NEW DATA ON THE EARLIEST ANIMALS AND EDIACARANS FROM SONORA, MEXICO

Recent geochronological estimates place the age of the Clemente Formation (Sonora, Mexico) at 580-610 ma, making the Clemente Biota the oldest known assemblage of megascopic Ediacarans and ichnofossils. Analysis of a sinusoidal trace fossil in the Clemente Formation reveals evidence for peristalsis. Several cycles of deep contraction and expansion may be seen along the length of the ichnofossil, suggesting a mode of burrowing that utilized an extroverted proboscis, as might be expected in a Proterozoic siphunculid worm.

A new hiemaloriid vendobiont from the Clemente Formation consists of dense clusters of radiating, cylindrical to lobate sediment-filled tubes. The tubes have wavy edges and proximal pinch-outs that are strongly reminiscent of the morphology of tubes seen in one of the youngest vendobionts, Stromatoveris from the Lower Cambrian of China. Morphological resemblances between Stromatoveris and charniids, dickinsoniids and the Clemente hiemaloriid suggest that all these organisms belong to an extinct clade with the same unusual body architecture.

The Clemente Formation has also yielded the hiemaloriid Evandavia aureola, and a specimen of Sekwia that compares closely to specimens of Sekwia collected from the Carolina Slate Belt.