Olenellus is an extinctgenus of redlichiid trilobites, with species of average size. It lived during the Botomian and Toyonian stages,, in what is currently North-America, part of the paleocontinent Laurentia.
Etymology
Olenellus means small Olenus, after a genus belonging to the Ptychopariida, to which the type speciesO. thompsoni was originally assigned. The name Olenus refers to a mythological figure who was turned to stone by the gods. The names of the species have the following derivations.
agellus comes from the Latin word for field or hamlet.
chiefensis refers to the Chief Range, which includes the Ruin Wash section, that holds the last of the Olenellina.
fowleri was named in honor of Ed Fowler, whose quarrying skills exposed the type locality of this species.
getzi is called after , on whose Lancaster estate several Olenellus species were first collected.
nevadensis refers to the state of Nevada, where this species is found.
parvofrontatus means ‘small front’ from the Latin words parvus and frontatus, indicating the short distance between the anterior border and the glabella in this species.
roddyi was named in honor of Dr. H. Justin Roddy, an internationally known naturalist, curator and professor of geology.
"Paedeumias" was previously regarded as a genus related to Olenellus or a subgenus being part of Olenellus. Recent analysis shows that there is a group of species formerly assigned to Olenellus nested within Olenellus. However, this group is more closely related to the majority of the remainder of Olenellus species than to O. agellus and O. romensis. This implies that either two new monophyletic subgenera need to be erected, or Olenellus and Olenellus need to be dropped as subgenera, the latter being proposed by Lieberman.
Reassigned species
O. alabamensis = Fremontella halli
O. altifrontatus = Bolbolenellus altifrontatus
O. argentus pl. 40, fig 12, 13, 15, 16, non fig. 14 = Grandinasus argentus
O. argentus pl. 40, fig 14, non fig. 12, 13, 15, 16 = Holmiella falx
O. bondoni = Fallotaspis bondoni
O. bonnensis = Mesonacis bonnensis
O. brevoculus = Mesonacis bonnensis
O. broegeri = Callavia broegeri
O. bristolensis = Bristolia bristolensis
O. bristolensis p. 8. fig 1-11, non pl. 7, fig 1, 2, 5 = Bristolia harringtoni
O. bufrontis = Bolbolenellus sphaerulosus
O. callavei = Callavonia callavei
O. cylindricus = Mesonacis cylindricus
O. eagerensis = Mesonacis eagerensis
O. euryparia = Bolbolenellus euryparia
O. forresti = Redlichia forresti
O. fremonti pl. 15, fig. 18 = Bristolia fragilis
O. fremonti pl. 37, fig. 1, 4-5 = Bolbolenellus euryparia
O. fremonti pl. 37, fig. 1-2 = Mesonacis fremonti
O. georgiensis, p. 220, pl. 5, fig. 7, non fig. 6 = Mesonacis vermontanus
O. gigas = Andalusiana cornuta
O. gilberti = Bristolia bristolensis
O. groenlandicus = Bolbolenellus groenlandicus
O. halli = Fremontella halli
O. hamoculus = Mesonacis hamoculus
O. hermani = Bolbolenellus hermani
O. hyperboreus = Mesolenellus hyperboreus
O. insolens = Bristolia insolens
O. intermedius = Fritzolenellus lapworthi or F. reticulatus
O. kentensis = Bolbolenellus groenlandicus
O. lapworthi = Fritzolenellus lapworthi
O. laxocules = Elliptocephala laxocules
O. logani = Elliptocephala logani
O. mickwitzi = Schmidtiellus mickwitzi mickwitzi
O. mohavensis = Bristolia mohavensis
O. multinodus = Nephrolenellus multinodus
O. paraocules = Elliptocephala paraocules
O. praenuntius = Elliptocephala praenuntius
O. reticulatus = Fritzolenellus reticulatus
O. sequomalus = Elliptocephala sequomalus
O. sphaerulosus = Bolbolenellus sphaerulosus
O. svalbardensis = Mesolenellus svalbardensis
O. terranovicus = Mesonacis bonnensis
O. torelli = Schmidtiellus mickwitzi torelli
O. truemani = Elliptocephala walcotti
O. truemani = Fritzolenellus truemani
O. truncatooculatus = Mummaspis truncatooculatus
O. vermontanus = Mesonacis vermontanus
O. walcottanus = Wanneria walcottana
Distribution
O. thompsoni is found in the middle Upper Olenellus-zone of Vermont. O. agellus is present in the middle Upper Olenellus-zone of Vermont. O. chiefensis has been collected from the final layer of the Upper Olenellus-zone of Nevada. O. clarki is found in Upper Olenellus-zone of California ; and in Nevada. O. crassimarginatus has been collected in the middle Upper Olenellus-zone of Vermont ; and ½ mile South of East Petersburg; 2 miles North of York and Fruitville, 3 miles North of Lancaster. O. fowleri has been collected from the final layer of the Upper Olenellus-zone of Nevada. O. getzi is found in Upper Olenellus-zone of Pennsylvania. O. howelli occurs in the final layer of the Upper Olenellus-zone of Nevada. O. nevadensis has been collected in the Upper Olenellus-zone, Bristolia-zonule of California ; and from the Latham Shale – treated as the Bristolia-zonule – at the South end of the Marble Mountains, near Chambless in the Mohave Desert portion of San Bernardino County. It also occurs in the Bristolia-zonule, Upper Olenellus-zone of Nevada. O. parvifrontatus has been collected in the Olenellus-zone of the Yukon Territory, Canada. O. puertoblancoensis was found in the Botonian/Toyonian Olenellus-zone of the Caborca Region, Mexico O. robsonensis occurs in the ?Middle Olenellus-zone of British Columbia, Canada. O. roddyi occurs in the Olenellus-zone of Pennsylvania. O. romensis occurs in the middle Upper Olenellus-zone of Virginia. O. terminatus has been collected from the final layer of the Upper Olenellus-zone of Nevada. O. transitans has been collected from the middle Upper Olenellus-zone of Vermont.
Description
As with most early trilobites, Olenellus has an almost flat exoskeleton, that is only thinly calcified, and has crescent-shaped eye ridges. As part of the suborder Olenellina, Olenellus lacks dorsal sutures. Like all other members of the superfamily Olenelloide, the eye-ridges emerge from the back of the frontal lobe of the central area of the cephalon, that is called glabella. Olenellus also shares the typical character of whole family Olenellidae that the frontal and middle pair of lateral lobes of the glabella are partially merged. This creates two very typical, isolated slits. It can be distinguished from the other two genera in the family, Mesolenellus and Mesonacis, because the angle in the back rim of the cephalon is less than 15°, making the head approximately semi-circular. The genal spines are reaching back no further than the 6th thorax segment, making them 4-5 times as long as the most backward lobe of the glabella 1. The thorax is 4-4½ times wider that the axis, measured at the 3rd segment. The base of the spine on the 15th thorax segment is almost as wide as the axis itself.
Key to the species
This key is based on Lieberman, which describes only part of the species that are recognized today.
