Problematicum

From Palaeos

A problematicum (pl. problematica) is a (usually fossil) organism of uncertain relationships. While in theory almost any organism could be labelled a problematicum under this definition (almost every species has some degree of uncertainty about its relationships, even if only within its genus), in practice the term is generally reserved for those taxa for which the uncertainty runs to a very high level, generally phylum level or higher. Also, this uncertainty generally should not be due to poor preservation alone, but reflect a true shortage of shared characters with modern phyla. The study of problematica has received a fair amount of attention in recent years, as many taxa previously regarded as problematica (such as Anomalocaris and Halkieria) have been demonstrated to lie in the stem group of modern phyla, and may be very informative about how the characters of those phyla evolved.

The majority of taxa regarded as problematica come from the Ediacaran or Cambrian periods, such as the Vendozoa for the former and many members of the Burgess Shale, Chengjiang and small shelly faunas for the latter. Most of the remaining problematica are also from the Palaeozoic, with the Carboniferous Mazon Creek fauna including a number of problematica such as Tullimonstrum. Few post-Palaeozoic taxa are regarded as problematica, but even some modern organisms such as Lobatocerebrum are arguably problematic.

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CKT061214