The "old man of longevity" in the "mud basin"? Owl: I actually have the same face as the "old man"!

In the fossil exhibition areas of many natural museums, you can see a type of larger "shell" fossils. There are not only single complete individuals, but also many individuals gathered together. Each one has a plump shape and a smooth shell, looking like the birthday star with a protruding forehead in mythology, or the longevity peach held in the birthday star's hand. It is the owl-headed clam.

The owl-headed clam is not a bivalve mollusk commonly known as a shellfish, but belongs to the brachiopod class, the order Perforatus, the family Owlheaded Clam. Among brachiopods, they are the largest species, with a single individual usually between 8 and 10 cm. The shell has the common characteristics of brachiopods: two valves, the upper and lower valves are of different sizes, with the large valve as the abdomen and the small valve as the dorsal. Each valve is horizontally mirror-symmetrical on the left and right. However, unlike the common "ridge in the back and groove in the abdomen" feature of other brachiopods, their two valves are raised and have no groove in the middle.

Because the ventral valve is larger in degree and size than the dorsal valve, the shell beak of the ventral valve (that is, the part of the shell that initially grows, shaped like a bird's beak) is more obvious. The curved and hooked shell beak of the ventral valve resembles the beak of an owl, and owls are also called owls. The scientific name of the owl-headed shell comes from this, and it is also called eagle-beak stone in the folk.

Owl-headed clams lived in the Middle Devonian period, about 387-374 million years ago. They were shallow-sea benthic creatures that lived in a warm shallow sea environment of about 200 meters. They could extend a fleshy stem from the back of their shells as an anchor to fix their bodies in the mud and sand. They fed on small diatoms, dinoflagellates, or small larvae of other mollusks by filtering. Due to the turbulent water environment and the difficulty in fixing the muddy seabed, they knew the power of sticking together. In addition to making themselves heavier and bigger and evolving the largest and thickest body among brachiopods, they also lived in groups, tightly together, and pressed their living area into a concave "mud basin". To avoid misunderstanding, this is not the origin of the name Devonian. The name Devonian comes from Devonshire, England, because that was the place where the strata of this period were first studied. Most countries' languages ​​use a pronunciation similar to English to call it, but Japanese English, which is full of incongruity, does not have the pronunciation of "von". Instead, it is pronounced "bon" and written as the Chinese character "Devonian". my country also used this name. A similar situation is the Cambrian period.

Back to the topic, due to the lifestyle adopted by owl clam, we can often find well-preserved and numerous owl clam fossils in limestone and marl. Among them, marl is easily weathered and peeled off, so the fossils produced are easier to collect and more complete. In addition, as mentioned at the beginning, its shape resembles a birthday star or a longevity peach, which implies longevity. Therefore, it is deeply favored by stone collectors. It has unique ornamental value and high collection value. At the same time, as one of the important standard fossils of the Devonian period, their fossils are of great scientific significance for the study of geological changes, especially the paleogeographic environment of the main production areas of owl clam such as Yunnan and Guangxi in my country.