Redlichiida
Encyclopedia
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
.
Redlichid trilobites are the first arthropods to appear in the fossil
record. The earliest known trilobite seems to be the genus
Fallotaspis, which is a Redlichid. They are common fossils in Lower Cambrian faunas worldwide. They die out before the end of the Middle Cambrian. The two major Lagerstätte
n, at which Redlichids are found, are the Emu Bay shales of Southern Australia and the Maotianshan shales
near Chengjiang in China.
article for a definition of morphological terms)
Redlichids look primitive in comparison with later and (by the Middle Cambrian) contemporary trilobites. They typically have a large, semicircular cephalon and a highly-segmented 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. They are often quite spiny with some or all of the following: genal, glabular, tail, 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, gill
s, etc.
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.
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
within the major extinct arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
class Trilobita. The Redlichids are one of the four older classes of trilobites that originated in the Lower Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
.
Redlichid trilobites are the first arthropods to appear in the fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
record. The earliest known trilobite seems to be the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Fallotaspis, which is a Redlichid. They are common fossils in Lower Cambrian faunas worldwide. They die out before the end of the Middle Cambrian. The two major Lagerstätte
Lagerstätte
A Lagerstätte is a sedimentary deposit that exhibits extraordinary fossil richness or completeness.Palaeontologists distinguish two kinds....
n, at which Redlichids are found, are the Emu Bay shales of Southern Australia and the Maotianshan shales
Maotianshan shales
The Maotianshan Shales are a series of lower Cambrian deposits in the Chiungchussu formation, famous for their Konservat Lagerstätten, or high number of fossils preserved in place...
near Chengjiang in China.
Physical description
(See the TrilobiteTrilobite
Trilobites are a well-known fossil group of extinct marine arthropods that form the class Trilobita. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period , and they flourished throughout the lower Paleozoic era before...
article for a definition of morphological terms)
Redlichids look primitive in comparison with later and (by the Middle Cambrian) contemporary trilobites. They typically have a large, semicircular cephalon and a highly-segmented thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
that tapers back to a small pygidium
Pygidium
The pygidium is the posterior body part or shield of crustaceans and some other arthropods, such as insects and the extinct trilobites. It contains the anus and, in females, the ovipositor...
. Unlike many other trilobite orders, the Redlichids were probably not capable of defensive enrollment. The Redlichids generally have prominent, long, crescent-shaped eyes. They are often quite spiny with some or all of the following: genal, glabular, tail, 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, gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s, etc.
Suborders
The Redlichiids are divided into two suborders: OlenellinaOlenellina
Olenellina is a suborder of the order Redlichiida of Trilobites. The suborder contains two superfamilies: Olenelloidea , and Fallotaspidoidea . The Olenillina are some of the most primitive trilobites...
and Redlichiina
Redlichiina
Redlichiina is a suborder of the order Redlichiida of Trilobites. The suborder contains three superfamilies: Emuelloidea, Redlichioidea and Paradoxidoidea. These trilobites are some of the oldest trilobites known...
.
The Olenellids are found in North America and associated areas that comprised the Cambrian continent of Laurentia
Laurentia
Laurentia is a large area of continental craton, which forms the ancient geological core of the North American continent...
. 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.