Amphiaspidiformes

Amphiaspidiformes
Reconstruction of Amphiaspis argo
Reconstruction of Hibernaspis
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Infraphylum: Agnatha
Class: †Pteraspidomorpha
Subclass: †Heterostraci
Order: †Amphiaspidiformes
Suborders and families
Synonyms

Amphiaspidida

Amphiaspidiformes, or Amphiaspidida, is a taxon of extinct heterostracan agnathans whose fossils are restricted to Lower Devonian marine strata of Siberia near the Taimyr Peninsula. Some authorities treat it as a suborder of Cyathaspidiformes, while others treat it as an order in its own right.

In life, they are thought to be benthic animals that lived most of their lives mostly buried in the sediment of a series of hypersaline lagoons. Amphiaspids are easily distinguished from other heterostracans in that all of the plates of the cephalothorax armor are fused into a single, muff-like unit, so that the forebody of the living animal would have looked like a potpie or a hot waterbottle with a pair of small, or degenerated eyes sometimes flanked by preorbital openings, a pair of branchial openings for exhaling, and a simple, slit-like, or tube-like mouth.

Taxonomy

Amphiaspidiformes is traditionally regarded as the sister-taxon or daughter-taxon of the cyathaspidid family Ctenaspidae (ne "Ctenaspididae"), though no formal shared traits are identified between the two groups. The ctenaspidid cyathaspid, Boothiaspis, of Lower Devonian Canada, was initially described as an amphiaspid.

As mentioned earlier, Amphiaspidiformes is treated as either a suborder of Cyathaspidiformes, or as an order in its own right, sometimes referred to as "Amphiaspidiformes." Regardless of its own status, Amphiaspidiformes is divided into three superfamilies, Amphiaspidoidei, Hibernaspidoidei, and Siberiaspidoidei. An additional species, Gunaspis orientalis, was listed as an amphiaspid by Novitskaya 2008, although, because it is only known from a fragment with distinctive armor micro-ornamentation, it's assignment is questionable.

Tuxeraspis and Litotaspis are known primarily from fragments and portions of the head-region, while Dotaspis is known from a mostly intact headshield.

In Novitskaya & Afanassieva (2004), Novitskaya recognized most of the following taxonomic organization of the group, with the questionable addition and placement of Gunaspis following Novitskaya (2008):

Order Amphiaspidiformes

References

  1. 1 2 3 Novitskaya, L. I. (March 2008). "Evolution of taxonomic diversity in amphiaspids (Agnatha, Heterostraci: Amphiaspidiformes) and the causes of extinction in ecologically favorable conditions". Paleontological Journal. 42 (2): 181–191. doi:10.1134/S0031030108020093. ISSN 0031-0301.
  2. 1 2 Lundgren, Mette; Blom, Henning (2013-03-01). "Phylogenetic relationships of the cyathaspidids (Heterostraci)". GFF. 135 (1): 74–84. doi:10.1080/11035897.2013.770792. ISSN 1103-5897.
  3. ↑ Novitskaya, L. (1971). Les Amphiaspides (Heterostraci) du Dévonien de la Sibérie. Cahiers de Paleontologie. Vol. 12. Paris: Centre National de la Recherche Scientifique. pp. 1–130.
  4. ↑ Новицкая ЛИ (1986), "Древнейшие бесчелюстные СССР: Гетеростраки: Циaтacпиды, Aмфиacпиды, Птepacпиды." Труды ПИН 219: 159c. [Novitskaya, LI (1986), The most ancient agnathans of the USSR: Heterostraci: Cyathaspidae, Amphiaspidae, Pteraspidae. Trudy Paleontol. Inst. Nauk 219: 159 pp.]
  5. ↑ Novitskaya, L. I.; Afanassieva, O. B., eds. (2004). Ископаемые позвоночные России и сопредельных стран. Бесчелюстные и древние рыбы. Справочник для палеонтологов, биологов и геологов [Fossil vertebrates of Russia and adjacent countries. Agnathans and early fishes. The reference book for palaeontologists, biologists and geologists.] (in Russian). Moscow: ГЕОС [GEOS]. pp. 1–435. ISBN 5-89118-368-7.{{cite book}}: CS1 maint: ignored ISBN errors (link)