Microraptoria (Greek, μίκρος, mīkros: "small"; Latin, raptor: "one who seizes") is a clade of basal Dromaeosauridae theropod . Definitive microraptorians lived during the Barremian to Aptian stages of the Early Cretaceous in China. Probable microraptorian ichnotaxon Dromaeosauriformipes was discovered from the Jinju Formation of South Korea,[.] Most microraptorians were relatively small; adult specimens of Microraptor range between ) and weigh up to , making them some of the Dinosaur size.[Holtz, Thomas R. Jr. (2011) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages, Winter 2010 Appendix.]
Description
Microraptorians were a group of basal
Dromaeosauridae (popularly known as "raptors") with slender proportions and long limbs. All definitive members have been found in the
Yixian Formation and Jifuotang Formations of Liaoning County of China, so they're referred to as "Liaoning dromaeosaurids" by some researchers.
These formations (collectively known as the
Jehol Biota) 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. Some fragmentary
Paraves fossils from the
Late Cretaceous (
Campanian-
Maastrichtian stages) of North America have been putatively suggested as microraptorians, though their taxonomic referral are considered controversial, namely
Hesperonychus being recovered as an
Avialae in one phylogenetic analysis.
Size and proportions
Most microraptorians were small dinosaurs, with taxa such as
Microraptor and especially
Zhongjianosaurus being among the smallest nonavian dinosaurs known. However, some microraptorians, such as
Tianyuraptor 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
Eudromaeosauria, 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
Paraves and early birds such as
Anchiornis and
Archaeopteryx.
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
Microraptor possibly were able to use these wings to glide or take off from the ground,
and perhaps even capable of powered flight.
Characteristic features
Sources:
Microraptorines can be distinguished from other dromaeosaurids by these features:
In addition, several features are present in microraptorines with the exception of
Tianyuraptor, which is believed to be a basal member of the clade:
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A large oval fenestra in the coracoid
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Significantly shortened penultimate manual phalanges
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The posterior end of the ilium extending ventral to the ischial peduncle
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Lateral projections halfway down the pubis
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A strongly anteriorly curved pubic shaft
Classification
Microraptoria is usually classified as a clade of
Dromaeosauridae, though some consider the group to be outside the dromaeosaurid family.
Senter and colleagues expressly coined the name without the subfamily suffix
-inae to avoid perceived issues with erecting a
Linnean taxonomy 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.
In a 2024 paper which reported the smallest known juvenile specimen of Microraptor, Wang and Pei included microraptorians and within a new clade Serraraptoria.
See also
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Timeline of dromaeosaurid research
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"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
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2.http://www.taxonsearch.org/dev/taxon_edit.php?tax_id=483&Action=View
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3.http://theropoddatabase.blogspot.com/2010/03/article-1311-means-lewisuchinaeidae-is.html
