Short answers, pulled from the story.
No consistent biological distinction exists between cormorants and shags. The names were originally applied to the two species found in Britain and Ireland: the great cormorant (Phalacrocorax carbo) and the European shag (Gulosus aristotelis). As explorers encountered other species worldwide, the names were assigned haphazardly, sometimes based on whether a bird had a crest and sometimes not.
Imperial shags fitted with miniaturized video recorders have been filmed diving to depths of as much as 80 metres to forage on the sea floor. Some cormorant species have been recorded diving to 45 metres.
"Cormorant" is a contraction probably derived from the Latin corvus marinus, meaning "sea raven." In Germanic languages, the birds were called "sea ravens" until after the Middle Ages. The French explorer Andre Thevet noted in 1558 that people still believed the birds were related to ravens.
Cormorant fishing, known as ukai and performed by a fisherman called an usho, has continued uninterrupted on the Nagara River in Gifu, Gifu Prefecture, for 1,300 years. Japanese fishermen use the Japanese cormorant (Phalacrocorax capillatus) for this tradition.
In 1853, a woman was found on San Nicolas Island, off the southern coast of California, wearing a dress made of cormorant feathers sewn with whale sinews. She had lived alone on the island for 18 years, and after rescue was baptised "Juana Maria," as her original name was lost. The dress she brought with her is reported to have been taken to the Vatican, and her story inspired the children's novel Island of the Blue Dolphins.
Current phylogenetic evidence indicates the family diverged from its closest relatives in the Early Oligocene, approximately 30 million years ago, with the split from darters occurring during the Late Oligocene. Proposed Cretaceous fossils, including a scapula from the Nemegt Formation in Mongolia dating to about 70 million years ago, are now considered likely misidentifications.
The International Ornithologists' Union adopted a consensus taxonomy in 2021 recognising seven genera and approximately 40 species in the family Phalacrocoracidae. This seven-genera arrangement was first proposed in a multigene molecular phylogenetic study published in 2014 and was also adopted by the IUCN Red List and BirdLife International.