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telegraph

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 kilograms, 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 body weight of more than about 10 to 25 kilograms died in the mass extinction event.

Huh.

Huh. A load of BS but Huh

Problem 1: Mammals did not take over immediately after the KT event. For a few ten million years, terror birds did.

Problem 2: Parental care. Dinosaurs had it, and did it for extended periods. This negates the competitive advantage of suckling. Titanosaurs did not (which BTW are just grown up Edmontosaurs) send their young into the serpent's nest of the cretaceous period willy nilly. They kept them in the nest, and probably helped them feed.

Problem 3: There is a prediction we can make here. Namely, that other egg-laying taxa would have been wiped out. Turtles, birds, lizards, crocodiles, snakes, sphenodon. They are still around. Not all animals with a body weight over 25 kilos died off. Crocodiles survived, to name one.

Problem 4: Size limitations on offspring are not necessarily a liability. If they are small, it allows niche partitioning in the same way that being of different size does in organisms today. They simply would not have eaten the same things. Speaking of which, mom has to go out and eat. While she is doing that, she runs the risk of being eaten by a surviving dromeosaur.

Did competition and size play a role? Probably. Is it the only cause? Fuck no. A god damn asteroid just plopped down on the god damn planet, created a category 12 or thirteen earthquake (it hit in mexico. The ground shook in India, on the other side of the world at the time where the shockwaves from the vibrations converged, to the point that the trampoline-like effect was 60 meters in amplitude) burning all the plants and preventing the exposure of germinating seeds to the sun for YEARS. Big things die because they burn. Little things die because they starve (little things could find shelter from the burning in burrows). Things in the water wont burn, but may or may not starve. Scavengers survive (plenty of food for scavengers). Things that can hibernate or go into torpor survive.

Dinosaurs? Many were too big and burned. The small ones have fast metabolisms and unlike small mammals, cannot hibernate. I say this because birds cannot hibernate, therefore the little dinosaurs probably could not. So they die.

Small mammals can hibernate and many were scavengers. Birds were often scavengers.

Crocodiles are big, CAN hide in burrows, are scavengers, and go without food for years due to being ectotherms. They survive.

Other reptiles can hide, many can scavenge, and many can go into a cold induced torpor. They survive.

Amphibians can often hide in burrows or are aquatic and thus dont burn. They can go into a cold induced torpor. They survive.

Sharks are aquatic and all the death is a feast.

Insects are small, can be sheltered, many scavenge, and many many many species can go into diapause, which is basically the insect version of hibernation.

The list goes on.