Keller believes she has evidence that they were, thanks to microscopic fossils of foraminifera, a type of plankton that largely died with the dinosaurs.
They were found in an ancient seabed in the Pondaung Hills west of Mandalay, embedded below a layer of marine organisms called foraminifera, dating from about 40 million years ago.
The foraminifera aren't picky; they just incorporate oxygen into their shells, in whichever form.
Scientists solve a 14,000-year-old ocean mystery At the end of the last Ice Age, as the world began to warm, a swath of the North Pacific Ocean came to life. During a brief pulse of biological productivity 14,000 years ago, this stretch of the sea teemed with phytoplankton, amoeba-like foraminifera and other tiny creatures, who thrived in large numbers until the productivity ended — as mysteriously as it began — just a few hundred years later ...
July 15, 2013 - TG Daily
Gerta Keller in FOXNews Before the mass extinction, most of the foraminifera species were comparatively large, very flamboyant, very specialized, very ornate, with many chambers,Keller explained.