("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 Aves
and the Alvarezsauridae
are also often included. Together with the next closest sister group, the Ornithomimosauria
, Maniraptora comprises the more inclusive clade Maniraptoriformes
. Maniraptors first appear in the fossil record during the Jurassic Period
), and are regarded as surviving today
as over 9,000 species of living birds.
Maniraptors are characterized by elongated arms and tridactyl
hands, as well as a "half-moon shaped" (semi-lunate
) bone in the wrist (carpus
). Maniraptors are the only dinosaurs known to have ossified sternal plates
. Holtz and Osmolska (2004) name six other maniraptoran characters, including a reduced or absent olecranon process
of the ulna
, and the 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. Turner et al.
(2007) name seven synapomorphies that diagnose Maniraptora.
Modern pennaceous feathers and remiges are known from all maniraptoran groups except therizinosaurs, but they are inferred there as well. Fossils of Beipiaosaurus preserve some sort of feathers but their structure is not clear. Powered flight is present in members of Aves (or Avialae), and possibly in some dromaeosaurids such as Rahonavis. Also, simple feathers are known from more primitive dinosaurs such as Sinosauropteryx. Thus it appears as if some form of feathers or down-like integument may have been present in all maniraptorans at least when they were young. Powered flight on the other hand is probably an autapomorphy of only avialan lineages.
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 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 Turner et al. 2007, with omitted clade names after the definitions in Sereno, 2005.
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 maniraptorans, and hypothesized that maniraptorans may have branched off from theropods at a very early point, or may even have descended from pre-theropod dinosaurs. 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.