February 7, 2012 Weddell Seal Flippers
This journal is brought to you by:
- Tanjara Wiggins and her 2nd grade students at Jackson Elementary
A Closer Look at … a Weddell Seal’s Flippers
Weddell seals have four flippers – two fore flippers and two hind flippers. The two fore flippers are located on either side of the seal’s body, similar to where a person’s arms might be located. The two hind flippers are located at the end of the seal, where you might expect to find legs.
Marine mammal flippers are wide, flat, fin-like structures. They are webbed, covered in fur, and have claws near the end. Now that you have some of the basics – let’s go a little deeper.
You may think flippers are completely different from the limbs of other mammals – such as humans, and they are – but only on the outside! Externally, they look quite different because flippers are webbed and the limbs appear shorter than most other mammals. Internally, the bone structure is surprisingly similar – the fore flippers are very similar in structure to human hands; and the hind flippers are similar in structure to human feet. Weddell seals even have bones like our ankle and wrist bones, which allow their flippers to rotate. Here’s another interesting fact: much of the Weddell seal ‘arm’ and ‘leg’ bones are located within the seal’s body – and do not stick out like human arms and legs.
Wow! The first thing I notice about the seal’s fore flipper, besides its incredible size, is the blunt, thick, rugged claws at the tips of their ‘fingers’. The hair also looks incredibly thick. The ‘fingers’ are all together in one structure and there is little webbing between the digits. The Weddell’s fore flipper has 5 digits - all around equal length, and they use them for scratching, grooming, and propping the body upright. They also use them for steering and balance when swimming. Pretty amazing!
Hind flippers also have 5 digits, like our toes. But, unlike our toes, the 2 outside digits on a hind flipper are the longest and thickest, and the middle ones are shorter and thinner. Hind flippers are used mostly for swimming – they are very powerful! When spread out, they look like a wide fan. Unlike the forelimbs, there is webbing (skin with fur) between the 'toes'. Also, the claws on the hind flippers are not at the absolute end; they are very short and don’t project at all – they are essentially remnant claws that aren’t really used for anything.
In reference to photos provided by Daniel Costa and Jennifer Burns: The activity/animal depicted was conducted pursuant to NMFS Permit No 87-1851.