Scansoriopteryx

Taxobox
name = "Scansoriopteryx"
fossil_range = Late Jurassic or Early Cretaceous


image_width = 200px
image_caption = Restoration of a hatchling "Scansoriopteryx heilmanni".
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
subordo = Theropoda
unranked_familia = Maniraptora
familia = Scansoriopterygidae
genus = "Scansoriopteryx"
genus_authority = Czerkas & Yuan, 2002
subdivision_ranks = Species
subdivision =
*"S. heilmanni" Czerkas & Yuan, 2002 (type)

"Scansoriopteryx" ("climbing wing") is a genus of maniraptoran dinosaur. Kevin Padian and Alan Feduccia have treated this genus as a synonym of "Epidendrosaurus"; the former making "Scansoriopteryx" a junior synonym.Padian, Kevin. (2001) "Basal Avialae" in "The Dinosauria" in "The Dinosauria: Second Edition" University of California Press. 2004.] Feduccia, Alan, Lingham-Soliar, Theagarten, Hinchliffe, J. Richard. "Do feathered dinosaurs exist? Testing the hypothesis on neontological and paleontological evidence" "Journal of Morphology" 266:125-166] The genus name may be formally invalidated at some point in the future, as a dispute is underway as to whether the name "Epidendrosaurus" or "Scansoriopteryx" was published first.Sereno, P. C. 2005. [http://www.taxonsearch.org/Archive/stem-archosauria-1.0.php Stem Archosauria—TaxonSearch] [version 1.0, 2005 November 7] ]

Described from only a single juvenile fossil specimen found in Liaoning, China, "Scansoriopteryx" is a sparrow - sized animal that shows pedal adaptations that indicate an arboreal (tree-dwelling) lifestyle. It possessed an unusual, elongated third finger. The type specimen of "Scansoriopteryx" also contains the fossilized impression of feathers.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. [http://www.dinosaur-museum.org/featheredinosaurs/arboreal_maniraptoran.pdf PDF abridged version] ]

"Scansoriopteryx" had wispy, down-like impressions around select parts of the body, forming V-shaped patterns similar to those seen in modern down feathers. The most prominent feather impressions trail from the left forearm and hand. Scales were also preserved near the base of the tail.

Taxonomy

"Scansoriopteryx" lent its name to the family Scansoriopterygidae, though the exact taxonomic placement of this family is currently uncertain. Also uncertain is the status of the name "Scansoriopteryx". The type specimen was described only a few months after a very similar animal, "Epidendrosaurus", was described online, though the name "Epidendrosaurus" was not published in print until after "Scansoriopteryx". These two specimens are so similar that they may be the same genus, in which case the name published first would have priority. The body which sets the rules for the naming of animals, the ICZN, has seen an amendment to the code that would favor the name "Epidendrosaurus" if/when formally adopted.Harris, J.D. (2004). " [http://www.iczn.org/BZNSep2004general_articles.htm 'Published works' in the Electronic Age: recommended amendments to Articles 8 and 9 of the Code.] " "Bulletin of Zoological Nomenclature" 61(3): 138-148.] See "Epidendrosaurus" for more information.

The type species is "Scansoriopteryx heilmanni" (type specimen number CAGS02-IG-gausa-1/DM 607).

Implications

Czerkas and Yuan used the suite of primitive and birdlike characters in "Scansoriopteryx" to argue for an unorthodox interpretation of dinosaur evolution. They stated that "Scansoriopteryx" was "clearly more primitive than "Archaeopteryx", based on its primitive, "saurischian-style" pubis and robust ischia. "Scansoriopteryx" also lacks a fully perforated acetabulum, the hole in the hip socket which is a key characteristic of Dinosauria and has traditionally been used to define the group. While the authors allowed that the hole may have closed secondarily, having evolved from a more traditional dinosaurian hip socket, they cited the other primitive features to argue that it is a true primitive trait, which would make "Scansoriopteryx" among the most birdlike "and" the most primitive known dinosaurs. Czerkas and Yuan called it a "proto-maniraptoran", supporting the hypothesis of Gregory S. Paul that the lager, ground-dwelling maniraptorans like "Velociraptor" evolved from small, flying or gliding forms that lived in trees. The authors took this idea further than Paul, however, and lent support to George Olshevsky's 1992 "birds came first" hypothesis, that "all" true theropods are secondarily flightless or at least secondarily arboreal, having evolved from small, tree-dwelling, "Scansoriopteryx"-like ancestors. Czerkas and Yuan also argued that, contrary to most phylogenetic trees, maniraptorans form a separate lineage from other theropods, and that this split occurred very early in theropod evolution.

Provenance

The provenance of "Scansoriopteryx" is uncertain, though Wang "et al." (2006), in their study of the age of the Daohugou Beds, suggested that it probably hails from the same beds, and thus is likely a synonym of "Epidendrosaurus". The Daohugou Beds supposedly date to the mid-late Jurassic Period.Wang, X., Zhou, Z., He, H., Jin, F., Wang, Y., Zhang, J., Wang, Y., Xu, X. & Zhang, F. (2005). "Stratigraphy and age of the Daohugou Bed in Ningcheng, Inner Mongolia." "Chinese Science Bulletin", 50(20): 2369-2376.] , but this is hotly contested. See the Daohugou Beds article for details.

Paleobiology

In describing "Scansoriopteryx", Czerkas & Yuan cited evidence for an arboreal lifestyle. They noted that, unlike all modern bird hatchlings, the forelimbs of "Scansoriopteryx" are longer than the hind limbs. The authors argued that this anomaly indicates the forelimbs played an important role in locomotion even at an extremely early developmental stage. "Scansoriopteryx" has a well-preserved foot, and the authors interpreted the hallux as reversed, the condition of a backward-pointing toe being widespread among modern tree-dwelling birds. Furthermore, the authors pointed to the short, stiffened tail of the "Scansoriopteryx" specimen as a tree-climbing adaptation. The tail may have been used as a prop, much like the tails of modern woodpeckers. Comparison with the hands of modern climbing species with elongated third digits, like iguanid lizards, also supports the tree-climbing hypothesis. Indeed, the hands of "Scansoriopteryx" are much better adapted to climbing than the modern tree-climbing hatchling of the Hoatzin.

"Scansoriopteryx" preserves impressions of simple, down-like feathers, especially around the hand and arm. The longer feathers in this region led Czerkas and Yuan to speculate that adult scansoriopterygids may have had reasonably well-developed wing feathers which could have aided in leaping or rudimentary gliding, though they ruled out the possibility that "Scansoriopteryx" could have achieved powered flight. Like other maniraptorans, "Scansoriopteryx" had a semilunate (half-moon shaped) bone in the wrist that allowed for bird-like folding motion in the hand. Even if powered flight was not possible, this motion could have aided manuverablitiy in leaping from branch to branch.

References

External links

* [http://dino.lm.com/images/display.php?id=294 Skeletal diagrams] of scansoriopterygids from The Dinosauricon.
* [http://dino.lm.com/taxa/display.php?name=Scansoriopteryx "Scansoriopteryx" image gallery] , from The Dinosauricon.