Olenoides is a group of trilobites that lived during the Cambrian period. Fossils of this group, including their soft body parts, have been found in the Burgess Shale in Canada. Fossils of Olenoides are also present in the Wheeler Shale and Marjum Formation in Utah, United States, as well as other locations. The size of species in this group varies, with most being medium-sized trilobites. For example, Olenoides Serratus from the Burgess Shale can grow up to 9 centimeters long. Another species, Olenoides Superbus, can reach lengths of more than 10 centimeters. Olenoides belongs to the order Corynexochida, which is one of the oldest trilobite orders.
Etymology
Olenoides is a scientific name for a group of ancient sea creatures called trilobites. The name comes from Olenus, a figure in Greek mythology who, along with his wife Lethaea, was turned to stone. In 1827, the name "Olenus" was first used as a trilobite genus name. Later, the suffix "-oides," which means "resembling," was added to the name.
Discussion
Olenoides had the same basic body structure as all trilobites: a cephalon (head shield), a thorax made of seven connected sections, and a semicircular pygidium (tail section). Its long antennae curved backward along its sides. Its thin legs suggest it did not swim but instead crawled along the seafloor to find food. This is supported by fossil tracks discovered in the area. Some Olenoides fossils show noticeable W-shaped wounds, often partially healed, which may have been caused by attacks from Anomalocaris.
Key features of Olenoides include a large, flat glabella (a part of the head), deep grooves on the pygidium, and thin spines on the tail. It is also the most common trilobite species with limbs found in the Burgess Shale.
Fossils of Olenoides have been found in the Marjumian area of the United States, such as Utah and New York. General Cambrian fossils have also been discovered in Canada (British Columbia and Newfoundland), Greenland, Kazakhstan, Russia, and the USA (Idaho, Nevada—where O. nevadensis is named, New York, Pennsylvania—where O. pennsylvanicus is named, Virginia, Utah, and Wyoming).
A total of 213 Olenoides specimens have been identified in the Greater Phyllopod bed, where they make up 0.4% of the community. The Burgess Shale’s ability to preserve fossils has helped scientists learn a great deal about Olenoides and its role in ancient ecosystems.
Synonyms
Olenoides was previously called Neolenus. Scientists now believe that the species in Kootenia are not different enough from those in Olenoides to be placed in a separate genus.
Description
Olenoides is a trilobite that grows up to 9 cm long and has an oval shape. Its head, called the cephalon, is semi-circular. The glabella, a central part of the cephalon, is flat on the sides and rounded at the front. It nearly reaches the front edge of the cephalon. Narrow ridges near the eyes curve backward from the front of the glabella to the small, outwardly curved eyes. The librigenae, which are parts of the cephalon, narrow backward into straight, thin spines that extend to the third thorax segment. The thorax has seven segments and ends with needle-like spines. The pygidium has six axial rings that become smaller toward the back and four or five pairs of spines pointing backward. The cephalon, thorax, and pygidium are all about the same length.
Olenoides serratus is one of about twenty trilobite species where non-calcified parts, such as soft tissues, are known because of a special type of preservation called soft tissue preservation. The antennae are the first pair of appendages on trilobites. In O. serratus, the antennae are attached halfway along the hypostome and appear from the top side of the cephalon near the front of the glabella. The antennae were flexible and tubular, narrowing toward the front. They had 40 to 50 segments, each shorter in width than in length. Olenoides serratus is the only trilobite known to have cerci, which are unbranched appendages on the underside of the last pygidial segment. These cerci are shaped similarly to the antennae.