Sunday, October 4, 2015

Fossil dolphin ear bones

Fossil-dolphin ear bones, which can somewhat resemble small pebbles, consist of very hard, dense bone that can be readily fossilized. Most examples of these fossils that are illustrated online these days are from rocks of Miocene to Pleistocene age from the Atlantic coast of the United States (e.g., Miocene rocks in Calvert Cliffs, Maryland; and Pliocene rocks at the Lee Creek Mine, North Carolina.

During life, the earbones were located in a cavity in the middle-ear area, located near the back of the dolphin skull. This cavity is filled with a dense foam that, along with ligaments, to support the ear bones. The bones consist of the tympanic and the periotic bones, and the entire structure is referred to as the “tympano-periotic complex.” The two bones are partially fused together with flanges, grooves, small holes, and a large bulbous (i.e., bowl-shaped area) region, called the bulla. The inner ear is located within the tympano-periotic complex.

Examples of fossil tympano-periotic complexes are shown below. They are from the shallow-marine Miocene Temblor Formation found at Sharktooth Hill in southern-central California.
Miocene tympano-perdiotic complex, greatest dimension 42 mm (approximately 1.75 inches).

Opposite side of same specimen shown above.
A different specimen, greatest dimension 43.5 mm.

Note: In one of my previous posts (8/15/2014) entitled “Fossil whale ear bone,” I illustrated a whale tympanic bulla.

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