Although the mosasaur that appears on the cover of the second and fifth issues of the series appears similar to Mosasaurus or Tylosaurus, the animal in the actual comic is depicted with webbed feet and the ability to travel on land for a brief period of time, which fits neither of the two genera. The animal's amphibious nature is similar to the early mosasaur relative Dallasaurus, which also possessed the webbed feet seen in the mosasaur depicted in the comic. However, the mosasaur in the comic series is far larger than the real animal, leaving its official identity ambiguous.
At some point, the mosasaur was able to escape from Isla Nublar and swim towards the mainland, eventually reaching the waters outside of a nuclear power plant in Glen Rose, Texas, breaking through the plant's fencing and leaving some tracks on the bank on its way in. Eventually, a power plant worker discovered the hole in the fence and the tracks on the bank, only to be killed by the mosasaur.
Later on, a security guard noticed the mosasaur on the power plant's live security cameras, forcing him to turn on the plant's alarm system to warn the town of the possible danger. However, this warning siren attracted the attention of a Giganotosaurus that had been terrorizing the town, causing it to run towards the power plant under the mistaken belief that the siren was a mating call. Fearing that it could cause severe damage to the plant, Tim and Lex Murphy, Alan Grant, a Glen Rose deputy, and a SWAT team member rushed to the plant in order to turn off the siren. Although Alan and the SWAT member were prevented from reaching the plant by a pair of attacking Pachycephalosaurus, Tim, Lex, and the deputy were able to break through the fence and enter the plant, noticing the mosasaur on their way in. The Giganotosaurus followed them in, causing the deputy to flee for his life, abandoning the Murphys. As the security guard continued to watch the chaos unfold over the cameras, Tim lead the Giganotosaurus away while the mosasaur made a meal out of the terrified deputy. Although Lex was able to convince the guard to shut off the siren, the Giganotosaurus destroyed Tim's car and prepared to kill him before being attacked itself by a pack of Velociraptor that were led to the scene by Alan, Ellie Sattler, and Dr. Backer. As the raptors attacked, the Giganotosaurus moved closer and closer to the water, attracting the mosasaur with the blood dripping into the water from the animal's open wounds. The mosasaur quickly launched itself out of the water and grabbed on to the Giganotosaurus, pulling it deeper into the lake to drown and eat its new prey, while the raptors jumped off of the Giganotosaurus and fled into the wilds of Texas.
It is unknown what happened to the mosasaur after the incident, but it is likely that it was recaptured and transported to either Isla Nublar or Isla Sorna with the other surviving animals, as Alan Grant suggested.