^ Hu, Dongyu; Lianhi, Hou; Zhang, Lijun; Xu, Xing (2009). "A pre-Archaeopteryx troodontid theropod from China with long feathers on the metatarsus". Nature. 461 (7264): 640–643. Bibcode:2009Natur.461..640H. doi:10.1038/nature08322. PMID 19794491. S2CID 205218015.
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  16. ^ Dinosaurs 'shrank' regularly to become birds
  17. ^ How Dinosaurs Shrank and Became Birds
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  23. ^ Federico L. Agnolín and Fernando E. Novas (2013). Avian ancestors. A review of the phylogenetic relationships of the theropods Unenlagiidae, Microraptoria, Anchiornis and Scansoriopterygidae. SpringerBriefs in Earth System Sciences. pp. 1–96. doi:10.1007/978-94-007-5637-3. ISBN 978-94-007-5636-6. S2CID 199493087.
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  29. ^ Foth, C.; et al. (Jul 2014). "New specimen of Archaeopteryx provides insights into the evolution of pennaceous feathers". Nature. 511 (7507): 79–82. Bibcode:2014Natur.511...79F. doi:10.1038/nature13467. PMID 24990749. S2CID 4464659.

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Media files used on this page

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Swooping Eagle Edit this at Structured Data on Commons
Ichthyornis restoration.jpeg
Author/Creator: El fosilmaníaco, Licence: CC BY-SA 4.0
Life restoration of Ichthyornis dispar, a primitive seabird that lived in the Western Interior Seaway (North America)during the Late Cretaceous.
Mononykus Restoration.png
Author/Creator: PaleoNeolitic, Licence: CC BY 4.0
Life restoration of the Mongolian alvarezsaurid Mononykus olecranus.
Therizinosaurus Restoration.png
Author/Creator: PaleoNeolitic, Licence: CC BY 4.0
Life restoration of the gigantic, Late Cretaceous therizinosaurid Therizinosaurus cheloniformis. Claws and arms based on holotype PIN 551-483 and specimens IGM 100/15, 100/16 and 100/17.
Melopsittacus undulatus -Atlanta Zoo, Georgia, USA-8a-2c.jpg
Author/Creator: , Licence: CC BY-SA 3.0
A female Budgerigar at Atlanta Zoo, Georgia, USA.
Cruralispennia reconstruction.tif
Author/Creator: Fanboyphilosopher (Neil Pezzoni), Licence: CC BY-SA 4.0
A life reconstruction of the enantiornithean Cruralispennia multidonta.
Utahraptor Restoration.png
Author/Creator: Fred Wierum, Licence: CC BY-SA 4.0
Artistic restoration of Utahraptor ostrommaysorum
Deinonychus patte arrière gauche.jpg
Author/Creator: Didier Descouens, Licence: CC BY-SA 4.0
Cast of left hind foot of Deinonychus antirrhopus (holotype YPM 5205) (Ostrom 1969) Restored by John Ostrom of Peabody Museum of Natural History. Private collection.
Stage : Cretaceus. 115-108 million years Before the Current Era (from the mid-aptian to early albian stages)
Locality : Cloverly formation, Montana, USA.
This photograph is published in Audubon Magazine January - February 2015
Confuciusornis plumage pattern.jpg
Author/Creator: Art by Velizar Simeonovski. Published by Quanguo Li​, Julia A. Clarke, Ke-Qin Gao, Jennifer A. Peteya, Matthew D. Shawkey, Licence: CC BY 4.0

Reconstruction of the plumage in Confuciusornis CUGB P140.

Morphological data and probable eumelanin signatures are consistent darker preserved regions as associated with dark colors in the fossil (sampling regime explained in Fig. 1).
Austroraptor Restoration.png
Author/Creator: Fred Wierum, Licence: CC BY-SA 4.0
Artistic restoration of Austroraptor cabazai
Tyrannoskull.jpg
Complete Tyrannosaurus rex skull, AMNH 5027.
Allosaurus Jardin des Plantes.png
Author/Creator: Eric Gaba (Sting - fr:Sting), Licence: CC BY-SA 1.0
Skeleton of an Allosaurus, a dinosaur of the Late Jurassic. Molding of a specimen discovered in Utah, USA.
Ambopteryx restoration.png
Author/Creator: Audrey.m.horn, Licence: CC BY-SA 4.0
Restoration of Ambopteryx longibrachium based on known fossil elements
Anchiornis martyniuk.png
Author/Creator: Matt Martyniuk, Licence: CC BY 3.0
Illustration of the basal troodontid Anchiornis huxleyi, by Matt Martyniuk. Digital. Colors based on the patterns recovered by Li et al. 2010.
Patagopteryx deferrariisi.jpg
Author/Creator: FunkMonk (Michael B. H.), Licence: CC BY-SA 3.0
Patagopteryx deferrariisi
Apatoraptor NT small.jpg
Author/Creator: Nobu Tamura email:nobu.tamura@yahoo.com http://spinops.blogspot.com/ http://paleoexhibit.blogspot.com/, Licence: CC BY-SA 4.0
Apatoraptor pennatus
Crossopterygii fins tetrapod legs.svg
Comparison between the fins of A., Crossopterygiin fishes and the legs of B., tetrapods. Bones which correspond to each other have the same color.
Archaeopteryx lithographica - Pedro José Salas Fontelles (flipped).jpg
Author/Creator: Pedro José Salas Fontelles, Licence: CC BY-SA 3.0
Restauración del aspecto en vida del dinosaurio transicional Archaeopteryx lithographica que habitó en el Jurásico tardío, hace unos 150 millones de años, en lo que hoy es el sur de Alemania. Está realizado a partir del esqueletal realizado por el paleontólogo Scott Hartman.

http://www.skeletaldrawing.com/theropods/archaeopteryx

Éste fósil tiene una importancia vital en el estudio de las aves y su evolución a partir de los dinosaurios, así como la aparición del vuelo en estos animales.

La ilustración representa la coloración que se le atribuye a Archaeopteryx gracias al estudio de los melanosomas. Se sabe que predominaba una coloración oscura o negruzca en todo el animal con las puntas de las plumas de vuelo de color más oscuro que el resto del cuerpo. Me he inspirado en el plumaje del Cormorán grande Phalacrocorax carbo.
Tree of life.svg
Author/Creator: Samsara, Licence: CC-BY-SA-3.0

A phylogenetic tree of living things, based on rRNA data, showing the separation of bacteria, archaea, and eukaryotes. Trees constructed with other genes are generally similar, although they may place some early-branching groups very differently, thanks to long branch attraction. The exact relationships of the three domains are still being debated, as is the position of the root of the tree. It has also been suggested that due to lateral gene transfer, a tree may not be the best representation of the genetic relationships of all organisms.

(Replacing en:Image:Tree_of_life.jpg) Original creator User:Samsara.
Longipteryx restoration.jpg
Author/Creator: El fosilmaníaco, Licence: CC BY-SA 4.0
Life restoration of Longipteryx chaoyangensis, an enantiornithine bird which lived in China during the Early Cretaceous period, around 120 million years ago
Dromaeo-avemorphs.png
Author/Creator: Titomaurer, Eduard Solà Vázquez, Dinoguy2, Stacie DaPonte[1], Bernard Sandler[2], Greg Heartsfield[3], Jim The Photographer[4], and Jonathan Chen., Licence: CC BY-SA 4.0
The "dromaeo-avemorphs", as they are informally known (Paul, 2002), represent a group of early paravian theropods with asymmetrical feathers and an Archaeopteryx-like body. According to Hartman et al. (2019), the animals shown in this image might, together, form a clade (monophyletic group) without modern birds.
Patagonykuspuertai.jpg
Author/Creator: GabrielNU, Licence: CC BY-SA 4.0
Reconstruction of Patagonykus puertai. Based on Novas (1997); missing portions follow typical alvarezsaurid proportions (e.g. Shuvuuia)
Zanabazar.jpg
(c) FunkMonk, CC BY 3.0
Zanabazar junior (formerly Saurornithoides).
Microraptor Restoration (cropped).png
Author/Creator: Fred Wierum, Licence: CC BY-SA 4.0
Microraptor gui reconstruction cropped for use in navboxes, etc.