The enormous asteroid that struck the Earth 66 million years ago not only wiped out the dinosaurs, but drastically changed the behaviour of mammals.
A new study has found that mammals only started being active in the daytime after non-avian dinosaurs were wiped out.
The findings provide key insights into the changing behaviour of animals through history.
A new study has found that mammals only started being active in the daytime after non-avian dinosaurs were wiped out. The illustration is an artist’s impression of Mesozoic animals found fossilised in the Kayenta rock formation
Researchers from UCL and Tel Aviv University’s Steinhardt Museum of Natural History have discovered when mammals started living in the daytime for the first time.
The researchers analysed data of 2,415 species of mammals alive today using computer algorithms to reconstruct the likely activity of the ancient ancestors who lived millions of years ago.
Two different mammalian family trees portraying alternative timelines for the evolution of mammals were used in the analysis.
Results showed that mammals switched to daytime activity shortly after the dinosaurs disappeared.
This change wasn’t instantaneous – it involved an intermediate stage of mixed day and night activity over millions of years.
Mr Roi Maor, lead author of the study, said: ‘We were very surprised to find such close correlation between the disappearance of dinosaurs and the beginning of daytime activity in mammals, but we found the same result unanimously using several alternative analyses.’
Activity pattern distributions across the two models estimates mammalian evolution. Species activity patterns are denoted by different colours in the perimeter circle, where nocturnal is blue, diurnal is yellow, cathemeral is green and ambiguous is magenta
The team found that the ancestors of simian primates – including gorillas, gibbons and tamarins – were among the first to give up nocturnal activity altogether.
But the two evolutionary timelines varied, giving a window between 52-33 million years ago for this to have occurred.
This discovery fits well with the fact that simian primates are the only mammals that have evolved adaptations to seeing well in daylight.
These observations led to the development of the ‘nocturnal bottleneck’ theory.
This theory suggests early mammals had to restrict their activity to the night time to avoid conflict with dinosaurs that were active by day.
When the dinosaurs died out mammals were able to move into the newly available daytime niche.
Simians have comparable visual acuity and colour perception as diurnal reptiles and birds – groups that have always lived in the daytime.
Professor Kate Jones, co-author of the study, said: ‘It’s very difficult to relate behaviour changes in mammals that lived so long ago to ecological conditions at the time, so we can’t say that the dinosaurs dying out caused mammals to start being active in the daytime.
The observations led to the development of the ‘nocturnal bottleneck’ theory. This theory suggests early mammals had to restrict their activity to the night time to avoid conflict with dinosaurs that were active by day (stock image)
‘However, we see a clear correlation in our findings.’
Professor Tamar Dayan, co-author of the study, added: ‘We analysed a lot of data on the behaviour and ancestry of living animals for two reasons – firstly, because the fossil record from that era is very limited and secondly, behaviour as a trait is very hard to infer from fossils.
‘You have to observe a living mammal to see if it is active at night or in the day.
WHAT HAPPENED WHEN THE ASTEROID HIT EARTH?
Within 10 hours of the impact, a massive tsunami waved ripped through the Gulf coast.
This caused earthquakes and landslides in areas as far as Argentina.
The creatures living at the time were not just suffering from the waves – the heat was much worse.
While investigating ‘dooms day’ researchers found small particles of rock and other debris that was shot into the air when the asteroid crashed.
After the asteroid had hit, the researchers believe that the Earth would have behaved like a ‘slow-moving fluid’
Called spherules, these small particles covered the world with a one-tenth inch thick layer of soot.
Experts explain that losing the light from the sun caused a complete collapse in the aquatic system as the phytoplankton base of almost all aquatic food chains would have been eliminated.
It’s believed that the more than 180 million years of evolution that brought the world to the Cretaceous point was destroyed in less than the lifetime of a Tyrannosaurus rex, which is about 20 to 30 years.
‘Fossil evidence from mammals often suggest that they were nocturnal even if they were not.
‘Many subsequent adaptations that allow us to live in daylight are in our soft tissues.’
The team say further research is needed to better understand the mammalian family tree to give more accurate information on when the behaviour of species changes from night time to day time activity.