What does the amber-encased mosquito in Jurassic Park contain?

The amber-encased mosquito in Jurassic Park contains dinosaur blood. That blood is presented as the source of ancient dinosaur DNA, which scientists extract to recreate extinct animals.

John Hammond’s scientists explain that mosquitoes fed on dinosaurs, became trapped in tree resin, and were preserved as amber fossils. Researchers then recover the blood—and therefore genetic material—from the mosquito. Missing sections of the dinosaur genomes are filled with DNA from modern animals, especially frogs.

The idea is central to Michael Crichton’s 1990 novel and Steven Spielberg’s 1993 film, but it is fictional science. DNA degrades over geological timescales, and a mosquito’s digestive process would make recovering a complete dinosaur genome extremely unlikely. The mosquito itself is therefore not described as containing a living dinosaur or a fossilized insect: its important payload is the dinosaur blood inside it.

A related detail is that the franchise’s cloned animals are not genetically pure dinosaurs, because frog DNA was used to complete their genetic sequences.