The fossil record is a window into the past, revealing the diversity and complexity of life that has existed on Earth. However, not all fossils are equally informative or complete.
Some fossil sites, known as lagerstätten, are exceptionally rich and well-preserved, offering unparalleled insights into evolutionary relationships between different fossil groups.
One such site is the Late Cretaceous Gobi Desert, which boasts an extraordinarily diverse and well-preserved fossil lizard record.
A new study published in PLOS ONE introduces a novel metric to measure and visualize fossils' completeness and demonstrates how these sites shape our understanding of evolutionary history.
The Gobi Desert's Hidden Treasures
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The Gobi Desert is a vast expanse of land that covers parts of China and Mongolia. It is one of the most arid and inhospitable regions on Earth, with extreme temperatures and scarce vegetation.
However, beneath its surface lies a treasure trove of fossils, particularly of lizards. Lizards are a diverse group of reptiles that have adapted to various habitats and lifestyles. They are also important indicators of environmental changes and biogeographic patterns.
The fossil lizards from the Gobi Desert date back to the Late Cretaceous period, about 66 to 100 million years ago. This was a time of major transformations in the Earth's climate, geography, and biodiversity, leading to the extinction of many groups, including the non-avian dinosaurs.
The Gobi Desert preserves a remarkable snapshot of this era, with fossils of lizards and other animals that are rarely found elsewhere.
The fossil lizards from the Gobi Desert are not only abundant but also exceptionally well-preserved. Many of them retain soft tissues, such as skin, scales, and internal organs, which are usually lost during fossilization.
These soft tissues provide crucial information about the anatomy, physiology, and ecology of these ancient animals. They also allow scientists to reconstruct their appearance and behavior more accurately.
To quantify and compare the completeness of fossils from different sites, a team of researchers from the Natural History Museum of Los Angeles County and other institutions developed a new tool called the Character Completeness Metric (CCM2).
This metric uses a scoring system to assign values to different parts of a fossil, such as bones, teeth, and soft tissues. The higher the score, the more complete the fossil.
The CCM2 also produces a visualization of the fossil's completeness, using colors to indicate the presence or absence of different features.
The researchers applied the CCM2 to a dataset of 248 fossil lizards from 18 sites around the world, spanning from the Jurassic to the Paleogene periods.
They found that the Gobi Desert had the highest average CCM2 score, indicating that it had the most complete fossil lizards. They also found that the Gobi Desert had the highest diversity of fossil lizards, with 21 different genera and 26 different species.
Then, researchers used the CCM2 scores to assess how the completeness of fossils affects the reconstruction of evolutionary relationships.
They performed a phylogenetic analysis, which is a method of inferring the evolutionary history and relatedness of different organisms based on their shared characteristics.
They found that the inclusion or exclusion of the Gobi Desert fossils had a significant impact on the results, altering the position and support of many branches in the lizard tree of life. This shows that the Gobi Desert fossils provide valuable information that enhances our grasp of lizard evolution.
The researchers concluded that the CCM2 is a useful tool for measuring and visualizing the completeness of fossils, and that the Gobi Desert is a key site for understanding the evolution of lizards and other groups.
Moreover, they also suggested that the CCM2 could be applied to other fossil groups and sites, and that more studies are needed to explore the factors that influence the preservation and discovery of fossils. They hoped that their work will inspire more research and appreciation of the fossil record and its role in revealing the secrets of life on Earth.
