The Bristoliinae is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...

trilobites Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the At ...

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

marine

arthropods Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

, 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 Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, althoug ...

, including what are today Mexico, the

Appalachian Mountains The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. They ...

and the south-western United States, and Canada (

Northwest Territories The Northwest Territories (abbreviated ''NT'' or ''NWT''; french: Territoires du Nord-Ouest, formerly ''North-Western Territory'' and ''North-West Territories'' and namely shortened as ''Northwest Territory'') is a federal territory of Canada. ...

Etymology

The Bristoliinae are named for the type species '' Bristolia bristolensis''.

Description

The headshield (or cephalon) carries spines (called genal spines) of approximately 4-8 thorax segments long (measured parallel to the midline). The genal spines are attached in front of the back of the headshield. The central raised portion of the cephalon that represents the axis in the cephalon (or

glabella The glabella, in humans, is the area of skin between the eyebrows and above the nose. The term also refers to the underlying bone that is slightly depressed, and joins the two brow ridges. It is a cephalometric landmark that is just superior to ...

) touches the flattened ledge that borders the cephalon. The furrows that separate border, eye ridges, glabella and its lobes are distinct.

Communalities and differences with Biceratopsinae

The Bristolinae can be distinguished from its sister subfamily the Biceratopsinae that has effaced cephalic features (no furrows except for the border furrow).

Distribution

All Bristoliinae occur in the late Lower Cambrian (''Olenellus''-zone) of the former

paleocontinent A paleocontinent or palaeocontinent is a distinct area of continental crust that existed as a major landmass in the geological past. There have been many different landmasses throughout Earth's time. They range in sizes, some are just a collection ...

. ''Fremontella halli'' is known from eastern Laurentia (Rome Formation, Alabama, USA). All other species are known from western Laurentia: ''Lochmanolenellus mexicana'' from northern Mexico and South-East California, the species of ''Bristolia'' from southeastern California and southern Nevada, and an undescribed ''Bristolia''-species from the North-West Territories, Canada.

Habitat

The Bristolinae were probably marine bottom dwellers, like all Olenellina.

References

Cambrian trilobites Cambrian first appearances Cambrian Series 2 extinctions Biceratopsidae Arthropod subfamilies {{Redlichiida-stub