The Amber Mosquito is a pet-summoning item that spawns a Baby Dinosaur to follow the player around. If it is too far away from the player, a pterosaur will carry it by the tail to continue following the player. This item can only be obtained by putting Silt, Slush, or Desert Fossil into an Extractinator. With Silt or Slush, it has a 0.01*1/10,000 (0.01%) chance to drop, with Desert Fossils it has a slightly higher chance of 0.027*27/100,000 (0.027%). It does not produce light.
This item is a reference to the American science fiction media franchise Jurassic Park, where dinosaurs are cloned using blood found in mosquitoes trapped in amber.