Think back to the last time you put together a puzzle. How long did it take you to connect the first piece? Did you aim for the edge pieces, or did you look for random pairs? Now imagine that the puzzle pieces are fossils of marine creatures that lived in ancient oceans. How would you put the pieces together? Which animals appeared first, and how long did they live for? This is the “puzzle” paleontologists face when studying the fossil record.
Researchers studying the fossil record have found that a mass extinction occurred at the end of the Permian Period 250 million years ago, leaving the oceans largely empty. They propose that the Earth's higher temperatures and changes in water chemistry killed 80% of marine life, ending the Paleozoic Era. Sometime later, during the Triassic Period, marine communities were reorganized to include a diversity of organisms similar to those found in today's oceans. As such, scientists believe that Triassic marine life is a precursor to modern marine ecosystems.
Paleontologists initially thought that marine animals recovered slowly from this extinction, because complex fossil ecosystems were only discovered 10 million years later. More recently, researchers have found diverse marine animal fossils just 3 million years after this mass extinction. However, these studies leave a gap of 3 million years between the mass extinction and the appearance of modern-like marine life in the earliest Triassic period.
An international team of researchers hypothesized that a collection of fossils in southern China called the Guiyang Biota could help fill in this gap: These ancient animals were covered in deep-sea sand, forming a layer of exceptionally well-preserved fossils, LagerstätteLagerstätten often form in calm undersea environments that can preserve delicate animal parts like bones and scales. Based on their location and their position within the rocks, the team proposed that the Guiyang fossils date to the Early Triassic period.
The scientists explained that the fossils at the site included animals across all five levels of the food chain, including 10 species of bony fish, two species of shrimp, lobsters, sponges, eels, and plankton. They found that fish ate lobsters, which ate clams, which ate plankton, which ate algae, which provided energy, forming a complete modern-day marine community. The scientists suggested that these fossils may be younger than the oldest diverse fossil ecosystem scientists have ever unearthed from the Early Triassic Period.
The researchers used three methods to determine the age of the Guiyang fossils: First, they looked at the eel-like creature's teeth. ConodontsThey only lived during certain periods in Earth's history, and the researchers found that conodont teeth from the southern China fossils belonged to Triassic conodonts, supporting their original dating estimates.
Second, the researchers measured chemical signals. Carbon isotopesfound in the rock walls surrounding the fossils. Scientists have measured carbon isotopes in rocks throughout Earth's history. By matching the increases and decreases in carbon isotopes in rocks to patterns of carbon isotopes from different periods in the rock record, researchers can estimate the age of the rocks. They found that the carbon isotopes in the Guiyang rocks matched the patterns of carbon isotopes in rocks from the Early Triassic Period, further supporting the Triassic age of the fossils.
Finally, the researchers needed to establish a precise age for the Guiyang rocks to determine how rapidly the fossil assemblage developed after the mass extinction event. They used a dating method based on the radioactive decay of uranium into lead. U-Pb datingIt is found in minerals extracted from two volcanic ash layers in the rock wall.
The team explained that these ash layers were located just below and just above the fossil layers in the rocks, meaning they fell just before and just after the fossils formed. U-Pb dating determined that the fossils were between 250.79 and 250.92 million years old. The team interpreted these dates as indicating that the marine creatures lived only 10,000 to 1 million years after their extinction 250 million years ago.
From the Triassic Lagerstätte fossils, the researchers concluded that marine ecosystems recovered quickly from the end-Permian extinction, re-establishing complete food chains within one million years of the mass extinction. The researchers propose that this diverse group of organisms thrived during a cold period in the warming Triassic environment. The researchers suggest that future researchers should examine whether a short period of cool weather allowed these organisms to survive the heat, or whether other factors, such as favorable ocean chemistry, were involved.
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Source: sciworthy.com
