Yukoniidae S. Zhang, 1980 'nom. transl''. et ''emend''. Jell, ''in'' Whittington ''et al''., 1997 ''ex'' Yukoniinae S. Zhang in W. Zhang, Lu ''et al''., 1980is a small

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...

s, belonging to the

Eodiscina Eodiscina is trilobite suborder. The Eodiscina first developed near the end of the Cambrian, Lower Cambrian period (late Atdabanian) and became extinct at the end of the Middle Cambrian. Species are tiny to small, and have a thorax of two or thre ...

Type genus and species

''Yukonia intermedia'' Palmer 1968 (Plate 2, figures 14, 17–19, 22, 23, 27, 28; text figure 4).

Taxonomy

The Yukoniidae probably descended from the Tsunyidiscidae and gave rise to the

Eodiscidae Eodiscidae is a family of agnostid trilobites that lived during the final Lower Cambrian (late Toyonian) and the Middle Cambrian. They are small or very small, and have a thorax of two or three segments. Eodiscidae includes nine genera (see box). ...

. cited in

Description

Yukoniidae are typically isopygous, belonging to the Superfamily Eodiscoidea. The narrow

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 ...

is usually parallel sided, anteriorly rounded and separated from smooth anterior border by broad (''sag''.) preglabellar field which occupies about 25% of cephalic length excluding occipital spine. Posterior glabellar furrows are reduced to a pair of slits low on sides of glabella and directed backwards. Occipital ring bears a strong backwardly directed spine. ''Yukonia intermedia'' Palmer (1968) has three thoracic segments, the anterior of which has strong backwardly directed pleural spines. Pygidium of Yukoniidae has an axis of three to seven rings.

References

Eodiscina Trilobite families Cambrian trilobites Cambrian first appearances Cambrian Series 2 extinctions Trilobites of North America {{agnostida-stub