Baculite
From Freepedia
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| Image:SouthDakotaBaculites.jpg Baculite fossils from South Dakota. Some still have traces of the original nacre (shells). | ||||||||||||||||
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all extinct |
Baculites ("walking stick rock") is a genus of extinct marine animals in the phylum Mollusca and class Cephalopoda. They are a nearly straight-shelled type of heteromorph ammonite that lived worldwide throughout the Late Cretaceous period. The genus was named by the French paleontologist Alcide Dessalines d'Orbigny in 1850.
Baculites grew up to two meters long and are thought to have lived in a vertical orientation with the head hanging straight down. As there is no counterweight to the head at the apex of complete shells, researchers believe this was the only way the animal could have been oriented, so the animal could have swum vertically, but probably very poorly, if at all, horizontally.
The shells of baculites grew in a coil during the juvenile stage, but as the animal matured, the shells grew long and straight. Adult baculites ranged in size from about seven centimeters (Baculites larsoni) up to two meters in length. From shell isotope studies, it is known that baculites inhabited the middle part of the water column, not too close to either the bottom or surface of the ocean.
In some rock deposits baculite fossils are common, and they are thought to have lived in great shoals. One strange feature about these animals is that it is believed the males were a third to a half the size of the females and had much lighter ribbing on the surface of the shell. As in ammonites, the shell consisted of a series of camerae, or body chambers, that contained gas which kept the animal buoyant. These chambers were connected together by a tiny tube called a siphuncle, which connected with the head of the animal. The animal itself lived in the last chamber. In this way, the baculite could regulate the gas levels in each chamber and control its buoyancy in the same manner as the nautilus does today. The walls separating these chambers are called septa, and, like ammonites, baculites have intricate suture patterns on their shells that can be used to identify different species.
Baculite fossils are very brittle and almost always break. They are most commonly found broken in half or several pieces, usually along suture lines.
