It would seem that being able to drink sea water would allow a coastal animal of some sort exist in ecological niches where there isn’t sufficient fresh water to support them, and yet I can’t recall ever reading about a land based mammal that could survive off of salt water.
I’m guessing there are amphibians that fit this description, but they’re not truly land animals.
If there are no such animals, why not? Is there something inherent about land animal physiology? It seems to me that as whales and dolphins can do it, there’s nothing inherently limiting about mammalian physiology. Is the presence of fresh water in coastal regions common enough that this adaptation would be of limited usefulness?
Camels are pretty tolerant of drinking salty water, and at least one population of Bactrian camels seems able to survive by drinking from salty inland springs.
Amphibians (frogs, toads, salamanders, etc.) are actually very intolerant of salt water. Few can tolerate even brackish water.
It’s actually not entirely clear that most marine mammals actually do drink all that much seawater. They get their water from their food, rather than by drinking.
But aren’t there lots of mammals that don’t actually drink anything? I think there are certain rodents that live in desert climates that don’t really drink. I don’t think sea otters drink either. Drinking… it’s overrated!
Kangaroo ratsrarely drink water. It’s possible that some of them go their whole life without drinking any water. They are able to recover* enough water from their food, either the water of hydration bound up in the molecules of the food, or the free water that’s in the seeds.
They also have elaborate water saving mechanisms in their makeup and don’t require all that much water because they lose so little.
The cite says they convert some of their food to water but that’s misleading. The water is already there, they just are able to recover it.
Actually, they really do convert their food partly to water, but then pretty much all animals do. This is “metabolic water,” and is different from water of hydration or free water that’s in the seeds.
“Metabolic water” refers to the water created by the oxidation of carbohydrates and other foods through respiration and involves the chemical breakdown of the original compounds. This water was not previously present in the food in the form of H20.
As a sidenote, kangaroo rats are quarrelsome little devils. Very territorial and if two of them are in an area they are in a fight. Suppose their bad temper is because they are always thirsty?
Yes. Birds and reptiles have special salt glands located over the eyes. A salt solution is excreted through the nostrils. Sea birds in general possess such glands. In species such as some ducks which may switch between freshwater and marine habitats at different times during the year, the gland will hypertrophy or regress depending on whether it is being used or not.
Birds and reptiles have an advantage over mammals because their main nitrogenous excretory product is uric acid instead of urea. Uric acid is much less soluble than urea and thus requires less water to “flush” out to the system.
