''Holyoakia'' is a genus of very small (up to 7½ mm long)

trilobite 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 ...

s of the family Dorypygidae, from the late Lower Cambrian (Late Botonian) of South Australia and Antarctica.

Etymology

''H. simpsoni'' was named in honor of David Simpson from Adelaide, who collected the first specimens.

Distribution

* ''H. granulosa'' has only been collected from the late Lower Cambrian of Antarctica (presumably Botomian,

Shackleton Limestone The Shackleton Limestone is a Cambrian limestone formation of the Byrd Group of Antarctica. The age of the formation is established to be Cambrian Stage 3, dated at ranging from 520 to 516 Ma. This period correlates with the End-Botomian mass ext ...

, Central Transantarctic Mountains) * ''H. simpsoni'' only occurs in the late Lower Cambrian of South Australia (mid-late Botomian,

Emu Bay Shale The Emu Bay Shale is a geological formation in Emu Bay, South Australia, containing a major Konservat-Lagerstätte (fossil beds with soft tissue preservation). It is one of two in the world containing Redlichiidan trilobites. The Emu Bay Shale ...

, Big Gully, Kangaroo Island).

Taxonomy

The genus was originally with reservation placed in the

Emuellidae Emuellidae are a small family of trilobites, a group of extinct marine arthropods, that lived during the late Lower Cambrian (late Botomian) of the East Gondwana supercontinent, in what are today South-Australia and Antarctica. Emuellidae can b ...

. The genus however lacks the specific characteristics of this family, most notably, the clearly furrowed

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 ...

that is rounded at the frontal end, the hook-shaped eye ridges that run parallel to the margin of the head shield (or cephalon), clearly distinguishable prothorax of six segments, the most backward one with much larger spines than all others, and opistothorax of many segments, while the pygidium is tiny. ''Holyoakia'' however, has a rectangular glabella, difficult to discern eye ridges, a thorax of eight segments which is not differentiated and has no macropleural segment, and the pygidium is not much smaller than the cephalon.

Ecology

''H. simpsoni'' occurs together with ''

Redlichia takooensis ''Redlichia takooensis'' is a species of redlichiid trilobite from the lower Cambrian-aged Emu Shale of Kangaroo Island, Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of ...

'', '' Estaingia bilobata'', '' Balcoracania dailyi'', and '' Megapharanaspis nedini''.

Etymology

Distribution

Taxonomy

Ecology

Key to the species

References

Further reading