The earliest growth stages of Amphipora

摘要

The ontogenetic changes expressed in the earliest Amphipora-skeleton growth stages suggest that the observed successions can be very different from those of common stromatoporoids. The amphiporid organisms built first their bottom discs or directly the complex first chambers (diameters -0.2 mm), and these structures were directly continued by upright growth of first single tubes. The first occurrences of gradually developing amphiporid skeleton fiber meshworks were concentrated in the zone of metamorphosis, where the first tubes decayed. The attributes of adult amphiporid stages (axial canal and sparsely perforated outer casings or walls) developed with a little delay. The Amphipora stems increased mainly during the first millimeters of their length (to -1.5-2 mm), but further increase of the stems (to -3 or 5 mm) was a very slow process. It can be suggested that amphiporids can be linked to very old ancestors, somewhere around archaeocyaths or common metazoan sources at -0.8 Ga.