Welcome to DU! The truly grassroots left-of-center political community where regular people, not algorithms, drive the discussions and set the standards. Join the community: Create a free account Support DU (and get rid of ads!): Become a Star Member All Forums Issue Forums Culture Forums Alliance Forums Region Forums Support Forums Help & Search

unhappycamper

(60,364 posts)
Thu Sep 4, 2014, 07:08 AM Sep 2014

Ancient mammal relatives were active at night 100 million years before origin of mammals

http://esciencenews.com/articles/2014/09/04/ancient.mammal.relatives.were.active.night.100.million.years.origin.mammals



Ancient mammal relatives were active at night 100 million years before origin of mammals
Published: Thursday, September 4, 2014 - 00:52 in Paleontology & Archaeology

Most living mammals are active at night (or nocturnal), and many other mammal species are active during twilight conditions. It has long been thought that the transition to nocturnality occurred at about the same time as mammals evolved, around 200 million years ago. This thinking was based on on features such as the large brains of mammals (good for processing information from senses like hearing, touch, and smell) and the details of light-sensitive chemicals in the eyes of mammals. It turns out that nocturnal activity might have a much older origin among ancient mammal relatives, called synapsids.

"Synapsids are most common in the fossil record between about 315 million years ago and 200 million years ago. The conventional wisdom has always been that they were active during the day (or diurnal), but we never had hard evidence to say that this was definitely the case," says Kenneth Angielczyk, a curator at The Field Museum. He's the lead author of a paper appearing September 3 in the early edition of Proceedings of the Royal Society B entitled "Nocturnality in Synapsids Predates the Origin of Mammals by 100 Million Years."

The new insights come from an analysis of tiny bones, called scleral ossicles, that are found in the eyes of many backboned animals, including birds and lizards. Living mammals lack scleral ossicles, but they were present in many of their ancient synapsid relatives. "The scleral ossicles tell us about the size and shape of different parts of the eyeball," said Lars Schmitz, a professor of biology at Claremont McKenna, Pitzer, and Scripps Colleges, located near Los Angeles. "In turn, this information allows us to make predictions about the light sensitivity of the eye, which usually reflects the time of day an animal is active.

Because scleral ossicles are very delicate, they usually aren't preserved in synapsid fossils. However, by scouring museum collections in the United States and South Africa, and with help from other paleontologists, Angielczyk and Schmitz were able to collect data on scleral ossicles from 24 species that represent most major groups of synapsids. The synapsid data were then compared to a large dataset of similar measurements for living lizards and birds that have known daily activity patterns, using a statistical technique developed by Schmitz.
1 replies = new reply since forum marked as read
Highlight: NoneDon't highlight anything 5 newestHighlight 5 most recent replies
Ancient mammal relatives were active at night 100 million years before origin of mammals (Original Post) unhappycamper Sep 2014 OP
Nocturnal synapsids? Dale Neiburg Sep 2014 #1

Dale Neiburg

(694 posts)
1. Nocturnal synapsids?
Thu Sep 4, 2014, 08:01 AM
Sep 2014

Very cool. But I was always taught that (based on the extensive blood supply in Dimetrodon's sail) it was probably a device for regulating body temperature. (Turn your sail broadside to the sun to warm up, end toward the sun to cool off.) But if they were out at night, and presumably under some kind of shelter during the day, temperature regulation doesn't seem to work so well as an explanation for that vulnerable sail -- no way to protect it from an attacker, and with copious blood flow even relatively minor damage might lead to the animal bleeding out.

So now I'm puzzled again....

Latest Discussions»Culture Forums»Science»Ancient mammal relatives ...