This mother T. rex is serving her yearlings some lean meat in the form of an okapi (Okapia johnstoni) while her mate keeps watch in the background. Small giraffids may not have as much meat to spare as a twelve-ton Triceratops, but they’re less fattening.
I like to imagine Tyrannosaurus rex as a pair-bonding species with more or less egalitarian gender roles, with the male and female switching hunting and parenting responsibilities between each other on a regular basis. Today it was the female’s turn to hunt; next time it will be her hubby’s.
And yes, the yearling to the right is a melanistic (all black) variant like you see in leopards and jaguars today, whereas her brother to the left has more typical juvenile coloring for their species.