Dinosaurs put eggs in wrong evolutionary basket: scientists

The fact that land-bound dinosaurs laid eggs is what sealed their fate of mass extinction millions of years ago while live birthing mammals went on to thrive, scientists said Wednesday.

In a new explanation for mammals' evolutionary victory over dinosaurs, researchers said a mathematical model has shown that infant size was the clincher.

Given physical limitations to egg size, dinosaurs had comparatively small young. Some came out of the egg weighing as little as two to 10 kilogrammes (4.4 to 22 pounds), yet had to bulk up to a hefty 30 or 50 tonnes.

Growing up, the youngsters had to compete in several size categories with adults of other animal groups for food, University of Zurich scientist Marcus Clauss told AFP.

This meant that all the small and medium animal size categories supported by the natural environment were "occupied", leaving no room for smaller dinosaur species in which to thrive, according to the findings published in Biology Letters, a journal of Britain's Royal Society.

"There is a lot of room in the ecosystem for small species, but (in such a scenario) that room is taken up by the young ones of the large species," Clauss explained.

"That was not a problem for 150 million years but as soon as something happens that takes away all the large species so that only small species remain, if there are no small species to remain you are gone as a whole group."

The catastrophic event that wiped out all larger life forms some 65 million years ago meant the end for terrestrial dinosaurs.

Scientists disagree on whether the scaly reptiles died out before or after a meteorite smashed into Earth in what is known as the Cretaceous-Tertiary impact, causing billions of tonnes of wind-borne ash and dust to filter out light from the Sun and triggering a "nuclear winter" that cooled the planet and withered vegetation.

Mammals did not have the same limitations in size spread, said Clauss, because their young were not born as comparatively small and did not need to compete with other species for food, instead suckling on their mothers.

This meant there were smaller mammal species able to cope with the new post-catastrophe environment and evolve into new species alongside birds, which are also dinosaurs.

"The question that haunted some people including me is ... why did the mammals survive and why did the dinosaurs not. I think we have a very good answer for that," Clauss said.

The researchers said egg size is constricted by upper limits to the thickness of shells, which have to allow oxygen through to the embryo.

The average four-tonne titanosaur, the largest type of vertebrate that ever lived, was 2,500 times heavier than its newborn. A modern-day elephant mother weighs 22 times more than her calf.

Scientists say all animals with a bodyweight of more than about 10 to 25 kilogrammes (22 to 55 pounds) died in the mass extinction event.

Editor’s note:Yahoo Philippines encourages responsible comments that add dimension to the discussion. No bashing or hate speech, please. You can express your opinion without slamming others or making derogatory remarks.

  • Holy Week in Mt Banahaw: Mysticism meets Catholicism VERA Files - The Inbox

    Text and photos by Patricia Isabel Gloria, VERA Files Dolores, Quezon—Around this time each year, hundreds of devotees flock to Barangay Sta. Lucia in Dolores, Quezon on the slopes of Mount Banahaw to celebrate Holy Week. Here, mysticism meets Catholicism, … Continue reading → …

  • Simbang lakad for Lolo Uweng VERA Files - The Inbox
    Simbang lakad for Lolo Uweng

    By April Anne Benjamin, VERA Files San Pedro, Laguna--For 14 Maundy Thursdays now, Inding Amoranto has prayed the rosary while walking the eight-kilometer distance from her house to the Shrine of Jesus in the Holy Sepulcher in the village of … Continue reading → …

  • Batangas women bear ‘the cross’ to save loved ones VERA Files - The Inbox
    Batangas women bear ‘the cross’ to save loved ones

    Text and photos by Jane Dasal, VERA Files Nasugbu, Batangas—At the break of dawn on Good Friday, Celilia Zafra donned a black dress and shrouded her face with a black cloth. Then she walked to a place called “putol na … Continue reading → …

POLL
Loading...
Poll Choice Options