Evolution: dinosaurs not as dominant as thought (Introduction)

by David Turell @, Thursday, August 10, 2017, 19:07 (194 days ago) @ dhw

Discoveries is China show that mammals were much more diversified than thought 160 million years ago, well before dinosaurs died out 60 million years ago:


"The earliest examples of gliding mammals yet discovered, dated to the Jurassic period about 160 million years ago, suggest dinosaurs did not dominate the prehistoric Earth as much as has been believed.

"As the first winged mammals, the identified fossils of two gliders demonstrate the wide ecological diversity attained by early mammals, says Zhe-Xi Luo, professor of organismal biology and anatomy at the University of Chicago, who is co-author of two new papers analysing the animals, published in Nature. This degree of early evolutionary diversity, he suggests, “means dinosaurs likely did not dominate the Mesozoic landscape as much as previously thought”.

"Bearing some similarities in appearance to modern gliding mammals such as flying squirrels and possums, the “exquisitely fossilised” remains of the two animals unearthed from China’s renowned Tiaojishan Formation show wing-like skin membranes between long fore and hind limbs, and skeletal features in their shoulder joints and forelimbs that would make them capable gliders. Their long fingers (or toes) are suited to gripping branches, indicating trees were their natural habitat, while their teeth indicate they ate a mainly herbivorous diet.


"So while in absolute geological terms all three fossils are about the same age, Luo says, the two new gliders evolved at an earlier point in mammalian evolution, prior to the diversification of modern mammals into monotremes, marsupials and placentals. “The evolutionary antiquity is much older for the newly found Maiopatagium and Vilevolodon than for Volaticotherium. That’s why we say they are the first winged mammals.”


"Together with many other fossils described by Luo and colleagues over the past decade or so, the new fossils provide strong evidence that mammals adapted well and were more ubiquitous in an age once presumed to have been the domain of dinosaurs.

“'The traditional and historical view was that when dinosaurs dominated the world, mammals were small, generalised and without much functional or ecological diversity,” Luo says. “In simple terms, mammals were not able to diversify when dinosaurs dominated the terrestrial ecosystem. The popular version of this view was that mammals always lived in the shadow of dinosaurs. But that was then.

"A stream of new discoveries in the past 15 years has shown that mammals which co-existed with dinosaurs during the Mesozoic evolved into semi-aquatic forms, such as Castorocauda, subterranean forms, such as Docofossor, and many arboreal forms, such as Agilodocodon and Arboroharamiya.

“'Mesozoic mammals essentially evolved all the distinctive ecomorphotypes like those of modern mammals of small-to-mid-sized bodies,” Luo says."

Comment: This degree of diversification means mammals could develop worldwide much more quickly after the Chicxulub event.

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