Redlichiida

Redlichiida
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Class: Trilobita Order: Redlichiida
Families
Suborder Olenellina    Superfamily Olenelloidea     Olenellidae     Holmiidae    Superfamily Fallotaspidoidea     Archaeaspididae     Fallotaspididae     Judomiidae     Neltneriidae     Nevadiidae Suborder Redlichiina    Superfamily Emuelloidea     Emuellidae    Superfamily Redlichioidea     Abadiellidae     Chengkouaspidae     Dolerolenidae     Gigantopygidae     Kuechowiidae     Mayiellidae     Menneraspididae     Metadoxididae     Redlichiidae     Redlichinidae     Saukiandidae     Yinitidae    Superfamily Paradoxidoidea     Centropleuridae     Paradoxididae     Xystriduridae

Redlichiida is an order within the major extinct arthropod class Trilobita. The Redlichids are one of the four older classes of trilobites that originated in the Lower Cambrian. The earliest known trilobite seems to be the genus Fallotaspis, which is a Redlichid. Redlichids look primitive. 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 Redlichids are divided into three suborders. 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. Redlichids 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. The Redlichids died out before the end of the Middle Cambrian.

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.

Redlichid trilobites are the first arthropods to appear in the fossil record. They are common fossils in Lower Cambrian faunas worldwide.