Mammals went through 'evolutionary burst' during mid-Jurassic period - study
Mammals went through an explosion of evolution just as dinosaurs were getting into their stride, new research has shown.
The rapid changes reached their peak in the middle of the Jurassic period, between 200 million and 145 million years ago.
During this time mammals diversified at break-neck speed, developing a wide range of adaptations for feeding and locomotion including gliding, digging and swimming.
At one time, early mammals living alongside the dinosaurs were thought of as somewhat uninteresting - nondescript, small, nocturnal creatures that fed on insects and kept out of the dinosaurs' way.
Lead scientist Dr Roger Close, from Oxford University, said: "What our study suggests is that mammal 'experimentation' with different body plans and tooth types peaked in the mid-Jurassic.
"This period of radical change produced characteristic body shapes that remained recognisable for tens of millions of years.
"We don't know what instigated this evolutionary burst. It could be due to environmental change, or perhaps mammals had acquired a 'critical mass' of 'key innovations' - such as live birth, hot bloodedness, and fur - that enabled them to thrive in different habitats and diversify ecologically.
"Once high ecological diversity had evolved, the pace of innovation slowed.
"In the Jurassic we see a profusion of weird and wonderful bodies suddenly appear and these are then 'winnowed down' so that only the most successful survive. What we may have identified in this study is mammals' own 'Cambrian explosion' moment, when evolutionary experimentation ran wild and the future shape of mammals was up for grabs."
The Oxford team carried out the first large-scale analysis of skeletal and dental changes in mammals throughout the Mesozoic era, which began 252 million years ago and led to the end of the dinosaurs' reign 66 million years ago.
The scientists, whose findings are reported in the journal Current Biology, recorded the number of significant changes to body plans or teeth that occurred in mammal lineages every million years.
During the mid-Jurassic, the frequency of change reached eight per million years per lineage - almost 10 times that seen at the end of the period.