Nectridea

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Nectridea
Diplocaulus

Diplocaulus

Temporal occurrence
Lower Pennsylvania to Guadalupian
315 to 259.9 million years
Locations
Systematics
Chordates (chordata)
Vertebrates (vertebrata)
Jaw mouths (Gnathostomata)
Land vertebrates (Tetrapoda)
Lepospondyli
Nectridea
Scientific name
Nectridea
Miall , 1875

The Nectridea are a group of extinct terrestrial vertebrates from the Carboniferous and Permian eras that live permanently in the water . Nectridea fossils were first found near Kilkenny , Ireland , in 1864 . Finds in France , the Czech Republic , England , North America and Morocco followed . The first forms were Arizonerpeton wellsi and Urocordylus wandesfordii from the Middle Carboniferous 315 million years ago. They resembled today's tailed amphibians and also had a way of life like this, but are probably not closely related to them, but belong to the Lepospondyli , a group of amphibian-like animals that is on the trunk line of the amniotes .

features

The Nectridea were rather small animals, the largest reached a length of half a meter. They were mostly pig-like, with a long, laterally flattened tail that could take up two thirds of the body's length and served as a swimming organ. The limbs were small but well developed. Some early forms had five toes, later only four.

The Nectridea are defined by the characteristics of their vertebrae . The number of trunk vertebrae is increased at 15 and 26. All vertebrae were coiled and holospondyl , i.e. h., they had only one ossification ( ossification ) per segment. Each vertebra had a neural arch that had an enlarged, fluted, and fan-shaped neural spine. In the caudal spine, the neural arches stood opposite symmetrical hemal arches and increased the area of ​​the tail. This distinguishes them from all other amphibian-like animals of the Paleozoic . Struts in addition to the normal zygapophyses restricted the mobility of the spine in the dorsal - ventral direction, but allowed lateral movements.

They had no otic indentation in the skull, a small indentation on the back of the skull of modern amphibians. Furthermore, the columella (a bone of the inner ear in amphibians, reptiles and birds, which corresponds to the stapes of mammals ) has not been described in any member of the Nectridea and was probably not present.

Diploculid skull

Particularly noteworthy are Diplocaulus and Diploceraspis ("Diplocaulidea") from the lower Permian of North America , the adult specimens of which had long, massive protrusions on the scaled bone on the side of the flattened head that gave the head the shape of a boomerang . The outgrowths were formed by the scaly bone and the tabulare (another skull bone). They might have helped swim and functioned like the wings of an airplane in flowing water. The diploculids had shorter bodies than other nectrids, with a maximum of 17 vertebrae in front of the pelvic vertebrae, and the tail was also shorter than that of the Urocordylidae.

The skull of the urocordylidea is long and arrow-shaped with high sides. Their slender lower jaws contained long, conical teeth that were well spaced apart. The best known genera of the Urocordylidea are Ptyonius and Urocordylus , they had 20 to 22 vertebrae in front of the pelvic vertebrae. Her tail was very long and consistently high for two thirds of its length. In the last third the height decreased steadily towards the top.

The Scincosauridea do not share any specialized skull features with the other nectrids. Their skulls were square, a possibly primitive feature of the Nectridae. Although their fossils were found in layers of the lower Cisuralium in the middle part of the Nectridae lifespan, they probably represent an ancient branch of the group.

Way of life

Most forms of the Nectridea were exclusively aquatic and an important part of the marsh fauna 300 million years ago. Some Diplocaulus fossils have been found in the Old Red Sandstone , possibly in a river delta environment with a monsoon climate . Accompanying fauna are carbonic amphibians, microsaurs , primitive reptiles and pelycosaurs . Diploceraspis fossils were found in pond and lake deposits. Scincosaurus' short legs and small feet indicate that it was likely more adapted to a terrestrial way of life or lived aquatic only at certain times of the year. He may have lived on the leafy soil of the Carboniferous forests.

A fossilized trace from the lower Permian of southern New Mexico is interpreted as a trace of an amphibian-like being (possibly a nectride) that moved in the shallow water like a sidewinder rattlesnake . Most nectrids moved in the water by sideways, sinusoidal winding of the tail, while the trunk was kept largely rigid, a type of locomotion that today's newts also use. The legs were only used for support. Diceratosaurus seems to have swum with the help of the hind legs.

The Nectridea may have fallen victim to freshwater sharks (Xenacanthiformes) and predatory coelacanthiformes (Coelacanthiformes).

Although there is no evidence of an amphibian-like metamorphosis in the Nectridea, it is assumed that their eggs were similar, without an amnion or shell, and had to be placed in water or in damp places to protect them from drying out. In the boomerang-headed species Diploceraspis and Diplocaulus , the young do not yet have "horns" pointing backwards. These only grow later, but not continuously, but in two growth spurts .

nutrition

The Nectridea probably ate mostly tadpoles and small fish. Scincosaurus could have been an insect eater . The diploculid nectrids, possibly lurking in the mud of a water bed, could have used their boomerang-shaped heads to create buoyancy by suddenly lifting their heads in weakly flowing water, and to grab the prey swimming by more quickly.

Systematics

Of the Nectridea three families and a total of 26 species have been described. Only Arizona peton wellsi cannot be assigned to any family. A new cladistic study sees the Nectridea in its previous composition as a polyphyletic group that does not contain all descendants of their common ancestor. The group to be included in the Nectridea are the Aïstopoda , which are likely the sister group of the Urocordylidae.

Urocordylus wandesfordii , living reconstruction
Live reconstruction of sauropleura from the Pennsylvania ("Upper Carboniferous") of Europe and North America

literature

Individual evidence

  1. ↑ Temporal distribution of nectridan
  2. ↑ a b Department of Earth Sciences at the University of Bristol. Page to the fossil record of the Nectridea
  3. ↑ a b c d e Department of Earth Sciences at the University of Bristol. Page on the anatomy of the Nectridea
  4. ↑ Lepospondylia seminar (PDF; 2.0 MB)
  5. ^ Department of Earth Sciences at the University of Bristol. Page on the Environments and Behavior of the Nectridea
  6. ^ Department of Earth Sciences at the University of Bristol. Page on the growth and development of Nectridea
  7. ^ Department of Earth Sciences at the University of Bristol. Page on the nutrition of the Nectridea
  8. ↑ Department of Earth Sciences at the University of Bristol. Page: Major Subgroups of the Nectrideans
  9. ↑ Marcello Ruta, Michael I. Coates & Donald LJ Quickie (2003): Early tetrapod relationships revisited. Biological Reviews, 78, pp 251-345 doi : 10.1017 / S1464793102006103
  10. ↑ Michael J. Benton. Vertebrate Palaeontology , 3rd edition. Wiley-Blackwell, 2005. page 90

Web links

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