Yukoniidae
| Yukoniidae Temporal range: Atdabanian to Toyonian | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Trilobita |
| Order: | Agnostida |
| Suborder: | Eodiscina |
| Superfamily: | Eodiscoidea |
| Family: | Yukoniidae S. Zhang, 1980 |
| genera | |
| |
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]
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.