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Microsauria

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Microsauria is a group of extinct animals known as tetrapods. Tetrapods are animals with four limbs. These creatures lived during the late Carboniferous and early Permian periods.

Microbrachis BW
Microbrachis BW

They belong to a larger category of animals called lepospondyls. Within that category, microsaurs were the most diverse and species-rich group. This means they had a very high number of different species. Today, scientists often use the name Microsauria as a collective term. It describes a grade of lepospondyls that were once classified together.

Marjanovic & Laurin 2009 tree from SOM
Marjanovic & Laurin 2009 tree from SOM

The physical forms of these animals varied quite a bit. Most microsaurs shared certain features like short tails and small legs. However, their lifestyles were very different. Some species were lizard-like and lived on dry land. Other species were built for burrowing into the ground. Some microsaurs never left the water at all. They retained their gills even as adults. This is similar to the modern axolotl. Their skeletons were heavily ossified, meaning they had very hard bone. Their development was likely gradual and involved no metamorphosis.

Microbrachis BW
Microbrachis BW

Scientists have changed how they classify these animals over time. Microsauria was once thought to be a single, distinct order. Now, it is considered possibly polyphyletic. This means the members might not all share a single common ancestor. It is also considered paraphyletic. This is because other groups, like Lysorophia, seem to be nested inside it. Recent studies have helped clarify these relationships. A 2017 study by Pardo and others looked at their shapes. This research placed recumbirostran microsaurs and lysorophians into a group called Amniota.

Marjanovic & Laurin 2009 tree from SOM
Marjanovic & Laurin 2009 tree from SOM

Fossil remains provide a map of where these animals lived. Microsaurs are known to have inhabited Europe and North America. In North America, most fossils come from the United States. You can find them in Arizona, Texas, Oklahoma, Ohio, and Illinois. They are also found in Kansas and Nebraska. Some remains have been discovered in Nova Scotia as well. In Europe, researchers have found them in Germany and the Czech Republic.

Microsauria (geographic distribution)
Microsauria (geographic distribution)

Evidence of these animals has even been found in Russia. Possible remains were located in the Vladimir Oblast. These specific layers of earth are from the Late Permian. They are located near the Permo-Triassic boundary. If these remains are correct, they represent the youngest record of microsaurs. This would extend their known time on Earth by about 20 million years. There are also fossils from Gansu Province. These fossils show a possible record of microsaurs in the Triassic period.

Microsauria (geographic distribution)
Microsauria (geographic distribution)

The study of these fossils helps scientists understand ancient ecosystems. By looking at the bones, they can see how animals adapted to different environments. For example, the difference between a land-dweller and a water-dweller is very clear in their bodies. The heavy ossification of their skeletons tells us about their growth patterns. Researchers use tools like micro-computed tomography to study their cranial morphology. This helps them see the tiny details of their skull shapes.

Microbrachis BW
Microbrachis BW

Microsauria connects to many larger ideas in biology and paleontology. Their classification helps scientists understand the evolution of all tetrapods. Understanding how they relate to groups like Amniota is very important. It helps us trace the history of how animals moved from water to land. The distribution of their fossils also tells us about the ancient geography of the world. Every new fossil found helps complete the puzzle of life's history.

Marjanovic & Laurin 2009 tree from SOM
Marjanovic & Laurin 2009 tree from SOM
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File:Microbrachis BW.jpg
Microbrachis BW.jpg
File:Microsauria (geographic distribution).png
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Marjanovic & Laurin 2009 tree from SOM.tif
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