Porophoraspis

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Porophoraspis
Temporal occurrence
Floium to Darriwilium
477 to 461 million years
Locations
Systematics
Sub-stem : Vertebrates (vertebrata)
Class : Pteraspidomorphi
Subclass : Arandaspida
Order : Arandaspidiformes
Family : Arandaspididae
Genre : Porophoraspis
Scientific name
Porophoraspis
Ritchie and Gilbert-Tomlinson , 1977

Porophoraspis is an extinct genus ofthe Arandaspididae family belongingto the Pteraspidomorphi . This oldest known, primitive jawless fish ( Agnatha ) lived in the Lower Ordovician in Australia .

etymology

The term Porophoraspis ( pore-bearing shield ) is a combination of the three Greek words πόρος póros (pore), φόρος phóros (carrier) and ἀσπίς aspis (shield). This takes into account the fact that the tubercles of the shield have a holey structure.

Initial description

Porophoraspis was first scientifically described in 1977 by Alexander Ritchie and Joyce Gilbert-Tomlinson. A more recent revision was made by Jack Sepkoski (published posthumously in 2002).

Taxonomy

Robert Lynn Carroll (1988) places the genus Porophoraspis in the family of the Arandaspididae , together with the controversial taxon Anatolepis and Arandaspis . Sacabambaspis is another possible sister taxon, but it is now assigned to its own family. The only known subtaxon so far is Porophoraspis crenulata .

features

In contrast to Arandaspis , only a single plate with a strongly curved edge and fragments of the outer shell of Porophoraspis have been preserved in fossil form, so the animal cannot be reconstructed. These fragments resemble in a certain way the tubercles of Arandaspis , but on closer inspection they are fundamentally different in shape and ornamentation. The tubercles of Arandaspis are significantly ausgelängt and diamond-shaped and are covered with small pores, it whereas in Porophoraspis have and (up to three rows) arranged by row-like holes that is substantially greater than the pores of an only approximately oval shape Arandaspis are perforated . The tubercles of Porophoraspis are slightly rolled up at the edges and, due to the pores, are strongly indented or frayed. They will not be larger than 0.8 millimeters.

However, there are greater similarities to the oak-leaf-shaped tubercles of Sacabambaspis , the formation of which can be explained from the tubercles of Porophoraspis by an increase in the pore dimension. There is also a certain relationship with the as yet unclassified find by Young (1996) from the Upper Cambrian. Tubercles with relatively large pores should therefore represent a primitive trait.

meaning

Even if some scientists like Ørvig (1989), similar to Anatolepis, questioned the vertebrate nature of Porophoraspis , they are clearly refuted by findings from the Pacoota Sandstone - including a remains of a shell that reveals the canals of a lateral line organ . Thus Porophoraspis can undeniably be seen as the oldest unequivocal representative of a vertebrate.

Occurrence

Occurrences of Porophoraspis are so far only known from the Amadeus Basin of Australia . The original find, first described in 1977, comes from the Stairways Sandstone Formation on Mount Watt , about 150 kilometers south of Alice Springs . The Stairways Sandstone was deposited near the beach during the high level of an Epeirian shallow sea. If the somewhat questionable find from the older Pacoota Sandstone actually turns out to be true, it should represent the oldest known fish find .

Porophoraspis has so far been discovered in the following formations :

See also

Individual evidence

  1. ↑ Alexander Ritchie and Joyce Gilbert-Tomlinson: First Ordovician vertebrates from the Southern Hemisphere . In: Alcheringa . tape 1 , 1977, pp. 351-368 .
  2. ^ Joseph John Sepkoski: A compendium of fossil marine animal genera . In: Bulletins of American Paleontology . tape 363 , 2002, p. 1-560 .
  3. ^ Robert Lynn Carroll : Vertebrate Paleontology and Evolution . WH Freeman and Company, New York 1988, ISBN 0-7167-1822-7 .
  4. ↑ Shergold, JS et al.: Late Proterozoic and early Palaeozoic palaeontology and biostratigraphy of the Amadeus Basin . 1991, p. 97-111 .
  5. ^ Young, Gavin C. et al.: A possible Late Cambrian vertebrate from Australia . In: Nature . tape 383 , 1996, pp. 810-812 .
  6. ↑ Ørvig, T .: Histoloic studies of ostracoderms, placoderms and fossil elasmobranchs. 6. Hard tissues of Ordovician vertebrates. In: Zoologica Scripta . tape 18 , 1989, pp. 427-446 .
  7. ^ Janvier, P .: Les vertébrés avant le Silurien . In: GEOBIOS . tape 30, 7 , 1998, pp. 931-950 , doi : 10.1016 / S0016-6995 (97) 80217-3 .
  8. ↑ Davies, Neil S., Sansom, Ivan J., Nicoll, Robert S. and Ritchie, Alex: Ichnofacies of the Stairway Sandstone fishfossil beds (Middle Ordovician, Northern Territory, Australia) . In: Alcheringa . 2011, ISSN  0311-5518 , p. 1–17 , doi : 10.1080 / 03115518.2011.557565 .
  9. ^ Gavin C. Young: Ordovician Microvertebrate Remains from the Amadeus Basin, Central Australia . In: Journal of Vertebrate Paleontology . tape 17 (1) , 1997, pp. 1-25 .
  10. ^ Wells, AT, Forman, DJ and Ranford, LC: Geological reconnaissance of the north-western part of the Amadeus Basin, Northern Territory . In: Bureau of Mineral Resources, Australia, Report . tape 85 , 1965, pp. 45 .