Redlichiida

From Palaeos

o Arthropoda
`--o TRILOBITA
   |?-Agnostina
   `--+--o Redlichiida
      |  |--Olenellina
      |  `--Redlichiina
      |--Corynexochida
      |--Phacopida
      |--Lichida
      `--o Librostoma
         |--Proetida
         |--Harpetida [Harpoidea]
         |--Ptychopariida
         |?-Eodiscina
         `--Asaphida

Olenellus fowleri (Palmer 1998), Lower Cambrian, Order Redlichiida, Suborder Olenellina, Family Olenellidae, Pioche Shale Formation, Lincoln County, Nevada

Introduction

The trilobites of the Order Redlichiida were the earliest known true trilobites (with eyes and calcified exoskeletons), appearing at the very start of the Cambrian period, and dying out some time during the Ordovician period. The Redlichiids were possibly driven extinct by a combination of factors, such as competition from other trilobite groups,environmental changes, and new forms of predators.

The remainder of this page is copied from Wikipedia

Occurance in the fossil record

One of the earliest if not the earliest known trilobite is the Redlichid genus Fallotaspis. Redlichids are common fossils in Lower Cambrian faunas worldwide. They die out before the end of the Middle Cambrian. The two major Lagerstätten, at which Redlichids are found, are the Emu Bay shales of Southern Australia and the Maotianshan shales near Chengjiang in China.

Physical description

Redlichids have a primitive appearance. They typically have a large, semicircular cephalon and a highly-segemented thorax that tapers back to a small pygidium. Unlike many other trilobite orders, the Redlichids were probably not capable of defensive enrollment. The Redlichids generally have prominent, long, crescent-shaped eyes. The Redlichids are often quite spiny with genal, and/or glabular, and/or tail, and/or segment spines. One Redlichid family, the Olenellids, typically have long spines on the third thoracic segment.

The appendages have been preserved in a few specimens. They follow typical trilobite patterns in terms of the number, placement, and types of legs, antennae, gills, etc.

Suborders

The Redlichiids are divided into two suborders: Olenellina and Redlichiina.

The Olenellids are found in North America and associated areas that comprised the Cambrian continent of Laurentia. They are very common and are used to define the scope of Laurentia. Their abrupt disappearance marks the Lower-Middle Cambrian boundary in areas where the Olenellids are found. Olenellids do not have a facial suture.

Members of suborder Redlichiina are associated with Cambrian regions other than Laurentia. They have facial sutures and their remains are frequently found without their librigena, or "free cheeks". The relatively uncommon Bathynotids had facial sutures, long genal spines, and long spines on the final thoracic segment.

Credits

Introduction: Roger Perkins; Remainder of text: DanielCD Wikipedia