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Earth 5 million years from now

New mosasaurs are a group of large aquatic varanoid lizards that encompass the families Aquavaranidae, Marevaranidae, Pistronatatoridae, and the related offshoot species.

Like the distantly related true mosasaurs of the Cretaceous period, they are among the top predators of their time. They evolved from modern day water monitors 5 million years in the future; they survived much later, up to 130 million years from now, one of the longest of any family.

Aquavaranids

Generally accepted aquavaranid phylogeny

Lizard-whale

Most aquavaranids look like this, but with a somewhat orca-like colour pattern

EvolutionEdit

Initially, they existed in a similar manner to marine iguanas, although water monitors currently live in freshwater and coastal habitats, they could easily become better adapted to a marine existence. And in the high sea levels of the Holocene/Anthropocene, with a combined local extinction of crocodiles, they did.

They became pelagic over time as smaller marine mammals in the South Pacific and Southeast Asia experienced a decline. Eventually, their feet not only became webbed, but turn into appendages that resembled flippers more than anything else, and they developed the ability to hold their breath for longer periods. While their distribution initially remained largely limited to the area around Indonesia, Australia and Oceania, they were an extraordinarily successful clade, dominating niches otherwise held by marine mammals. Eventually, as the marine mammals all but went extinct, the New Mosasaurs took over completely, and spread out over the worlds oceans. 

The first true Aquavaranoids evolved around 5 million years in the future, and are defined from their earlier relatives by possessing the ability to tolerate saltwater for long periods, and the lack of venom, which their semiaquatic ancestors still possessed. After about 25 MyF, they had evolved a more streamlined, shark-like body plan, and soon after they took over from marine mammals. This design existed with little modification until their utimate extinction at the hands of a flood basalt eruption, some 125 million years after they evolved.

AnatomyEdit

The anatomy of Aquavaranids is complex. The earliest members of the lineage looked like terrestrial monitors, but had flattened limbs, much like penguins or seals, which were properly considered flippers. The group evolved live birth quickly after this stage, and from then exploded in diversity, producing genera that range from elongated leviathans of the shallow seas, to small pelagic ichthyosaur-like piscivores, to massive orca-like pelagic macropredators. 

The general Aquavaranid skeleton has many features adapted to aquatic life. The bones are solid and very strong, which means they are less bouyant. They also have a collapsable ribcage and relatively small lungs compared to other squamates, but more like cetaceans and some of the more traditional mesozoic marine reptiles. The ancestral water monitor had a flexible jaw that enabled it to swallow large prey whole. The shallow seas and semi-aquatic genera also kept this method of feeding, but the pelagic genera abandoned this method for a much stronger skull and more streamlined body design. The family Aquavaranidae, which is the most derived of the three families, evolved a blowhole, which enabled them to become better adapted to the open ocean, though the more primative Pistronatatoridae also had this lifestyle, and lacked a blowhole. 

Genera and SpeciesEdit

The three families of New Mosasaurs contain over 32 genera.

MarevaranidaeEdit

This family are the dominant predators of the shallow seas between Australia and South East Asia. They go extinct when their habitat is destroyed during the formation of Borealia. The genus Oravaranus is tentatively placed in this family, but is likely more basal, the sister genus to the Seal Goanna, and may be the common ancestor of the whole group.

Terreovenator (2 species)

  • Ryvena, T. thalassus

Oravaranus (5+ species)

  • Beach Monitor, O. littoralis
  • Crocmonitor, O. aquatios

Marevaranus (3 species)

  • Northern Ghost, M. grandis

Squalovaranus (1 species)

  • Lizard Whale, S. pelagicos

AquavaranidaeEdit

This family is the most advanced of the three, with all members having a blowhole, a shark-like tail fin, and a dorsal fin. Due to their frequent inhabitance of deep bays, they are commonly known as gulfies. This group was the only family to survive to the extinction of the clade.

Aquavaranus (8+ species)

  • Common Gulfie, A. orcinus
  • Snake Gulfie, A. serpentes

PistronatatoridaeEdit

This family includes the most pelagically adapted group. All members of this family have an Ichthyosaur-like body form, indeed some look superficially almost identical to the more derived ichthyosaurs. The largest species, however, have a robust skull, and look more like the modern killer whale, which they are closest to ecologically.

RelativesEdit

The New Mosasaurs went through a brief but productive evolution between the ancestral modern day water monitor and the first true Aquavaranids. Some of these species have survived. They include:

  • Seal Goanna (Neovaranus pinnipus)
  • Marine Water Monitor (Varanus marinus)

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