In the deepest parts of the ocean, the metabolic rates of animals slow down dramatically. While this means they grow slowly, it grants them sustained, uninterrupted periods of growth that can last decades or even centuries. This is one of the main driving forces behind\u00a0deep-sea gigantism<\/a>\u00a0and the reason why\u00a0colossal squids<\/a>,\u00a0greenland sharks<\/a>,\u00a0oarfish<\/a>, and other strange, deep-sea behemoths exist.<\/p>\n There are also abundant energy sources in the ocean. Yes, the open ocean may often be described as a \u2018marine desert\u2019, but there are\u00a0areas of deep-sea nutrient upwelling<\/a>\u00a0where small, energy-dense prey like krill congregate in their billions. These \u2018ocean oases\u2019 are veritable buffets, particularly for filter-feeders like baleen whales<\/a>, and provide the immense amount of calories needed to sustain giant body sizes.<\/p>\n The factors that facilitate gigantism in the ocean aren\u2019t just affecting animals now, they\u2019ve affected them ever since the emergence of complex life roughly half-a-billion years ago. In the last few hundred million years, the ocean has seen many giants come and go (and some stick around until the present day). <\/p>\n Here are 10 of the largest, in no particular order\u2026<\/p>\n 10 biggest marine animals The largest animal that has ever lived is still alive today. The\u00a0blue whale<\/a>, or\u00a0Balaenoptera musculus, is a real-life Leviathan, measuring up to 33m in length and weighing up to 200 tons. Its tongue alone weighs as much as an adult\u00a0elephant<\/a>\u00a0and its heart is roughly the size of a baby grand piano – the aorta that carries oxygenated blood away from this huge heart is so wide that a small child could crawl through it!<\/p>\n These supersized statistics make blue whales the heaviest animals of all time, surpassing even the most fanciful estimates of the\u00a0heaviest known dinosaurs<\/a>.\u00a0<\/p>\n Argentinosaurus, the largest dinosaur<\/a> that ever lived, may have been longer than a blue whale at 40m, but weighing in at\u00a0just\u00a090 tons, it was less than half the mass of the heaviest blue whale ever recorded – a 190-ton female caught in the Southern Ocean near Antarctica in 1947.<\/p>\n Otodus megalodon While it may be long gone, having faced extinction roughly 3.5 million years ago,\u00a0megalodon<\/a>\u00a0still makes some people think twice before they dip their toes in the ocean – no thanks to the conspiracy theorists perpetuating the myth that this giant shark still exists.<\/p>\n At roughly 20m in length, or 24.3m if the most recent size estimates are to be believed,\u00a0Otodus megalodon\u00a0is not only the largest shark that has ever lived, but the largest fish. At the upper end of its estimated size range, it was more than twice the length of the largest fish alive today, the\u00a0whale shark<\/a>\u00a0(Rhincodon typus).<\/p>\n Like their close cousins great whites<\/a>, megalodon were apex predators<\/a> and rather indiscriminate hunters, preying on everything from whales, dolphins, seals<\/a>, and turtles<\/a>, to other sharks.<\/p>\n Perucetus colossus The clue is in the name when it comes to this particular species of early whale.\u00a0Perucetus colossus\u00a0belongs to a family of cetaceans known as the basilosaurids, which were some of the first whales to look like, well, whales. Before basilosaurids appeared, the\u00a0ancestors of whales<\/a>\u00a0had four limbs, looked something like a cross between seals<\/a> and dogs<\/a>, and – believe it or not – spent much of their time on land.<\/p>\n These first cetaceans were dwarfed by the fully aquatic, 20m-long\u00a0Perucetus colossus\u00a0– an animal that, following its discovery, was claimed to have\u00a0rivalled or even exceeded the modern blue whale in terms of weigh<\/a>t – the largest estimates suggesting a max weight of 340 tons!\u00a0<\/p>\n However, a later study argued that such estimates were physically impossible for an animal that was significantly shorter than a blue whale. The researchers involved in this particular study estimated a max weight of 70 tons, which is roughly the weight of a\u00a0modern sperm whale<\/a>.<\/p>\n Ichthyotitan Measuring nearly 25m from snout to tail,\u00a0Ichthyotitan\u00a0is only a few metres shorter than a blue whale<\/a>. This makes it the largest marine reptile ever discovered and, by far, the largest animal from the Late Triassic (205 to 202 million years ago).<\/p>\n This slender-snouted monster belongs to a family of ichthyosaurs known as the shastasaurids, which had a near global distribution and inhabited warm, shallow seas where prey was particularly abundant. They\u2019re thought to have hunted a variety of different animals, from cephalopods and molluscs to other marine reptiles.<\/p>\n Ichthyotitan\u00a0was\u00a0described as recently as 2024<\/a>, following the discovery of several fossils<\/a> by an avid, 11-year-old fossil collector and her father on a\u00a0beach in Somerset, south-west England<\/a>.<\/p>\n Fin whale (Balaenoptera physalus) At 26m in length and 80 tons in weight,\u00a0fin whales<\/a>\u00a0(Balaenoptera physalus) are the second-largest animals alive today, after blue whales. They may also be the second-largest animals to have ever lived, larger even than\u00a0Ichthyotitan.<\/p>\n As their latin name suggests, fin whales are closely related to blue whales. The two species<\/a> belong to the same genus (Balaenoptera) and are thought to have diverged during the Late Miocene, roughly 8.4 million years ago. Despite diverging a long time ago, fin whales and blue whales are known to\u00a0successfully interbreed<\/a>\u00a0and produce fertile offspring.<\/p>\n Like blue whales, fin whales are found in all major oceans, from polar to tropical waters. They\u2019re filter feeders too and rely on krill, small schooling fish, and squid<\/a> to fill their bellies and meet their enormous daily energy demands – which can be as high as 20 million calories, the equivalent of 39,293 McDonald\u2019s Big Macs!<\/p>\n Nanaimoteuthis haggarti The giants discussed so far have all been vertebrates;\u00a0Nanaimoteuthis haggarti\u00a0bucks this particular trend as the largest non-colonial invertebrate ever discovered. This\u00a0kraken-like creature<\/a>\u00a0belongs to a family of octopuses<\/a> known as the cirrate octopuses, which today live exclusively in the deep-sea.<\/p>\n Nanaimoteuthis haggarti\u00a0was discovered back in 2008, but a recent study<\/a>, published in April 2026, re-examined existing material and managed to paint a clearer picture of this boneless behemoth. Based on some novel modelling, the researchers involved in this latest study estimated\u00a0Nanaimoteuthis haggarti\u00a0could have grown to sizes of 19m.<\/p>\n This makes\u00a0Nanaimoteuthis haggarti\u00a0almost twice the size of today\u2019s largest cephalapod, the colossal squid<\/a>, and nearly four times the size of the largest living species of octopus – the\u00a0giant Pacific octopus<\/a>. However, not everyone agrees with these estimates; several prominent body size experts have already poked holes in this recent study.<\/p>\n Right whale (Eubalaena) While they may tip the scales at a similar weight to fin whales<\/a>, right whales are nowhere near as long and slender. These stocky cetaceans average 15.5m in length, which is roughly the length of just one standard school bus.<\/p>\n There are three different species of right whales: the\u00a0North Atlantic right whale<\/a>\u00a0(Eubalaena glacialis), the North Pacific right whale (Eubalaena japonica) and the southern right whale (Eubalaena australis). They\u2019re all similarly sized, but it’s the North Pacific variety that takes the title of \u2018largest\u2019.<\/p>\n How right whales got their name is unclear. Some suggest it\u2019s because they were historically regarded as the\u00a0right\u00a0ones to hunt, as they float when killed and tend to swim within sight of shore. Today, the North Atlantic and North Pacific species are some of the\u00a0most endangered whales in the world<\/a>.<\/p>\n Leedsichthys Megalodon may be the largest fish that ever lived, but as a cartilaginous fish, it\u2019s excluded from the rankings of the largest ever\u00a0bony\u00a0fish.\u00a0That title instead belongs to\u00a0Leedsichthys, a 16.5m-long ray-finned fish that lived during the Jurassic (165 to 148 million years ago). It dwarfed the largest bony fish alive today – the\u00a0giant sunfish<\/a>\u00a0– reaching roughly five times its size.<\/p>\n Like many ocean-cruising giants,\u00a0Leedsichthys\u00a0was a filter feeder that used thousands of pipecleaner-like structures attached to its gill arches to extract zooplankton and other small animals from the water column. It likely occupied a similar niche to today\u2019s whale sharks<\/a>,\u00a0basking sharks<\/a>, and baleen whales<\/a>.<\/p>\n Tylosaurus rex<\/p>\n It might share its name with the largest meat-eating dinosaur that ever lived, but this isn\u2019t the\u00a0T.rex<\/a>\u00a0we all know and recognise.\u00a0Tylosaurus rex\u00a0belongs to a group of ancient marine reptiles known as mosasaurs, and based on some early estimates it may be the largest of its kind, measuring 13.2m from snout to tail.<\/p>\n As well as being roughly twice the length of the largest great white sharks<\/a>,\u00a0Tylosaurus rex\u00a0is thought to have been a lot \u2018meaner\u2019 than other mosasaurs. This is based on studies<\/a> of specimens that show clear evidence of intraspecies aggression, such as fractured lower jaws that could have only been inflicted by members of its own species<\/a>.<\/p>\n Tylosaurus rex\u00a0was described in May, 2026, based on a specimen nicknamed \u2018Bunker\u2019. This specimen was initially assigned to another species,\u00a0Tylosaurus proriger, but a recent re-examination concluded that it was different from all other known specimens and was substantially larger, warranting the designation of a new species.<\/p>\n Coral reefs While many might not view coral<\/a> as \u2018animals\u2019, they are indeed members of Animalia. They belong to a phylum known as Cnidaria, which includes other strange invertebrates that often blur the lines between animals and other forms of life, such as jellyfish<\/a>, hydroids<\/a>, and sea anemones<\/a>.<\/p>\n Not all corals are colonial – some are solitary and exist as single, individual organisms – but the largest are, forming massive colonies made up of thousands of genetically identical polyps that house billions of symbiotic, single-celled organisms called zooxanthellae. These colonies function like a single organism and are known to share nutrients from polyp to polyp.<\/p>\n The largest continuous colony ever found measures 34m by 32m and is thought to be more than 300 years old! This colossal colony can be seen from space and is made up of a type of hard coral known as\u00a0Pavona clavus, or shoulder blade coral. It\u2019s located just off the coast of the Solomon Islands in the South Pacific and was\u00a0discovered by citizen scientists<\/a>\u00a0participating in the Great Reef Census in 2024.\u00a0<\/p>\n Top image: A close-up of a humpback whale. Credit: Stanislav Stelmakhovich\/Getty Images <\/p>\n","protected":false},"excerpt":{"rendered":"It\u2019s not a coincidence that nearly all of the largest animals that have ever existed lived underwater. Thanks…\n","protected":false},"author":2,"featured_media":830788,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[26],"tags":[49,48,66,323],"class_list":["post-830787","post","type-post","status-publish","format-standard","has-post-thumbnail","category-wildlife","tag-ca","tag-canada","tag-science","tag-wildlife"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/830787","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/comments?post=830787"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/830787\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media\/830788"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media?parent=830787"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/categories?post=830787"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/tags?post=830787"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
\nBlue whale (Balaenoptera musculus)
\n![\"A](\"https:\/\/www.newsbeep.com\/ca\/wp-content\/uploads\/2026\/07\/960px-Anim1754_-_Flickr_-_NOAA_Photo_Library.jpg\")
NOAA Photo Library, Public domain, via Wikimedia Commons<\/p>\n
\n![\"MEGALADON](\"https:\/\/www.newsbeep.com\/ca\/wp-content\/uploads\/2026\/07\/GettyImages-1345530710-2-scaled.jpg\")
MEGALADON 3D rendering. Racksuz\/Getty Images<\/p>\n
\n![\"Perucetus](\"https:\/\/www.newsbeep.com\/ca\/wp-content\/uploads\/2026\/07\/960px-Perucetus_colossus_Holotype_skeletal_drawing.png\")
Perucetus colossus Holotype skeletal drawing. Ivan Iofrida, CC BY-SA 4.0, via Wikimedia Commons<\/p>\n
\n![\"Ichthyotitan](\"https:\/\/www.newsbeep.com\/ca\/wp-content\/uploads\/2026\/07\/960px-Ichthyotitan_severnensis_speculative_restoration.png\")
Ichthyotitan severnensis speculative restoration. This paleontological restoration is highly hypothetical, as very little fossil material of the animal is known. Ansh Saxena 7163, CC0, via Wikimedia Commons<\/p>\n
\n![\"Fin](\"https:\/\/www.newsbeep.com\/ca\/wp-content\/uploads\/2026\/07\/GettyImages-1336087306.jpg\")
wildestanimal\/Getty Images<\/p>\n
\n![\"The](\"https:\/\/www.newsbeep.com\/ca\/wp-content\/uploads\/2026\/07\/960px-Nanaimoteuthis_hikidai.jpg\")
The holotype specimen of\u00a0Nanaimoteuthis hikidai. Tanabe, Kazushige, Akihiro Misaki, and Takao Ubukata., CC BY 4.0, via Wikimedia Commons<\/p>\n
\n![\"Southern](\"https:\/\/www.newsbeep.com\/ca\/wp-content\/uploads\/2026\/07\/GettyImages-2172441490.jpg\")
Southern riight whale (Eubalaena australis). Julian Gunther\/Getty Images<\/p>\n
\n![\"Life](\"https:\/\/www.newsbeep.com\/ca\/wp-content\/uploads\/2026\/07\/960px-Leedsichthys_paleoart.jpg\")
Life reconstruction of Leedsichthys problematicus. This paleontological restoration is highly hypothetical, as very little fossil material of the animal is known. LiterallyMiguel, CC BY 4.0, via Wikimedia Commons<\/p>\n
\n![\"coral](\"https:\/\/www.newsbeep.com\/ca\/wp-content\/uploads\/2026\/07\/GettyImages-2274310160.jpg\")
Avatarmin\/Getty Images<\/p>\n