Kirkbyelloidea

Left valve of Kirkbyella delicata, from Hoare & Merrill (2004).

Belongs within: Palaeocopida.

Kirkby’s small ostracods (or small Kirkby’s ostracods)
Published 11 July 2022

I do not envy those who find themselves working with ostracods. These minute crustaceans, typically less than a millimetre in length, seem altogether too fiddly to handle. Nevertheless, the long history of ostracods, together with their diversity and the high fossilisation potential of their calcified carapace valves, have made them a common focus for studying biostratigraphy and historical environments. The classification of modern ostracods is commonly informed by features of the legs and other appendages but such characters are not commonly preserved in fossil representatives. As a result, there are many groups of ostracods known from the Palaeozoic whose relationships remain uncertain.

One such group is classified by Liebau (2005) as the superfamily Kirkbyelloidea. Members of this group are small ostracods with reticulate valves. The dorsal and ventral margins of the valves tend to be more or less straight. They are commonly impressed with a single dorsal sulcus, extending downwards from the dorsal margin about halfway along the valve’s length. Below this sulcus is a protruding horizontal lobe ending in members of the family Kirkbyellidae in a small spine. Evidence of sexual dimorphism, a not-uncommon feature of Palaeozoic ostracods, is not known from kirkbyelloids.

Definite kirkbyelloids are known from the Devonian to the Permian. If the earlier family Ordovizonidae is included, their record extends all the way back to the Ordovician. As noted above, it is unclear where kirkbyelloids sit in the ostracod family tree. Becker (1994) suggested a relationship via Ordovizona to the Ordovician Monotiopleuridae which resemble kirkbyelloids in the outline of the carapace valves and features of the adductor muscle scars. Though long-lived, kirkbyelloids don’t seem to have ever been massively diverse, and they can probably be counted among the many lineages of organisms that never made it past the end of the Palaeozoic.

Systematics of Kirkbyelloidea
<==KirkbyelloideaL05
|--KirkbyellidaeBB61
| |--Psilokirkbyella prominens Becker & Wang 1992WSB93
| `--Kirkbyella Coryell & Booth 1933HM04
| |--*K. (Kirkbyella) typa Coryell & Booth 1933BB61
| `--K. (Berdanella Sohn 1961)HM04
| |--K. (B.) delicata Hoare & Merrill 2004HM04
| |--K. (B.) gutkei (Croneis & Bristol 1939)HM04
| `--K. (B.) quadrata (Croneis & Gutke 1939)HM04
|--Ordovizona Schallreuter 1969B94 [OrdovizonidaeL05]
| |--*O. sulcata Schallreuter 1969B94
| |--O. immanis Becker 1994B94
| `--O. longa Schallreuter 1983B94
`--ParvikirkbyidaeL05

*Type species of generic name indicated

References

[B94] Becker, G. 1994. A remarkable Ordovician ostracod fauna from Orphan Knoll, Labrador Sea. Scripta Geologica 107: 1–25.

[BB61] Benson, R. H., J. M. Berdan, W. A. van den Bold, T. Hanai, I. Hessland, H. V. Howe, R. V. Kesling, S. A. Levinson, R. A. Reyment, R. C. Moore, H. W. Scott, R. H. Shaver, I. G. Sohn, L. E. Stover, F. M. Swain & P. C. Sylvester-Bradley. 1961. Systematic descriptions. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt Q. Arthropoda 3: Crustacea: Ostracoda pp. Q99–Q421. Geological Society of America and University of Kansas Press.

[HM04] Hoare, R. D., & G. K. Merrill. 2004. A Pennsylvanian (Morrowan) ostracode fauna from Texas. Journal of Paleontology 78 (1): 185–204.

[L05] Liebau, A. 2005. A revised classification of the higher taxa of the Ostracoda (Crustacea). Hydrobiologia 538: 115–137.

[WSB93] Whatley, R. C., D. J. Siveter & I. D. Boomer. 1993. Arthropoda (Crustacea: Ostracoda). In: Benton, M. J. (ed.) The Fossil Record 2 pp. 343–356. Chapman & Hall: London.

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