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.
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.