How large fossil sites shape our understanding of evolutionary relationships between fossil groups

A new study published in the journal PLOS ONE explores the weight of large fossil sites on our understanding of the evolutionary relationships between fossil groups – the Lagerstätten effect – and, for the first time, has quantified the power of these sites on our understanding of evolutionary history.

Surprisingly, the authors discovered that the windswept sand deposits of the extraordinarily diverse and well-preserved fossil lizard record of the Gobi Desert, Late Cretaceous, shape our understanding of their evolutionary history more than any other site on the planet.

Although famous for being the region where the velociraptor was discovered, the Gobi Desert of China and Mongolia during the Late Cretaceous may have a greater impact on our understanding of ancient and modern life thanks to its rich records of fossil lizards.

“What’s great about these Late Cretaceous Gobi Desert deposits is that you get extremely diverse, exceptionally complete and three-dimensionally preserved lizard skeletons,” said lead author and postdoctoral researcher Dr. Hank Woolley. NSF at the Dinosaur Institute. “You get many lineages on the squamate Tree of Life represented from this single unit, giving us this remarkable fossil signal of biodiversity in the rock record, something that stands out like a beacon in the deep, dark chasms of the evolutionary history of squamates.”

More complete skeletons make it easier to trace relationships over time by making it easier to compare similarities and differences. The more complete a skeleton is, the more traits are preserved and these traits are translated into phylogenetic data, data used to construct the tree of life.

“When there is exceptional preservation – hundreds of species from one part of the world in a very specific time period – that doesn’t necessarily give you a good sense of global signals,” Woolley said. “It’s putting your thumb on the scale.”

To measure the impact of deposits of exceptional fossil preservation (known in the paleontological community by the German term “lagerstätten”) on the broader understanding of evolutionary relationships through time, Woolley and his co-authors, including Dr Nathan Smith, curator of the Dinosaur Institute. , combed through published records of 1,327 species of non-avian theropod dinosaurs, Mesozoic birds, and fossil squamates (the group of reptiles that includes mosasaurs, snakes, and lizards).

The fossil meta-narrative

For squamates, the researchers found no correlation between sampling intensity and the impact of a given site on phylogenetic data on a global scale. Instead, they found a signal coming from depositional environments, the different types of sites where accumulated sediment preserved distinctly different groups.

Because the Gobi Desert squamate record is so complete, it shapes our understanding of how squamates evolved around the world and over time, an excellent example of the “lagerstätten effect”, although it is not This is not a typical lagerstätte. Traditional lagerstätten deposits come from marine chalks, salt lagoons and ancient lake environments, not arid sand dunes. The ancient environment shapes what is preserved in the fossil record.

“We didn’t expect to find such detailed records of lizards in a desert sand dune deposit,” Woolley said.

“We often think of Lagerstätten deposits as preserving soft tissues and organisms that rarely fossilize, or particularly rich concentrations of fossils. What makes the Gobi squamate archive unique is that it includes both “Exceptionally complete skeletons and a wide diversity of species from all over the group’s family tree,” Smith said.

“We are at this boundary between rarely overlapping areas of paleontology: assessing the evolutionary relationships of fossil groups (phylogenetics) and assessing how things fossilize (taphonomy). Exploring this “The border will help incorporate more of Earth’s extinct biodiversity into museum collections as we piece together the past,” Woolley said.