Puzzle of how dinosaurs got so big finally solved

By Mark Waghorn via SWNS

The puzzle of how dinosaurs got to be so big has finally been solved.

From the Jurassic to the Cretaceous, when our ancestors were the size of voles and shrews, Supersaurus, Sauroposeidon and Argentinosaurus were shaking the Earth.

Patagotitan was around 125 feet from nose to tail and weighed an estimated 57 tons - making it 50 percent longer and four times heavier than Diplodocus.

Some were as big as a five-story building.

How the giant plant-eating dinosaurs got so big has stumped scientists for decades - until now.

The first evolutionary tree of its kind shows they achieved their record-breaking sizes in dozens of phases.

A US team mapped their body masses onto geologic time - with each branch representing a species.

Lead author Dr. Michael D'Emic, of Adelphi University in New York, said: "It was previously thought sauropods evolved their exceptional sizes independently a few times in their evolutionary history.

"But through a new analysis, we now know this number is much higher, with around three dozen instances over the course of 100 million years around the globe."

The findings are based on measurements of the circumferences of hundreds of weight-bearing bones - linked to the heaviness of the animal to which they belonged.

A technique called ancestral state reconstruction was then applied to nearly 200 species. It provides estimates of otherwise unobservable processes.

Results indicated sauropods reached exceptional sizes early in their evolution - and that with each new family, one or more lineages independently attained superlative status.

Dr D'Emic explained: "Before going extinct with the other dinosaurs - besides birds - at the end of the Cretaceous Period sauropods evolved their unrivaled sizes a total of three dozen times.

"These largest-of-the-largest sauropods were ecologically distinct - having differently shaped teeth and heads and differently proportioned bodies. They occupied the 'large bodied' niche somewhat differently from one another."

Microscopic analysis of their bones revealed sauropods also had different growth rates - suggesting the largest were metabolically distinct.

It mirrors the pattern in mammals which evolved very large body sizes quickly in the wake of the dinosaur extinction - before plateauing in the gigantic range.

The study, published in the journal Current Biology, contradicts a popular 19th-century theory called 'Cope's Rule' which states animals' size evolves over time.

Instead, it sees them achieving different body sizes depending on their ecological context and whatever niches happened to be available - which can appear random when looked at from a large scale.

Dr. D'Emic said: "While other researchers have explained sauropods' immense size in general based on their unique combination of features there is no one feature or set of features that characterize the sauropods that did surpass terrestrial mammal size from the ones that didn't."

Blue whales can reach over 100 feet long and weigh up to 200 tons due to buoyancy and blubber. Land mammals face different challenges as air puts more strain on bones.

The largest living species is the African bush elephant. At 24 ft long and weighing 11 tons, it would have been dwarfed by Patagotitan.

Dr. D'Emic next plans to untangle why certain lineages evolved their super-giant sizes - while others didn't.