Paja fossils: a marine transition worth understanding better
· BehindLines newsroom
A release from McGill University, circulated on 30 October, puts a fossilized marine ecosystem in Colombia back in the spotlight. Near Villa de Leyva, the researchers propose reading the Paja Formation as a moment when ancient lineages in decline met groups poised to diversify. Their scientific synthesis was published on 22 June in Frontiers in Ecology and Evolution: the recent release therefore does not correspond to a new excavation announced this week.
Animals from different evolutionary generations
Dirley Cortés and Hans Larsson propose the term "biotic inflection" to describe this coexistence. The Museum of Evolution of the Polish Academy of Sciences places this tropical sea about 120 million years ago. It mentions in particular large marine reptiles, turtles, fish, ammonites and crabs.
The McGill release presents the fossils as an opportunity to study a turnover in marine life that cannot be reduced to a mass extinction followed by replacement. The authors envisage a combination of favorable conditions: nutrient-rich coastal waters, high sea level, a warm climate and new ocean connections.
This explanation remains a proposal to be tested. McGill stresses that more fossils, refined dating and comparisons with other regions will be needed to determine how widespread this phenomenon was in Earth's history.
A rich site, a designation still open
The scientific paper is a review of available knowledge, rather than the report of a single experiment. Its authors gather information on the geological layers, the preserved organisms and their feeding relationships in order to examine this transition.
They point out, however, that current data are not sufficient to formally classify Paja as an ancient biodiversity hotspot under modern criteria. Limits in sampling, dating and geographic resolution restrict this designation.
The interest of the case thus lies in a distinction: noting a remarkable diversity in the fossils, then testing the mechanism proposed to explain it. Comparison with other deposits will have to clarify whether Paja illustrates a more general pattern or a particular combination of conditions.