BSCI392
10-25-07
Cnidaria, Bilateria, and the Conulariid Enigma

Text only

In this lecture, we consider a true taxonomic and ecological enigma at the base of the Metazoan tree. First, the problem:

Conulariida: (Conulariids) Cambrian (maybe Ediacaran) - Triassic. Distinctive hard bodied fossils in the form of tall inverted pyramids composed of apatite (= calcium phosphate). Very conservative in general morphology throughout time range.

Morphologic features:

WTF?

Here we have creatures that persisted, largely unchanged (at least their skeletons) from the Ediacaran to the Triassic, survived the Permo-Triassic extinction event, and we are clueless about how they lived and who their relatives are. In the absence of obvious living or fossil analogs, we thrash helplessly, grasping at a wide range of hypotheses that fall into two broad categories:

Reasons for caution:

Any serious consideration of the problem requires some familiarity with Cnidaria.

Cnidaria

Characteristics:

Major cnidarian groups:

  • Hydrozoa: Hydras, fire coral (Cretaceous - Recent)

  • Cubozoa: Box jellies (Pennsylvanian - Recent)