DC Special changes to all-new material with issue 27 (April/May 1977), Danger: Dinosaurs at Large! The story, by Bob Rozakis, Rich Buckler and Josef Rubenstein, stars Captain Comet, who was currently appearing in Secret Society of Super-Villains, and Tommy Tomorrow, who had not been seen since the end of his run in Showcase, back in 1963.
The two heroes begin the tale in their own time periods, and both see a huge comet flaming through the sky. The comet has such a marge gravitational pull that it "grabs" the ship that Tommy is on, pulling it along as the comet passes through a time warp.
Tommy's ship manages to get free of the comet, but only after it has been dragged all the way back to prehistoric times. I should also mention that Brent Wood, Tommy's old sidekick, is in this story. Brent had been dropped from the Tommy Tomorrow series after its run in World's Finest Comics ended. Despite this, he is wearing a matching uniform to Tommy, who is wearing the outfit he donned only when his run in Showcase began.
Captain Comet was hanging out with Hawkman on the Justice League satellite when the comet passed their time period. The time warp it went through has resulted in a number of dinosaurs emerging in their era. Hawkman makes Captain Comet an honourary member of the Justice League, but also leaves him behind in the satellite, as he goes off to fight dinosaurs. Jerk. Comet watches on the monitor board as Superman, Green Lantern, Wonder Woman and Black Canary all fight the beasties. But only Captain Comet sees the villain Chronos is involved with the dinosaurs as well. Chronos had last appeared the previous year in DC Super Stars.
As for Tommy Tomorrow, he and some of his crew go out to try to find the comet that pulled them through time. It's a much more potent item than they had suspected, capable of evolving one dinosaur that comes into contact with it.
As for Captain Comet, he leaves the satellite to go join in the fun. He works alongside Chronos to stop a rampaging stegosaurus. Chronos tries to pretend that he is one of the heroes, but Comet's mind reading ability let him know otherwise.
And, as is not too surprising, it turns out to be Chronos who is behind all of this. He opened the time warp to pull the comet to his own era, to try to gain power from it. But he messed up, and couldn't control the warp or the comet. Chronos tries to take down Captain Comet, but fails dismally at that as well.
Comet tries to use his mental powers to seal the time warp. At the same time, Tommy Tomorrow and his crew are trying to use it to get back to their era. The mutated dinosaur makes it onto their ship, and winds up in the present, along with Tommy and his crew.
So everyone is around for the big final battle. Tommy Tomorrow recognizes Captain Comet, which says a lot for his impact on history. There is a bit of villain trading at the end, with Come taking down the dinosaur and Tommy Tomorrow defeating Chronos. Comet brings Tommy back to the JLA satellite, and Superman takes him and his crew back to their own era.
Captain Comet continues appearing in Secret Society of Super-Villains, and Tommy Tomorrow is next seen the following year in Showcase 100. Chronos returns the following month in Justice League of America, as part of the Injustice Gang.