Kingdom Animalia Class Trilobita Suborder Olenellina Rank Genus | Phylum Arthropoda Order Redlichiida Superfamily Olenelloidea | |
Similar Nephrolenellus, Mesonacis, Olenelloidea, Fritzolenellus, Olenelloides | ||
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.
Contents
Etymology
Bolbolenellus is the combination of Greek βολβός (bolbos, “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.
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 an 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 sistergroup.
Distribution
Habitat
Bolbolenellus was probably a marine bottom dweller, like all Olenellina.