Maniraptora

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Maniraptorans
Temporal range:
Ma[1]
Possible Early Jurassic record[2]
Collage of nine maniraptorans. From top left to right:
Pelecanus onocrotalus
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Maniraptoriformes
Clade: Maniraptora
Gauthier, 1986
Subgroups
Synonyms
  • Metornithes Perle et al., 1993

Maniraptora is a

Jurassic Period (see Eshanosaurus), and survive today
as living birds.

Description

Microraptor specimen with feather impressions

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-

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.[3]

Technical diagnosis

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.[3] Turner et al. (2007) named seven synapomorphies that diagnose Maniraptora.[4]

Feathers and flight

Canada goose flying

Modern

Tianyulong confuciusi 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.[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 gliding

dromaeosaurid, 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 the Oviraptorosauria who had a tail with a tail fan of feathers with caudal anatomy resembling a pygostyle, are not known to have been capable of flight, but some scientists, such as Gregory S. Paul, have suggested that they could be descended from ancestors which flew. Paul has gone as far as to propose that Therizinosauria, Alvarezsauroidea, and the non-maniraptoran group Ornithomimosauria also descended from flying ancestors.[9]

Classification

The Maniraptora was originally named by

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 Dromaeosauridae, Troodontidae, Oviraptorosauria, Therizinosauria, and Avialae.[10] Other taxa often found to be maniraptorans include the alvarezsaurs and Ornitholestes.[4] 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.

In 1993, Perle and colleagues coined the name Metornithes 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 of Mononykus and modern birds, and all its descendants.[11]

The following cladogram follows the results of a phylogenetic study by Cau (2020).[12]

Maniraptora

Alternative interpretations

In 2002, Czerkas and Yuan reported that some maniraptoran traits, such as a long, backwards-pointed

Epidendrosaurus (now considered a synonym of Scansoriopteryx), 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 due to a number of synapomorphies.[14]

Paleobiology

Diet

Jinfengopteryx elegans
specimen with seeds preserved in the stomach region

Scientists traditionally assumed that maniraptorans were ancestrally hypercarnivorous, that is, that most non-avialan species 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 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 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.[10][15][16]

Reproduction

A 2023 study analyzing fossil eggshells assigned to Troodon with clumped isotope thermometry found that Troodon, 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 functional ovaries, contrasting with the one functional ovary in birds, and were thus limited in the numbers of eggs each individual could produce.[17]

References

  1. doi:10.1007/s11434-008-0287-4
    .
  2. doi:10.1111/j.1475-4983.2009.00887.x
    .
  3. ^ 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.
  4. ^
    S2CID 2519726
    .
  5. S2CID 204993327
    .
  6. doi:10.1073/pnas.0810055106
  7. ^ Chiappe, L.M. (2007). Glorified Dinosaurs: The Origin and Early Evolution of Birds. Sydney: UNSW Press.
  8. ^ Scientists find a new dinosaur with well preserved, bird-like wings — but not for flight
  9. ^ Paul, G.S. (2002). Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Baltimore: Johns Hopkins University Press.
  10. ^
    doi:10.1098/rspb.2009.1029
    .
  11. S2CID 4245171
    .
  12. ^ Cau, Andrea. “The body plan of Halszkaraptor escuilliei (Dinosauria, Theropoda) is not a transitional form along the evolution of dromaeosaurid hypercarnivory.” PeerJ vol. 8 e8672. 25 Feb. 2020, doi:10.7717/peerj.8672
  13. ^ 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
  14. ^ 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.
  15. doi:10.1016/j.cretres.2008.07.005
    .
  16. ^ Holtz, T.R. Jr.; Brinkman, D.L.; Chandler, C.L. (1998). "Dental morphometrics and a possibly omnivorous feeding habit for the theropod dinosaur Troodon". GAIA. 15: 159–166.
  17. PMID 37011196
    .
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