Topps, Cera's belligerent father, and his first wife are seen to have several children in the first film. However, when he and Cera are reunited in the Great Valley at the end of the film, his wife and all of Cera's siblings are absent. This suggests that they died on the herds' journey to the Great Valley. Still, the existence of Dinah and Dana - Cera's niece and nephew and Topps's grandchildren - implies that at least one of Cera's older siblings survived to adulthood. However Cera's parents (whether her mother or father) must have had a earlier relationship before the start of the franchise. This is highly supported by two full-grown Triceratops (one resembling Cera) appearing near the end of the film to close the opening to the Mysterious Beyond in the second film. Topps' family's fate remains unknown.
Dinah and Dana have only appeared in The Secret of Saurus Rock, which implies that this older sibling of Cera's, and his or her family, live outside the Great Valley. They occasionally visit their relatives within.
Cera is seen to have nestmate siblings at her hatching; they seem to be mostly sisters, according to Cera: Littlefoot (trying to persuade Cera to come with him): "Well at least we wouldn't be alone!" Cera: "Well, when I find my sisters, I won't be alone!". They, along with their mother, have mostly disappeared from the film series, and it is disputed as to what exactly happened to them. Their possible fates are:
- Because of the fatalistic nature of the original film, they and their mother may have died on their way to the Great Valley; possibly from from hunger, thirst, exhaustion, or being attacked by Sharpteeth. However this can contradicted since in The Land Before Time II: The Great Valley Adventure a Triceratops in the background next to Topps responded to Cera's cry for help when she and her friends were sinking in quicksand, along with the appearance of a three baby Triceratops who look similar to Cera (interestingly enough this is the exact same number of sisters, Cera had).
- It is revealed in The Stone of Cold Fire that Pterano, Petrie's uncle, manipulated a large portion of the herd into breaking away and following him instead of Topps and Grandpa Longneck. After a while, they were attacked by Fast Biters, and presumably most if not all of them were eaten or killed. Cera's mother and her siblings may have been among these ill-fated dinosaurs as, what appear to be Triceratops are seen with a number of unknown dinosaurs. However this isn't possible as among the dinosaurs of Pterano's herd the only Ceratopsid dinosaur to be apart in the group is a Styracosaurus.
- Cera's mother may have, for whatever reason left or maybe divorced Topps because he said to Cera:"Threehorns Never Play With Longnecks!" and Cera's mom likes Longnecks and taken custody of all the children except Cera. This theory would lead to the questioning of why they seem to have left the Great Valley, since the Great Valley had everything that all the plant eaters could possibly need (This could be his attitude of being a Speciest, towards longnecks. which make's him a bad influence towards Cera of judging Longnecks that she knows her children will get that attitude from her husband). However some of this can contradicted has she may have left due to Topps irrational behavior over the lack of water in the Valley during the third film and towards his mistreatment towards Cera may have gotten into an arguement and may have left for this reason. This can be supported in The Land Before Time XI: Invasion of the Tinysauruses when Topps acts harsh against his old time friend Tria, in distaste for siding against him to harm the Tiny longnecks and then temporarily left him. Another fact is in the third movie a herd of Threehorns is traveling together to appears to be them leaving the Great Valley with only Topps staying behind. This can be well supported with Cera's dad stopping at a gorge that was once a river while traveling with the Threehorn herd and then turns his direction towards where the herd is heading as the screen pans to the mountainous scenery.
- Another theory is that in the production foregrounds the characters didn't have much of a role within the story and thus were dropped from the franchise at forehand.
Two of Cera's sisters may appear in The Great Valley Adventure and The Land Before Time III: Time of the Great Giving; in which two baby Threehorns, colored same as Cera, are seen playing near Topps in the pool beneath the Thundering Falls. It is not made clear if these are Cera's younger sisters, nephews and/or nieces, cousins, or unrelated Threehorns that are in the valley.
Baby Threehorns seen in first two sequels
The death theory is heavily disputed by the end scene (the Peaceful Valley reprise) of The Great Valley Adventure, in which, along with Ducky's younger siblings and one Petrie's younger siblings hatching, three or four little Threehorns run up behind Cera and grab her in play. Two Threehorns identical to these also appear in The Time of the Great Giving when Littlefoot is at the Thundering Falls. This could suggest that Cera's mother does make it to the Valley alive and has more children with Topps before her definite disappearance. However, it is still fully possible that these little Threehorns are completely unrelated to Cera. It is nearly impossible to draw any conclusions about the fate of Cera's family, as the early sequels are not clear on this.
Tricia is a young dark pink Triceratops. She is the daughter of Tria and Topps and the paternal half-sister of Cera. Her first appearance is in The Land Before Time XII: The Great Day of the Flyers.