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Spec: Chondrichthyes

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Chonhead

INTRODUCTION & 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.

Mud Shark (Sepiaichthis microcephalus)

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Mud Shark, Sepiaichthis microcephalus (Waters of Southern North America)

The mud shark (Sepiaichthis microcephalus) is a small chondrichthian that lives in the brackish waters of the mangrove forests of southern North America.  Only about one meter long, the mud shark feeds on food trapped in the mud, burrowing between the mangrove roots with its small, blunt head. In shallow waters, this shark uses its highly developed front fins to craw across the swamp bed.

Xenohybodus (Xenohybodus maximus)

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Xenohybodus, Xenohybodus maximus (Oceanwide Waters)

While the air breathing saurocetids have conquered most of the Photic zones of the ocean, sharks such as Xenohybodus maximus rule the dark abyss and frigid polar waters. These large chondrichthians migrate huge distances across the world's oceans, often followed by a convoy of parasites.  They often swim upstream, in fresh water to rid themselves of these vermin. Torpedo-like in shape, Xenohybodus will eat almost anything it can fit in its mouth (A recent stomach pump of a juvenile Xenohybodus show the remains of what looks to be a small theropod!).

EUHYBODINDAE (MUUSKINBEK HYBODONTS )

Hybodont sharks experienced a sharp decline during the latter part of the Cretaceous period in both Spec and HE. OTL's last hybodonts expired early into the Danian. Spec is a different case, with one deep-water species, the backscratcher known in the present day, but this is a Lazarus taxon with roots that stretch back before the Campanian. The most interesting modern members of the group are the muuskinbeks. The Neogene has seen these American endemics radically reinvent themselves and actually increase in diversity and size. This was a response to the teleost fish that diversified rapidly after the Oligocene extinction events. The ancestry of these muuskinbeks is not entirely clear, but the tiny lissodine Lonchidion sp. of the latest Maastrichian is believed to represent the closest example. The Paleogene record of hybodonts is rather spotty, with just a few uncertain heterodont teeth and a single late Eocene vertebrate known. The latest Oligocene/earliest Miocene is an entirely different story, with thousands of pisciphagous teeth and an abundance of preserved vertebrates known in many deposits across North America into the most recent times. The hybodonts have taken the niche largely filled by HE's diverse "bass" type fishes as well as the deep-water cruising of Old World Spec coelacanths. These selachians are present throughout the Americas.

The diversity of euhybodont species is fairly high for a freshwater clade of selachians. 6 species are known and 4 more awaiting description. As selachians go, they are rather small, with the largest female mishiginabig reaching around 1 meter in length. A single, quite miniscule African species less than 10 cm in length makes a living as a shellfish crusher within the Congo River basin. Hybodonts tend to have many primitive characteristics. The lack of a true hypostylic jaw suspension limits their jaw strength compared to most of the neoselachians. This amphistylic suspension is shared to a degree with cow sharks, present in both timelines. While modern euhybodonts have either pursued a multi-cusped shearing tooth dentition (Muuskinbeks) or a mostly shell-crushing set of chompers (Bumba), their Paleogene ancestor likely had a heterodont set of slicing and crushing teeth. They also have more triangular fins than neoselachians, though muuskinbeks seem to have little trouble stabilizing them to vegetation while waiting in ambush for prey.

BUMBAINAE

Bumba (Bumba crustavora)

Within the shallower reaches of the Congo River system lives the bumba. The presence of this hybodont shark in the African Congo was a great surprise.

Initially, this chondricthyan was linked with some Aptian LK Asian predecessors. The discovery of both the American muuskinbeks and deepwater backscratchers later disproved this. DNA and morphological analysis show without a doubt this is an euhybodont, which split off from the muuskinbek line prior to the Oligocene. The Paleogene split is still perplexing, as it indicates a marine ancestry from either the Americas, or perhaps even Eurasia possibly as far back as the Eocene. Frustratingly, old world Paleogene hybodonts refuse to reveal themselves, leaving either scenario within the realm of possibility. Whatever the case, this chondricthyan seeks out freshwater mollusks and small, hard-shelled crustaceans. They’ve also been seen gamely attacking belostomatid water bugs as big as or bigger than themselves by crushing their thorax. Bizarrely, they vomit up the calciferous and chitinous shells of their prey within communal latrines.

This behavior has been tentatively speculated to signify social and reproductive status. Prey items are predominately eaten by specific sexes and age groups, further work is needed. The latrines eventually grow quite large, often breaking the surface in calm backwaters. These piles are extensively utilized by water plants and small fish and arthropods in the sparse barren sand stretches lined with reeds the bumbas prefer for their hidden mollusk and arthropod prey. Many of these "small fry" eventually fall prey to the freshwater selachian. The bumba itself is rather unremarkable, with a body plan vaguely resembling the Heterodontus neoselachians of both Spec's and HE temperate marine environmentss. The main differences are the reduced numbers of anterior grasping teeth and the greater prevalence of posterior crushing teeth which have an odd low exterior cusp arrangement that may hold the small bivalves that make up the bulk of their diet. The eyes are huge for sighting about their often murky riverine habitat.

Massive, venomous spines that prominently jut in front of both dorsal fins ensure that predation is very rare, even the giant coelacanths and crocodiles will spit these selachians out. The odd cephalic claspers so pronounced with the muuskinbek hybodonts are rather small in the males of this species.

Bumbas reproduce once every year, with females laying up to 6 eggs. The deposition of the eggs is interesting, being secreted within the communal vomitoriums. The incubation period lasts roughly 3 months, at which point, those eggs that survived predation or other calamities hatch out 4 cm long miniatures of the adult bumbas. Maturation is quite long, with bumbas reproducing beginning in their fifth or sixth year. Lifespan is speculated to be several decades.

EUHYBODINAE (Muuskinbeks)

Without a doubt, these are the most interesting of the modern hybodonts with regards to their evolutionary progression since the Miocene. Descended from the last of the American lonchidionids, they have claimed their place as the bruisers of the North American waterways. Most species range 15 to 40 cm in length, with the giant of the clade, the Mishiginabig reaching 1 meter. These are predominately loners, as ambushing the wary pan fish of the weedy shallows and the mud suckers of the riverine depths doesn't engender itself to cooperative endeavors. This is a far cry from the molluscivorous diet of their ancestors. Many characteristics make them stand apart from neoselachians. The jaws can't drop down as far as neoselachians, but the muuskinbeks have developed a fleshy “tongue” to create negative pressure for sucking in prey. While the jaws are somewhat weaker than typical neoselachians, the teeth are no less sharp or capable of hooking slippery fish. They possess the archaic seven gill arrangement of basal chondricthyans, as well as the dorsal spines for defense. The stranger but not odd for selachian characters include independently evolving a more mobile pectoral fin, the ability to maintain neutral buoyancy by gulping air into their intestines along with adjusting liver oils. The truly bizarre traits include the enormous cephalic horns which are present in most species; the ability to enter into winter torpor within river bottom gravel or lake mud is a point of great interest. Last but not least, they can derive at least part of their oxygen needs from air.

Reproduction is an exciting springtime affair for muuskinbeks; both sexes compete in leks in the open waters away from shore weeds. The males display their prominent horns to each other in dominance displays with arched backs and head wagging. Physical fights are rare and generally one male establishes himself within a particularly choice spot, usually an exposed log or large rock. Females are hardly passive about this either, they out right intimidate and threaten each other for the right to approach the high ranking males. Such a situation mutually benefits both sexes of a clade which birth very few young at a time. High ranking males and females select each other and mate.

The high ranking females then seek out the best sites for their eggs, which are usually areas of high flow and gravel bottoms in rivers, deeper waters in lakes. There is always a wetland marsh close by for the pups to hide in after birth. The early bird females will remain in the area for weeks after laying, attempting to prevent lower ranking females from accessing those prime sites,

The 4 to 16 eggs hatch after 3 to 4 months. The pups take several hours to hatch, but once they do; they head into the nearest bed of vegetation. The rest of the summer and autumn seasons are spent hiding and hunting. Their first winter sees them in secluded mud burrows or rock outcroppings in deep waters. Growth is quite long, usually taking 5 years before they join their first lek.

Muuskinbeks tend to be very territorial, though mishiginabigs will congregate in loose informal packs in large bodies of water. The need for concrete home ranges with sufficient fish is hotly contested. Severe injuries and death are not uncommon. The winner retains or usurps the territory. The loser is driven away or cannibalized. These affairs are usually sex determined, as the females are larger than the males. Both sexes utilized conjoining parts of a given area and tend to eat different prey.

Mishiginabig (Cornulynx diabolis)

Named after the fearsome horned water lynx of Algonquin legends; this is a fierce predator of open water fish. They leave the weedy shallows to their smaller muuskinbek kin. Their range extends throughout the Mississippi drainage; with two separate populations in the great lakes complex above and below the Niagara River. Many species of shads and pan fish are important prey items. Immature sturgeon and paddlefish also are taken. They will occasionally attack aquatic mammals like juvenile selters and afancs. Hatchling duckgongs have also been seen killed and eaten near the mouth of the Mississippi. The cephalic horns on old males can be quite impressive, nearly 10 cm long. Unlike the smaller muuskinbeks, mishiginabigs do not enter winter torpor except when immature or under stressed conditions. They prefer to stay in deeper waters, following their prey. Small prey is gulped whole, larger prey is ripped apart.

Muuskinbek (Euhybodus algonquinae)

This is the first described euhybodont and its nomer is used for the American species. They are the most widespread and common of the clade; with a range extending throughout most waters of northern North America. This is the only muuskinbek species known in arctic waters, often swimming out to sea to enter adjoining river mouths. Small populations are also found in Greenland and Iceland lakes. Like most of the clade, this selachian makes a living stalking among shallow water weeds. They eat large pan fish too bulky for pikes. Crawfish and other invertebrates are opportunistically taken. Occasionally, they will crunch up exposed mollusks in a throwback to their lissodine ancestors.

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.

Reef Krono (Kronorhinoides swainstoni)

It is generally agreed that there are two cosmopolitan monotypic genera of kronoshark. The reef krono (Kronorhinoides swainstoni) is an uncommon 6-metre-long tropical form that stays fairly close to the outer continental and insular shelves.

King Krono (Kronorhinus compagnoi)

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It is dwarfed by its infamous cousin, the king krono (Kronorhinus compagnoi) which is at home close inshore or out in the open ocean and ranges from the equator (where it is very rare) to the cool-temperate regions. This nightmare can reach a wetsuit-soiling 12 metres in length, making it the largest carnivorous shark on the planet.

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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.)

At first glance, a king krono looks similar to its distant Home-Earth cousin, the great white (Carcharodon carcharias), in sharing its white belly, soulless black eyes and overall heart-pounding scariness. A closer examination shows that the two fish are actually quite differently put together – whereas the white is a stout and bullet-shaped creature, the krono has a more elongated, cigar-shaped form with longer pectoral fins, a design optimized for economical cruising rather than underwater dogfighting.

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.

Gigamouth2

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.

Antarctic Yawn (Ultrachiasma antarcticus)

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Antarctic Yawn, Ultrachiasma antarcticus (Antarctic Ocean)

This gentle leviathan is the largest animal to feed on the vast swarms of krill that gather near the surface of the south polar seas. A primitive lamniform, it strains plankton through bristle-like gill rakers in a manner similar to it's cousin on our world, the basking shark.

It's vast dorsal fin, packed with blood vessels acts as a sort of solar-radiator and allows the shark to remain active in the cold antarctic waters. The fin juts out of the water when the shark feeds near the surface-when the shark swims edge-on to the sun, absorbative pigments collect the sun's energy and heat the blood flowing through the fin. When the shark gets too hot, it swims face on to the sun, reducing the surface-area exposed while glittering reflective pigments on the leading edge of the fin help keep the shark cool.  

- Brian Choo and David Marjanović

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