A lighthouse in the Gobi desert

A new study published in the journal PLOS ONE explores the weight great fossil sites have on our understanding of evolutionary relationships between fossil groups -- the lagerstätten effect -- and for the first time, quantified the power these sites have on our understanding of evolutionary history. Surprisingly, the authors discovered that the wind-swept sand deposits of the Late Cretaceous Gobi Desert's extraordinarily diverse and well-preserved fossil lizard record shapes our understanding of their evolutionary history more than any other site on the planet.

While famous as the region where Velociraptor was discovered, China and Mongolia's Late Cretaceous Gobi Desert might have more of an impact on our understanding of ancient -- and modern -- life thanks to its rich record of fossil lizards.

"What's so cool about these Late Cretaceous Gobi Desert deposits is that you're getting extremely diverse, exceptionally complete, three-dimensionally-preserved lizard skeletons," said Dr. Hank Woolley, lead author and NSF Postdoctoral Research Fellow at the Dinosaur Institute.

"You're getting 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 as a lighthouse in the deep dark chasms of squamate evolutionary history."

More complete skeletons make it easier to trace relationships through time by making it easier to compare similarities and differences.

The more complete a skeleton is, the more traits are preserved, and those traits translate into phylogenetic data -- data that are used to construct the tree of life.

"Where there's exceptional preservation -- hundreds of species from one part of the world at one period of very specific time -- that doesn't necessarily give you a good idea of global signals," said Woolley.

"It's putting its thumb on the scale."

To measure how impactful deposits of exceptional fossil preservation (known in the paleontology community by the German term "lagerstätten") are on the broader understanding of evolutionary relationships through time, Woolley and 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

When it came to squamates, the researchers found no correlation between the intensity of sampling and whether any given site impacted phylogenetic data on a global scale.

Instead, they found a signal from depositional environments, the different kinds of sites where sediments accumulated preserved markedly different groups.

Because the squamate record from the Gobi Desert is so complete, it shapes our understanding of squamate evolution around the world and across time, a prime example of the "lagerstätten effect" -- despite not being a typical lagerstätte.

Traditional lagerstätten deposits come from marine chalks, salty lagoons, and ancient lake environments -- not from arid sand dunes.

The ancient environment shapes what gets preserved in the fossil record.

"We were not expecting to find this detailed record from lizards in a desert sand dune deposit," said Woolley.

"We often think of lagerstätten deposits as preserving soft tissues and organisms that rarely fossilize, or especially rich concentrations of fossils. What makes the Gobi squamate record unique, is that it includes both exceptionally complete skeletons, and a high diversity of species from across the group's family tree," said Smith.

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Fossil site reveals giant arthropods dominated the seas 470 million years ago

Discoveries at a major new fossil site in Morocco suggest giant arthropods -- relatives of modern creatures including shrimps, insects and spiders -- dominated the seas 470 million years ago.

Early evidence from the site at Taichoute, once undersea but now a desert, records numerous large "free-swimming" arthropods.

More research is needed to analyse these fragments, but based on previously described specimens, the giant arthropods could be up to 2m long.

An international research team say the site and its fossil record are very different from other previously described and studied Fezouata Shale sites from 80km away.

They say Taichoute (considered part of the wider "Fezouata Biota") opens new avenues for paleontological and ecological research.

"Everything is new about this locality -- its sedimentology, paleontology, and even the preservation of fossils -- further highlighting the importance of the Fezouata Biota in completing our understanding of past life on Earth," said lead author Dr Farid Saleh, from the University of Lausanne and and Yunnan University.

Dr Xiaoya Ma, from the University of Exeter and Yunnan University, added: "While the giant arthropods we discovered have not yet been fully identified, some may belong to previously described species of the Fezouata Biota, and some will certainly be new species.

"Nevertheless, their large size and free-swimming lifestyle suggest they played a unique role in these ecosystems."

The Fezouata Shale was recently selected as one of the 100 most important geological sites worldwide because of its importance for understanding the evolution during the Early Ordovician period, about 470 million years ago.

Fossils discovered in these rocks include mineralised elements (eg shells), but some also show exceptional preservation of soft parts such as internal organs, allowing scientists to investigate the anatomy of early animal life on Earth.

Animals of the Fezouata Shale, in Morocco's Zagora region, lived in a shallow sea that experienced repeated storm and wave activities, which buried the animal communities and preserved them in place as exceptional fossils.

However, nektonic (or free-swimming) animals remain a relatively minor component overall in the Fezouata Biota.

The new study reports the discovery of the Taichoute fossils, preserved in sediments that are a few million years younger than those from the Zagora area and are dominated by fragments of giant arthropods.

"Carcasses were transported to a relatively deep marine environment by underwater landslides, which contrasts with previous discoveries of carcass preservation in shallower settings, which were buried in place by storm deposits," said Dr Romain Vaucher, from the University of Lausanne.

Professor Allison Daley, also from the University of Lausanne, added: "Animals such as brachiopods are found attached to some arthropod fragments, indicating that these large carapaces acted as nutrient stores for the seafloor dwelling community once they were dead and lying on the seafloor."

Dr Lukáš Laibl, from the Czech Academy of Sciences, who had the opportunity to participate in the initial fieldwork, said: "Taichoute is not only important due to the dominance of large nektonic arthropods.

"Even when it comes to trilobites, new species so far unknown from the Fezouata Biota are found in Taichoute."

Dr Bertrand Lefebvre, from the University of Lyon, who is the senior author on the paper, and who has been working on the Fezouata Biota for the past two decades, concluded: "The Fezouata Biota keeps surprising us with new unexpected discoveries."

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