|Scientific name||Hyaenodon cayluxi|
|Home era||Late Eocene to Early Miocene|
|Appearances||Episode 4.6 (only appearance)|
Hyaenodons are mammals that hunted and killed in packs.
An anomaly opened in a Castle, leading two Hyaenodon and three cubs through. A lady finds two of the cubs in a box, but the adult attacks and kills her. It is possible that the man she grabbed the wine from was also killed. Connor, Abby and Matt go and lock the anomaly, but hear a roar. After hearing other noises, and after Abby told Connor to shut up, a male Hyaenodon races at her, but Connor quickly moves her out of the way and EMDs it. It then is put back through the anomaly. However, the two cubs are still in the box, and the female Hyaenodon is with them, unknown to the entire team.
But while Jenny goes to get something, she hears some squawks from the babies. The mother and her two cubs are let loose. A third, slightly more matured baby escapes and walks around the castle, before running out into the outside during the night, unknown to Emily or Matt, who are talking outside. When Connor knocks of the door to the room Abby and Jenny are sleeping, he hears the noise and investigates. He goes down to see the cubs in the box, and tries to call Abby, but there is no reception, and on his way up, he encounters the female Hyaenodon who chases him where the cubs are, and he closes the door, and the cubs wake up, bitting him while he kicks them. He locks the door and throws a metal circle shaped plate on the ground, and pours some wine on it, and the cubs drink it, and Connor puts a box on them.
After a while he goes up to the exit to the outside, but still no reception. It is then that he encounters the third one cub and Connor uses a wine bottle and sprays out the cork, hitting the cub. After he opens the door, he returns the two cubs through the anomaly. The third one arrives, but the male Hyaenodon arrives through the anomaly, and instead of returning them, he makes them upset.
As the wedding starts, and after Connor runs to warn everybody to run, the cub arrives, and the audience acts like its cute. Then, screaming, and the two Hyaenodon appear. One Hyaenodon corners some people, but Matt grabs a medieval weapon and smacks it with it. It goes to Matt and the Hyaenodon rams into the shield Matt is holding, but Matt pushes it away and rams the shield into it.
When Emily and Abby go outside, a Hyaenodon goes and leaps out the window, getting another weapon in it by Emily, and she throws it. They run, but the Hyaenodon gets back up and chases them. Abby gets into van, and the Hyaenodon follows her, and she shuts the door, and Emily shuts the other door, trapping it.
The Hyaenodon in the castle attacks Michael and another man. The cub encounters the petrified man, but the adult appears, and as they go down the Hyaenodon follows them, and corners Michael, but Jenny appears and smacks it down the staircase. The Hyaenodons are then returned back through the anomaly.
- This is the third creature from the Eocene to appear in Primeval.
- It is possible that the Hyaenodon killed the man that was with Michael and Jenny as they were getting married.