Fossils reveal a previously unknown pattern of evolutionary transition
‘Biotic Inflection,’ seen in central Colombia, describes a biodiversity-rich period of overlap between declining and newer lineages
image: Giant marine reptiles like long-necked plesiosaurs and marine crocodile relatives, as well as turtles, sharks, crustaceans and others, formed the Paja Biota, "one of the most ecologically complex marine communities found to date," says researcher Dirley Cortés.
Credit: Juan Giraldo
A remarkably diverse fossil ecosystem in central Colombia that preserves an unusual overlap between survivors of older Jurassic groups and newer Cretaceous lineages has led researchers at McGill University and the Centro de Investigaciones Paleontológicas (CIP) to recognize a new pattern of large-scale evolutionary transition, one that does not include mass extinctions.
Based on their research of the Paja Formation, PhD graduate Dirley Cortés and Professor Hans Larsson, Department of Biology, propose the concept of a “Biotic Inflection,” a period when many evolutionary lineages on the brink of extinction coexist with newly emerging groups that later diversify.
The researchers said they believe this extreme biodiversity and biological transition found at this formation was probably facilitated by a rare convergence of environmental conditions that included greenhouse temperatures, high sea levels, nutrient-rich coastal waters and new marine connections between the eastern Pacific and early Atlantic oceans through what is now Colombia. They noted that these are many of the same factors that drive biodiversity today.
“The Paja Formation records an extraordinary process in the history of life, when a ‘perfect storm’ of environmental factors we know to promote ecological complexity coincided with ancient lineages that were about to disappear. At the same time, new groups were beginning to flourish,” Larsson said.
An exceptionally rich fossil record
The team identified the pattern in the Early Cretaceous Paja Formation near Villa de Leyva, Colombia, where the CIP houses most of its fossils.
“This geological formation has produced an exceptionally rich fossil record that includes giant marine reptiles like long-necked plesiosaurs and marine crocodile relatives, as well as turtles, sharks, crustaceans and others,” Cortés explained. “Together, these animals formed the Paja Biota, one of the most ecologically complex marine communities found to date.”
The researchers had already estimated the Paja Biota’s food web in a previous study and discovered it was one of the most complex to have ever evolved, with a high diversity of apex predators.
Additional fossil sampling, more precise dating and comparisons with deposits elsewhere in the world will be needed to test how widespread the Biotic Inflection pattern was and when similar events may have occurred in Earth’s history.
“I think we’ve discovered a new model of global biodiversity change. Now we’ll need to see just how widespread this could be in Earth’s history and how we can quantify its impacts,” Larsson said.
About the study
“The Paja Formation of Colombia records uniquely high biodiversity during a biotic inflection in an Early Cretaceous Gondwanan marine ecosystem,” by Dirley Cortés and Hans Larsson, was published in Frontiers in Ecology and Evolution.