Bolbolenellus

''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 (which in all other trilobite suborders assist in moulding by splitting open), and a distinctly bulbous frontal lobe (L4) of the raised axial area in the head (or cephalon) called glabella. The species lived at the end of the Lower Cambrian.

Etymology

''Bolbolenellus'' is the combination of Greek (, “plant with round swelling on underground stem”), and ''Olenellus'', the rather distantly related genus to which all of the species were previously assigned. This refers to the bulb-like swelling of the frontal lobe of the glabella. The names of the species have the following derivations.
* ''B. altifrons'' from the Latin altus (“high”) and from Latin frons (“forehead”), to express the species has a bulbous frontal glabellar lobe.
* ''B. brevispinus'' from brevis the Latin word for "short" and spinus the Latin word for "spine".
* ''B. groenlandicus'' is named for Greenland, where the species occurs.
* ''B. sphaerulosus'' from the Latin sphaerula (small ball).

Description

As with most early trilobites, ''Bolbolenellus'' has an only thinly calcified exoskeleton. Although most of the body is rather flat, the frontal lobe (L4) of the central area of the cephalon (or glabella) is prominent, bulbous (or subglobular), and may overlap the border at the front in dorsal view. It also shares crescent-shaped eye ridges, but these rise above the exoskeleton. As part of the Olenellina suborder, '' Bolbolenellus '' lacks dorsal sutures. Like all other members of the Olenelloidea superfamily, the eye-ridges spring from the back of the frontal lobe (L4) of the glabella. The posterior margin of cephalon is nearly straight or angles to the front (anterolaterally) on the outside of the intergenal spine or intergenal angle. The short genal spine protrudes opposite or posterior to the most backward side lobe of the glabella (or L1). There may be an intergenal spine. The frontal lobe of the glabella touches the border of the cephalon (or the preglabellar field is absent). The most backward tips of eye ridges (or ocular lobes) are approximately opposite occipital furrow. Although the third thorax) segment (or T3, this is counted from the headshield to the tailshield) has strongly enlarged side lobes (or pleurae), the spine on their end is not much enlarged compared to the spines of neighboring segments. The 14th segment carries a backward pointing axial spine that is approximately as long as the thorax axis. There seems to be no opistothorax.

Differences with some other Biceratopsinae

Most other Biceratopsinae, i.e. '' Biceratops nevadensis'', '' Emigrantia'' and '' Peachella'' and to a lesser extend '' Eopeachella'' have effaced cephalic features. ''Biceratops'' lacks genal spines. In ''Emigrantia'' the genal spines are longer than the cephalon and attach halfway down its side (or lateral margin). ''Peachella'' has club-like genal spines. In ''Nephrolenellus'' the eye ridges extend outwards, the second pair of side lobes of the glabella are very narrow, the genal spines attach further to the front of the cephalon, T3 carries massive pleural spines, the axial spine on T14 is absent, and there is a prominent opistothorax.

Relations with other Biceratopsinae

The closest relative of the six species of ''Bolbolenellus'' is the genus ''Nephrolenellus''. The other genera of the Biceratopsinae (''Biceratops'', ''Emigrantia'', ''Eopeachella'', ''Peachella'', and ''Olenelloides'') constitute the sister group.

Distribution

* ''B. euryparia'' is present in the Upper Olenellus-zone of California (lower half of the ''B. euryparia''-subzone of the Carrara Formation, Eagle Mountain, White-Inyo Mountains, and the middle part of the Latham Shale, East slope of hill 1440 in the southern end of the Marble Mountains, San Bernardino County).
* ''B. altifrons'' occurs in the Middle ''Olenellus''-zone of the Northwest Territories (type section of the type section of the Sekwi Formation, 0.2 miles Southeast of June Lake, Mackenzie Mountains).
* ''B. brevispinus'' has been collected in the Upper Olenellus-zone of Nevada (near Oak Spring Summit, Pioche Formation, Lincoln County).
* ''B. groenlandicus'' is found in Northwestern Greenland, questionably from the Upper ''Olenellus''-zone (Wulff River Formation, Marshall Bugt, Inglefield Land).
* ''B. hermani'' occurs in the Upper ''Olenellus''-zone of Vermont (Monkton Quartzite, near Clay and Red Rock Points on Lake Champlain, and Parker Slate, 2 miles west of Georgia Centre), of California (White, Inyo Mountain region)
* ''B. sphaerulosus'' has been collected in the ''Olenellus''-zone of the Yukon Territory, Canada (Unit 6 of the Upper Illtyd Formation, Wernecke Mountains).

Habitat

''Bolbolenellus'' was probably a marine bottom dweller, like all Olenellina.

References

External links

Oblique picture of Bolbolenellus brevispinus

picture of Bolbolenellus brevispinus from a dorsal point of view

{{Taxonbar, from=Q4939012

Redlichiida genera
Biceratopsidae
Cambrian trilobites
Extinct animals of North America