Marine vertebrate
The combination of endoskeleton (which allows much larger body sizes for the same skeletal mass) and a more robust and efficient nervous system (which enables more acute perception and more sophisticated motor control) gives vertebrates much quicker body reactivity and behavioral adaptability, which have led to marine vertebrates dominating most of the higher-level niches in the marine ecosystems.
Fish anatomy and physiology generally includes a two-chambered heart, eyes adapted to seeing underwater, and a skin protected by scales and mucous.
It looked much like a stocky version of the great white shark, but was much larger with fossil lengths reaching 20.3 metres (67 ft).
[10] Found in all oceans[11] it was one of the largest and most powerful predators in vertebrate history,[10] and probably had a profound impact on marine life.
[16] Lobe fins evolved into the legs of the first tetrapod land vertebrates, so by extension an early ancestor of humans was a lobe-finned fish.
These are made of webs of skin supported by bony or horny spines (rays) which can be erected to control the fin stiffness.
Tetrapods evolved from ancient lobe-finned fishes about 400 million years ago during the Devonian Period when their earliest ancestors emerged from the sea and adapted to living on land.
Most reptiles are oviparous, although several species of squamates are viviparous, as were some extinct aquatic clades[25] — the fetus develops within the mother, contained in a placenta rather than an eggshell.
As amniotes, reptile eggs are surrounded by membranes for protection and transport, which adapt them to reproduction on dry land.
Many of the viviparous species feed their fetuses through various forms of placenta analogous to those of mammals, with some providing initial care for their hatchlings.
[30] Except for some sea snakes, most extant marine reptiles are oviparous and need to return to land to lay their eggs.
While marine birds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations.
Many species are famous for undertaking long annual migrations, crossing the equator or circumnavigating the Earth in some cases.
Marine birds can be highly pelagic, coastal, or in some cases spend a part of the year away from the sea entirely.
Some marine birds plummet from heights, plunging through the water leaving vapour-like trails, similar to that of fighter planes.
Mammals (from Latin for breast) are characterised by the presence of mammary glands which in females produce milk for feeding (nursing) their young.
There are about 130 living and recently extinct marine mammal species such as seals, dolphins, whales, manatees, sea otters and polar bears.
Seals and sea-lions are semiaquatic; they spend the majority of their time in the water, but need to return to land for important activities such as mating, breeding and molting.
