Susannah Porter on Tiny Vampires in Ancient Seas
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Susannah Porter is a Professor in the Department of Earth Sciences at the University of California, Santa Barbara. She studies microfossils of eukaryotic life forms that lived in the Neoproterozoic, about 750 million years ago. In the podcast, she describes her discovery of conclusive evidence that these creatures were predating on each other. Did this predation lead to diversification and evolutionary innovation at this time? Was it a microscopic foreshadowing of the enormous diversification seen about 200 million years later in the Cambrian?
Podcast Illustrations
All images courtesy of Susannah Porter except where otherwise indicated.
The Chuar Group
Susannah Porter found the microfossils she discusses in the podcast in the 1,600-meter-thick Chuar Group, which consists mainly of shales and siltstones exposed over 15 square kilometers in the eastern Grand Canyon. The rocks were deposited in a shallow marine seaway near the equator about 750 million years ago in the early Neoproterozoic, about 20 million years before the ‘snowball Earth’ glaciations. The people visible in the image above provide a sense of scale.
Drill holes in vase-shaped microfossils: Half-moon shaped holes (black arrows) and circular holes (white arrows) in 780–740-million-year-old fossils of shell-forming (testate) amoebae from the Chuar Group of the Grand Canyon, Arizona. The holes are approximately 15 to 35 micrometers in size, and the shells are 75 to 150 micrometers in length.
Circular holes, thought to have been formed by predatory 'vampire-like' protists that drilled into the walls of their prey, in a 780–740-million-year-old microfossil from the Chuar Group of the Grand Canyon, Arizona. The holes are ~0.2 micrometers in diameter, and the microfossil is 50 micrometers in diameter. It was originally a spherical vesicle, but has been flattened by the pressure of overlying rocks.
Comparison of the vase-shaped microfossil species Bonniea dacruchares with a modern testate amoeba. The cell lived inside the test and extended its pseudopods through the circular opening. (Bonniea dacruchares is named in honor of Bonnie Bloeser, who first discovered vase-shaped microfossils in the Chuar Group. The specific epithet, dacruchares, is an ancient Greek word meaning 'the delight one gets from tears', — fitting for these fine, tear-shaped fossils.)
As explained in the podcast, it was her familiarity with the tiny holes made by modern amoebae that first made Susannah Porter suspect that the holes in the ancient microfossils were made by a predator. These images show perforations in spores of the fungus Cochliobolus sativus made by the modern vampyrellid amoebae. (a) Overview of spores, several showing circular perforations. (b) Close-up view of spore, showing several circular perforations, each approximately 0.2 mm in diameter. Scale bar is 20 micrometers in (a), 2 micrometers in (b).
Old, K. & Patrick, Z. (1976), Ca. Bot. 54, 2798
Modern vampire amoebae can be seen hollowing out an algal body, entering it, reproducing, and releasing many daughter cells that swarm out from the algal husk.
Another vampire amoeba searching for food.
Further Reading
Porter, S.M. (2016), Proc. R. Soc. B 283:20160221
Dehler, C.M., Porter, S.M., & Timmons, M. (2012), in Timmons, J.M. & Karlstrom, K.E., eds. Grand Canyon Geology: Two Billion Years of Earth History: Geol. Soc. America Special Paper 489, 49
Lyons et al. (2018), Emerging Topics in Life Sciences, 2, 121
http://www.penard.de/ for images of protistans. Clcik on Explorer+ > Amoebozoa > Tubilinea > Arcellinida to see testate amoebae that are living descendants of the Neoproterozoic vase-shaped microfossils.
https://www.sciencephoto.com/media/688167/view/vampyrella-feeding-on-algae-time-lapse