Varanopidae

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Varanopidae
Varanops brevirostris, live reconstruction

Varanops brevirostris , live reconstruction

Temporal occurrence
Upper Carbon to Middle Perm
304 to 260 million years
Locations
Systematics
Meat finisher (Sarcopterygia)
Land vertebrates (Tetrapoda)
Amniotes (Amniota)
Synapsids (Synapsida)
Eupelycosauria
Varanopidae
Scientific name
Varanopidae
Romer & Price , 1940

The Varanopidae , sometimes also Varanopseidae , are amniotic terrestrial vertebrates of the late Paleozoic Era which, as "primitive" synapsids, are assigned to the level of development of the " pelycosaurs ". The Varanopiden were relatively small, carnivorous or insectivorous animals outside of monitor lizards reminded.

features

The skull of the Varanopidae was elongated and slightly built, the eyes were more at the back of the head and the lower jaw was narrow and long. The teeth of these animals were approximately uniform (homodont), sharp and slightly curved backwards. The rest of the body was also lightly built, with slender limbs and a long tail.

The Varanopidae were rather small animals and were probably among the fastest predators of their era. Varanodontine representatives of the Varanopidae such as Varanops could reach a maximum length of 1.5 to 2 meters. Myctosaurine genera were smaller overall. The external appearance was strongly reminiscent of the modern monitor lizards , without the two groups being related to each other. Varanopidae presumably ate meat, possibly insects or fish.

Occurrence and spread

The Varanopidae appeared for the first time in the Carboniferous North America and achieved almost worldwide distribution in the Permian , later finds are also known from Russia , among others . The oldest representative is Archaeovenator hamiltonensis , the most recent fossils include Mesenosaurus romeri and Pyozia mesenensis from Russia and Elliotsmithia longiceps and Heleosaurus scholtzi from South Africa. Thus, the Varanopidae also have the longest temporal extent of all Paleozoic synapsids . Elliotsmithia , the remains of which have been found in South Africa , is the only well-preserved pelycosaur found in Gondwana .

Live reconstruction of Archaeovenator hamiltonensis

The relative rarity of the Varanopidae in the fossil record can be explained as follows, according to Reisz and Modesto: Although they are a relatively rare part of the Permian terrestrial vertebrate communities, the available fossil record suggests that the Varanopseida had a long and varied history. The rare fossil record can be explained by the nature of the deposit in which terrestrial vertebrate communities have been preserved in fossil form. With the exception of the deposits in Bromacker in the Thuringian Forest and Richard's Spur in Oklahoma , all sites of the Lower Permian represent different fauna communities of the lowlands, which were either aquatic or located near water. These included lake and pond deposits or deposits from floodplains and floodplains. For this reason, vertebrates that lived in the lowlands near the water are mainly preserved in such deposits. In higher fossil societies, however, the Varanopidae are often represented with various taxa. The Dolese mine in Richard Spurs contains two representatives of the smaller myctosaurins as well as the large varanopid Varanops . Since the vertebrates are generally smaller in higher habitats , the Varanopidae occupy the ecological niche of the top predators in their ecosystem .

The Varanopidae became extinct by the end of the Permian period at the latest.

Systematics

Varanodon , live reconstruction
Skull reconstructions (without lower jaw) of Mesenosaurus (A) and Varanodon (B), not to scale ( Varanodon is at least twice as large as Mesenosaurus ))

The most important representatives of this group were:

The Varanopidae systematically form the most basic representatives of the Eupelycosauria , from which the therapsids (“mammal-like reptiles”) and finally the mammals later developed. This classification is controversial, however, since some groups that are considered more developed, such as the Ophiacodontidae , appear earlier than the Varanopsis in the fossil record . The similarity of the Varanopidae with today's monitor lizards often led in the past to wrong classifications and the like. a. of Mesenosaurus , Archaeovenator and Apsisaurus as diapsids .

Paleoecology

The Varanopidae were small, agile hunters. Interestingly, among the vast majority of contemporary therapsids from South Africa were numerous large carnivores and herbivores . Accordingly, the Varanopidae seem to have successfully established themselves in a specialized niche, as their extended occurrence in the fossil record shows. At higher altitudes the Varanopidae occupied the role of the top predators, while in the lowlands and near the water, where larger synapsid predators were present, they occupied the niche of the small predators. The only carnivore from the Permian South Africa of comparable size was Youngina capensis . However, this had neither the long and slender limbs nor the jagged teeth, which were typical of the Varanopidae. Youngina is also passed down from the late Permian, while Heleosaurus and Elliotsmithia were Middle Permian forms. In the Permian deposits of northern Russia, the fossils of the diapsid genus Lanthanolania can be found , which reached a size comparable to the Varanopidae. Differences in the dentition suggest, however, that Lanthanolania and the representatives of the Varanopidae occupied different ecological niches.

There is evidence that some genera of the Varanopidae took care of their young. In South Africa, for example, the well-preserved remains of five individuals of Heleosaurus - one adult and four young animals of the same size - were found close together. This is the oldest evidence of parental care in pelycosaurs and amniotes at all, around 140 million years before this could be demonstrated in the dinosaur genera Psittacosaurus and Oryctodromeus . Brood care meant an enormous survival advantage in a Paleozoic environment dominated by therapsids.

Individual evidence

  1. ↑ a b c d Reisz, RR & Modesto, SP (2007): Heleosaurus scholtzi from the Permian of South Africa: a varanopid synapsid, not a diapsid reptile. Journal of Vertebrate Paleontology 27 (3): 734-739.
  2. ↑ Nicolás E. Campione and Robert R. Reisz (2010): "Varanops brevirostris (Eupelycosauria: Varanopidae) from the Lower Permian of Texas, with discussion of varanopid morphology and interrelationships", in: Journal of Vertebrate Paleontology 30 (3), p 724-746.
  3. ↑ Frederik Spindler, Ralf Werneburg, Joerg W. Schneider, Ludwig Luthardt, Volker Annacker, Ronny Rößler: First arboreal 'pelycosaurs' (Synapsida: Varanopidae) from the early Permian Chemnitz Fossil Lagerstätte, SE Germany, with a review of varanopid phylogeny. PalZ - Paleontological Journal. Vol. 92, No. 2, 2018, pp. 315–364, doi: 10.1007 / s12542-018-0405-9 (alternative full text access : ResearchGate )
  4. ^ Neil Brocklehurst, Robert R. Reisz, Vincent Fernandez, and Jörg Fröbisch: A Re-Description of 'Mycterosaurus' smithae, an Early Permian Eothyridid, and Its Impact on the Phylogeny of Pelycosaurian-Grade Synapsids. In: PLoS ONE. 11 (6): e0156810. doi: 10.1371 / journal.pone.0156810
  5. ↑ Jennifer Botha-Brink and Sean P. Modesto: A Mixed-Age Classed 'Pelycosaur' Aggregation from South Africa: Earliest Evidence of Parental Care in Amniotes? In: Proceedings of the Royal Society B: Biological Sciences. Volume 274, No. 1627, 2007, pp. 2829-2834, doi: 10.1098 / rspb.2007.0803

literature

  • TS Kemp: The Origin & Evolution of Mammals. Oxford University Press, Oxford 2005. ISBN 0198507615

Web links

Commons : Varanopidae  - Collection of images, videos and audio files