Land Shark?
The Epaulette Shark is my favorite fish and I've touched one! They are about 3ft long (90cm) and they spend their day hiding under rocks in the reef. They're named after their striking shoulder pads or their epaulettes. These act like eye spots to deter predators. And like distinguished military members, they march!
Yes, they march. Every evening, they march up the beaches during low tide to raid various tide pools for worms and crabs. And every morning, during low tide again, they'll march back to the ocean. They take advantage of low tide to avoid dealing with large predators, and at 3ft long in the tide pools, they are the large predators. But if they're marching up the beaches and between tide pools..? Yes! This shark can take to the land!
They have four muscularized, flexible fins that they use to pull themselves across sand and exposed reef. Even when they can fully swim, they like to walk around! Most sharks have thick stiff cartilage in their fins, using them like plane wings. But these guys have greatly reduced and separated cartilage boosted by increased muscle. This is so cool because it resembles our own clamber onto land 375 million years ago.
This alternating turn the whole body walk is still found in salamanders and reptiles that keep their bodies low to the ground. The epaulette shark just isn't that good at full weight on land.
The tide pools are full of life and all that life needs oxygen. Through the night, the water sits undisturbed without new sea water to replenish it, so the oxygen level drops. Oxygen levels can drop by 80% in a night. Testing found that the epaulette shark can remain responsive in 95% depleted water for 3 hours and without any oxygen at all for 1 hour. The shark is able to lower its metabolism, breathing, heart rate, and brain function so it needs as little oxygen as possible. It can also restrict its blood flow to specifically protect its heart and brain from dying. I wish I could turn my brain off sometimes!
The shark above is actually breathing air kinda like we do. They don't have lungs, but you can see the gills inflating. To breathe, we use our diaphragm to move fresh air into our wet lungs where the gas can exchange with our blood over the wet barrier. This shark is doing the same thing using its cheek muscles! The difference is our lungs make themselves wet and too much air moving over the gills will dry them out and damage them. There are land animals that still have gills today like roly polys. Maybe in 100 million years, this shark will have gill pouches sloshing full of water as it runs through grassy fields.
They're friends!
I love this salamander puppy shark thing! It is far from the best animal, but I love it! So many things are happening here. No other shark does it like this. This is so unlike the mudskippers. It's absolutely gorgeous. It commmutes to work. It's great! Sharks have been around for 450 million years and we get to be where when they finally emerge, what a blessing! I wish I could sit and watch them for another 50 million years and watch them get better and cooler and weirder.