Yukoniidae

Yukoniidae; Temporal range: Atdabanian to Toyonian PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Trilobita
Order:	Agnostida
Suborder:	Eodiscina
Superfamily:	Eodiscoidea
Family:	Yukoniidae; S. Zhang, 1980
genera
	Yukonia Palmer, 1968; 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); Yukonides Fritz, 1972 (Atdabanian);

Yukoniidae is a family of trilobites, belonging to the Eodiscina, small trilobites with headshield and tailshield of equal size and shape, and with two or three thorax segments.[1][2]

Taxonomy

The Yukoniidae probably descended from the Tsunydiscidae and gave rise to the Eodiscidae.[3]

Description

Like all Agnostida, the Yukoniidae are diminutive and the headshield (or cephalon) and tailshield (or pygidium) are of approximately the same size (or isopygous) and outline. The central raised area of the cephalon (or glabella) is narrow, usually parallel sided and anteriorly rounded. The most backward transglabellar furrow is reduced to a pair of pits low on sides of glabella and curving back under the massive spine that points backward from the back of the glabella. There is a substantial distanced between the glabella and the smooth anterior border. Pygidium has an axis of three to seven rings.[4]

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References

S. M. Gon III. "Order Agnostida". Retrieved December 3, 2010.
Mikko Haaramo (March 11, 2008). "†Yukoniidae". Mikko's Phylogeny Archive. Retrieved December 3, 2010.
Jell, P.A. (1975). "Australian Middle Cambrian Eodiscoids with a review of the superfamily". Palaeontographica Abteilung A. 150: 1–97. cited in H.B. Whittington; et al., eds. (1997). Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida.
Whittington, H.B.; et al. (1997). Introduction, Order Agnostida, Order Redlichiida. Treatise on Invertebrate Paleontology. Part O.Revised, Volume 1 – Trilobita. Boulder, Colorado/Lawrence, Kansas: Geological Society of America/University of Kansas Press. pp. 398–400. ISBN 0-8137-3108-9.

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[1] S. M. Gon III. "Order Agnostida". Retrieved December 3, 2010.

[2] Mikko Haaramo (March 11, 2008). "†Yukoniidae". Mikko's Phylogeny Archive. Retrieved December 3, 2010.

[3] Jell, P.A. (1975). "Australian Middle Cambrian Eodiscoids with a review of the superfamily". Palaeontographica Abteilung A. 150: 1–97. cited in H.B. Whittington; et al., eds. (1997). Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida.

[Treatise-4] Whittington, H.B.; et al. (1997). Introduction, Order Agnostida, Order Redlichiida. Treatise on Invertebrate Paleontology. Part O.Revised, Volume 1 – Trilobita. Boulder, Colorado/Lawrence, Kansas: Geological Society of America/University of Kansas Press. pp. 398–400. ISBN 0-8137-3108-9.