January 2013

Beach bones

Can you help identify these bones? They were found in 2011 at the high tide area on Fraser Island near Sandy Cape.

Answer

Figure 1: Decomposing carcass of a young dolphin Dolphin vertebrae Figure 2: A single vertebra from the carcass

The skeleton is from a young dolphin. The shape and structure of the vertebrae (back bones) are typical of mammals and there are several features which identify it. The long spine seen at the top of the vertebra (called the dorsal spine) and the two side spines (called the transverse processes) are typical of marine mammals (Fig. 2). These spines and processes on the vertebra are anchor points for the powerful muscles used for swimming. The bones are also not as robust as those found in dugongs, so a dolphin is the likely identity.

We can also tell that this is a young dolphin from the vertebra in Figure 2.  In Figure 2 you can see that the centrum (the barrel-shaped, central part of the vertebra) has a rough texture on the surface and it appears to be separated from the main bone by a ridge of brown tissue. This piece of bone has actually broken away from the adjacent vertebra (these are called Loose Caps).  In young mammals, the loose caps do not fuse to the main body of the vertebra until the bone has stopped growing or the animal reaches adult size. Loose caps, such as the rough-textured disc in your photo are indicative of young animals.

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