The Protectorate by ff_b
Munching on his breakfast of salmon, the evolved dolphin watched the news and noted with dismay that a severed human arm had been found in an apartment minus its owner. The flesh on the upper portion of the arm bore ragged edges that indicated it had been removed by some kind of forceful bite. There was only one thing that this could indicate to the dolphin...the land sharks were active again, and had become so bold as to abandon their usual cleansing of a feeding scene. Like the dolphin, sharks had evolved to extend their habitat to dry land when the oceans became polluted beyond habitation in the year 7510.
He wasn't sure why his kind had been driven to protect the humans, but ascribed it to instinct. Besides, the humans had proven over many millenniums that they were too arrogant to see to their own protection to say nothing of that of other species, and actually seemed to have a bent for self-destruction. The dolphins and other species had developed mimicry by which they now somewhat resembled humans, their fins becoming limbs suitable for land use just as once in the distant past those limbs had specialized for aquatic life.
Linking himself telepathically with others of his kind, the dolphin drew several of his brethren together to get on the path of the land shark before the trail grew cold, and the shark struck again. They caught up with the shark in a warehouse, and framed him in the middle of a tightening circle of dolphins. Now a single dolphin probably couldn't best a shark as they lacked equivalent dentition, but several dolphins could work cooperatively to take out the more savage animal...so the dolphins tossed the shark back and forth between themselves, bouncing and thumping him like a soccer ball with their powerful tails before flinging him into a cage for relocation to a remote location inhospitable to humans. The dolphins congratulated one another on another successful land shark neutralization, and promised to all get together sometime when not working to share a few fish.
The dolphins couldn't socialize for long, however. A land sperm whale and a giant land squid were duking it out in the northern part of the city, and they weren't quite certain how to separate those combatants or how many cetaceans would be required to do the job...