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Chonhead

HISTORY[]

The chondrichthyans (hybodonts, sharks, rays and chimeras) are jawed fish that possess skeletons made out of cartilage rather than bone. An ancient and phenomenally resilient group of fish, they combine extreme morphological refinement with archaic features that are little-changed from their Devonian ancestors. In either timeline, they include some of the weirdest, biggest and most feared creatures in the sea.

While concentrating on those forms that are unique to Spec, it must be stressed that the chondrichthyan faunas of both timelines share remarkable overall similarities. In fact, Spec and Home-Earth share at least 60 % of their cartilaginous fish species. Any diver or fisherman from Home-Earth who is suddenly dropped into the seas of Spec should be able to recognise some familiar toothy-grins.

The vast majority of shared species groups belong to forms whose fossil record extends well back into the Mesozoic Era. When one considers that these clades have remained essentially unchanged in our timeline since the Cretaceous or even the Jurassic, it is not surprising that they have shown a similar degree of resilience and conservatism on Spec.

HYBODONTIFORMES[]

Hybodonts are shark-like chondrichthyans that were common and widespread during the Late Jurassic and Early Cretaceous. They are believed to be an early evolutionary offshoot on the line that led to the true-sharks and rays (the Neoselachii). Hybodonts have an unusual, heterodont dentition combining piercing anterior teeth and flat, crushing posterior teeth. They retain some primitive features that have been lost or refined in the more derived true-sharks – for example hybodonts have a primitive amphistylic jaw suspension as opposed to the hyostylic suspension (articulations that permit a greater range of jaw positions) of neoselachians and chimeras.

Hybodonts became increasingly rare towards the end of the Cretaceous, at least in part because of competition with the true sharks. Whereas the last hybodonts of Home-Earth faced oblivion at the close of the Mesozoic, those on Spec managed to cling to life. Their main saving grace was in being some of the few chondrichthyans to have found a foothold in freshwater habitats. Today, fewer than ten known hybodont species remain, mostly conservative freshwater forms in Africa and the Americas. The odd one out is the backscratcher, a highly aberrant and specialised creature of the deepest oceans.

Backscratcher (Bathydrepanus rodloxi)[]

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Backscratcher, Bathydrepanus rodloxi, right-side-up (circumglobal in very deep oceans)

The first evidence of this creature were several rib-like bony structures that were recovered in deep sea dredges. No one knew what they could be, however their shape and rough inner texture provided a useful tool for itchy crewmen, giving rise to its common name of "backscratcher". It was some time before this incredible fish was finally seen in the flesh and identified as the sole-surviving marine hybodont. It is a rare species, up to 2 metres long, that lives at the base of seamounts at depths of over 2000 m.

Its most striking feature is the huge, curved dorsal spine that arches forwards over the animal’s head. This chisel-like structure is continually regrowing and resembles an enormous rodent-incisor. When foraging on the seafloor, the sharks flips onto its back, searching for invertebrates buried in the substrate with the ampullae of Lorenzini arranged over the top of it’s head. Upon finding a clam or sand-dollar, it drives the spine into the mud, latching it onto the target. Powerful adductor muscles to move the spine with a strong vertical motion and the unfortunate invertebrate is forced to the surface, straight into the shark’s upturned jaws where batteries of crushing teeth make short work of it.

LAMNIFORMES[]

This is an exclusively marine neoselachian clade that has included some of the top oceanic predators since the Late Cretaceous. Lamnoids lack a moveable lower eyelid, possess a ring-like intestinal valve and give birth to live young. Some are able to maintain a steady body-core temperature above that of the surrounding water, allowing them to remain active and dangerous in cooler regions.

In the oceans of Spec lurk the huge carnivorous kronosharks that indiscriminately feed on anything that will fit into their cavernous mouths. Named after the titan who gobbled down his Olympian progeny, the stomach contents of these monsters have included entire ammonoids, turtles, small saurocetes and stingrays.

King Krono (Kronorhinus compagnoi)[]

It is generally accepted that there are two cosmopolitan monotypic genera of crown sharks. The Kronorhinoides swainstoni shark is a rare, 6-meter-long tropical species that stays fairly close to the outer continental and island shelves. However, it looks like a pitiful creature next to its notorious cousin, the king shark ( Kronorhinus compagnoi ), which is at home in both coastal waters and the open ocean, and is distributed from the equator (where it is very rare) to the cool-temperate regions. This nightmare that will make you wet your wetsuit can reach up to 12 meters in length, making it the largest carnivorous shark on the planet.

King kronoshark, Kronorhinus compagnoi (worldwide in temperate-subtropical seas)

At first glance, the King Kronos shark looks similar to its distant relative from Earth, the great white shark ( Carcharodon carcharias ) - it has the same white belly, soulless black eyes and a terrible appearance that makes the heart clench. Closer examination, however, reveals that the two fish are quite different from each other: while the white shark is a muscular, bullet-shaped creature, the Kronos shark is more elongated, cigar-shaped, and has longer pectoral fins - a body type that is more likely to be optimal. for economical long-term swimming than for underwater fighting.

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Scaled silhouettes of a white shark from Home-Earth (top left) and a human alongside that of a 12 m long king kronoshark.)

Kronosharks gracefully cruise through the waters, almost casually engulfing their food with great bites. Even their feeding frenzies appear to be in slow-motion compared to those of other sharks. In some ways, these scavenger-predators are Spec-analogues of the Home-Earth tigershark (Galeocerdo cuvier). A look inside the mouth of a kronorhinoid takes the tigershark-theme even further. Their teeth appear to be larger mirror-images of those of Galeocerdo with broad, rectangular roots topped with a slanted triangular blade.

Part of the reason why there are such mega-scavengers in the oceans of Spec is that there is a lot more dead meat to clean up. Most of the huge ocean-wanderers of Home-Earth are whales, animals with lifespans of many decades and a low fecundity. On Spec, many of those niches are instead the domain of huge cephalopods. These animals have much shorter lifespans and a much higher population turnover. This leads to a greater number of giant floating carcasses than on HE and has created a lucrative niche-market for big ocean scavengers with a taste for calamari.

Kronotooth

Upper teeth of three oceanic scavenging sharks. A: Home-Earth tigershark (Galeocerdo cuvier), B: Late Cretaceous crowshark (Squalicorax kaupi), C: a medium-sized king kronoshark (Kronorhinus compagnoi).)

Teeth attributable to both clades of kronoshark go all the way back to the early Eocene. It is widely accepted that they are descendants of the Cretaceous “crow shark” Squalicorax; along with it, they are placed in the Anacoracidae. Like the modern-day chompers, the crow-sharks were master-scavengers with their fossil teeth being found embedded in the remains of mosasaurs, other sharks and even dinosaurs. Vanishing from Home-Earth 65 million years ago, the descendants of Squalicorax on Spec continue to stuff their faces with as much gusto as their Cretaceous forefathers.

Gigamouth (Jasconius pelaganax)[]

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Gigamouth, Jasconius pelaganax (worldwide at temperate latitudes)

Almost too big to be real, the gigamouth is the biggest shark, the biggest fish, the biggest animal... just about the biggest everything on Spec. Its titanic, fusiform body approaches or may even exceed 30 metres in length.

In overall appearance, the gigamouth looks like an enormous hybrid of the two great filter-feeding lamniform-sharks of Home-Earth, the basking (Cetorhinus) and the megamouth (Megachasma), the latter of which may possibly exist on Spec as well. Its wide mouth that forms the tip of the snout and its rows of minute teeth arranged on the rim of the jaw closely resembles the whale-like head of the megamouth while its gill slits are immense and equipped with straining rakers like those of the basker. The gigamouth’s exact relationships to these and other lamniformes are still unclear.

In terms of its ecological niche, the gigamouth appears to be broadly analagous to the migratory basking shark, seasonally visiting cold to warm temperate waters to feed on the summer plankton-blooms. They may appear at temperate latitudes around the globe but appear to be only common in the North Atlantic, where congregations of up to a dozen animals may be seen close to shore, allowing divers a unique opportunity to witness these immense creatures as they feed. As it slowly swims through the clouds of copepods and other plankton, the gigamouth opens and distends its titanic jaws, forming a circular intake. Plankton-laden water passes across the huge gill-rakers which strain out the unfortunate creatures before the water is forced out the gill slits.

These summer banquets provide the bulk of our knowledge of these giant wanderers. Just about everything else about the gigamouths is unknown, including how they reproduce, how fast they grow, and where they go during the colder months. It has been suggested that the rows of tiny but prominent teeth allude to the consumption of larger prey in deeper waters, preventing salps and jellies from dropping from its maw. If this adaptation allows the gigamouth to feed continuously during the year (in the coasts during summer, in the depths during winter), it may help to explain how it has grown so much larger than any similar shark on Home-Earth.

Gigamouth shark alongside the scaled silhouettes of a blue whale and a human

On a final note, the gigamouth is the only Specworld animal that comes close to rivaling the Home-Earth blue whale in overall size. However, with a skeleton composed of cartilage rather than bone, and with much smaller fat reserves, the shark is probably substantially lighter than a comparably sized whale. In one of nature’s biggest ironies, while Spec may be a world filled with giants, the greatest animal of all time is from the other timeline.

- Brian Choo and David Marjanović[1]

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