Why mammals 150 millions years ago lived ‘substantially’ longer

By Stephen Beech via SWNS

Early mammals lived "substantially" longer 150 million years ago than their descendants today, reveals new research.

They grew much more slowly and it took them "years" to reach sexual maturity in contrast to modern mammals, say scientists.

The study suggests that early mammals lived for eight to 14 years instead of just one or two as in modern mice.

An international team, led by paleontologists at Queen Mary University of London (QMUL) and the University of Bonn in Germany, used state-of-the-art technology to study growth rings in fossilized tooth roots.

They wanted to distinguish the growth and development patterns of early mammals of the Jurassic period.

Study lead author Dr. Elis Newham, of QMUL, said: “Never before have we been able to reconstruct the growth patterns of these early mammals in such detail."

For the study, published in the journal Science Advances , the team analyzed fossilized tooth roots of mammal species from the Early to Late Jurassic periods, 150 to 200 million years ago, found at three separate sites.

The finds made in Wales are of some of the oldest known mammalian precursors from the Early Jurassic period, while fossils found in Oxfordshire are of a "very broad" array of coexisting early mammals.

Fossils from the third site in Portugal date from the Late Jurassic.

The researchers studied the fossils using a technique called synchrotron X-ray tomography in which electrons are accelerated to near light speed.

They explained that the technique allows several advantages, starting with the fact that the fossils no longer have to be cut up into slices.

Images obtained via synchrotron X-ray tomography are also of higher quality than images from conventional X-ray microtomography, say the researchers.

They were able to image tiny growth rings in fossilized root cement - the bone tissue that attaches the teeth to the jaw.

Study senior author Professor Thomas Martin, of the University of Bonn Institute of Organismic Biology , said: “The rings are similar to those in trees, but on a microscopic level.

“Counting the rings and analyzing their thickness and texture enabled us to reconstruct the growth patterns and lifespans of these extinct animals.”

The research team determined that the first signs of the growth patterns characteristic of modern mammals, such as a puberty growth spurt, started emerging around 150 million years ago.

They say early mammals grew much more slowly - but lived much longer than today’s small mammals, with lifespans of eight to 14 years.

Dr. Newham said: “Our findings suggest that the distinctive life history patterns of mammals, characterized by high metabolic rates and extended parental care phases for example, have evolved over millions of years."

He added: “The Jurassic period appears to have been a crucial time for this shift.”

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