Navigation Links
New study shows effects of prehistoric nocturnal life on mammalian vision

AUSTIN, Texas Since the age of dinosaurs, most species of day-active mammals have retained the imprint of nocturnal life in their eye structures. Humans and other anthropoid primates, such as monkeys and apes, are the only groups that deviate from this pattern, according to a new study from The University of Texas at Austin and Midwestern University.

The findings, published in a forthcoming issue of Proceedings of the Royal Society B, are the first to provide a large-scale body of evidence for the "nocturnal bottleneck theory," which suggests that mammalian sensory traits have been profoundly influenced by an extended period of adaptation to nocturnality during the Mesozoic Era. This period lasted from 250 million years ago to 65 million years ago.

To survive in the night, mammals had a host of visual capabilities, such as good color vision and high acuity, which were lost as they passed through the nocturnal "bottleneck."

"The fact that nearly all living mammals have eye shapes that appear 'nocturnal' by comparison with other amniotes [mammals, reptiles and birds] is a testament to the strong influence that evolutionary history can have on modern anatomy," says Chris Kirk, associate professor of anthropology at The University of Texas at Austin.

According to Kirk, early mammals were predominantly nocturnal during the Mesozoic partly as a strategy for avoiding predation by day-active dinosaurs.

"It's a bit surprising to still see the effects of this long period of nocturnality on living mammals more than 65 million years after non-avian dinosaurs went extinct, but that's exactly what we found," Kirk says.

The research team, led by Margaret Hall, an evolutionary biologist at Midwestern University's Arizona College of Osteopathic Medicine, analyzed one of the largest datasets on eye morphology ever assembled. Using a sample of eyeballs from 266 mammal species, the researchers used a multivariate statistical method to show that mammals active by day or night show only minor differences in eye morphology.

The researchers then compared the eyes of mammals, birds and lizards using the ratio of cornea size and eye length two functionally important measures of the eye's ability to admit light and form sharp images. These analyses showed that diurnal (only active by day) and cathemeral (active by both day and night) mammals don't differ in their eye shapes. At the same time, both groups have eye shapes that are very similar to those of nocturnal birds and lizards. These results reveal that most day-active mammals have eye shapes that appear "nocturnal" when compared with other vertebrates.

One likely reason for these findings, Kirk says, is that after the extinction of non-avian dinosaurs, some nocturnal mammals became day-active and there was less pressure to evolve eye shapes for acute diurnal vision like those of other day-active vertebrates.

Anthropoid primates are the only mammalian group that re-evolved eye shape for fine detailed daytime vision. Like diurnal birds and lizards, most anthropoids have small corneas relative to eye length as an adaptation for enhanced visual acuity.

Kirk says the study provides a deeper understanding of human sensory systems and our intrinsic connection with our closest living primate relatives: the monkeys and apes.

"Humans and other anthropoid primates are so dependent on vision for everything that they do," Kirk says. "In this case, we are radically different from other mammals. We found that the distinctive eye shapes that set humans apart from most other mammals evolved a long time ago way back with the origin of anthropoid primates."


Contact: Chris Kirk
University of Texas at Austin

Related medicine news :

1. 1000 genomes study is guidebook to how genes vary
2. Water Workouts a Great Alternative: Study
3. Gene Study Yields New Clues to Crohns Disease, Colitis
4. Health inequalities could be reduced by more effective health care, says new study
5. Automated calls help patients in under-developed countries manage blood pressure, U-M study finds
6. Health inequalities could be reduced by more effective healthcare, says new study
7. Study suggests too much risk associated with SSRI usage and pregnancy
8. Flirting Works as Negotiation Tactic for Women: Study
9. Study suggests new way to prevent recurrent ear infections
10. Using Canadas Health System as Model Might Cut U.S. Costs: Study
11. The Biggest Loser May Sour Viewers on Exercise, Study Finds
Post Your Comments:
(Date:10/13/2017)... (PRWEB) , ... October 13, 2017 , ... ... established the certification process to promote standards of excellence for the field of ... scheduled for March 22 – 25, 2018 in Orlando, Florida at the Omni ...
(Date:10/13/2017)... ... October 13, 2017 , ... Apple Rehab Shelton Lakes ... a mock evacuation of the facility as part of a disaster drill on October ... Hose EMS and Shelton City Emergency Manager, as well as the Connecticut Long ...
(Date:10/13/2017)... ... , ... Global Healthcare Management’s 4th Annual Kids Fun Run brought out many ... event, sponsored by Global Healthcare Management’s CEO, Jon Letko, is aimed at getting kids ... of all ages; it is a non-competitive, non-timed event, which is all about having ...
(Date:10/13/2017)... ... October 13, 2017 , ... “The Journey: From the ... danger possible to save lost souls in the Philippines. “The Journey: From the Mountains ... a dedicated teacher of the Bible. She has taught all ages and currently teaches ...
(Date:10/12/2017)... New Orleans, LA (PRWEB) , ... October 12, 2017 , ... ... fitness centers in the U.S., announced today its plans to open a flagship location ... club will occupy the former Rooms To Go store next to Office Depot in ...
Breaking Medicine News(10 mins):
(Date:10/4/2017)... Mass. , Oct. 4, 2017  According to the Centers for ... the end of October . PhysicianOne Urgent Care is helping communities across ... Westchester, NY , by offering no-cost* flu shots through the ... as mandated by certain health insurance regulations. ... The best time to get a flu shot is by the ...
(Date:10/2/2017)... 2, 2017  AllianceRx Walgreens Prime, the combined central ... and pharmacy benefit manager Prime Therapeutics LLC (Prime), today ... included the unveiling of new signage at its headquarters ... as at a few other company-owned facilities across the ... patients, some of whom will begin to see the ...
(Date:9/28/2017)... , Sept. 28, 2017 Cohen Veterans ... advance the use of wearable and home sensors for ... disorders. Early Signal Foundation, a nonprofit organization focused on ... will provide an affordable analytical system to record and ... ...
Breaking Medicine Technology: