MACROALGAE THROUGH PROTEROZOIC: MORPHOLOGICAL AND PALEOECOLOGICAL ANALYSES

Benthic marine macroalgae or seaweeds are key ecological players in oceans today and have been since the Proterozoic. However, their fossil record and evolutionary patterns are poorly documented. To address this knowledge gap, we updated a dataset of Proterozoic (with the addition of early Paleozoic) noncalcified macroalgae fossils preserved as macroscopic carbonaceous compressions. Non-parametric multidimensional scaling (NMDS) and functional-form group (FFG) approaches were used to analyze collected data, in order to characterize morphological and ecological evolutionary patterns of these macroalgae. The results show a progressive increase in morphospace range, thallus size, and aspects of ecological complexity such as canopy heights, surface area/volume ratios, and functional-form groups through time. These increases, however, are not monotonous. One of the most significant increases in macroalgal morphological and ecological diversity appears to have occurred during the Neoproterozoic (Cryogenian-Ediacaran) and not the Cambrian Period as a case with animals. These results suggest that the initial diversification of macroalgae appear to have occurred in the late Cryogenian to early Ediacaran time prior to the main episode of the Cambrian explosion (which consistent with biomarkers data). Because we have only one assemblage of macroalgae from the Cryogenian (the Nantuo Formation), it is hard to see dynamic of macroalgae diversification during this time. In contrast, more than 10 assemblages are known from the Ediacaran Period, which enables detailed analyses of morphometrics inside of this crucial period of macroalgal diversification. Analysis of Ediacaran macroalgal assemblages shows that macroalgae have greater morphospace range, taxonomic diversity, thallus size, and ecological diversity during the early portion of that period (635–550 Ma), and experienced a significant drop in these metrics at the termination of the period (~ 550–540 Ma). The latter event occurs during the Kotlinian crisis experienced by Ediacara-type macro-organisms, highlighting the possibility that this extinction event during the Ediacaran-Cambrian transition affected both macroalgae and Ediacara-type macro-organisms.