Varanosaurus

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Varanosaurus
Temporal occurrence
Unterperm
284.4 to 270.6 million years
Locations
Systematics
Land vertebrates (Tetrapoda)
Synapsids (Synapsida)
Pelycosaur (Pelycosauria)
Eupelycosauria
Ophiacodontidae
Varanosaurus
Scientific name
Varanosaurus
Broili , 1904
Art
  • Varanosaurus acutirostris Broili, 1904

Varanosaurus ( Greek "monitor lizard") is a genus of early Pelycosaurier from the lower Permian ( Artinskian to Kungurium ) of Texas and Oklahoma . In1904 theGerman paleontologist Ferdinand Broili published the first scientific description of the type species Varanosaurus acutirostris .

The appearance of the approximately 1.5 meter long Varanosaurus is reminiscent of today's monitor lizards , which explains the generic name. Despite the good tradition of several fossils , little is known about the genus. In addition to Varanosaurus acutirostris , another species has been described, Varanosaurus wichitaensis , which is, however, a synonym for Varanosaurus acutirostris with high probability .

description

From varanosaurus two fossil skulls are in good condition and other postcranial before items. The skull is elongated, low and narrow. As with other representatives of the Ophiacodontidae , the skull area from the eye sockets to the tip of the snout (the antorbital area) is more than twice as long as the part of the skull located behind the eye sockets (postorbital). The skull window was relatively small compared to that of other synapsids .

Dimetrodon incisive captured varanosaurus acutirostris (artist's impression)

The upper jaw was covered with a number of quite narrow, pointed and slightly curved teeth as well as two larger fangs in the front area, which suggest a predatory diet. In the lower jaw there were around 60 small, uniform teeth with no significant size variations.

The preserved vertebral arches are robust and appear "swollen", the spinous processes sometimes vary in height and structure. The spine of Varanosaurus thus resembled that of more primitive tetrapods such as Diadectes , Seymouria or the Captorhinidae , but this is due to convergence . Probably such a structure of the vertebrae, together with the almost horizontal alignment of the vertebral arch joints, gave the animal greater maneuverability during the hunt, since the back muscles attached to the high spinous processes could run freely over the lower spinous processes.

Varanosaurus likely lived in swamps and ate fish.

classification

There is no final clarity about the position of Varanosaurus within the Eupelycosaurier . Due to the many anatomical similarities with Ophiacodon , most scientists assume a close relationship between the two genera and assign Varanosaurus to the Ophiacodontidae . In some works, however, the genus is also assigned to the Varanopseidae , but not without pointing out the possible alternative position as a close relative of Ophiacodon .

Synonyms

There are two synonyms for Varanosaurus acutirostris . In 1917 Poecilospondylus francisi was described by Ermine Cowles Case (1871-1953), but later identified by Alfred Sherwood Romer (1894-1973) as a younger synonym of Varanosaurus acutirostris . Romer himself described in 1937 a hip bone as another species, Varanosaurus wichitaensis, due to its smaller size compared to V. acutirostris and the earlier occurrence. However, the validity of this type is questioned. It is very likely that it is a synonym of the type species.

In 1911, Samuel Wendell Williston initially incorrectly assigned Varanops brevirostris as Varanosaurus brevirostris of the genus Varanosaurus . A few years later, however, he corrected his mistake and placed Varanops brevirostris as a type species in its own genus Varanops .

Individual evidence

  1. ↑ a b c d e Stuart Sumida: Reinterpretation of Vertebral Structure in the Early Permian Pelycosaur Varanosaurus acutirostris (Amniota, Synapsida). in: Journal of Vertebrate Paleontology , Vol. 9, No. 4 (Dec. 19, 1989), p. 451.
  2. ↑ Broili, F .: Permische Stegocephalen and Reptilien. in: Palaeontographica , Abt A., 1904: pp. 1-120.
  3. ↑ a b c d e David S. Berman et alii: The Cranial Anatomy Relationships of the Synapsid Varanosaurus (Eupalycosauria: Ophiaconodontiae) from the Early Permian of Texas and Oklahoma. in: Annals of the Carnegie Museum , Vol. 64, No. 2, p. 100 ( PDF )
  4. ↑ a b c T. S. Kemp: The Origin & Evolution of Mammals. Oxford University Press, Oxford 2005
  5. ^ Alfred Sherwood Romer and LI Price: Review of the Pelycosauria. in: Bulletin of the Geological Society of America Special Papers 28 (1940), pp. 1-538
  6. ^ Alfred Sherwood Romer: New Genera and Species of Pelycosaurian Reptiles. in: Proceedings of the New England Zoological Club 16, pp. 83-96
  7. ^ Samuel W. Williston: American Permian vertebrates. University of Chicago Press, Chicago 1911, pp. 130f.
  8. ^ Samuel W. Williston: The Osteology of some American Permian Vertebrates. in: Contributions of the Walker Museum 1 (1914), pp. 107-162.