First tiger shark Galeocerdo cuvier bite in 75 years in French Polynesia (Eastern Central Pacific)

Paleozoic and Mesozoic SeasEarth’s oceans were full of life during the Paleozoic and Mesozoic eras. In the Paleozoic Era, 541 to 252 million years ago, the seas were home to trilobites, brachiopods, and early fish. Coral reefs began to form, and the first vertebrates with jaws appeared. The Mesozoic Era, 252 to 66 million years ago, is often called the Age of Reptiles, but the oceans were just as important. Large marine reptiles like plesiosaurs and mosasaurs ruled the seas, along with...

Jawless FishJawless fish are some of the oldest and most interesting animals on Earth. They show us what early vertebrates (animals with backbones) may have looked like hundreds of millions of years ago. Jawless fish help scientists understand how important features like bones, jaws, and fins developed over time. These fish live in many places today, from freshwater rivers to deep ocean waters. Studying them helps scientists learn about the history of life and how ecosystems have...

The fossil record documents only a small fraction of all organisms that have ever inhabited Earth. Fossilization is a rare process, and most organisms never become fossils. Moreover, the fossil record only exhibits fossils that have been discovered. Nevertheless, sedimentary rock fossils of long-lived, abundant, hard-bodied organisms dominate the fossil record. These fossils offer valuable information, such as an organism's physical form, behavior, and age. Studying the fossil record helps...

Bony FishBony fish are the largest group of fish in the world. They are important because they show how fish evolved strong skeletons, new ways to stay afloat, and different feeding and movement methods. Bony fish are found in almost every kind of water, from freshwater rivers to deep oceans. Studying bony fish helps scientists understand how animals adapt to different aquatic environments.Bony fish belong to a group called Osteichthyes. Their skeletons are made of hard bone instead of...

Cartilaginous FishCartilaginous fish are a special animal group that includes sharks, rays, and skates. They differ from most other fish because their skeletons are made of cartilage, not bone. Cartilage is lighter and more flexible than bone, which helps these fish move easily through the water. Studying cartilaginous fish helps scientists learn how animals adapt to their environments and how different body parts, like fins and teeth, evolved to help fish survive in oceans...

Retroviruses and retrotransposons both insert copies of their genetic elements into the genome of the host cell. Thus, the viral genes are passed on when the host genome is replicated or translated. A typical retroviral DNA sequence contains 3-4 genes that encode the different proteins required for its structural assembly and function as a molecular parasite. This DNA is transcribed into a single mRNA, which is very similar in structure to conventional mRNAs, i.e., it is capped at the 5’...