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A whale of a job part 6: Grandpa

Posted on 06-09-2017 by Becky Desjardins

Recently we discovered a very interesting specimen, a really really old Bottlenose dolphin that we nicknamed “Grandpa”.

A better name might be great, great, great grandpa! Dolphins can live almost 50 years, and this one died prior to 1865.  Though we do not know if it is male or female, there are many skeletal indications that it was an old animal.  For example, the teeth are incredibly worn down. Dolphins have lots of teeth, 18 to 27 per side, and they start out shaped like cones. Over the years of use, they are worn down and look more like tree stumps. That is what Grandpa the dolphin has.  This dolphin also has a number of teeth missing from the bottom left jaw bone.  In the space where the teeth should be is a massive abscess, probably brought on by an infection in the empty tooth socket This big hole in the jaw must have been very painful!

This dolphin also has lots of naturally healed rib fractures, which is very common in cetaceans.  It is a bit of a mystery as to why this is so regularly seen, because dolphins in general steer clear of rocky shores (where accidental impact could cause an injury), and they carry a thick layer of fat under the skin, which acts as a buffer in the case of collisions between dolphins or between dolphins and ships.  Ship and cetacean collisions are commonplace: a recent paper suggested 15% of all Humpback whales had been hit by a ship (Hill 2017), but this particular skeleton died prior to 1865, prior to the invention of fast ship motors.  Slower moving boats sailed in the early days of the 19th century did not cause collisions as frequently as speedy ships now. 

An article written by W.M.A. de Smet in 1977 suggests that most cetaceans in museum collections died by stranding on beaches or getting lost in rivers.  He also considers that animals which are more likely to strand are sick or weak animals unable to resist wave force.  For example, an older animal which cannot eat without pain probably is not ingesting enough calories and then gets lost in a river and dies, or starves and washes up somewhere.  Mr. de Smet hypothesizes that most of the cetaceans in museum collections are animals that have died this way and were easy for museum staff to collect and preserve.  Which means that we this first Grandpa might not be the last one that we come across!

A.N. Hill, C. Karniski, J. Robbins, et al. 2017. Vessel collision injuries on live humpback whales, Megaptera novaeangliae, in the southern Gulf of Maine. Marine Mammal Science. Volume 33, Issue 2, pages 558–573.

W.M.A. De Smet 1977. The Fate of Old Bottlenose Dolphins, Tursiops Truncatus, in Nature as Revealed by the Condition of Their Skeletons. Aquatic Mammals. Volume 5, no 3, pages 78-86.

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