Mesolenellus

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Mesolenellus
Temporal range: 516–513  Ma
Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Class:
Trilobita
Order:
Redlichiida
Suborder:
Olenellina
Superfamily:
Olenelloidea
Family:
Olenellidae
Subfamily:
Mesonacinae
Genus:
Mesolenellus

Palmer & Repina, 1993
Species
  • Mesolenellus hyperborea
    (Poulsen, 1974) type species, synonyms Olenellus hyperborea, Holmia hyperborea [1]
  • Mesolenellus svalbardensis
    (Kielan, 1960), synonym Olenellus svalbardensis [1] [2]

Mesolenellus is an extinct genus of trilobites that lived during the lower Cambrian (Botomian), found in Greenland and Spitsbergen. [1]

Contents

Etymology

Mesolenellus is a contraction of meso - middle - and Olenellus, the genus from which it was split off. The epithet hyperborea is a contraction of hyper (Greek ὑπέρ "excess") and Boreas (Greek : Βορέας), god of the North Wind in Greek mythology, referencing the current geographical position of the deposits of its type location. M. svalbardensis has been named for the Norwegian island group Svalbard or Spitsbergen, where it was originally collected.

Taxonomy

It was considered a subgenus of Olenellus before. [3] The nearest relatives of Mesolenellus are the species of the genus Mesonacis , with which it constitutes the subfamily Mesonacinae.

Distribution

Habitat

The mudstone in which both species were found indicates deeper, quiet waters. [5]

Ecology

Mesolenellus hyperborea occurs together with Limniphacos perspiculum , Serrodiscus, hyoliths, Petrianna fulmenta (Bradoriida), and inarticulate brachiopods. [5]

Description

As with most early trilobites, Mesolenellus 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 Olenelloidea, the eye-ridges spring from the back of the frontal lobe (L4) of the central area of the cephalon, that is called glabella. Mesolenellus also shares the typical character of the whole family Olenellidae that the frontal (L3) and middle pair (L2) of lateral lobes of the glabella are partially merged. This creates two very typical, isolated slits. Mesolenellus is a genus within the Mesonacinae, with eye-ridges curved but almost parallel to the midline. The back of the eye-ridges is opposite the most backward ring of the glabella (L0 or occipital ring). Genal spines are 6-8 times as long as L0. The outer furrows of the glabella are parallel to the midline between the back of the cephalon and the furrow between side lobes L2 and L3. The thorax is 3 times as wide as the axis at the 3rd segment. Mesolenellus can be distinguished from the sister-genus Mesonacis , where the back of the eye-ridge extends only to the most backward side lobes (L1), genal spines are only 1-5 times as long as L0, and the glabella widens forwards along L1 and L2. Except for in Mesonacis fremonti the curved eye-ridges are at an angle of 15°-20° with the midline. A third genus Olenellus, that constitutes the second subfamily of the family Olenellidae differs from Mesolenellus in having genal spines 4-5 times as long as L0, the glabella widens forwards along L1 and L2, and the thorax 4-4½ times wider that the axis at the 3rd segment. [1]

Key to the species

1A short ridge (called plectrum) connects the frontal lobe of the glabella with the frontal border of the headshield. The section of the border of the back of the head (posterior cephalic border) halfway between the midline and the genal angle (between the axis and the intergenal angle) has a backward angle. The base of the genal spine is opposite the most backward ring of the glabella (L0). The furrow between the 2nd and 3rd ring (S2) does not contact the furrow that outlines the glabella (or axial furrow). [1] Nevadella-zone. Svalbard (Vestspitsbergen, Hornsund) and Greenland (Peary Land, Schley Fjord Formation and Buen Formation).
→ M. svalbardensis (Kielan, 1960)
-Plectrum absent. The midsection of the posterior cephalic border is transverse. The base of the genal spine is opposite the middle ring of the glabella (L2). S2 contacts the axial furrow. [1] Nevadella-zone. Greenland (Buen Formation).
→ M. hyperborea (Poulsen, 1974)

Related Research Articles

<i>Olenellus</i> Extinct genus of trilobites

Olenellus is an extinct genus of redlichiid trilobites, with species of average size. It lived during the Botomian and Toyonian stages (Olenellus-zone), 522 to 510 million years ago, in what is currently North-America, part of the palaeocontinent Laurentia.

<i>Acimetopus</i>

Acimetopus Rasetti, 1966, is a genus of Eodiscinid trilobite belonging to the family Weymouthiidae Kobayashi (1943), Order Agnostida Salter (1864). It lived during the Botomian stage. = late Lower Cambrian Stage 4 ; the upper Botomian boundary corresponds to base of the Middle Cambrian, Miaolingian Series and Wuliuan stage.

<i>Analox</i>

Analox Rasetti, 1966 is a genus of Eodiscinid trilobites belonging to the family Weymouthiidae Kobayashi T. (1943), Order Agnostida It lived during the Botomian stage. It can easily be distinguished from other trilobites by the two furrows that extend forwards and sidewards from the front of the glabella.

<i>Olenelloides</i>

Olenelloides armatus is an extinct, small sized olenelloid redlichiid trilobite arthropod. It lived during the later part of the Botomian stage, which lasted from approximately 524 to 518.5 million years ago. This faunal stage was part of the Cambrian Period. The most conspicuous feature is the hexagonal head shield that carries 6 ray-like spines..

<i>Wanneria</i>

Wanneria is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the later part of the Botomian stage, which lasted from approximately 524 to 518.5 million years ago. This faunal stage was part of the Cambrian Period. Wanneria walcottana is the only known species in this genus.

Elliptocephala is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived from the later part of the Tommotian to the upper Botomian. Elliptocephala can easily be confused with Ellipsocephalus, a trilobite genus of the Ptychopariida order.

Fremontella is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the part of the Toyonian stage. This faunal stage was part of the Cambrian Period. Fremontella shares with the other genera of the Bristoliinae subfamily, Lochmanolenellus and Bristolia conspicuous and long curved spines on the headshield. These reach back equal to 4-5 thorax segments. The furrows that separate border, eye ridges, glabella and its lobes are distinct. The area outside of the axis of the third segment of the thorax is enlarged, and carries large trailing spine on each side.

<i>Buenellus</i> Species of trilobite (fossil)

Buenellus higginsi is an average size trilobite, which lived during the Lower Cambrian period, in what is now North-West Greenland. It is a prominent member of the Sirius Passet fauna. Buenellus higginsi is the only known species in the genus Buenellus.

Cirquella is an extinct genus from a well-known class of fossil marine arthropods, the trilobites. It lived during the Atdabanian stage, in the former continent Laurentia.

<i>Nephrolenellus</i>

Nephrolenellus is an extinct genus of trilobite, fossil marine arthropods, of relatively small size. Currently two species are attributed to it. Nephrolenellus lived at the end of the Lower Cambrian. Species are known from the Great Basin of California, Nevada and Arizona, with one specimen from Canada.

<i>Mesonacis</i>

Mesonacis is an extinct genus of trilobite that lived during the Botomian, found in North-America, and the United Kingdom. Some of the species now regarded part of Mesonacis, have previously been assigned to Angustolenellus or Olenellus (Angustolenellus). Angustolenellus is now regarded a junior synonym of Mesonacis.

<span class="mw-page-title-main">Holmiidae</span> Family of trilobites

Holmiidae is a family of trilobites, that lived during the Lower Cambrian (Atdabanian). The Holmiidae is a diverse family of eight genera containing at least 17 species. It includes some of the earliest trilobites of Baltica. Holmiidae occur throughout Baltica and Western Laurentia, and also in Morocco.

<span class="mw-page-title-main">Olenellidae</span> Extinct family of trilobites

Olenellidae is an extinct family of redlichiid trilobite arthropods. Olenellids lived during the late Lower Cambrian (Botomian/Toyonian) in the so-called Olenellus-zone in the former paleocontinent of Laurentia plus parts of what became the Famatinian orogen in what is now Argentina. This family can be distinguished from most other Olenellina by the partial merger of the frontal (L3) and middle pair (L2) of lateral lobes of the central area of the cephalon, that is called glabella, creating two isolated slits.

<span class="mw-page-title-main">Olenelloidea</span> Extinct superfamily of trilobites

The Olenelloidea are a superfamily of trilobites, a group of extinct marine arthropods. They lived during the late Lower Cambrian and species occurred on all paleocontinents.

<i>Bristoliinae</i>

The Bristoliinae is an extinct subfamily of trilobites, fossil marine arthropods, with species of small to average size. Species belonging to this subfamily lived during the Botomian and Toyonian stage (Olenellus-zone), 522-513 million years ago, in the former continent of Laurentia, including what are today Mexico, the Appalachian Mountains and the south-western United States, and Canada.

Lochmanolenellus is an extinct genus of trilobites, fossil marine arthropods, with one small species, L. mexicana. It lived during the Botomian stage (Olenellus-zone), 522–513 million years ago, in the South-West of the former continent of Laurentia, in what are today Mexico, and the South-Western United States.

<i>Bristolia</i>

Bristolia is an extinct genus of trilobite, fossil marine arthropods, with eight or more small to average size species. It is common in and limited to the Lower Cambrian shelf deposits across the southwestern US, which constitutes part of the former paleocontinent of Laurentia.

<i>Emigrantia</i>

Emigrantia is an extinct genus of trilobites, fossil marine arthropods, of small to average size. It lived during the Toyonian stage, in what is today the South-Western United States. Emigrantia can easily be distinguished from other trilobites by the sturdy but not inflated genal spines, that are attached at midlength of the cephalon, in combination with effaced features of the raised axial area of the head shield.

Bolbolenellus is an extinct genus of trilobites, fossil marine arthropods, with five species attributed to it currently. It can be easily distinguished from all other trilobites by the combination of the absence of dorsal sutures in the head shield like all Olenellina, and a distinctly bulbous frontal lobe (L4) of the raised axial area in the head called glabella. The species lived at the end of the Lower Cambrian.

Ovatoryctocara is a genus of small corynexochid trilobites from the Cambrian, that lived in what now are Siberia, China, Greenland and Canada (Newfoundland). Ovatoryctocara can be recognised by the combination of the following characters: the central raised area of the cephalon is approximately cylindrical and has two rows of four triangular or round pits. The thorax only has 5 or 6 segments. The tailshield has an axis of 6 to 12 rings, the pleural furrows are well developed and the border is absent or narrow as a hair.

References

  1. 1 2 3 4 5 6 Lieberman, B.S. (1999). "Systematic Revision of the Olenelloidea (Trilobita, Cambrian)" (PDF). Bulletin of the Peabody Museum of Natural History. 45. Archived from the original (PDF) on 2016-06-24. Retrieved 2012-10-30.
  2. ↑ Cowie, J.; McNamara, K.J. (1978). "Olenellus (Trilobita) from the Lower Cambrian Strata of North-West Scotland" (PDF). Palaeontology. 21 (3): 615–634. Archived from the original (PDF) on 2012-05-26.
  3. ↑ H. B. Whittington; et al. (1997). "Introduction, Order Agnostida, Order Redlichiida". Treatise on Invertebrate Paleontology. Part O, Revised. Trilobita.
  4. ↑ Poulsen, V. (1974). "Olenellacean trilobites from eastern North Greenland". Bulletin of the Geological Society of Denmark. 23: 79–101.
  5. 1 2 3 4 Mark R. Blaker & John S. Peel (1997). Lower Cambrian trilobites from North Greenland. Meddelelser om Grønland. Geoscience. Vol. 35. ISBN   978-87-635-1241-1.
  6. ↑ Kielan, Z. (1960). "On two olenellid trilobites from Hornsund, Vestspitsvergen". Studia Geologica Polonica. 4: 133–139.
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