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Marine vertebrates which were in their past terrestrial, often move back and forth between marine and fresh water. Both in extant and fossil populations.
Why can’t marine animals survive in fresh water?
Helen Scales 2022
If you plopped a marine fish in fresh water, it would start absorbing
lots of water across its gills. It wouldn’t take long for it to get
into trouble with the balance of water & salt in its body.
It might even swell up!
Their bodies are more salty than fresh water, so they absorb water via
Freshwater fish face this same problem, but they’re adapted to get rid
of water quickly – mainly by peeing a lot.
Some fish (eels, salmon,)move between sea & fresh water by altering
their biology, but it takes a lot of energy & time to switch from sea &
H.erectus = salt water: pachy-osteo-sclerosis++.
H.neand. (less POS) was more riverside? seasonally following the