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Maniraptorans
Fossil range: Late JurassicRecent,
Possible Early Jurassic record.
Archaeo-deinony hands
The hands of Deinonychus (left) and Archaeopteryx (right) are typical of maniraptorans.
Scientific classification

Class

Reptilia

Superorder

Dinosauria

Order

Saurischia

Suborder

Theropoda

(Unranked)

Maniraptoriformes

(Unranked)

Maniraptoriformes

(Unranked)

Maniraptora
Gauthier, 1986

Subclades

See text.


Maniraptora ("hand snatchers") is a clade of coelurosaurian dinosaurs which includes the birds and the dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauridae 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 (see Eshanosaurus). Many maniraptorans were feathered, and are regarded as surviving today as over 9,000 species of living birds.

CharacteristicsEdit

Maniraptorans are characterized by long arms and three-fingered hands, as well as a "half-moon shaped" (semi-lunate) bone in the wrist (carpus). Maniraptorans are the only dinosaurs known to have breast bones (ossified sternal plates). In 2004, Tom Holtz and Halszka Osmólska pointed out six other maniraptoran characters relating to specific details of the skeleton (see Technical diagnosis below). Unlike most other saurischian dinosaurs, which have pubic bones that point forward, several groups of maniraptorans have an ornithischian-like backwards-pointing hip bone. A backward-pointing hip characterizes the therizinosaurs, dromaeosaurids, avialans, and some primitive troodontids. 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 and oviraptorosaurs is an evolutionary reversal, and that these groups evolved from ancestors with backward-pointing hips.[1]

Feathers and flightEdit

MicroraptorGui-PaleozoologicalMuseumOfChina-May23-08

Microraptor specimen with feather impressions

Modern pennaceous feathers and remiges are known from advanced maniraptoran groups (Oviraptorosauria and Paraves). More primitive maniraptorans, such as therizinosaurs (specifically Beipiaosaurus), preserve a combination of simple downy filaments and unique elongated quills.[2][3] Powered and/or gliding flight is present in members of Avialae, and possibly in some dromaeosaurids such as Rahonavis and Microraptor.[4] Simple feathers are known from more primitive coelurosaurs such as Sinosauropteryx, and possibly from even more distntly related species such as the ornithischian Tianyulong and the flying pterosaurs. Thus it appears as if some form of feathers or down-like integument would have been present in all maniraptorans, at least when they were young.[5]

DietEdit

Jinfengopteryx elegans 2

Jinfengopteryx specimen with seeds preserved in the stomach region

Scientists have traditionally assumed that all maniraptorans were primarily hypercarnivorous, that is, that they primarily ate and hunted only other vertebrates. 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 primarily omnivorous, giving rise to a number of 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 lead scientists such as Lindsay 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.[6][7][8]

ClassificationEdit

File:Eoconfuciusornis BW.jpg
Velociraptor BW

Velociraptor, a deinonychosaur

Gigantoraptor BW

Gigantoraptor, an oviraptorosaur

Nothronychus BW2

Nothronychus, a therizinosaur

The Maniraptora was originally named by Jacques Gauthier in 1986, for a branch-based clade defined as all dinosaurs closer to modern birds than to the ornithomimids. 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 (an apomorphy-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 groups Deinonychosauria, Oviraptorosauria, Therizinosauria, and Aves. Other taxa often found to be maniraptorans include the alvarezsaurids, Ornitholestes[5] and, less frequently, the compsognathids. Several taxa have been assigned to the maniraptora more definitively, though their exact placement within the group remains uncertain. These forms include the scansoriopterygids, Pedopenna, and Yixianosaurus, and the dubious Bradycneme.

The following cladogram follows Zanno et al. 2009, with omitted clade names after the definitions in Sereno, 2005.[6][9]


Maniraptora

Ornitholestes


unnamed

Therizinosauria


unnamed

Alvarezsauridae


unnamed

Oviraptorosauria


Paraves

Avialae


Deinonychosauria

Troodontidae



Dromaeosauridae








Alternate interpretationsEdit

In 2002, Czerkas and Yuan reported that some maniraptoran traits, such as a long, backwards-pointed, pubis, short ischia, as well as a perforated acetabulum (a hip socket that is a hole) are apparently absent in Scansoriopteryx. 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.[10] Zhang et al., in describing the closely related or conspecific specimen Epidendrosaurus, did not report any of the primitive traits mentioned by Czerkas and Yuan, but did find that the shoulder blade of Epidendrosaurus appeared primitive. Despite this, they placed Epidendrosaurus firmly within Maniraptora.[11]

Technical diagnosisEdit

Holtz and Osmólska (2004) diagnosed the clade Maniraptora based on the following characters: reduced or absent olecranon process of the ulna, greater trochanter and cranial trochanter of the femur fused into a trochanteric crest. An elongated, backwards-pointing pubic bone is present in therizinosauroids, dromaeosaurids, avialans, and the basal troodontid Sinovenator, which suggests that the propubic condition in advanced troodontids and oviraptorosaurs is a reversal.[1] Turner et al. (2007) named seven synapomorphies that diagnose Maniraptora.[5]

ReferencesEdit

  1. ^ a b Holtz, T.R. and Osmólska, H. (2004). "Saurischia." In Weishampel, Dodson and Osmólska (eds.), The Dinosauria, second edition. Berkeley: University of California Press.
  2. ^ Xu, X., Tang, Z-L., and Wang, X-L. (1999). "A therizinosauroid dinosaur with integumentary structures from China." Nature, 399: 350-354.
  3. ^ Xu X., Zheng X.-t. and You, H.-l. (2009). "A new feather type in a nonavian theropod and the early evolution of feathers." Proceedings of the National Academy of Sciences (Philadelphia), . doi: 10.1073/pnas.0810055106
  4. ^ Chiappe, L.M. (2007). Glorified Dinosaurs: The Origin and Early Evolution of Birds. Sydney: UNSW Press.
  5. ^ a b c Turner, A.H.; Pol, D., Clarke, J.A., Erickson, G.M., and Norell, M. (2007). "A basal dromaeosaurid and size evolution preceding avian flight" (pdf). Science 317: 1378–1381. doi:10.1126/science.1144066. PMID 17823350. http://www.sciencemag.org/cgi/reprint/317/5843/1378.pdf. 
  6. ^ a b Zanno, L.E., Gillette, D.D., Albright, L.B., and Titus, A.L. (2009). "A new North American therizinosaurid and the role of herbivory in 'predatory' dinosaur evolution." Proceedings of the Royal Society B, Published online before print July 15, 2009, doi: 10.1098/rspb.2009.1029.
  7. ^ Longrich, N.R.; and Currie, P.J. (2008). "Albertonykus borealis, a new alvarezsaur (Dinosauria: Theropoda) from the Early Maastrichtian of Alberta, Canada: Implications for the systematics and ecology of the Alvarezsauridae". Cretaceous Research online preprint: 239. doi:10.1016/j.cretres.2008.07.005. 
  8. ^ Holtz, T.R., Jr., Brinkman, D.L., and Chandler, C.L. (1998). "Dental morphometrics and a possibly omnivorous feeding habit for the theropod dinosaur Troodon." GAIA, 15: 159-166.
  9. ^ Sereno, P. C., McAllister, S., and Brusatte, S. L. (2005). "TaxonSearch: a relational database for suprageneric taxa and phylogenetic definitions." PhyloInformatics, 8: 1-21.[1]
  10. ^ Czerkas, S.A., and Yuan, C. (2002). "An arboreal maniraptoran from northeast China." Pp. 63-95 in Czerkas, S.J. (Ed.), Feathered Dinosaurs and the Origin of Flight. The Dinosaur Museum Journal 1. The Dinosaur Museum, Blanding, U.S.A. PDF abridged version
  11. ^ Zhang, F., Zhou, Z., Xu, X. & Wang, X. (2002). "A juvenile coelurosaurian theropod from China indicates arboreal habits." Naturwissenschaften, 89(9): 394-398. doi:10.1007 /s00114-002-0353-8.


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