WINNIPEG, MB – UWinnipeg associate professor in anthropology and resident fossil specialist, Dr. Mary Silcox and UWinnipeg student Claire Dalmyn, now a graduate student at York University have cracked open the details to the brain of a small primate that lived 54 million years ago, known as Ignacius graybullianus. This collaborative research project was done with University of Florida’s Florida Museum of Natural History Vertebrate Paleontology Curator Dr. Jonathan Bloch. Their findings were published yesterday in Proceedings of the National Academy of Sciences of the United States of America (PNAS), one of the world’s most-cited multidisciplinary scientific journals.
Paleontology 101
On average living primates have brains that are relatively larger than those of other mammalian groups, with this feature reaching its pinnacle in the extremely enlarged brain of humans. Studying the evolution of this distinctive trait is difficult by the fact that brains don’t fossilize. The closest that paleontologists can come to studying “fossil brains” is to study endocasts, three dimensional models of the internal surface of the skull, which in mammals quite closely approximate the size and form of the brains from living animals.
“Until now, practically nothing was known of the earliest chapters of primate brain evolution because no complete endocasts were available from the most primitive “stem” members of the group”, explained Silcox. “This new study gives us an important tool and a new way to test theories on why primates evolved their unusually large brains.”
Best-Preserved Skull
In this published study, the researchers used ultra high-resolution CT (“catscan”) data to develop an endocast for the best-preserved skull of a stem primate. The specimen pertains to Ignacius graybullianus, an early primate that lived in what is today Wyoming. Dalmyn painstakingly traced the contours of the inside of the skull on 821 separate CT slices through the specimen, producing one of the most detailed endocasts known for any small extinct mammal.
The brain of Ignacius was quite small (perhaps ½ to 2/3rd the size of a typical living mammal), which is surprising in an animal that was behaviourally quite like a living primate. This allows researchers to rule out certain factors as being critical to the evolution of large brain size in primates, including eating fruit and living in the trees.
“Eyes-First” Animal
The differences between the form of the endocast of Ignacius, and those from primates from the next “phase” of primate evolution suggest that at least a portion of the brain size increase characteristic of primates was related to becoming more of an “eyes-first” animal. Interestingly, although apparently in some ways quite like a living primate in behavior, Ignacius exhibited a combination of features not seen in any living member of the group. This highlights the importance of the fossil record to understanding how the Earth’s biota has changed through time, and to comprehending the process by which we ourselves evolved.
Proceedings of the National Academy of Sciences of the United States of America
PNAS is one of the world’s most-cited multidisciplinary scientific serials. Since its establishment in 1914, it continues to publish cutting-edge research reports, commentaries, reviews, perspectives, colloquium papers, and actions of the Academy. Coverage in PNAS spans the biological, physical, and social sciences. PNAS is published weekly in print, and daily online in PNAS Early Edition.
