Pectoral fins in the context of "Jawed fish"

The humpback whale (Megaptera novaeangliae) is a species of baleen whale. It is a rorqual (a member of the family Balaenopteridae) and is the only species in the genus Megaptera. Adults range in length from 14–17 m (46–56 ft) and weigh up to 40 metric tons (44 short tons). The humpback has a distinctive body shape, with long pectoral fins and tubercles on its head. It is known for breaching and other distinctive surface behaviors, making it popular with whale watchers. Males produce a complex song that typically lasts from 4 to 33 minutes.

Found in oceans and seas around the world, humpback whales typically migrate between feeding areas towards the poles and breeding areas near the equator. Their diet consists mostly of krill and small fish, and they usually use bubbles to catch prey. They are polygynandrous breeders, with both sexes having multiple partners. Males will follow females and fight off rivals. Mothers give birth to calves in shallower water. Orcas are the main natural predators of humpback whales. The bodies of humpbacks host barnacles and whale lice.

Sarcopterygii (/ˌsɑːrkɒptəˈrɪdʒi.aɪ/; from Ancient Greek σάρξ (sárx) 'flesh' and πτέρυξ (ptérux) 'wing, fin')—sometimes considered synonymous with Crossopterygii (κροσσός, krossós, 'fringe')—is a clade (traditionally a class or subclass) of vertebrate animals which includes a group of bony fish commonly referred to as lobe-finned fish. These vertebrates are characterised by prominent muscular limb buds (lobes) within their fins, which are supported by articulated appendicular skeletons. This is in contrast to the other clade of bony fish, the Actinopterygii, which have only skin-covered bony spines supporting the fins.

The tetrapods, a mostly terrestrial clade of vertebrates, are now recognized as having evolved from sarcopterygian ancestors and are most closely related to lungfishes. Their paired pectoral and pelvic fins evolved into limbs, and their foregut diverticulum eventually evolved into air-breathing lungs. Cladistically, this would make the tetrapods a subgroup within Sarcopterygii and thus sarcopterygians themselves. As a result, the phrase "lobe-finned fish" normally refers to not the entire clade but only aquatic members that are not tetrapods, i.e. a paraphyletic group.

Antiarchi ("opposite anus") is an order of heavily armored placoderms. The antiarchs form the second-most successful group of placoderms after the arthrodires in terms of numbers of species and range of environments. The order's name was coined by Edward Drinker Cope, who, when examining some fossils that he thought were armored tunicates related to Chelyosoma, mistakenly thought that the orbital fenestra (i.e., the hole in the headshield for the eyes, nose and pineal foramen) was the opening for the mouth, or oral siphon, and that the opening for the anal siphon was on the other side of the body, as opposed to having both oral and anal siphons together at one end.

The front portions of their bodies were heavily armored, to the point of literally resembling a box with eyes, with the sometimes scaled, sometimes naked rear portions often becoming sinuous, particularly with later forms. The pair of pectoral fins were modified into a pair of caliper-like, or arthropod-like limbs. In primitive forms, such as Yunnanolepis, the limbs were thick and short, while in advanced forms, such as Bothriolepis, the limbs were long and had elbow-like joints. The function of the limbs are still not perfectly understood, but, most hypothesize that they helped their owners pull themselves across the substrate, as well as allow their owners to bury themselves into the substrate.

The leafy seadragon (Phycodurus eques) or Glauert's seadragon, is a marine fish. It is the only member of the genus Phycodurus in the family Syngnathidae, which includes seadragons, pipefish, and seahorses.

It is found along the southern and western coasts of Australia. The name is derived from their appearance, with long leaf-like protrusions coming from all over the body. These protrusions are not used for propulsion; they serve only as camouflage. The leafy seadragon propels itself utilising a pair of pectoral fins on the sides of its neck and a dorsal fin on its back closer to the tail end. These small fins are almost completely transparent and difficult to see as they undulate minutely to move the creature sedately through the water, completing the illusion of floating seaweed.