Card Capsules are egg-shaped capsules that split into two pieces (top and bottom) along a zig-zag in the center. The top area of the capsule and four smaller knobs on the bottom glowed when the card the capsule contained activated, but this pattern stopped after episode 2. While the material of the capsules is left unspecified, they may be plastic, or just some fictional material.
Most Card Capsules contained either one Dinosaur Card, or one Dinosaur and one Move Card. A few contained one Assist Move Card (a Move that summons a dinosaur as part of its effect; they are never found with a Dinosaur Card), and one even had two Dinosaur Cards (the Saurolophus pair). Also, Chomp's Capsule contained the Lightning Stone and Spiny's contained the Water Stone.
A collection of these capsules was scattered across the world by the Backlander malfunctioning and crashing. It is unclear when they entered the timeline. Baby Rex seems to have arrived about 12 years before the Alpha Gang, and Jonathan an unspecified time before the Alpha Gang. Some of the capsules are buried underground or embeded in rock, and some are even found at fossil dig sites, but others are just lying around.
A Card Capsule first appears in Prehistory in the Making, containing Chomp's card and Electric Charge. After that, almost all Series 1 episodes at some point involved a Card Capsule opening and the Dinosaur Card activating (though not all Dinosaur Cards were found in Capsules, notably Therizinosaurus and Velociraptor). Capsules containing only a Move Card are found without them activating, typically by the Alpha Gang, who then use the Move against the D-Team.
In Mesozoic Meltdown, Genie's card is found in a Card Capsule in Ancient Persia. It's unclear how this capsule got here, as a missing Isisaurus card was never mentioned by Dr. Ancient, indicating it might somehow have not been among the "regular" collection of cards in the Capsules.