This article, file, template, or category has been reviewed.

Click here to see the review.

This page is part of What if the Asteroid Missed?, a project run by member KaptainWombat.

The oceans are Earth's largest habitat, so it is no surprise that they are teeming with life.

Herpetocetacea (Mosasauria)Edit


A selection of mosasaurs, from top to bottom they are 1) lesser plungediver, 2) carcharine delph, and 3) greater saurca

The largest and most feared animals in the sea are the Mosasaurs, now a clade encompassing several families, the orca-like saurcas, or Squalosauridae; the massive sperm whale-like plungedivers, or Abyssosauridae; the graceful dolphin-like delphs, or nuticosaurs; and the walrus-like wolros, or Odobenocetidae. Because of the diversity of mosasaurs that have evolved, most scientists have elected to rename the clade the Herpetocetacea, the "reptilian whales". For convenience however, the clade will still be known as the mosasaurs.


The piscisauroideans are the dominating group of mosasaurs today, containing over 30 species. The group contains several families, each being classified by the shape of their teeth. All piscisauroideans evolved in the Paleocene from Plotosaurus, and as such, are convergently quite similar to whales and ichthyosaurs.

Squalosauridae (Saurcas)Edit

The saurcas are massive apex predators that will attack anything that they know is edible, and have sharp, serrated teeth. They generally live in large pods, similar to home earth killer whales. The family includes 7 species, ranging from the 6 metre Arctic saurca to the 13 metre greater saurca, the apex predator of the open seas. Saurcas are the fastest marine reptiles that currently live, and can easily outswim almost all of their prey, save for the fastest bony fish. Unlike home earth orcas, the saurcas don't have localized pod preferences toward particular prey, though they more consistently target other mosasaurs in the Atlantic Ocean, while those in the Pacific and Indian Oceans largely subsist on sharks and gigafish. The waters around the southern coast of Australia and New Zealand, and around South Africa, harbour the largest of these monsters, with a record 14 metre individual observed in Bass Strait. Despite their predatory attitude, and unusual willingness to flip boats, saurcas have never been known to kill people in the wild.

Sample species:

  • Common saurca, Squalosaurus navigans

Abyssosauridae (Plungedivers)Edit

The plungedivers are huge deep divers that hunt for giant squid in the depths, they don't actually closely resemble sperm whales, but have similarly small and reduced teeth, a diet of deep sea cephalopods, and massive body size. The family includes three species, with the moby plungediver being the most commonly seen species. Plungedivers are the largest modern day mosasaurs, and by extension the largest living animals, reaching up to 25 metres long and weighing up to 80 tons.

Sample species:

  • Moby plungediver, Abyssosaurus mergus

Nuticosauridae (Delphs)Edit

Delphs are very similar to dolphins and ichthyosaurs, and are rather intelligent compared to other mosasaurs; this intelligence has led some scientists to include the Squalosauridae as part of Nuticosauridae, though this is debated. Most delphs have small conical teeth. Delphs are very social animals, and will work together to herd baitfish.

Sample species:

  • Spotted delph, Nuticosaurus varius


This group is restricted to one family of Arctic mosasaurs, though they were once more diverse.

Odobenocetidae (Wolros)Edit

The wolros don't appear to be closely related to any other mosasaurs, and some people have found them to be part of a lineage that had its origins with the Late Cretaceous Globidens. Though they fill the niche of walruses, they aren't restricted to the poles and have been sighted almost anywhere in the northern hemisphere where there is a mollusk field of sufficient size to support them. Wolros lack the tusks of their Home Earth mammalian counterparts. In some situations, large gangs of wolros will often opportunistically attack large land animals.

Odobeocetoideans were once very diverse, occupying niches of most of the large toothed whales today, but in the Miocene, their diversity waned dramatically, and the whole group is now restricted to the colder latitudes of the northern hemisphere, where they eat bivalves and crustaceans.

Sample species:

  • Greanland wolros, Odobenocetus greenlandicus
  • Pacific wolros, Odobenocetus pacificus

Other MosasaursEdit

Controversial fossils from Europe suggest that "true mosasaurs" (those in the family Mosasauridae) may have survived until as recently as the late Miocene with the genus Deinoneustes, which probably went extinct in the Messinian Salt Bowl event. Elsewhere, the mosasaurids had long since been outcompeted by their pelagic descendants. One group of archaic mosasaurs survives to the present day, however, the Cetivenandidae.

  • The skull of Globidens, the ancestor of the Odobenocetoidea
  • The skull of Plotosaurus, the ancestor of the Piscisauroidea
  • The skull of Tylosaurus, the ancestor of the Cetivenandidae
  • Evolution of modern mosasaur groups

Cetivenandidae (Leviathans, Caddies)Edit

The Cetivenandidae family has been traced directly to Tylosaurus. The family has somewhat converged with the Ppiscisauroids, but has retained the serpentine shape and built on it, with the neck growing longer, so that the front flippers are about half way down the body. The modern cetivenandi, or leviathan, is one of the longest living mosasaurs at over 22 metres, although a skull and some vertebrae from a related, but even larger, mosasaur have been found in late Miocene to early Pliocene sediments in Europe, North America, Australia, and New Zealand. This extinct species is the longest known animal to ever evolve since the Jurassic, and far outclasses any known Cretaceous mosasaur. 

The only other known modern cetivenandid is a presumably common but rarely seen animal from the Pacific coast of North America. In conjunction with real Home Earth sightings of sea monsters in this area, the animal has been called the "caddie", which is derived from the Home Earth monster's pseudoscientific name, "Cadborosaurus". Unlike its infamous larger cousin, the caddie is a relatively small, secretive animal.

Sample species:

  • Leviathan, Cetivenandus carnifex
  • Cetivenandus dracones
  • Caddie, Carcharoserpens conger

The oceans aren't all about mosasaurs, however, there are also giant fish that fill the niche of baleen whales in Home Earth, large lamniform sharks, relict plesiosaurs, and even seal-like monotremes around southern Australia, New Zealand and Antarctica. Above the waves are a vast array of seabirds, many of which are similar to forms that exist on home earth, but some are members of the Ichthyornithiformes, and bare teeth in their beaks. In fact, one species of ichthyornithiform bird looks so similar to seagulls that people mistook as one until it opened its mouth and revealed a set of teeth. People called it "Satan's scary seagull" as a joke, but the name has stuck ever since. Sharing the skies with the seabirds are hydras, enormous pterosaurs descended from azhdarchids.


Plesiosaurs are now rather rare, though they are found in all oceans.


Ever since the mid Cretaceous, when the last of the pliosaurs died out, the Plesiosauria have been represented solely by the Plesiosauroidea.

Elasmosauridae (Bergs, etc.)Edit

Elasmosaur skeleton

The neck of the ROM Elasmosaurus mount; Elasmosaurus was a close relative of the direct ancestors of the berg

The elasmosaurids are the more diverse family of surviving plesiosaurs. There are four known living species, the largest and most studied elasmosaur, and largest living plesiosaur is the berg, or Svalbardinia, which measures close to 10 metres long and weighs over 3 tons. The Berg is an inhabitant of the Arctic Ocean, particularly around the island of Svalbard, and is a large, slow swimmer, comparable to its extinct relative, Elasmosaurus, though with a shorter neck. The carcass of a beached berg can attract arctic predators from miles around.

The other three species belong to the poorly known genus Surpestesaurus, which has been noted for its resemblance to a small fossil plesiosaur in early Paleocene rocks, hence the name, which means "survivor lizard". It is not clear as to whether this small species is closely related to the living members, however.

Sample species:

  • Berg, Svalbardinia svalbardensis
  • Surpestesaurus

Hastilodontidae (Spearteeth)Edit

The only other surviving plesiosaurs are the spearteeth, which occur in waters almost anywhere. Spearteeth are part of the family Hastilodontidae, which evolved out of the small pliosaur-like polycotylid plesiosaurs at the start of the Eocene.

Sample species:

  • Speartooth, Hastilodon cosmopolitus.


The early Cenozoic was a time of diversification for dinosaurs, and one lineage of ornithopods took to the seas in search of seagrass.

Sirenisauridae (Durgs)Edit

While many people associate plesiosaurs and mosasaurs with dinosaurs, true aquatic dinosaurs are not known from the Mesozoic. Cenozoic dinosaurs, however, experimented with many shapes and forms. One of the most successful lineages produced the durgs, or sirenisaurids. Durgs are related to land-dwelling dinosaurs like the hadrocorn, and are ornithopods. Unlike other herbivorous dinosaurs, durgs are aquatic. Like home earth sirenians, from which they derive their name, durgs feed on seagrass, kelp, and occasionally crustaceans and echinoderms, in shallow waters around the world, though most of the 6 known species live in the Pacific Ocean. Durgs are generally large animals, averaging 800 -1000 kg, but one species, the bruton, is much larger, over 2 tons, with the largest individuals weighing over 3 tons. Brutons are not particularily gregarious, but are not often seen alone. The herds provide protection for many animals, including delphs, wolros, smaller durgs, small gigafish and sea turtles. The only animal large enough to tackle a bruton is the cetivenandi, an enormous, and rare, relict serpentine mosasaur. But even these leviathans won't dare to go near a herd of elephant sized brutons. Like all dinosaurs, durgs leave the water to lay eggs, and still have well developed hind limbs to enable them to do so.

Sample species:

  • Bruton, Sirenisaurus maximus


Like the majority of living pterosaurs, the oceanic pterosaurs are descended from the family Azhdarchidae. Driven to the seas by competition with their relatives, the smaugids, the Hydroazhdarchidae have evolved into masters of the air.


Like nearly all living pterosaurs, hydroazhdarchids are descended from the azhdarchids.

Hydroazharchidae (Hydras)Edit

Like many large seabirds, the hydras have long narrow wings, with relatively small bodies. This enables them to fly for days on end, and with very little effort. Like their ancestors, hydras have huge heads, but their necks are much shorter for the size of their body. The family as a group are cosmopolitan, living on all continents, including Antarctica, and almost all known islands. The island of Hawai'i, in particular, has a huge colony of Pacific hydras, composed of almost half of a million members, which nest in the saddle of the two largest volcanoes on the island. The biggest and most wide ranging species, the so called "pteroplane" has a wingspan of almost 15 metres, making it the biggest known pterosaur of all time, based on wingspan.

Sample species:

  • Pteroplane, Hydroazhdarcho vivamus
  • Pacific hydra, Hydroazhdarcho pacificus

Marine MammalsEdit

Marine mammals are much less diverse than they are in home earth, with only seal-like niches being occupied.

Trunkocetacea (Trunkos)Edit

Unlike on home earth, marine mammals are comparatively rare, with the only completely aquatic species being from the common, but poorly understood order, Trunkocetacea. "Trunkos", as they are known, are large animals, being up to 2 tons in weight, and are distinguished by the presence of a trunk, similar to an elephant seal. Trunkos are similar in many aspects to archaeocete whales, and many species resemble animals like Ambulocetus, though the presence of mosasaurs restricts the group to a coastal lifestyle, like pinnipeds. The evolution of trunkos is almost unknown before the Miocene, and it may be that they evolved out of the newly evolved Wargidae family around that time. However a jaw bone, tentatively placed in this group, which predates the Wargidae has been uncovered in sediments in North America. One of the larger species, the Atlantic alligator otter, or "ottergator", is found in the North Atlantic, particularly in the North Sea, and has taken a liking to terrestrial prey, which it ambushes crocodile style at the water's edge. 

Sample species:

  • East African Ttrunko, Trunkocetus typus
  • Atlantic alligator otter, Vitalestes crocodylus

Cryovociferatidae (Skrylens, Bunyips)Edit

The Cryovociferatidae are a family of marine monotremes that are found in the Southern Ocean, and nest on Antarctica, southern Australia and New Zealand. The earliest marine fossils of the family are known from late Oligocene sediments, though the family are known from the Eocene in Australian terrestrial sediments, with one species, known as the bunyipus, being almost entirely terrestrial, occupying the ecological niche of the modern home earth Wolverine, though being quite a bit larger. Aside from this living relic, the rest of the species are derived, marine, seal-like animals. The largest species is the Antarctic skrylen, which can weigh in at almost a ton, and is the largest known monotreme.

Sample species:

  • Antarctic skrylen, Cryovociferatos antarcticus


The Chondrichthyes, which includes the sharks, rays and chimeras, are more or less the same as those on Home Earth, as many modern species had their origins in the Cretaceous, but there are several lineages that are extinct in Home Earth that have persisted to the present.


In home earth, the lamniformes are a well known group of sharks, including such infamous species as the great white shark. In this realm, these sharks are just as prominent, if not more so.

Anacoracidae (Hárkarl, Chainsaw Sharks)Edit

In most of the oceans there are giant sharks as big as orcas, known as Hárkarl, which are probably descendants of the common cretaceous shark Squalicorax, although some studies show it as part of the otodontid lineage, which in home earth included the famous megalodon.

The hárkarl was first discovered in the North Atlantic near Iceland ("hárkarl" is an old Icelandic name for the Greenland shark) but have since been found in other parts of the world and probably have a cosmopolitan distribution. The hárkarl is the largest predatory shark in this ocean; at 9 metres long, they are comparable in size to Home Earth basking sharks and smaller estimates for C. megalodon, and considerably bigger than any similar shark on Earth today.

Another odd shark is the chainsaw shark, which has a rostrum similar to that of sawfish, but lives a pelagic life. Chainsaw sharks are one of the biggest dangers for fishermen in small boats, even though the sharks themselves are only a modest size for a shark. Unlike the sharks' real teeth, the "teeth" on the saw are dermal denticles, and are not readily replaced if they are broken off. The chainsaw shark is, like all modern anacoracids, a descendant of Squalicorax, but has taken an unusual evolutionary path that no Home Earth shark ever did. Chainsaw sharks primarily inhabit the shallow coastal seas, rarely going into the open oceans.

Sample species:

  • Hárkarl, Carcharex atlanticus
  • Chainsaw shark, Carcharopristis motor


Giant filter-feeding marine tetrapods never evolved in this timeline, but giant filter feeding fish, known as "gigafish", are common. Gigafish are part of the order Pachycormiformes, which were common in the Mesozoic but are completely extinct in Home Earth. Also extinct in home earth, the Ichthyodectiformes have survived with an impressive diversity. Most other fish, from familiar Home Earth groups, are all relatively unchanged.

Pachycormiformes (Gigafish)Edit

Pachycormiformes are an ancient group of bony fish that split off crom their nearest relative, the Bowfin, in the Triassic. While their freshwater relative survives to the present in both timelines, the Pachycormiformes went extinct at the end of the mesozoic. In this timeline, they survived, and have taken up niches of baleen whales. In the Miocene, cooling ocean temperatures encouraged the growth of huge swarms of krill, and the evolution of another lineage of giant Pachycormiformes evolved. These giants are known as 'gigafish', and are the largest bony fish to have ever existed, even larger than Leedsichthys, with some giants being up to 25 metres long, though being fish with no blubber and light thin bones, no species even comes close to the weight of a whale of the same length. Some 15 species of gigafish are known, ranging from 4 to 25 metres long.

Cribubranchidae (Gigafish)Edit

This is the family to which all gigafish belong.

Ichthyodectiformes (Zifactins, Terror Tuna, Dinopike)Edit

This order also perished at the K-Pg boundary on home earth, but like the ancestors of the Gigafish, they have survived with impressive diversity in WitAM. Both of the Mesozoic families, the Ichthyodectidae and Saurodontidae, have persisted strongly through the Cenozoic, with the latter being the more common. Ranging from 40 cm to 5 metres in length, they are dangerous predators, the equivalents to home earth Carcharhinid sharks and barracudas.

Ichthyodectidae (Zifactins)Edit

These fish are predominantly predatory, and seem to prefer smaller fish, including smaller members of their own species. Modern genera and species are all generally named zifactins, largely because of their resemblance to their extinct relative Xiphactinus, though this is largely convergent. There are roughly four species of zifactin, all measuring over 2 metres long, with the largest being over 4 metres long. Like many fish, they often swallow large prey whole, resulting in the death of the predator on occasions. Adult Bulldog Zifactin are even known to target small mosasaurs and in some areas crocodiles. There is also a substantial collection of reports of attacks on swimmers by this fish.

Sample Species:

  • Bulldog Zifactin, Taurichthys megalops.

Saurodontidae (Terror Tuna, Dinopike)Edit

Saurodonts of both timelines were/are large, generally predatory fish that share a common ancestor with the Ichthyodectidae in the Jurassic. Today they are found in all oceans, from the surface to depths of over 500 metres, from the poles to the equator. The family is split into two subfamilies, both of which are predominantly marine, though have rather different lifestyles.

Pavorichthyinae (Terror Tuna) Edit

The pelagic Pavorichthyinae, are mostly found around offshore drop-offs, and are voracious, though relatively small fish that live in small schools. Some species of 'Terror Tuna' as they have been commonly referred to, are fished commercially in the Atlantic.

Sample Species

  • Tooth Tuna, Pavorichthys typus.
Deinesocinae (Dinopike) Edit

The other prominent subfamily of saurodonts, the Deinesocinae, are rather different. Most members are large, solitary ambush predators, in many ways equivalent to crocodiles, and are often found quite far upstream, in brackish lakes and lagoons of the temperate northern hemisphere. Dinopike, as they are known internationally, are technically the largest river fish of WitAM, as the biggest known specimen, a 5 metre titan hooked in the fertile waters of the recently deglaciated St Lawrence Estuary, though Dinopike of various species are more common along coastlines. The characteristic tooth at the end of the lower jaw of mesozoic saurodonts is still presant in Dinopike, though it is now used more as a streamlining tool to swim between reeds and thick kelp more efficiently. These teeth have been dredged out of recent sediments in several of the lakes along the Atlantic Coasts.

American Dinopike, Deinesox deglaciator.


Cephalopods are as common in WitAM as they are in home earth, though the familiar groups - octopus and squid - are much less dominant and face stiff competition from the belemnites. The ammonites, once the dominant marine invertebrates during the entire time period from the caboniferous to the mid cretaceous, have all but gone, and are entirely almost absent from the top 1 km of the ocean. Below this line however, ammonites still exist in large numbers, slowly bobbing along in their eternal search for food. The nautilus of WitAM is not significantly different from the home earth ones, with the excepion of the bright red almost fluorescent eyes that they aquire during the breeding season.

Hastateuthia (Spearsquids)Edit

The spearsquids, also called needlesquids, despite their name, are not true squids, but belemnites, and they get their name from the shape of their pen, which is long and thin, with a sharp point at the end, and is so strong that only the powerful jaws of large sharks and mosasaurs can significantly damage them. Spearsquids are similar in their lifestyle to needlefish and flying fish, and some species are able to glide long distances above water, up to several hundred metres. Their jet propulsive mode of swimming is highly developed, and the highly streamlined shape of their mantle enables the cephalopods to accelerate to speeds of over 100 kph over distances of up to 20 metres under water, enough to escape most predators. Due to these habits, they have been often locally called 'missilesquids' and 'rocketsquids'. In some circumstances, the force of the acceleration is enough to puncture metal hulled boats. Ocean going vessels have to be reinforced with sheet steal and rbber to avoid prolonged damage. There are some 300+ species of spearsquids, ranging from less than 30 cm to over 3 metres long in the cold polar waters. 


This group is the last surviving group of ammonites, and is composed of two families of mostly deep sea creatures with similar lifestyles.