Sexual selection and dinosaur fossils

Sexual dimorphism in the pterosaur Darwinopterus. (Credit: Image by Mark Witton)

From the University of Southampton in England:

Survival of the prettiest: Sexual selection can be inferred from the fossil record

Detecting sexual selection in the fossil record is not impossible, according to scientists writing in Trends in Ecology and Evolution this month, co-authored by Dr Darren Naish of the University of Southampton.

The term “sexual selection” refers to the evolutionary pressures that relate to a species’ ability to repel rivals, meet mates and pass on genes. We can observe these processes happening in living animals but how do palaeontologists know that sexual selection operated in fossil ones?

Historically, palaeontologists have thought it challenging, even impossible, to recognise sexual selection in extinct animals. Many fossil animals have elaborate crests, horns, frills and other structures that look like they were used in sexual display but it can be difficult to distinguish these structures from those that might play a role in feeding behaviour, escaping predators, controlling body temperature and so on.

However in their review, the scientists argue that clues in the fossil record can indeed be used to infer sexual selection.

“We see much evidence from the fossil record suggesting that sexual selection played a major role in the evolution of many extinct groups,” says Dr Naish, of the University’s Vertebrate Palaeontology Research Group.

“Using observations of modern animal behaviour we can draw analogies with extinct animals and infer how certain features improve success during courtship and breeding.”

Modern examples of sexual selection, where species have evolved certain behaviours or ornamentation that repel rivals and attract members of the opposite sex, include the male peacock‘s display of feathers, and the male moose’s antlers for use in clashes during mating season.

Dr Naish and co-authors state that the fossil record holds many clues that point to the existence of sexual selection in extinct species, for example weaponry for fighting, bone fractures from duels, and ornamentation for display, such as fan-shaped crests on dinosaurs. Distinct differences between males and females of a species, called ‘sexual dimorphism’, can also suggest the presence of sexual selection, and features observed in sexually mature adults, where absent from the young, indicate that their purpose might be linked to reproduction.

We can also make inferences from features that are ‘costly’ in terms of how much energy they take to maintain, if we assume that the reproductive advantages outweighed the costs.

Whilst these features might have had multiple uses, the authors conclude that sexual selection should not be ruled out.

“Some scientists argue that many of the elaborate features on dinosaurs were not sexually selected at all,” adds Dr Naish, who is based at the National Oceanography Centre, Southampton.

“But as observations show that sexual selection is the most common process shaping evolutionary traits in modern animals, there is every reason to assume that things were exactly the same in the distant geological past.”

November 2013: Dinosaur fossils can be recreated by CT and 3-D printers, according to new research published online in the journal Radiology: here.

13 thoughts on “Sexual selection and dinosaur fossils

  1. SoundEagle contends that observed sexual dimorphism in the fossils of an extinct animal species is the most compelling reason and evidence for sexual selection, unless scientists can prove that the male and female members of the extinct animal species lived separately and thus were exposed to significantly different evolutionary pressures (feeding, predatory, environmental, climatic and so on) that lead to their anatomical differences.

    Besides, it would be very hard to believe that what has been as fundamental and prevalent as sexual selection since the advent of sexual reproduction could be absent in the past, not to mention the fact that 99% of all species on Earth are already extinct since life began. Hence, denying that sexual selection was present in extinct species is to erroneously assert that sexual selection was largely absent in the past and is only a modern phenomenon, even when similar morphological aspects, anatomical features, environmental niches and convergent evolution have been abound. How absurd!

    Thank you, dear kitty. Now, let’s hold SoundEagle’s wing tip and fly away together. . . . .


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