Endotherm

Warm-blooded mammals and birds are constrained: the Triassic.

During the Permian, every land animal was a reptile. They wandered the land sprawled out like a lizard. If they lived near water they could do as crocodiles do today. Over the Triassic, the synapsids evolved means to put more of their - our - weight directly on thighbones. Same with the first dinosaurs who later would spawn the birds. This helped the animals run; warmth evolved in our bodies to improve the metabolism of a running animal.

That Carnian extinction 233 Mya, for reference, will have done for Probainognathus and Chiniquodon. It spared, alone, the Prozostrodonts. True mammalia branched off them soon after that. Apparently paramammals like Tritylodon lasted into the Jurassic, I guess to end up in an allosaur's belly. So we don't see them anymore like we see, say, the platypus. [INDIA-MALAGASY 12/20: Unless...] Note that the platypus is still a swamp thing.

The new study adds that the dinos had feathers and the mammals, whiskers early on in the Triassic. Given the dino oxygen-efficient bone and feather structure, which Out of Thin Air taught us and which keeps getting into the press, I'd rather thought we'd inferred that already, for them. The Jurassic "Brontosauri" would have lost the feathers secondarily on their return to the marshes.