Manatee Adaptations: Skeleton, Flippers and Fat Bones and Skeleton Flippers Fat Bones Manatees have some pachyostotic bone, which means bone that is solid, with no marrow. In the ribs and in other long bone areas, the bone is very dense, with no marrow cavity. This contributes to their skeleton being relatively quite heavy. Watch Park Ranger Betsy Dearth describe the uniqueness of manatee bones: (Viewing Tips) Watch it now No "bones" about it--manatee bones are unique! Video: Oceanic Research Group, Inc. Biologist Bob Bonde of the Sirenia Project points out that some scientists view the manatees' dense, heavy bones as an evolutionary trait or adaptation, which helps supply ballast or weight while they forage for foods submerged along the bottom. These marrow-less, dense bones microscopically resemble fetal, developing bones in other mammals. Watch this adaptation in the video two clips below: (Viewing Tips) Video #1: Bouyancy- Rising to the Top Video #2: Bones provide ballast Photo Credit: Mote Marine Laboratory Photo Credit: FWC Video Credit: SMC, International Film Projects Bob Bonde says that Manatee bones in some ways are like sick bones of people and other animals. Two earlier scientists, Scholander and Irvine in 1941, suggest that manatee bones may be related to having low metabolic rates and oxygen consumption, which might be related to a form of athyroidism (a condition that can also be responsible for a disease in humans called osteopetrosis). Bob noted that evolutionarily speaking, with their heavy bones, Manatees may have found the perfect niche in the aquatic environment, but it may be at a cost. That cost would be their thyroid dysfunction which metabolically restricts them to the tropical and semi-tropical environments of the world (which makes Florida a less that optimal place for manatees). In terms of evolution, this raises another question. What allowed the Stellar sea cow to live in the cold waters of the Bering Sea? As Bob said, "Personally, I would love to have examined a Steller sea cow to see how that Sirenian tolerated the cold temperatures of the Bering Sea, but it's a bit too late for that!" Try This! Journaling Question Compare your bones to manatee bones. How are Manatee bones different from yours? or similar to yours? Flippers Sirenia Project's Cathy Beck says that Manatee pectoral flippers are analogous to canoe paddles. The finger bones are joined by skin and cartilage creating a solid paddle that is used primarily for steering.  A Manatee will also use her flippers to bring food to her mouth, gathering a mass of vegetation and scooping it toward her lips, spoon-like. Watch some of the ways Manatees use their flippers in these four video clips: (Viewing Tips) Video #1: Steering with Flippers Video #2: Eating with Flippers Photo Credit: Mote Marine Laboratory Photo Credit: USGS/FCSC Video Credit: SMC, International Film Projects Some say a manatee's flipper bones are like a human hand. Three or four nails are found at the end of each flipper. Cathy added that Manatees also will also use their flippers to "walk" on the tips of their flippers as they travel along the bottom (see video clips below). They may also "plant" their flippers into the substrate to help steady themselves as they feed in a grassbed. (Viewing Tips) Video #3: Dive in with a Diver Watch a Curious Manatee "Walk" Video #4: Watch a Manatee "Walk" Your Way Photo: USGS Video: Oceanic Research Group, Inc. Try This! Journaling Questions: Can Manatees really "walk" on their flippers? Describe what you think the manatee is really doing. Do you know of any other marine mammal that does this? Can you? Click on images for a closer look Similar to your hand?  Think you're the only one with fingernails?  Credit: Mote Marine Laboratory In what ways are Manatee flippers like a human hand? Fat Thickness Beneath their skin (which some describe as feeling like the covering of a basketball, or like the cork on a bulletin board), manatees carry a layer of body fat which helps to insulate them from the cold water. In different locations, Manatees will have a thicker or thinner layer of body fat depending on how cold the temperatures are or not. This layer of fat and its varying thickness could be considered a unique adaptation. Diagram of Fat Layers Sirenia scientist Bob Bonde explained that the changing thickness of fat could be explained even further. "Some very interesting work by Leslie Ward-Gieger from the Florida Marine Research Institute allows us to use a portable ultrasound machine in the field to assess thicknesses of manatee fat layers. This technique allows us to make assumptions about nutritional condition as well as how these layers change in formation during different times of the year, between various geographic areas, and across different age classes and sexes of manatees.  It has given us some insight into different survival strategies that manatees have adapted for making it through cold winters." For example, Bob says that "Manatees in the north part of Florida actively forage during winter, increasing their fat layers and using energy obtained from feeding to help generate body temperature. Whereas many manatees in south Florida do not appear to do that, but in turn they are not exposed to the much colder temperatures to the north.  Therefore, manatees in north Florida generally have larger layers of fat during winter than their counter parts in south Florida. I think with the advent of power plants this incentive for manatees to occupy northern habitats has necessitated certain strategies like this that allow them to survive in these areas where Mother Nature keeps trying to knock them back!  Keep in mind that many of these manatees are still dependent on a warm water source, and many of these sites are artificial (temporary) fixes to a long term commitment to occupy these areas." Try This! Journaling Question Why will Manatees in two different parts of Florida have different amounts of body fat? Try This! A Whale of a Question When people learn how cold sensitive Manatees are, many ask the question "Why do you think a large marine mammal like a Manatee cannot tolerate cold water when another large marine mammal like a Whale can?" If you'd like to try something extra, you can test "first-hand" if cold feels different to a manatee than it does to a whale. Try these experiments from Manatee expert Bob Bonde and whale expert Ann Smrcina. This may be a bit messy, but the experience is worth it! If you do either of the experiments, tell us how it went! Like Jumping In Snow Without a Jacket Staying Warm Lesson   Copyright 2002 Journey North. All Rights Reserved. Please send all questions, comments, and suggestions to our feedback form