Yukoniidae

Yukoniidae S. Zhang, 1980 [nom. transl. et emend. Jell, in Whittington et al., 1997 ex Yukoniinae S. Zhang in W. Zhang, Lu et al., 1980] is a small family of trilobites, belonging to the Eodiscina.^[1][2]

Yukoniidae Temporal range: Atdabanian to Toyonian PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Clade:	†Artiopoda
Class:	†Trilobita (?)
Order:	†Agnostida
Suborder:	†Eodiscina
Superfamily:	†Eodiscoidea
Family:	†Yukoniidae S. Zhang, 1980
Genera
Alaskadiscus S. Zhang in W. Zhang, Lu et al., 1980 Egyngolia Korobov, 1980 (Atdabanian) Ekwipagetia Fritz, 1973 (Atdabanian) Lenadiscus Repina in Khomentovskii & Repina, 1965 (Botomian) Yukonia Palmer, 1968 Yukonides Fritz, 1972 (Atdabanian)

Type genus and species

Yukonia intermedia Palmer 1968 (Plate 2, figures 14, 17–19, 22, 23, 27, 28; text figure 4). ^[3]

Taxonomy

The Yukoniidae probably descended from the Tsunyidiscidae and gave rise to the Eodiscidae.^[4]

Description

Yukoniidae are typically isopygous, belonging to the Superfamily Eodiscoidea. The narrow glabella 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.^[5]