The lizards in the books
The Farthing Wood Lizards are among the animals that begin the journey from Farthing Wood to White Deer Park in the first book. They are replaced by a family of newts for the TV series.
The lizards are among the slowest animals in the group and struggle greatly with the long distances required to make the journey. When the animals arrive at the army land, Lizard tells the other animals that the lizards have decided it would be best for them if they stay behind as the distance would be too much for them. Badger protests strongly against this idea, but he is eventually persuaded that they would be as safe there as in White Deer Park. The rest of the animals move on, leaving the lizards behind.
After the animals have moved on, a fire rages through the army land where the lizards have been left behind. The other animals all escape, but the fate of the lizards is unclear. When Mole mentions the lizards later, Badger immediately regrets letting them stay behind. Fox insists that they may have escaped from the fire, but Badger fears the worst and refuses to be consoled.
It is possible that the ancestors of the Farthing Wood lizards appear in Farthing Wood: The Adventure Begins, the prequel set five years before the journey to White Deer Park. When animals come out of hibernation for the spring, it is mentioned that there are reptiles among them, although it is not specificed which reptiles these are. It is likely that the reptiles refer to lizards and adders, as these creatures are part of the group that begins the journey to White Deer Park five years later.