| Maniraptorans | |
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| Collage of six maniraptorans. From top left to right: the Zamyn Khondtoviraptorid,Sinornithosaurus, thePrince Creektroodontid,Patagonykus, ashort-tailed albatross, andNothronychus | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Maniraptoriformes |
| Clade: | Maniraptora Gauthier, 1986 |
| Subgroups | |
| Synonyms | |
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Maniraptora is aclade ofcoelurosauriandinosaurs which includes thebirds and the non-avian dinosaurs that were more closely related to them than toOrnithomimus velox. It contains the major subgroupsAvialae,Dromaeosauridae,Troodontidae,Oviraptorosauria, andTherizinosauria.Ornitholestes and theAlvarezsauroidea are also often included. Together with the next closest sister group, theOrnithomimosauria, Maniraptora comprises the more inclusive cladeManiraptoriformes. Maniraptorans first appear in the fossil record during theJurassic Period (seeEshanosaurus), andsurvive today as living birds.
Maniraptorans are characterized by long arms and three-fingered hands (though reduced or fused in some lineages), as well as a "half-moon shaped" (semi-lunate) bone in the wrist (carpus). In 2004, Tom Holtz and Halszka Osmólska pointed out six other maniraptoran characteristics relating to specific details of the skeleton. Unlike most othersaurischian dinosaurs, which have pubic bones that point forward, several groups of maniraptorans have anornithischian-like backwards-pointing hip bone. A backward-pointing hip characterizes thetherizinosaurs,dromaeosaurids,avialans, and some primitivetroodontids. The fact that the backward-pointing hip is present in so many diverse maniraptoran groups has led most scientists to conclude that the "primitive" forward-pointing hip seen in advanced troodontids andoviraptorosaurs is an evolutionary reversal, and that these groups evolved from ancestors with backward-pointing hips.[3]
Holtz and Osmólska (2004) diagnosed the clade Maniraptora based on the following characters: reduced or absentolecranon process of theulna,greater trochanter andcranial trochanter of thefemur fused into atrochanteric crest. An elongated, backwards-pointing pubic bone is present in therizinosauroids, dromaeosaurids, avialans, and the basal troodontidSinovenator, which suggests that the propubic condition in advanced troodontids and oviraptorosaurs is a reversal.[3] Turneret al. (2007) named seven synapomorphies that diagnose Maniraptora.[4]
Modernpennaceous feathers andremiges are known in the advanced maniraptoran groupAviremigia. More primitive maniraptorans, such as therizinosaurs (specificallyBeipiaosaurus), preserve a combination of simple downy filaments and unique elongated quills.[5][6] Simple feathers are known from more primitive coelurosaurs such asSinosauropteryx prima, and possibly from even more distantly related species such as theornithischianTianyulong confuciusi and the flyingpterosaurs. Thus it appears as if some form of feathers or down-likeintegument would have been present in all maniraptorans, at least when they were young.[4]
Maniraptora is the only dinosaur group known to include flying members, though how far back in this lineage flight extends is controversial. Powered and/or glidingflight is believed to have been present in some types of non-avialan paravians, including dromaeosaurids, such asRahonavis andMicroraptor.[7]Zhenyuanlong suni, adromaeosaurid, was too heavy to fly but still had wings with feathers required for flying, which suggests its ancestors had the ability for aerial locomotion.[8] Other groups, like theOviraptorosauria who had a tail with a tail fan of feathers with caudal anatomy resembling apygostyle, are not known to have been capable of flight, but some scientists, such asGregory S. Paul, have suggested that they could be descended from ancestors which flew. Paul has gone as far as to propose thatTherizinosauria,Alvarezsauroidea, and the non-maniraptoran groupOrnithomimosauria also descended from flying ancestors.[9]
The Maniraptora was originally named byJacques Gauthier in 1986, for abranch-basedclade defined as all dinosaurs closer to modern birds than to theornithomimids. Gauthier noted that this group could be easily characterized by their long forelimbs and hands, which he interpreted as adaptations for grasping (hence the name Maniraptora, which means "hand snatchers" in relation to their 'seizing hands'). In 1994,Thomas R. Holtz attempted to define the group based on the characteristics of the hand and wrist alone (anapomorphy-based definition), and included the long, thin fingers, bowed, wing-like forearm bones, and half-moon shaped wrist bone as key characters. Most subsequent studies have not followed this definition, however, preferring the earlier branch-based definition.
The branch-based definition usually includes the major groupsDromaeosauridae,Troodontidae,Oviraptorosauria,Therizinosauria, andAvialae.[10] Other taxa often found to be maniraptorans include thealvarezsaurs andOrnitholestes.[4][11] Several taxa have been assigned to the Maniraptora more definitively, though their exact placement within the group remains uncertain. These forms include thescansoriopterygids,Pedopenna, andYixianosaurus.
In 1993, Perle and colleagues coined the nameMetornithes to include alvarezsaurids and modern birds, which the researchers believed were members of the Avialae. This group was defined as a clade by Luis Chiappe in 1995 as the last common ancestor ofMononykus and modern birds, and all its descendants.[12]
Pennaraptora (Latinpenna "bird feather" +raptor "thief", fromrapere "snatch"; a feathered bird-like predator) is aclade within Maniraptora, defined as the most recent common ancestor ofOviraptor philoceratops,Deinonychus antirrhopus, andPasser domesticus (the house sparrow), and all descendants thereof, by Fothet al., 2014.[13]
The clade "Aviremigia" was conditionally proposed along with several otherapomorphy-based clades relating tobirds byJacques Gauthier andKevin de Queiroz in a 2001 paper. Their proposed definition for the group was "the clade stemming from the firstpanavian with ...remiges andrectrices, that is, enlarged, stiff-shafted, closed-vaned (= barbules bearing hooked distal pennulae), pennaceous feathers arising from the distal forelimbs and tail".[14] Ancestral morphology relating to pennaceous feathers suggests that basal species of Pennaraptora were capable of scansorial locomotion and gliding, and further evolution of said adaptation within the clade would eventually give rise to the origin of flight in avian species.[15]
The followingcladogram follows the results of a phylogenetic study by Cau (2020).[16]
| Maniraptora | |
In 2002, Czerkas and Yuan reported that some maniraptoran traits, such as a long, backwards-pointedpubis and shortischia were present inScansoriopteryx, a scansoriopterygid. The authors considered it to be more primitive than true theropods, and hypothesized that maniraptorans may have branched off from theropods at a very early point, or may even have descended from pre-theropod dinosaurs.[17] Zhanget al., in describing the closely related or conspecific specimenEpidendrosaurus (now considered a synonym ofScansoriopteryx), did not report any of the primitive traits mentioned by Czerkas and Yuan, but did find that the shoulder blade ofEpidendrosaurus appeared primitive. Despite this, they placedEpidendrosaurus firmly within Maniraptora due to a number of synapomorphies.[18]
Scientists traditionally assumed that maniraptorans were ancestrallyhypercarnivorous, that is, that most non-avialan species primarily ate and hunted only othervertebrates. However, a number of discoveries made during the first decade of the 21st century, as well as re-evaluation of older evidence, began to suggest that maniraptorans were a primarilyomnivorous group, including a number of sub-groups that ate mainly plants, insects, or other food sources besides meat. Additionally, phylogenetic studies of maniraptoran relationships began to more consistently show that herbivorous or omnivorous groups were spread throughout the Maniraptora, rather than representing a single side-branch as previously thought. This led scientists such asLindsay Zanno to conclude that the ancestral maniraptoran must have been omnivorous, giving rise to several purely herbivorous groups (such as the therizinosaurs, primitive oviraptorosaurs, and some avialans) and that, among non-avians, only one group reverted to pure carnivores (the dromaeosaurids). Most other groups fell somewhere in between the two extremes, with alvarezsaurids and some avialans being insectivorous, and with advanced oviraptorosaurs and troodontids being omnivorous.[10][19][20]
A 2023 study analyzing fossil eggshells assigned toTroodon withclumped isotope thermometry found thatTroodon, and likely other non-avian maniraptorans, had a slowed calcification of eggs akin to that of most reptiles. This contrasts with the rapid calcification of eggs found in modern birds, indicating that most maniraptorans aside from birds retained this basal trait. This would also indicate that most non-avian maniraptorans possessed two functionalovaries, contrasting with the one functional ovary in birds, and were thus limited in the numbers of eggs each individual could produce.[21]
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