TINY VAMPIRES IN ANCIENT SEAS: EVIDENCE FOR PREDATION VIA PERFORATION IN MICROFOSSILS FROM THE 740-780 MA CHUAR GROUP, GRAND CANYON, ARIZONA

Predators play a key role in the evolution of their prey, driving both evolutionary innovation and diversification. Most studies have focused on the role of predation during the Phanerozoic Eon, but the wide distribution of predators across both bacterial and eukaryotic clades suggests a much deeper history. Recent phylogenetic analyses suggest that the earliest protists consumed bacteria and that the ability to eat other protists evolved independently in several clades that diversified during the early Neoproterozoic. This is consistent with other indirect evidence for predation on eukaryotes at this time, including the first appearance of mineralized skeletons and organic tests in protists and body fossil evidence for testate amoebae, whose modern relatives consume both bacteria and eukaryotes. Here I report the presence of circular holes in cyst and cell walls of eukaryotic microfossils from the ca. 780-740 Ma Chuar Group, Grand Canyon, Arizona. The holes are regular in shape and occur in specimens that may otherwise show no signs of pitting or degradation. They range in size from 0.1-3.5 µm in diameter, but show much narrower ranges within individual specimens. They are irregularly distributed on the fossil wall and number from 1 to >30 in a specimen. Some holes are beveled. Their irregular number and distribution within specimens and occurrence in a variety of species suggest they are not biological characters of the fossils, and their regular shape and narrow size distribution within specimens suggest they are not formed by mineral puncture. Their shape and distribution are also inconsistent with post-mortem biodegradation. Instead, the holes are interpreted to be the work of predators that perforated the walls of their prey to consume the cell contents inside. Similar behavior is known today in some opisthokonts, amoebozoans, and rhizarians, as well as in Myxobacteria, but the Chuar holes are most closely comparable to perforations formed by members of the Vampyrellidae (Cercozoa, Rhizaria), a diverse group of predatory amoebae found in marine, freshwater, and terrestrial environments. These holes provide the earliest direct evidence for predation on protists, and support the view that, by 740 Ma, predation was an important agent shaping early eukaryote ecology and evolution.