How dinosaurs were born to be big: Their biology 'was skewed towards giant species'

How dinosaurs were born to be big: Their biology 'was skewed towards giant species'


The biology of dinosaurs explains why there were more giant species among the prehistoric animals than are found among modern vertebrates, a paper published yesterday claims.
Researchers say that dinosaurs were not only the largest animals to roam the Earth - they also had a greater number of larger species compared to all other back-boned animals.
Their findings shed light on how different life was on Earth during the age of the dinosaurs.

A T-rex at the Natural History Museum: A new study claims that the biology of dinosaurs was skewed towards big species, with many more mammoth examples than among today's animals

Despite the prevalence of massive dinosaurs in the fossil record, prior to the latest study many researchers had assumed that they simply came in the same range of small and large species that modern animals do.
'Turns out, nope, there really were tons and tons of big guys out there and not many little ones,' said David Hone from Queen Mary, University of London, in an interview withLiveScience.

 

Dr Hone and his colleague Eoin Gorman, both of Queen Mary's School of Biological and Chemical Sciences, compared the size of the femur bone of 329 different dinosaur species from fossil records.
Among palaeontologists, analysis of the length and weight of the femur bone is a recognised method for estimating a dinosaur's body mass.

Frequency distribution of body size for eight groups: (a) extinct dinosaurs; (b) extant birds; (c) extant reptiles; (d) extant amphibians; (e) extant fish; (f) extant mammals; (g) extinct pterosaurs; (h) Cenozoic mammals

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Our traditional conception of dinosaurs as sleek, leathery animals is based on images created by palaeoartists, who specialise in imagining extinct creatures by studying their skeletons.

The problem is that these sparse remains cannot tell us the whole story, offering little information about layers of body fat, skin type, colouring or poise.

All Yesterdays: Unique and Speculative Views of Dinosaurs and Other Prehistoric Animals, by palaeoartists C.M. Kosemen and John Conway, offers explores some of the possibilities.

The pictures present dinosaurs in ways that they never have been before.

Fierce beasts like Tyrannosaurus rex, for example, are typically shown in the middle of bloodily savaging their next meal, but modern day predators spend most of their days sleeping and digesting.

So Kosemen and Conway present the beast sleeping, curled up like a cat, making it look almost lovable.

They found that dinosaurs follow the opposite pattern of body size distribution as seen in other vertebrate species. For example, within living mammals there tends to be few larger species, such as elephants, compared to smaller animals, such as mice, which have many species.
The evidence from fossil records implies that in contrast there were many species of larger dinosaurs and few small species.
Dr Hone explains: 'What is remarkable is that this tendency to have more species at a bigger size seemed to evolve quite early on in dinosaurian evolution around the Late Triassic period, 225 million years ago, raising questions about why they got to be so big.
'Our evidence supports the hypothesis that young dinosaurs occupied a different ecological niche to their parents so they weren't in competition for the same sources of food as they ate smaller plants or preyed on smaller size animals.
'In fact, we see modern crocodiles following this pattern - baby crocodiles start by feeding off insects and tadpoles before graduating onto fish and then larger mammals.'
Dr Gorman added: 'There is growing evidence that dinosaurs produced a large number of offspring, which were immediately vulnerable to predation due to their smaller size.
'It was beneficial for the herbivores to grow to large size as rapidly as possible to escape this threat, but the carnivores had sufficient resources to live optimally at smaller sizes.
'These differences are reflected in our analyses and also offer an explanation why other groups do not follow a similar pattern.
'Several modern-day vertebrate groups are almost entirely carnivorous, while many of the herbivores are warm-blooded, which limits their size.'