Longisquama
| Longisquama | ||||||||||
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![Live reconstruction of Longisquama based on the only known skeleton specimen. Arrangement of the extended back scales based on Haubold & Buffetaut (1987). [1]](https://de.wikipedia.org/wiki/Datei:Longisquama_2.png)
Live reconstruction of Longisquama based on the only known skeleton specimen. Arrangement of the extended back scales based on Haubold & Buffetaut (1987). |
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| Temporal occurrence | ||||||||||
| Middle Triassic to Upper Triassic | ||||||||||
| about 230 to 220 million years ago | ||||||||||
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| Scientific name | ||||||||||
| Longisquama | ||||||||||
| Sharov , 1970 | ||||||||||
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Longisquama ("long scale") was a genus of diapsid reptiles , the fossils of which were discovered in sedimentary rocks of the Central to Upper Triassic Madygen Formation in southwest Kyrgyzstan . A number of presumably elongated scales attached to the back of the only known skeleton specimen is interpreted as an adaptation to gliding .
Find locality and type specimen
The Triassic clastic sedimentary rocks of the Madygen Formation are exposed in several places near the village of Madgyen in the Lyailyaksii district in the extreme southwest of Kyrgyzstan ( Batken region ). According to previous results, the rocks represent the sequence of river and lake deposits, estimated to be 500 m thick, in which some coal seams also occur.
In addition to Longisquama , the Madygen Formation has produced a variety of macrophytes (large plant fossils) and insects as well as bony fish (including a lungfish ), mussels , crustaceans , the amphibian Triassurus , the therapsid genus Madysaurus and Sharovipteryx , another small diapsid. In Sharovipteryx and Longisquama , both of which come from the clay / silt stones of the "Upper Gray Series" of the Madygen Formation, the outlines of the body are preserved in great detail as an imprint ( skin shadow preservation ) so that individual scales can be distinguished.
The approx. 15 cm long partial skeleton (PIN 2584/4, holotype ) described by Sharov in 1970 as Longisquama insignis is the only skeletal specimen of the genus that has been found to date. It includes the plate and counter-plate on which an incomplete skull , the neck , the front part of the chest , the shoulder girdle , the forelegs and skin prints on the neck, along the arms and back are preserved. Elongated, leaf-like body appendages that extend from the midline of the back are particularly noticeable. Five other specimens of these body appendages have been described so far without any connection to skeletal finds. The fossils are in the Paleontological Institute of the Russian Academy of Sciences in Moscow.
anatomy
Longisquama's skull is characterized by the greatly enlarged edge of the upper temporal window (an opening in the skull located behind the eye ). Sharov described two features that are considered characteristic of the group of archosaurs , which also includes crocodiles and dinosaurs : a cranial window that is located between the eye and nostrils (the antorbital foramen ), and an opening in the lower jaw (the mandibular foramen ). The existence of these openings and the systematic assignment derived from them have been questioned by Unwin & Benton (2001), among others. Jones et al. (2001), on the other hand, expressly confirm the presence of an antorbital foramen, according to the interpretation of Peters (2000) even three antorbital windows that become smaller towards the front can be distinguished (see figure).
Unlike archosaurs, but similar to scale lizards (lepidosaurs), Longisquama's teeth were apparently acrodontic , i.e. attached to the jawbone without tooth roots. The short neck consists of eight cervical vertebrae , for which the evidence of ribs is ambiguous. The first of the elongated leaf-like body appendages attach above the posterior cervical vertebrae. There are eight thin ribs of the thorax increasing in length towards the rear and a corresponding number of vertebrae , the part of the body adjoining it towards the tail is not preserved.
The shoulder girdle consists of long, narrow shoulder blades , short rod-shaped raven bones , two robust collarbones that together form a U-shape and are connected to an interclavicle . Unwin & Benton (2001) point out that the presence of an ossified intermediate collarbone is again atypical for archosaurs. Jones et al. a. (2001) counter that intermediate collarbones also occur in a number of archosaurs such as Euparkeria . Because of their shape and their overlapping, they refer to the two collarbones as a fork bone , the shape of which is similar to that of the ancient bird Archeopteryx . Peters (2000) describes a breastbone that is framed by the two collarbones, as well as a kind of keel that extends from the intermediate collarbone. However, he does not see any affinity to birds in the special morphology of Longisquama's shoulder girdle , but emphasizes the correspondence of the complex of clavicles, intermediate clavicle and sternum with that of a juvenile specimen of the primitive pterosaur Eudimorphodon .
The upper arms are slender, slightly S-shaped and are about as long as the forearm bones. Longisquama's hands are asymmetrical - for fingers No. I to V the number of phalanges is 2, 3, 4, 5 and 4. The second outermost phalanx of the fingers (those on which the claws are attached) are disproportionately long, a feature that often occurs as a result of adaptation to climbing. A characteristic ( autapomorphic ) feature of the genus Longisquama is the extremely elongated fourth finger, which is similar in length to the upper arm.
Scales or feathers?
The up to 15 cm long leaf-like body appendages protruding from the back are only known from specimens assigned to Longisquama from the Madygen formation. Sharov (1970) interpreted them as elongated horn scales and gave the new genus a corresponding name. He assumed that they had an aerodynamic function and functioned similarly to parachutes. Haubold & Buffetaut (1987) developed a model according to which the attachments were arranged in pairs and, as fold-out wings, enabled gliding flight (see illustration in the box).
It was not until Jones et al. (2000) doubted that the appendices actually represented reptile scales - they stated that they were feathers from a “non-bird” that were homologous to bird feathers and discussed various observations that should support this thesis. The central axis of each structure represents the feather shaft (rachis) and the branches from the central axis, which are otherwise interpreted as folds or struts, were interpreted as rays (radii) like the rays of a bird's feather. The feather plume , which, like birds, is made up of individual rays, has been misinterpreted in previous descriptions as a massive scale, in fact the "rays" in Longisquama only fused together at the outer edge, so that the "feathers" have a smooth outline and does not show a frayed edge, as expected.
Jones et al. (2001) cited the crossing of some "rays" as evidence, which cannot be explained when interpreted as massive scales. The hollow cylindrical base of the appendages, which, like the spindle (quill pen, calamus) of real bird feathers, are internally structured transversely, is one of the most important proofs in their opinion. Such structures could only be explained by the growth from a feather follicle , the same growth mechanism as that of feathers can therefore be assumed. Furthermore, near the base, the “feathers” are covered with a structure that resembles the feather sheath of modern feathers. Given the presence of a “follicular feather base”, a “quill pen”, a “feather sheath”, a “feather shaft” and a “feather flag” made up of “rays”, Jones et al. (2000, 2001) that Longisquama's body appendages must be feathers.
A large number of paleontologists familiar with the origins of birds consider this view to be a misinterpretation, which is based, among other things, on the overinterpretation of observed tissue impressions or on the disregard of contradicting findings. For example, there are no ticks (rami) to be found anywhere that connect the individual rays of contour and flight feathers (so that a continuous feather flag is present). Bird feathers fused at the edge are a very rare phenomenon in recent bird life and in the present case a far-fetched explanation. The structures of the appendages interpreted as “rays” would have z. Sometimes there is no resemblance to those of bird feathers and cannot be proven in many places. Prum (2001) agrees with Jones et al. (2000) agree that Longisquama's body appendages have a cylindrical base, but do not see the necessity that they were formed by feather follicles (or structures homologous with feather follicles).
In addition to the skepticism about the Jones et al. Observations and Conclusions published on Longisquama , a majority of paleontologists are convinced of the multitude of common inferred characters and of the results of many cladistic analyzes that identify birds as direct descendants of theropod dinosaurs . Fossils of feathered dinosaurs show various intermediate stages between hair-like body appendages and complex bird feathers with feather plumes, which can be explained with the help of developmental biology . The stages of feather development discussed for dinosaurs can also be generated in laboratory experiments by manipulating the responsible morphogens . For these reasons, and since there is no phylogenetic analysis that Longisquama actually places in the closer relationship of the birds, the thesis that the alleged elongated scales had something to do with the development of the feathers is generally only supported by opponents of the birds' dinosaur ancestry .
Systematics
Jones et al. (2001) assume that the evidence of an antorbital window (a skull opening in front of the eye socket) justifies the classification of the genus Longisquama in the group of archosaurs, as was already carried out by Sharov in the first description. In their view, the correspondence of the body appendages with bird feathers and the configuration of the collarbones, which resembles the wishbone of birds, suggest that Longisquamas are related to birds within the archosaurs .
In contrast, Peters (2000) considers the antorbital window (s) of Longisquama and some other diapsids not necessarily a feature of belonging to the archosaurs, but rather a consequence of convergent evolution . He examines Longisquama , Sharovipteryx , different genera of the Prolacertiformes and primeval pterosaurs with the aim of revising previous cladistic analyzes and obtained the following result (simplified):
| Archosauromorpha |
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In addition to the existence of three antorbital windows, which in later forms grow together into one, Peters discusses a number of other similarities on which the new taxon "Fenestrasauria" is said to be based.
Doubts about the robustness of this Longisquama's classification are due to the damage and ambiguity of the skull and shoulder girdle, on the interpretation of which the analysis result is essentially based. The putative prolacertiform Sharovipteryx shows similarities with pterosaurs, but their phylogenetic significance is controversial. According to the current majority opinion, pterosaurs belong to the archosaurs and together with the dinosaurs as well as Scleromochlus and Lagosuchus form the group Ornithodira .
An analysis published by Senter in 2004 places Longisquama as a questionable member of the Avicephala group , a newly defined subgroup of the Diapsids, to which the glider Coelurosauravus should also belong. The following cladogram represents this relationship hypothesis in a simplified manner:
| Diapsida |
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The unit of the ornithodira as a subgroup of the archosaurs would therefore remain unaffected.
Way of life
Longisquama was a small arboricoler (arboreal) Insectivore whose tip curved teeth cracking Chitin - exoskeletons were suitable. The relatively highly developed shoulder girdle, the proportions of the limb bones and the elongated outer phalanges, on which the slightly curved claws attached, indicate good climbing skills. If the putative elongated scales actually enabled Longisquama to glide, they may have proven particularly beneficial when moving from tree to tree. Otherwise, they could have served as a deterrent to enemies or for display (as part of mating behavior).
See also
Popular scientific literature
- Barry Cox, Dougal Dixon, Brian Gardiner, Robert J. G Savage: Dinosaurs and Other Animals of Ancient Times. The great encyclopedia of prehistoric wildlife. Mosaik-Verlag, Munich 1989, ISBN 3-570-03928-5 .
credentials
- ↑ a b Hartmut Haubold , Éric Buffetaut : A new interpretation of Longisquama insignis, an enigmatic reptile from the Upper Triassic of Central Asia. In: Comptes Rendus de l'Académie des Sciences. Series 2: Mécanique, Physique, Chimie, Astronomie, Sciences de la Terre et des Planètes. Vol. 305, 1987, ISSN 1477-2019 , pp. 65-70.
- ↑ Inna A. Dobruskina: Keuper (Triassic) flora from Middle Asia (Magygen, Southern Ferghana) (= . New Mexico Museum of Natural History and Science Bulletin. 5, ISSN 1524-4156 ). New Mexico Museum of Natural History and Science, Albuquerque NM 1995, pp. 1-49, online .
- ↑ Dmitry E. Shcherbakov : Madygen, Triassic deposit number one, before and after Sharov. In: Alavesia. Vol. 2, 2008, ISSN 1887-7419 , pp. 113–124, digitized version (PDF; 586.68 kB) ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. .
- ↑ a b c d e David M. Unwin, Vladimir R. Alifanov, Michael J. Benton : Enigmatic small reptiles from the Middle-Late Triassic of Kirgisztan. In: Michael J. Benton, Mikhail A. Shishkin, David M. Unwin, Evgenii N. Kurochkin : The Age of Dinosaurs in Russia and Mongolia. Cambridge University Press, Cambridge et al. 2000, ISBN 0-521-55476-4 , pp. 177-186.
- ↑ Александр Г. Шаров: Своеобразная рептилия из нижнего триаса Ферганы. In: Палеонтологический Журнал. No. 1, 1970, ISSN 0031-031X , pp. 127-131, [ An unusual reptile from the Lower Triassic of Fergana. ], (in Russian and Cyrillic script).
- ^ A b David M. Unwin, Michael J. Benton: Longisquama Fossil and Feather Morphology. In: Science . Vol. 291, No. 5510, 2001, pp. 1900-1901, doi : 10.1126 / science.291.5510.1899c .
- ↑ a b c d Terry D. Jones, John A. Ruben, Paul FA Maderson, Larry D. Martin : Longisquama Fossil and Feather Morphology. In: Science. Vol. 291, No. 5510, 2001, pp. 1901-1902, doi : 10.1126 / science.291.5510.1899c
- ↑ a b c David Peters: A reexamination of four prolacertiforms with implications for pterosaur phylogenesis. In: Rivista Italiana di Paleontologia e Stratigrafia. Vol. 106, No. 3, 2000, ISSN 0035-6883 , pp. 293-336.
- ↑ a b Terry D. Jones, John A. Ruben, Larry D. Martin, Evgeny N. Kurochkin, Alan Feduccia , Paul FA Maderson, Willem J. Hillenius, Nicholas R. Geist, Vladimir Alifanov: Nonavian Feathers in a Late Triassic Archosaur . In: Science. Vol. 288, No. 5474, 2000, pp. 2202-2205, doi : 10.1126 / science.288.5474.2202 .
- ^ Richard O. Prum: Longisquama Fossil and Feather Morphology. In: Science. Vol. 291, No. 5510, 2001, pp. 1899-1900, doi : 10.1126 / science.291.5510.1899c .
- ^ A b Erik Stokstad: Feathers, or Flight of Fancy? In: Science. Vol. 288, No. 5474, 2000, pp. 2124-2125, doi : 10.1126 / science.288.5474.2124 .
- ^ Richard O. Prum: Development and Evolutionary Origin of Feathers. In: Journal of Experimental Zoology. Vol. 285, No. 4, 1999, pp. 291-306, doi : 10.1002 / (SICI) 1097-010X (19991215) 285: 4 <291 :: AID-JEZ1> 3.0.CO; 2-9 .
- ↑ Mingke Yu, Ping Wu, Randall B. Widelitz, Cheng-Ming Chuong: The morphogenesis of feathers. In: Nature. Vol. 420, No. 6913, 2002, pp. 308-312, doi : 10.1038 / nature01196 .
- ↑ Some synapomorphies of Fenestrasauria according to Peters (2000): fusion of the ectopterygoids and pterygoids (bones that are involved in the structure of the palate ), an extensive rostrum ( snout ) and palatine ( gum bone ) as a result of the extension of the premaxillary ( intermaxillary bone ); Back swirls with enlarged laterally directed projections (transverse or Transversalfortsätzen); at least four pelvic vertebrae; Overlap of the collarbones; Intermediate collarbones with reduced shaft; a strut-like raven bone connected to the sternum complex; an elongated fourth finger that is at least three times the length of the fourth metacarpal bone . In addition, only in Longisquama and the pterosaurs the sternum fused with the collarbones.
- ↑ for a comparison see, for example, Christopher A. Brochu: Progress And Future Directions In Archosaur Phylogenetics. In: Journal of Paleontology. Vol. 75, No. 6, 2001, ISSN 0022-3360 , pp. 1185-1201, digital version (PDF; 685.05 kB) .
- ↑ Phil Senter: Phylogeny of Drepanosauridae (Reptilia: Diapsida). In: Journal of Systematic Palaeontology. Vol. 2, No. 3, 2004, pp. 257-268, doi : 10.1017 / S1477201904001427 .
