Swordsharks and Swordwhales

Swordsharks were significant ocean predators in Serinan seas for most of Serina's history throughout the Cryocene. Descended distantly from the Xiphophorus fishes (platies and swordtails) they filled the niche of sharks on Earth and broadly resemble a cross between a shark and a barracuda. Swordsharks had large, extensible jaws lined with dozens of sharp teeth, which were replaced throughout their lifetimes, and they were without exception carnivorous. The smallest species would have fit into a modest home aquarium, while the largest became monstrous apex predators, some of whom could reach lengths as long as a school bus, and surely were capable of hunting almost anything they wish to in the sea. They had large eyes, and unlike sharks were predominately visual hunters. Most species fed predominately on living prey and were fast and agile swimmers. They would also feed on carrion if they come across it, but only a small percentage make a habit of regularly scavenging as, also unlike sharks, most of them lack a particularly keen sense of smell.

Swordsharks as a clade were named for the appearance of their earliest representatives, some of which utilized an elongated lower tail fin to thrash through shoals of bait fish and stun them. Most such forms went extinct at the Cryocene-Thermocene boundary ocean acidification event. The surviving groups which reclaimed the open seas were more likely to belong to more generalized, small shallow-water predator guilds. The hunting techniques of the most specious group of surviving modern representatives, now called swordwhales, usually rely on either ambush from cover or from underneath sediment, in which cases the fishes have developed flattened bodies and highly reduced buoyancy, or active pursuit in fast, agile open water predators, with the prey being caught in the jaws which are either very strong and durable for biting and holding large prey or highly elastic and can be shot forward at rapid speed to grab small prey. Swordwhales since the end Cryocene have again become ecologically diverse and make use of many different diets, however, in addition to fish; some groups have evolved crushing molars to smash shellfish, while others have even become parasitic, biting and twisting away small circular plugs of tissue from other large fishes. The largest species have adopted filter-feeding techniques; their teeth absent or vestigial, they cruise along the surface and suck up whole shoals of copepods and shrimp with massive gapes.

With relatively large brains, some the surviving swordwhales could be considered very intelligent among fishes. Some are even social, not simply in a shoaling way, but working in groups to hunt. They cooperate in team to corral shoals of fish into tight formations which can be more easily managed. These tendencies evolved earlier in their line's descent; during the middle Cryocene there even existed a lineage of large, social swordshark in which the female which guarded its young in the safety of a pack until they were large enough to fend for themselves. Unfortunately, this group did not survive the end of the Cryocene, with modern representatives migrating to sheltered coastal environments to birth their young before abandoning them to their fate. The babies are born entirely capable to fend for themselves and proportionally large to their mother in litters which can range from just a couple in some large species to ten or more in the smaller types. All swordwhales nourish their developing young via a placental tie, giving birth to a few large offspring. This tendency is inherited from earlier swordshark ancestors.

The painted gulpy is the largest swordwhale, and one of the largest fish ever to evolve. It is a gentle giant, feeding upon plankton that it filters with rakers in its gills. The sexes are highly dimorphic, with males being very colorful and competing to attract the larger, more subdued females.