Sphenacodontidae

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Sphenacodontidae
Live reconstruction of Sphenacodon

Live reconstruction of Sphenacodon

Temporal occurrence
Upper Carboniferous (?  Moskovium ) to Lower Permian ( Kungurium )
? 308 to 272 million years
Locations
Systematics
Land vertebrates (Tetrapoda)
Synapsids (Synapsida)
Pelycosaur (Pelycosauria)
Eupelycosauria
Sphenacodontia
Sphenacodontidae
Scientific name
Sphenacodontidae
Williston , 1912
Dimetrodon

The sphenacodontidae are a family of carnivorous representatives of the order of Pelycosauria that from the late Carboniferous to the end of the Permian in the northern regions of the super continent Pangea lived. Smaller, original forms such as Haptodus were 60 centimeters to one meter long. Towards the end of the lower Permian, the Sphenacodontidae became bigger and bigger and, as top predators, reached body lengths of sometimes more than three meters.

description

Several large (around three meters) and advanced taxa such as Ctenospondylus , Secodontosaurus and Dimetrodon were characterized by large dorsal sails , which were spanned by the elongated spinous processes of the vertebrae . Blood vessels ran through her skin-like tissue. The function of these back sails was likely to achieve thermoregulation . But not all members of the Sphenacodontidae had this back sail. It is puzzling why Sphenacodon , the remains of which were found in New Mexico , had no back sail, whereas the very closely related Dimetrodon from Texas had a very large back sail. During the Lower Permian, both sites were only separated from each other by a narrow strait, so geographical isolation should not have played a role here.

Characteristic features

The main feature of the Sphenacodontidae is of course their primary cranial window in the temple region (temple or temporal window) behind the eye socket.

Their massive skull is long, deeply drawn down and narrow - an adaptation to strong jaw muscles. The intermaxillary bone (premaxillary) falls forward and forms a "hooked nose". The upper jaw is wide and expansive to accommodate the large catches; however, this prevents the tear bone from reaching the nose.

The pineal opening on the parietal bone has a distinctive ridge. The paraoccipital process is only in terminal contact with the scaly bone, its upper limit forms a sharp ridge.

The temporomandibular joint lies clearly below the row of teeth (the formation and positioning of the temporomandibular joint enabled the adductor muscles attached to the posterior end of the skull to be more efficient - the edge of the supraangular and the crown process on the lower jaw was almost perpendicular to the muscle fibers). The articular is enlarged. The Angular is composed of "reflected layers".

The very specialized front "incisors" are large and dagger-like, the teeth on the side and at the end of the jaw are much smaller (hence the name of the well-known genus Dimetrodon - which means something like "double measure tooth"). The cutting edge of the robust teeth, which are almost square at their base, is made up of ridges that only reach halfway down to the base of the tooth.

The vertebrae are much higher than they are wide, their elongated spinous processes spread a sail (probably used for thermoregulation and suggests that the Sphenacodontidae were animals of the same temperature). The vertebral processes are smooth, transverse processes are absent. The strong blood supply of the sails gives no indication of sexual dimorphism .

The limbs are relatively long and delicately built. The shoulder blade has a supraglenoid opening.

The Sphenacodontidae were possibly the first terrestrial vertebrates to hunt prey of comparable size.

Autapomorphies

The Sphenacodontidae are characterized by the following autapomorphies :

  • The lower process of the nasal bone forms the rear edge of the nasal cavity.
  • The front process of the frontal bone is narrower than the back (in other synapsids, both processes are equally wide).
  • The contact area between the postorbital and the scaly bone is very wide (with other synapsids it is narrow, if present).
  • The supratemporal touches the postorbital (most other Eupelycosauria do not have this contact).
  • The paraoccipital process widens sideways downwards and backwards (in most other synapsids it only expands horizontally). In some therapsids this feature is convergent.
  • The tooth root of the fang on the lower jaw presses against the choane (in other synapsids, the fang does not hinder the choane).

Systematics

Ctenorhachis
Ctenospondylus
Haptodus
Secodontosaurus

According to the scientific first description of sphenacodontidae they represent a paraphyletic represents group by means of its divided plesiomorphic for synapsids is defined typical essentials. The group occupies an evolutionary transition position from the original synapsids to the early therapsids ("early mammalian relatives").

The clade Sphenacodontia, however, is monophyletic since it includes all Sphenacodontids with all their descendants (including mammals). The "Sphenacodontidae sensu stricto" or the subfamily Sphenacodontinae only contain specialized pelycosaurs, earlier, more original forms such as Haptodus , Palaeohatteria , Pantelosaurus and Cutleria are excluded (in pre-cladist classifications these original forms were all listed under the genus Haptodus ).

The clade Sphenacodontoidea has been used by Laurin and Reisz since 1997 to mark the last common ancestor of the Sphenacodontidae and the Therapsids with all their descendants. It can be defined using certain skull features.

The Sphenacodontidae family comprises three subfamilies with the following genera:

distribution

Fossil finds of the Sphenacodontidae are known only from North America and Europe :

North America:

Europe:

See also

Individual evidence

  1. ↑ Hopson, JA (1991). Systematics of the Nonmammalian Synapsida and Implications for Patterns of Evolution in Synapsids. In: Schultze, HP and Trueb, L. Origins of the higher groups of tetrapods.
  2. ↑ Laurin, M. (1993). Anatomy and relationships of Haptodus garnettensis , a Pennsylvanian synapsid from Kansas. Journal of Vertebrate Paleontology 13 (2): 200-229.
  3. ^ Reisz, RR, Berman DS & Scott D. (1992). The cranial anatomy and relationships of Secodontosaurus , an unusual mammal-like reptile (Synapsida: Sphenacodontidae) from the early Permian of Texas. Zoological Journal of the Linnean Society 104: 127-184.
  4. ↑ Berman, D. S, Henrici, AC, Sumida, SS & Martens, T. (2004). New materials of Dimetrodon teutonis (Synapsida: Sphenacodontidae) from the Early Permian of central Germany. Annals of the Carnegie Museum of Natural History 73: 48–56.

swell

  • Carroll, RL (1988), Vertebrate Paleontology and Evolution , WH Freeman & Co.
  • Colbert, EH , (1969), Evolution of the Vertebrates , John Wiley & Sons Inc (2nd ed.)
  • Laurin, M. and Reisz, RR, 1997, Autapomorphies in main groups of synapsids
  • Reisz, RR , 1986, Handbuch der Paläoherpetologie - Encyclopedia of Paleoherpetology, Part 17A Pelycosauria Verlag Dr. Friedrich Pfeil, ISBN 3-89937-032-5
  • Romer, AS , (1947, revised ed. 1966) Vertebrate Paleontology, University of Chicago Press, Chicago
  • Romer, AS and Price, LI , (1940), Review of the Pelycosauria , Geological Society of America Special Papers, No 28.

Web links

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