Agnostina

from Wikipedia, the free encyclopedia
Agnostina
Ptychagnostus cuyanus

Ptychagnostus cuyanus

Temporal occurrence
Lower Cambrian to Upper Ordovician
Locations
  • Worldwide
Systematics
Primordial mouths (protostomia)
Molting animals (Ecdysozoa)
Arthropod (arthropoda)
Trilobites (Trilobita)
Agnostida
Agnostina
Scientific name
Agnostina
Salter , 1864
Agnostina.

The Agnostina are a suborder of the Agnostida , an order of the extinct trilobites (Trilobita).

The species of these small, eyeless trilobites were distributed worldwide and had a two-part thorax . Their fossil exuvia (moulting residues) are found very numerous or in large numbers in Cambrian deposits and are therefore also used to determine the sediments.

Stratigraphic reach

These small trilobites are typical of the Cambrian , but occur up to the Upper Ordovician .

Superfamilies

This subordination has two superfamilies , the agnostoid and the condylopygoid.

Agnostoid

The glabella has obliquely forward grooves without the occipital lobe (in some trilobite species it is found behind the glabella in the transition to the thorax). The front part of the glabella (anteroglabella) is the same or narrower than the rear part (posteroglabella). The thorax corresponds to that of Agnostus pisiformis . The spindle on the pygidium has very few structures: either it is completely fused or it has two segments and is only completely fused at the back. The spindle sometimes has a distinct axial tubercle on the second segment .

Families :

Condylopygoidea

In contrast to the agnostoid, the furrows on the glabella run transversely, ie perpendicular to the body axis. There is an occipital lobe. The anterior part of the glabella (anteroglabella) is laterally enlarged at the transition to the posterior part, which is close to the thorax (posteroglabella). The tip of the anteroglabella can be divided with a so-called central spine (suculus). The thorax here also corresponds to that of Agnostus pisiformis . The broad spindle, rounded at the back, has three segments.

Familys:

Web links

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

Individual evidence

  1. ↑ Heinz Kowalski: Trilobites: quick-change artists of the Paleozoic; an unorthodox foray through the realm of the Dreilappers , Goldschneck-Verlag Werner K. Weidert, Korb 1992, ISBN 3-9261-2912-3
  2. ↑ a b c order Agnostida , accessed July 31, 2008