Two hundred and fifty-two million years ago, a series of Siberian volcanoes erupted and sent the Earth into the greatest mass extinction of all time. Billions of tons of carbon were propelled into the atmosphere, radically altering the Earth’s climate. Yet, some animals thrived in the aftermath and scientists now know why.
In a new study published in Scientific Reports, paleontologists from the National Museum and University of the Free State (Bloemfontein, South Africa), the Natural History Museum and University of Utah (Salt Lake City, USA), the Field Museum of Natural History (Chicago, USA) and the University of Lincoln (UK) show that some ancient mammal relatives, known as therapsids, were suited to the drastic climate change by having short life expectancies. When combined with results from population survivorship models, this observation leads the team to suggest that these animals bred at younger ages than their predecessors.
The study involved Dr Marcello Ruta, Senior Lecturer in the University of Lincoln’s School of Life Sciences. He explained: “The study amalgamates information from body size and growth patterns in therapsids that survived the great extinction event, and uses mathematical modelling of population growth to identify possible factors that enabled therapsids to survive harsh environmental conditions and thrive afterwards.”
Field Museum paleontologist Ken Angielczyk, one of the paper’s authors, said: “Before the Permo-Triassic extinction, the therapsid Lystrosaurus had a life span of about 13 or 14 years based on the record of growth preserved in their bones. Yet, nearly all of the Lystrosaurus specimens we find from after the extinction are only 2 or 3 years old. This implies that they must have been breeding when they were still juveniles themselves.”
This adjustment in life history also meant a physical change for Lystrosaurus. Before the mass extinction, this creature would have been a couple of meters long and have weighed hundreds of pounds – about the size of a pygmy hippo. Post-extinction, its size dropped to that of a large dog, in large part due to its altered lifespan. Yet, these adaptations seemed to pay off for Lystrosaurus. Ecological simulations show that by breeding younger, Lystrosaurus could have increased its chance of survival by 40% in the unpredictable environments that existed in the aftermath of the extinction.
This change in breeding behavior is not isolated to ancient animals either. In the past century, the Atlantic cod has undergone a similar effect due to human interference. Industrial fishing has removed most large individuals from the population, shifting the average size of cod significantly downward. Likewise, the remaining individuals are forced to breed as early in their lives as possible. Similar shifts have also been demonstrated in African monitor lizards.
“With the world currently facing its sixth mass extinction, paleontological research helps us understand the world around us today,” said Angielczyk. “By studying how animals like Lystrosaurus adapted in the face of disaster, we can better predict how looming environmental changes may affect modern species.”
The findings are published today (Tuesday 5th April 2016) and the paper is available to read in full online: www.nature.com/articles/srep24053