Microraptoria (Greek, μίκρος, ''mīkros'': "small"; Latin, ''raptor'': "one who seizes") is a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...

of basal

dromaeosaurid Dromaeosauridae () is a family of feathered 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 ('), meaning ...

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s. The first microraptorians appeared 125 million years ago in

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...

. Many are known for long feathers on their legs and may have been semi

arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. The habitats pose nu ...

powered fliers, some of which were even capable of launching from the ground.. Most microraptorians were relatively small; adult specimens of ''

Microraptor ''Microraptor'' ( Greek, μικρός, ''mīkros'': "small"; Latin, ''raptor'': "one who seizes") is a genus of small, four-winged dromaeosaurid dinosaurs. Numerous well-preserved fossil specimens have been recovered from Liaoning, China. ...

'' range between ) and weigh up to , making them some of the smallest known nonavialan dinosaurs.Holtz, Thomas R. Jr. (2011) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,'
Winter 2010 Appendix.
/ref>

Description

Microraptorians were a group of basal

dromaeosaurids Dromaeosauridae () is a family of feathered 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 ('), meaning ...

(popularly known as "raptors") with slender proportions and long limbs. With the exception of ''

Hesperonychus ''Hesperonychus'' (meaning "western claw") was a small, carnivorous dinosaur. It was a member of the family Dromaeosauridae, along with its larger relatives ''Deinonychus'' and ''Velociraptor''. There is one described species, ''Hesperonychus eli ...

'' from the late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

of North America, all microraptorians have been found in the Yixian and Jifuotang Formations of Liaoning County, China, hence why microraptorians are sometimes referred to as "Liaoning dromaeosaurs". These formations (collectively known as the

Jehol group The Jehol Biota includes all the living organisms – the ecosystem – of northeastern China between 133 and 120 million years ago. This is the Lower Cretaceous ecosystem which left fossils in the Yixian Formation and Jiufotang Formation. These ...

) have been dated to the early Cretaceous and at that time would have been part of a temperate wetland ecosystem threatened by frequent volcanic eruptions. Like other dromaeosaurids, microraptorians were carnivores with relatively large, serrated teeth and a hyperextendable second toe equipped with a curved claw.

Size and proportions

Most microraptorians were small dinosaurs, with taxa such as ''

'' and especially ''

Zhongjianosaurus ''Zhongjianosaurus'' is a genus of dromaeosaurid Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosaur ...

'' being among the smallest nonavian dinosaurs known. However, some microraptorians, such as ''

Tianyuraptor ''Tianyuraptor'' is a genus of short-armed dromaeosaurid dinosaur ('running lizard'; a type of small dinosaur considered to be closely related to birds) that lived during the Early Cretaceous, about 122 million years ago. Its remains have been ...

'' and '' Changyuraptor'', were larger and similar to other dromaeosaurids in size. Many microraptorians also had long and robust arms and legs, in contrast to the stockier

eudromaeosaurs Eudromaeosauria ("true dromaeosaurs") is a subgroup of terrestrial dromaeosaurid theropod dinosaurs. They were relatively small to medium-sized, feathered hypercarnivores (with diets consisting almost entirely of other terrestrial vertebrates) ...

, although long arms are not universal to the group, since the basal microraptorian ''Tianyuraptor'' had unusually short arms by dromaeosaurid standards. Considering this, the small size and long wings of some microraptorians likely are examples of convergent evolution with other small paravians and early birds such as ''

Anchiornis ''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 " ...

'' and ''

Archaeopteryx ''Archaeopteryx'' (; ), sometimes referred to by its German name, "" ( ''Primeval Bird''), is a genus of bird-like dinosaurs. The name derives from the ancient Greek (''archaīos''), meaning "ancient", and (''ptéryx''), meaning "feather" ...

''.

Feathers

The fossilization conditions of the Jehol group are very accommodating to the preservation of soft structures in fossils, and as a result, many microraptorians have been preserved with a covering of feathers. Not only have long, advanced feathers been preserved on the arms and tails of many specimens, but a few species even have long feathers on their legs. This condition has also been seen in other paravians such as ''Anchiornis'', and has caused these kinds of dinosaurs to be labelled as "four-winged dinosaurs". The largest known "four-winged" dinosaur, '' Changyuraptor,'' is a microraptorian. Some microraptorians such as ''

'' possibly were able to use these wings to glide or take off from the ground.

Characteristic features

Microraptorines can be distinguished from other dromaeosaurids by these features: * A

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. T ...

laterally sculpted by small pits * A very short manual

phalanx The phalanx ( grc, φάλαγξ; plural phalanxes or phalanges, , ) was a rectangular mass military formation, usually composed entirely of heavy infantry armed with spears, pikes, sarissas, or similar pole weapons. The term is particularly ...

III-2 * A shortened first digit of the hand * A splatulate (rounded)

pubic symphysis The pubic symphysis is a secondary cartilaginous joint between the left and right superior rami of the pubis of the hip bones. It is in front of and below the urinary bladder. In males, the suspensory ligament of the penis attaches to the pubi ...

* A

metatarsal The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the me ...

III with a pinched proximal end * A slender metatarsal II In addition, several features are present in microraptorines with the exception of ''Tianyuraptor'', which is believed to be a basal member of the clade: * A large oval fenestra in the

coracoid A coracoid (from Greek κόραξ, ''koraks'', raven) is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is prese ...

* Significantly shortened penultimate manual phalanges * The posterior end of the ilium extending ventral to the ischial peduncle * Lateral projections halfway down the pubis * A strongly anteriorly curved pubic shaft

Classification

Microraptoria is usually classified as a clade of

. Senter and colleagues expressly coined the name without the subfamily suffix ''-inae'' to avoid perceived issues with erecting a

traditional A tradition is a belief or behavior (folk custom) passed down within a group or society with symbolic meaning or special significance with origins in the past. A component of cultural expressions and folklore, common examples include holidays or ...

family-group taxon, should the group be found to lie outside the Dromaeosauridae proper. Sereno offered a revised definition of the subgroup containing ''Microraptor'' to ensure that it would fall within the Dromaeosauridae, and erected the subfamily Microraptorinae, attributing it to Senter ''et al.'', though this usage has only appeared on his online TaxonSearch database and has not been formally published.Sereno, P. C. 2005
Stem Archosauria—TaxonSearch
[version 1.0, November 7, 2005 The cladogram below follows a 2012 analysis by paleontologists Phil Senter, James I. Kirkland, Donald D. DeBlieux, Scott Madsen and Natalie Toth.

References

*"Expand and Life history of a basal bird: morphometrics of the Early Cretaceous Confuciusornis" Luis M Chiappe, Jesús Marugán-Lobón, Shu'an Ji & Zhonghe Zhou (2008)

External links

*1.http://www.paleodb.org/cgi-bin/bridge.pl?a=basicTaxonInfo&taxon_no=143267 *2.http://www.taxonsearch.org/dev/taxon_edit.php?tax_id=483&Action=View *3.http://theropoddatabase.blogspot.com/2010/03/article-1311-means-lewisuchinaeidae-is.html {{Taxonbar, from=Q3312288 Dromaeosaurs