« "Mosasaur, eh? Cretaceous sea marine predator, ranging from two to twenty meters in length and two tonnes in weight, extinct 65 million years ago!" »
Tom reading Connor Temple's database[src]

Mosasaurs were serpentine marine reptiles and ferocious predators from the Cretaceous period.


Mosasaurs were large serpentine marine reptiles and aquatic predators; They were not dinosaurs, but evolved from semi-aquatic squamates known as the "aigialosaurs", close relatives of modern-day monitor lizards. Mosasaurs breathed air, and were powerful swimmers that were well-adapted to living in the warm, shallow epicontinental seas prevalent during the Late Cretaceous. They grew up to 20 metres long but juveniles averaged 6-7 metres.

The species encountered by the Home Office possessed crocodilian-like armour, a long serpentine-like body, and they attacked aquatic animals for food, but would also attack creatures that were above the surface. These Mosasaurs would also attack and eat smaller Mosasaurs as well as other aquatic creatures.

Incursions and encounters

1x3 Mosasaur 4

A Mosasaur in the Crystal Palace Diving Institute. (Episode 1.3)

Episode 1.3

A small Mosasaur came through an Anomaly into a swimming pool at the Crystal Palace Diving Institute in the present. There, the Mosasaur swallowed Anthony Barton whole while he was diving into the pool, killing him. Due to the chlorine in the swimming pool's water, the Mosasaur then returned through the Anomaly before it closed.

The Mosasaur later came through the same Anomaly again into a reservoir in the present when the Anomaly reopened there along a temporal fault line. It regurgitated a bolus of Anthony's undigested remains, then stalked the reservoir. When the Mosasaur came across Connor Temple and Abby Maitland, who had waded out into the reservoir to take water samples, they rushed onto land to a high metal fence. The Mosasaur then leaped partially ashore after the two, but Connor fought it off with an oar. The Mosasaur then retreated back into the reservoir and returned through the Anomaly just before it closed.

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A young Mosasaur is cannibalised by a larger adult. (Episode 1.3)

After Nick Cutter travelled through the reopened Anomaly looking for his wife Helen, when he tried to return through the Anomaly the Mosasaur attacked him in the oceans, at the Anomaly site. The Mosasaur managed to damage Cutter's scuba gear, and was protected against Cutter's Harpoon gun by its thick skin. As the Mosasaur launched its final attack, another, larger Mosasaur attacked and killed it, then swam off with the smaller Mosasaur's corpse.

Other references

Episode 1.1/1.3

A picture of a Tylosaur (Mosasaur) was visible on Connor Temple's database.

Episode 2.1

The Mosasaur appeared in Nick Cutter's recap of Series 1.

Real life

Mosasaurs (name meaning "Meuse river lizard") has been believed to have probably evolved from semiaquatic squamates such as aigialosaurs, and they were the dominant marine predators in the last 20 million years of the Cretaceous after the extinction of the ichthyosaurs and the decline of the plesiosaurs. Mosasaur had a lizard-like but more streamlined body, and it was a well-adapted Cretaceous swimmer and breathed air. Virtually all Mosasaur species were active predators of ammonites and fish, and a few of the largest species even preyed on other marine reptiles.


  • Mosasaur was the first Cretaceous creature to appear in Primeval, and the first marine reptile to be encountered. And also the first creature to kill a human on-screen.
  • The Mosasaur was featured on the Series 1 title sequence.


  • The Mosasaurs in Primeval were modified from their real life counterparts. Incorrect features were;
    • crocodilian-like armour.
    • the head shape; the real Mosasaurs had narrow, crocodile-like snouts, but the Primeval Mosasaur had a shorter, stockier, somewhat allosaur-esque head.
    • The largest mosasaur was shown to be twenty meters in length. However, the biggest Mosasaur specimens in real life were only seventeen meters.
    • a lack of a fluke on their tail, however it was discovered to be on Mosasaurs in 2011, four years after Mosasaur's appearance in Primeval.