Longisquama

Live reconstruction of Longisquama based on the only known skeleton instance. Arrangement of the elongated dorsal scales based on Haubold & Buffetaut (1987).

• Madygen ( Batken oblast, Südwestkirgisistan )

• Longisquama insignis

Longisquama ("long scale ") was a genus diapsider reptile whose fossils were found in sedimentary rocks of the mid-to upper Triassic Madygen Formation in southwestern Kyrgyzstan. A number of putative extended scales that ansetzten the back of the only known skeleton specimen is interpreted as an adaptation to gliding flight.

Fund locality and type - specimen

The Triassic clastic sedimentary rocks of the Madygen lineup are open ( Batken area ) in several places near the village Madgyen in Lyailyaksii district in southwestern Kyrgyzstan. According to previous results represent the rocks of the estimated 500 m thick sequence of river and lake deposits in which there are a few coal seams.

Besides Longisquama the Madygen lineup has a variety of macrophytes ( plants large fossils ) and insects as well as bony fish (including a lung fish ), mussels, crustaceans, the Amphib Triassurus, therapsides genus Madysaurus and Sharovipteryx, another small Diapsiden spawned. In Sharovipteryx and Longisquama, both "Upper horror episode" the Madygen lineup originate from the Ton-/Schluffsteinen of the outline of the body are very detailed as impression obtained ( skin shade preservation ), so that one can distinguish individual scales.

The 1970 described by Sharov as Longisquama insignis about 15 cm long partial skeleton (PIN 2584/4, holotype ) is the only skeletal specimen found so far of the genus. It includes plate and counter plate on which an incomplete skull, the neck, the front part of the chest, the shoulder girdle, the front limbs and skin marks on the neck, are preserved along the arms and back. Particularly striking are elongated sheet-like body appendages emanating from the midline of the back. Five additional copies of this body appendage unrelated to skeletal remains have been described.

Anatomy

Longisquamas skull is characterized by the strongly enhanced edge of the upper tempo Ralf Sters (one located behind the eye skull opening) from. Sharov described two characteristics that apply to the group of archosaurs, which includes crocodiles and dinosaurs are as characteristic: a skull window, which is located between eye and nostril ( the Antorbitalforamen ), and an opening in the lower jaw ( the Mandibularforamen ). The presence of these openings and the derived systematic mapping were drawn inter alia from Unwin & Benton ( 2001) in doubt. Jones et. al. (2001 ), however, expressly confirm the existence of a Antorbitalforamens, according to the interpretation of Peters ( 2000) are to be distinguished even three forwards decreasing Antorbitalfenster ( see figure).

Unlike archosaurs, but similar to dandruff lizards ( lepidosaurs ) were Longisquamas teeth apparently acrodont, that is, without roots attached to the jawbone. The short neck is made of eight cervical vertebrae, for which the proof of ribs is ambiguous. The first of the elongated sheet-like body tag put on above the posterior cervical vertebrae. There are eight thin back in the length of growing ribs of the chest and a corresponding number of vertebrae before, the tail upward subsequent part of the body is not preserved.

The shoulder girdle consists of long narrow shoulder blades, short rod-shaped Rabe legs, two robust clavicles, which together form a U- shape and are connected to an intermediate collarbone ( interclavicle ). Unwin & Benton ( 2001) point out that the presence of an ossified between the clavicle is again atypical of archosaurs. Jones et al (2001) respond that between clavicles occur such as Euparkeria also in a number of archosaurs. They describe the two clavicles due to their shape and overlap as a fork leg, the same in form to that of Archaeopteryx. Peters ( 2000) describes a sternum, which is framed by the two clavicles, and a kind of keel, which go out from the intermediate collarbone. However, he sees the particular morphology of the shoulder girdle of Longisquama no affinity for birds, but also emphasizes the conformity of the complex of clavicles, between the clavicle and sternum with a juvenile specimen of the primitive pterosaur Eudimorphodon.

The upper arms are slender, slightly S-shaped curved and as long as the forearm bones about. Longisquamas hands are asymmetric - for the fingers Nos. I to V, the number of phalanges 2, 3, 4, 5 or 4 The second outermost joints of the fingers is (those that will underpin the claws ) are disproportionately long, a feature of the often occurs as a result of adaptation to climbing. A characteristic for the genus Longisquama ( autapomorphes ) feature is the extremely elongated fourth finger that resembles the humerus in length.

Scales or feathers?

The up to 15 cm long blade-like protruding from the back body appendages are known only by the Longisquama assigned specimens from the Madygen lineup. Sharov (1970 ), they interpreted as extended cone scales and gave the new class an appropriate name. He assumed that they had an aerodynamic function and functioned much like parachutes. Haubold & Buffetaut (1987 ) developed a model in which the attachments were arranged in pairs and as a fold-out wings to glide enabled ( see figure in the box).

Only Jones et. al. (2000) doubted that the trailer actually reptilian scales represented - they declared that if it were feathers of a " non- bird ", which are homologous to bird feathers and discussed various observations that should support this thesis. The central axis of each structure represents therefore the spring shaft ( rachis ) and otherwise interpreted as wrinkling or struts branches from the central axis are taken as beams ( radii ) is equal to the rays of a bird's feather. The feather banner, which is composed is as in birds from individual beams, had been this idea after misinterpreted in previous descriptions as massive scale, actually are the "rays" at Longisquama grow together only at the outer edge, so that the " feathers" a smooth outline and not, as expected, show a frayed edge.

Jones et al. (2001 ) introduced as evidence the cross-over of some " rays " which can not be explained with the interpretation as a massive scale. The hollow cylindrical base of the trailer equal to the spindle ( quill, calamus ) real bird feathers were divided transversely internally, in their view, is one of the most important evidence. Such structures could only be explained by the growth of a feather follicle out of the same growth mechanism as springs should therefore be assumed. It should also be near the base of a serving of "feathers" with a structure to observe the spring vagina modern springs same. Given the existence of a " follicular spring base," a " quill ", a " spring vagina ", a " spring stem " and one of "rays" existing " feather banner ," concluded Jones et al. (2000, 2001) that there must be in the body appendages of Longisquama to feathers.

A lot of the familiar with the origin of birds paleontologists holds this view for misinterpretation, which is based among other things on the About Interpreting the observed tissue imprints or even to disregard contradictory findings. For example, are nowhere checkmark ( Rami ) to prove that the individual beams combine with contour and flight feathers ( so that there is a continuous feather banner ). At margins merged bird feathers are a very rare phenomenon and in this case a far-fetched explanation in the recent bird life. The as " rays" interpreted structures of the appendage had partly no resemblance to those of bird feathers and are not detectable in many places. Prum (2001) agrees with Jones et. al. (2000) agree that the body tag of Longisquama have a cylindrical base, but does not see the need for them to have been formed by Federfollikeln (or homologous with Federfollikeln structures).

In addition to skepticism about the Jones et. al. published to Longisquama observations and conclusions, a majority of paleontologists from the plurality of common features and derived from the results of many kladistischer analysis is convinced identify the birds as direct descendants of theropod dinosaurs. Fossils of feathered dinosaurs show various intermediate stages between hair-like appendages and complex body feathers with feather banner, which can be explained with the help of developmental biology. The discussed for dinosaur stages of spring development can also be produced in the laboratory by manipulating the morphogens responsible. For these reasons, and because there is no phylogenetic analysis exists, the Longisquama actually represents the close relationship of birds, is the thesis that the alleged prolonged shed had something to do with the evolution of feathers, usually only among opponents of the dinosaur lineage of birds Support.

System

Jones et al. (2001 ) assume that the detection of a Antorbitalfensters ( one located in front of the eye socket skull opening) the classification of the genus Longisquama in the group of archosaurs, as has already been completed by Sharov in the first description justifies. In their view, set the compliance of the body appendages with bird feathers and the configuration of the clavicles, which resembles the wishbone of birds, suggest that a relationship exists Longisquamas within the archosaurs with the birds.

In contrast, Peters ( 2000) holds or Antorbitalfenster of Longisquama and some other Diapsiden not necessarily a feature of belonging to the archosaurs but for a series of convergent evolution. He studied Longisquama, Sharovipteryx, different genres of Prolacertiformes and primitive pterosaurs with the goal of a revision of previous kladistischer analyzes and obtains the following result ( simplified):

Protorosaurus

Prolacerta

Macrocnemus

Tanystropheus

Langobardisaurus

Cosesaurus

Longisquama

Sharovipteryx

Pterosaurs

Archosauria

In addition to the presence of three Antorbitalfenstern that grow together in later forms into one, Peters discusses a number of other similarities on which the new taxon " Fenestrasauria " is to be based.

Doubts about the robustness of this classification Longisquamas are due to the infirmity and ambiguity of the skull and shoulder girdle, their interpretation, the analysis result is essentially attached. The alleged Prolacertiforme Sharovipteryx shows similarities with pterodactyls, their phylogenetic significance, however, is controversial. Under current majority opinion includes pterosaurs to archosaurs and, together with the dinosaurs and Scleromochlus and Lagosuchus the group Ornithodira.

A study published in 2004 by Senter analysis provides Longisquama as questionable member of the group Avicephala, a newly defined subset of Diapsiden, which becomes a part of the glider Coelurosauravus. The following cladogram, this relationship hypothesis in simplified form:

Neodiapsida (including Archosauria, Lepidosauria )

Longisquama

Coelurosauravus

Drepanosaurus

Megalancosaurus

Araeoscelidia

The unit of Ornithodira as a subgroup of the archosaurs remain therefore unchanged.

Way of life

Longisquama was a small arboricoler ( tree-dwelling ) insectivores, with sharp curved teeth were suitable for cracking of chitin exoskeletons. The relatively sophisticated shoulder girdle, the proportions of the limb bones and the extended outer phalanges, where set off for the slightly curved claws, indicate good climbing skills. If the alleged prolonged shed Longisquama actually qualified to gliding, they could have proved particularly when moving from tree to tree as beneficial. Otherwise, they might deterrence of enemies or the display have served (as part of mating behavior ).