From mammal-like reptiles to mammals

This 19 June 2019 video says about itself:

Synapsids were the world’s first-ever terrestrial megafauna but the vast majority of these giants were doomed to extinction. However, some lived on, keeping a low profile among the dinosaurs. And now our world is the way it is because of the time when the synapsids struck back.

Thanks to Ceri Thomas for the excellent Synapsid illustration (including Bulbasaurus!)!

A team of evolutionary biologists, led by Dr. Rui Diogo at Howard University, USA, and writing in the journal Development, have demonstrated that numerous atavistic limb muscles — known to be present in many limbed animals but usually absent in adult humans — are actually formed during early human development and then lost prior to birth. Strikingly, some of these muscles, such as the dorsometacarpales … disappeared from our adult ancestors more than 250 million years ago, during the transition from synapsid reptiles to mammals: here.