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Age of the chicken: why the Anthropocene will be geologically egg-ceptional

Chickens are now so ubiquitous on the planet that their bones will be written into the fossil record - Alamy
Chickens are now so ubiquitous on the planet that their bones will be written into the fossil record - Alamy

The age of man will not be defined by space flight, medical innovation or the rise of the internet but instead by the humble chicken, according to scientists.

Broiler chickens are now so ubiquitous on the planet that their bones will be written into the fossil record as a delineating species marking out the Anthropocene - the proposed new period in which humans started to have a lasting impact on the planet dating from around the 1950s.

Previous epochs, such as the Pleistocene, Jurassic or Devonian have been defined by animals such as dinosaurs, woolly mammoths and ancient armoured fish called placoderms.

But there are now 21 billion chickens living worldwide, and 62 billion are consumed each year, creating a combined mass three times that of all other birds on Earth combined.

And unlike most other birds or animals, their bones frequently end up in landfill, which provides a perfect environment for fossilisation, according to researchers at the University of Leicester.

Writing in the journal Royal Society Open Science, Dr Carys Bennett, said: “Bird carcasses in the wild are scavenger, and decay prone, and so do not commonly fossilize.

“Chicken bones, by contrast, are often sold intact within products for human consumption, such as chicken wings, drumsticks and whole birds, and the discarded bones form a common component of ordinary landfill sites as part of domestic garbage.

“The low skeletal density of chicken bones would normally mitigate against long-term preservation potential.

“However, organic materials are often well preserved within landfill deposits, where anaerobic conditions mean that bones do not so much degrade as mummify.”

Dr Bennett said the abundance of just one kind of bird is ‘unprecedented in Earth’s history.’

And the animals also make a good marker, the authors argue, because they have changed dramatically through domestication.

Breeding, diet and farming practices have caused body size to double since the late medieval period and there has been an up to five-fold increase in body mass since the mid twentieth century, when the 1948 ‘Chicken of Tomorrow’ contest in the US encouraged farmers to create a bird with the breast more like a turkey.

Until then birds were pretty scrawny, but competition entrants were asked to breed ‘one bird chunky enough for the whole family - a chicken with breast meat so thick you can carve it into steaks, costing less instead of more.’

The competition created a revolution in chicken welfare, and such huge change has affected the skeleton, genetics and bone chemistry of chickens making them easy to identify from their bones, compared to their ancestors.

“Given this global distribution, together with its huge population size and distinctive biology, genetics and bone geochemistry, the broiler chicken may be viewed as a key species indicator of the proposed Anthropocene Epoch,” added Dr Bennett.