Najash

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Najash
Pelvic region of the holotype of Najash rionegrina in a back view with clearly recognizable thigh bones

Pelvic region of the holotype of Najash rionegrina in a back view with clearly recognizable thigh bones
Temporal occurrence
Upper Cretaceous ( Cenomanian to Turonian )
101 to 90 million years
Locations
Systematics
Land vertebrates (Tetrapoda)
Amniotes (Amniota)
Sauropsida
Scale reptiles (Squamata)
Snakes i. w. S. (Ophidia)
Najash
Scientific name
Najash
Apestiguía & Zaher , 2006
Art
  • Najash rionegrina

Najash is an extinct genus of snake-like scale crawfish with missing front legs and functional hind limbs. The only known species of the so far monotypical genus is Najash rionegrina from the Upper Cretaceous of Argentina . The genus and its type provided essential aspects for the phylogenetic development of the snakes .

Research history and etymology

The first description of the genus and type species was carried out in 2006 by Sebastian Apesteguia and Hussam Zaher in the scientific journal Nature based on a nearly complete postcranial and articulate (in anatomical connection standing) skeleton and fragments of the left mandible ( holotype MPCA 390-398, 400). There were also two other specimens with parts of the skull and some presacral vertebrae (MPCA 385) and isolated skeletal elements of a larger individual (MPCA 380–383). All fossil records of the first description are kept at the "Museo Paleontológico Carlos Ameghino" (MPCA) in Cipolletti in the Argentine province of Río Negro .

A new description of genus and type species on the basis of the same evidence was carried out in 2009 by Hussam Zaher and co-authors .

In 2019 the discovery of three postcranial skeletal fragments and a total of eight skulls, including an almost complete, three-dimensionally preserved skull skeleton (MPCA 500), allowed new insights into the phylogenetic position of Najash . The new find material was only assigned to the genus Najash ( Najash sp. ), Not directly to the type species or to another species of the genus.

The generic name " Najash " refers to the biblical serpent Nachash (Hebrew: נחש), which seduced Adam and Eve in paradise. The additional species " rionegrina " refers to the place where it was found in the Argentine province of Río Negro.

Age assignment of the finds

All known finds of Najash come from the La Buitrera fossil deposit (La Buitrera Palaeontological Area - "LBPA") northwest of the city of Cerro Policía in the Argentine province of Río Negro. The terrestrial sediments of the LBPA are part of the upper Candeleros Formation as the deepest unit of the Neuquén Group .

No direct geochronological age data are available for the Candeleros Formation itself . The beginning of the sedimentation is put in the early Cenomanian . A Tufflage within the overlapping Huincul formation could with fission track dating of zirconium on an age of 88.0 ± 3.9  Ma are determined. In the first description, the chronostratigraphic age of Najash is accordingly cautiously given as “Cenomanium - Turonium ”, which would correspond to an absolute age of around 101–90 Ma.

Uranium-lead and lutetium-hafnium dates on detritic zircons of the Candeleros Formation are between 98.6 ± 2.5 and 104.3 ± 2.5 Ma, depending on the geographical position, which is roughly the border between Albium and Cenomanium corresponds. Unlike the dating of the Tufflage within the Huincul Formation, the dating of detritic minerals in clastic sediments only provides a maximum age for the time of deposition (the sediments must be younger than the youngest detritic mineral they contain), but does not contradict the presumed age allocation of Najash .

features

Najash rionegrina could reach a length of almost two meters. The physique was extremely elongated with an increased number of vertebrae . The holotype has 109 presacral vertebrae, two sacral vertebrae and eleven caudal vertebrae . There are no indications of anterior limbs or remnants of a shoulder girdle .

The pelvis , on the other hand, is well developed with a long, dorsally curved iliac bone , a similarly shaped but anteroventrally oriented pubic bone and a small, axel-shaped ischium . Of the hind limbs, only the thighbones , tibia and fibula are fossilized. The bones of the rear extremities are short but strongly built and the thigh bone shows a clearly formed trochanter as a muscle attachment point. The pelvic bones, including the hind legs, are in contact with the two sacral vertebrae and lie outside the rib cage. Najash therefore differs significantly from both extinct species of snakes with hind legs from the Cretaceous period ( Pachyrhachis , Haasiophis and Eupodophis ) as well as modern snakes after Spurs as rudiments of hind legs, such as pythons and boas . In these cases the sacral vertebrae are absent. The pelvic bones and hind legs have lost contact with the spine and are isolated and embedded in the muscles within the rib cage.

The skull skeleton of Najash exhibits a mixture of lizard-like features and typical skull features of more developed snakes. Lizard-like features are the presence of a distinctive, three-rayed zygomatic bone and the absence of a complete circumfenestral crista, a bony crest structure that in modern snakes surrounds the atrial window and the lateral opening in the scala tympani recess . A snake-like feature, however, is the lack of a postorbital .

Paleecology

The Candeleros formation is essentially of sandstones and conglomerates , in the interlaced to meandering river systems were deposited, but also partly from aeolian sediments greater dune fields , with frequent, marked by root horizons and tombs, palaeosols formed. The deposit area is interpreted as the fluviatil overprinted edge of an extensive sandy desert ("Kokorkom desert"). Most of Najash's specimen copies come from the dune sediments and associated paleo soils.

The following sections are not adequately provided with supporting documents ( e.g. individual evidence ). Information without sufficient evidence could be removed soon. Please help Wikipedia by researching the information and including good evidence.
See talk page.

Significance for science and research

The fossil remains of Najash rionegrina were found in the terrestrial deposits. This proved that the fossil from the Cretaceous Period was clearly a rural dweller. The skeleton shows features of both primeval snakes and basal lizards. In appearance, the reptile resembles a mixture of garter snake and skink , but it is not related to it:

The skull found in 2013 brought further new insights into the history of the development of snakes. So far, researchers thought that the first land-dwelling snakes were worm-like, burrowing, and cave-dwelling blind snakes- like animals. In contrast to them, however, Najash rionegrina had a large mouth with sharp teeth and was thus able to devour larger prey.

With the discovery of the fossil remains of Najash rionegrina , all previous knowledge on the evolutionary biology of snakes was thrown overboard. Until it was discovered, it was believed that the first snakes developed exclusively in the seas. However, the bones of this land-dwelling snake found in older layers of the earth point to a reverse path. The three almost completely preserved skeletons, as well as the eight skulls, are now among the best-studied ancient snake fossils ever. In addition to the usual procedures, they were x- rayed using micro-computed tomography . With the help of the new findings, some puzzles about the development from lizard to snake could be solved. Only which lizard was the real ancestor of the snakes still remains a secret.

Other prehistoric snakes with legs

In addition to Najash , other primal snakes with pronounced hind legs are known:

literature

  • Agustín Scanferla: Serpientes fósiles sudamericanas: piezas clave para comprender la evolución del grupo. May 1, 2015 (Spanish, Researchgate.net ).

Individual evidence

  1. ↑ a b c d e S. Apesteguía & H. Zaher: A Cretaceous terrestrial snake with robust hindlimbs and a sacrum. In: nature , Volume 440, 2006, pp. 1037-1040, doi : 10.1038 / nature04413 .
  2. ↑ a b c H. Zaher, S. Apesteguía & CA Scanferla: The anatomy of the upper cretaceous snake Najash rionegrina Apesteguía & Zaher, 2006, and the evolution of limblessness in snakes. In: Zoological Journal of the Linnean Society , Volume 156, 2009, pp. 801-826, ( digitized ).
  3. ↑ a b c d e FF Garberoglio, S. Apesteguía, TR Simões, A. Palci, RO Gómez, RL Nydam, HCE Larsson, MSY Lee & MW Caldwell: New skulls and skeletons of the Cretaceous legged snake Najash, and the evolution of the modern snake body plan. In: Science Advances , Volume 5, 2019, eaax5833, doi : 10.1126 / sciadv.aax5833 .
  4. ↑ a b HA Leanza, S. Apesteguía, FE Novas & MS de la Fuente: Cretaceous terrestrial beds from the Neuquén Basin (Argentina) and their tetrapod assemblages. In: Cretaceous Research , Volume 25, 2004, pp. 61-87, ( digitized version ).
  5. ^ H. Corbella, FE Novas, S. Apesteguía & HA Leanza: First fission-track age for the dinosaur-bearing Neuquén Group (Upper Cretaceous), Neuquén Basin, Argentina. In: Revista del Museo Argentino de Ciencias Naturales, Nueva Series , Volume 6, Number 2, 2004, pp. 227-232, ( digitized version ).
  6. ↑ M. Tunik, A. Folguera, M. Naipauer, M. Pimentel & VA Ramos: Early uplift and orogenic deformation in the Neuquén Basin: Constraints on theAndean uplift from U – Pb and Hf isotopic data of detrital zircons. In: Tectonophysics , Volume 489, Numbers 1-4, 2010, pp. 258-273, ( abstract ).
  7. ↑ F. Leal & MJ Cohn: Developmental, genetic, and genomic insights into the evolutionary loss of limbs in snakes. In: genesis , volume 56, number 1, 2017, e23077, doi : 10.1002 / dvg.23077 .
  8. ↑ A. Palci, MN Hutchinson, MW Caldwell, KT Smith & MSY Lee: The homo logies and evolutionary reduction of the pelvis and hindlimbs in snakes, with the first report of ossified pelvic vestiges in to anomalepidid (Liotyphlops BEUI). In: Zoological Journal of the Linnean Society , Volume XX, 2019, zlz098, doi : 10.1093 / zoolinnean / zlz098 , ( pdf ).

Web links

Commons : Najash  - collection of images, videos and audio files