Dailyatia bacata scleritome reconstruction

The camenellans, consisting of the genera ''Camenalla'', ''Dailyatia'', ''Kennardia'', ''Kelanella'', '' Wufengella'' and ''Lapworthella'', are a (probably

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

) group of Tommotiid invertebrates from the

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

period, reconstructed as sister to all others (plus brachiopods and phoronids). They are primarily known from isolated sclerites, but are believed to have a scleritomous, '' Halkieria''-like construction.Skovsted, C. B., Betts, M. J., Topper, T. P. & Brock, G. A. The early Cambrian tommotiid genus ''Dailyatia'' from South Australia. Mem. Assoc. Australas. Palaeontol. 48, 1–117 (2015).Murdock, D. J. E., Donoghue, P. C. J., Bengtson, S. & Marone, F. Ontogeny and micro-structure of the enigmatic Cambrian tommotiid ''Sunnaginia'' Missarzhevsky, 1969. Palaeontology 55, 661–676 (2012). This was confirmed by the discovery of '' Wufengella,'' known from articulated remains, which showed camenellans to be mobile, worm-like animals. ''Dailyatia'' and ''Camenella'' have distinct dorsal (symmetrical) and lateral (asymmetric) sclerite morphologies. The same has been asserted for ''Lapworthella'' even though that has not always been the common perception. It has been argued that ''Camenella'', ''Kelanella'' and ''Lapworthella'', assuming a slug-like anatomy, had an anterior 'head valve' followed by pairs of asymmetric valves running in pairs along their dorsal surface.Devaere, L. & Skovsted, C. B. New early Cambrian sclerites of ''Lapworthella schodakensis'' from NE Greenland: advancements in knowledge of lapworthellid taxonomy, sclerite growth and scleritome organization. Geol. Mag. (2016). doi:10.1017/S0016756816000698 The 'head valve' in ''Lapworthella'' - that is the bilaterally symmetric Morph A valve - is thought to have fused from two ontogenetically separate sclerites. ''Dailyatia'' has a similar double-mounded structure at the tip of its A type sclerites. Growth rings in all are marked out by prominent external ridges.

Taxonomy

Two families: Kennardiidae Laurie, 1986: three sclerite morphs, one of which (conventionally termed the A morph) is bilaterally symmetrical, the other two occurring in sinistral and dextral variants. Includes ''Kennardia'' and ''Dailyatia'', and questionably ''Shetlandia'' Lapworthellidae: sclerites occur in something of a morphological continuum, but essentially form a single type with a sinistral and dextral version, possibly with the anterior-most pair of sclerites fusing into a single bilaterally-symmetrical, dual-tipped sclerite. ''Dailyatia'' species:

References

Prehistoric protostomes Cambrian invertebrates Paleozoic life of New Brunswick Paleozoic life of Newfoundland and Labrador Paleozoic life of Nova Scotia {{Palaeo-protostome-stub Cambrian genus extinctions