08-26-2017, 06:14 PM
Class Chondrichthyes (Cartilaginous Fish)
Sub-class Elasmobranchii (Sharks and Rays)
(The waters of the Idu region probably contain representatives from most of the major groups from this Class that have surviving members on RL-Earth, although those families and orders whose RL ranges are basically just tropical might come to us only as occasional visitors to the region?s more southerly waters. [Also, if you accept my suggestions, the ecological niches as large plankton-feeders which the Whale Shark & Basking Shark fill in RL will be occupied here by species of ?primitive? ?bony fish? ? close relatives of the Sturgeon ? instead?]It seems likely to me that oceanic genera and species, especially the types that reach the greatest sizes,are more likely to be shared between the two worlds than are either the smaller oceanic types or the [more localised] coastal types. If the larger types present ever included Carcharodon megalodon, the largest shark that is known to us from RL-Earth fossils, then it also seems probable to me that this became extinct in both Earths at about the same time ? around the end of the Pliocene, c. 2.5 million years ago ? and for the same reason which is thought to have been the fact that the whales which had been one of its main food sources shifted to spending a lot of their time in polar waters too cold for this species.)
(The RL-Earth members of this sub-class, excluding those that became extinct during or before the ?K/T Event? at the end of the ?Age of the Dinosaurs?, fall into the following orders_)
(Infraclass Euselachii)
? (Division Hybodonta) *
=> ? (Order Hybodontiformes) *
=>=> Family Potamoselachidae *
(On RL-Earth this order, which had already lost its formerly dominant role among sharks in the seas but still retained a role in freshwater ecosystems, apparently was among the groups of organisms that became extinct during the Cretaceous / Palaeogene transition at the end of the ?Age of the Dinosaurs?. However in the Idu this one endemic family of river-dwelling sharks which survived at least until the end of the Palaeocene epoch [although it has become extinct by now ...])
(Infraclass Euselachii)
(Division Neoselachii) [= modern sharks]
=> (Superorder Galeomorphi)
=>=> (Order Heterodontiformes) [= Bullhead Sharks]
(This is a small order of sharks whose current range on RL-Earth is tropical & subtropical: We probably don?t have any of them in our region?s waters.)
=>=>=> (Family Heterodontidae)[N/A]
=>=> (Order Orectolobiformes) [= Carpet Sharks]
(The current range of this order on RL-Earth is tropical and temperate, but centres on the Indo-Pacific region with which we have had little contact: therefore, again, we probably don?t have any of them in our region?s waters.)
=>=>=> (Family Brachaeluridae = Blind Shark, Bluegrey Carpet Shark)[N/A]
=>=>=> (Family Ginglymostomatidae = (Nurse sharks [widespread enough in RL that they could be in our warmer waters]
=>=>=> (Family Hemiscylliidae = Bamboo, Longtail Carpet, &Epaulette, Sharks) [N/A]
=>=>=> (Family Orectolobidae = Wobbegong sharks [Indo-Pacific, one species to Japan?]
=>=>=> (Family Parascylliidae = Collared Carpet Sharks) [N/A]
=>=>=> (Family Rhincodontidae = Whale Shark [N/A)
=>=>=> (Family Stegostomatidae = Zebra Sharks [N/A]
=>=> (Order Carcharhiniformes) [= Ground Sharks]
(This is currently the largest order of sharks in RL; Many of the species within it are relatively small as sharks go, for example the ?Catsharks?, but it also contains two families of large sharks as well: These are the ?Requiem Sharks? [including such well-known species as the Tiger Shark, Blue Shark, Blacktip Sharks, and Bull Shark] and the ?Hammerhead Sharks?. We almost certainly have a number of species from this order present ? at least sometimes ? within our region?s waters?)
=>=>=> (Family Carcharhinidae) [= Requiem Sharks]
=>=>=>=>Carcharhinus iapetusi = ?Iapetic, or Iduan, Bull Shark?
(This is a distinct species from, although closely related to, C. leucas which is the ?Bull Shark? of RL-Earth: Evidently a population of either the latter species itself or a common ancestor of the two arrived here long enough ago for speciation to have occurred, because we now have a fairly new population of the RL form as well ? among the ?Amazonian? additions to Malabra?s fauna ? and where the two types meet they do not interbreed.).
?Hemigaleidae (Weasel sharks): The Atlantic Weasel Shark is the only one likely to reach us from RL
?Leptochariidae (Barbeled houndshark) [monospecific, tropical] N/A
?Proscylliidae (Finback catsharks)yes, at least in warmer waters
?Pseudotriakidae (False catsharks) yes, 1 of 4+ species is worldwide [in the deeps]
?Scyliorhinidae (Catsharks) yes
?Sphyrnidae (Hammerhead sharks) yes, some species' ranges extend into into warm temperate waters [at least?]
?Triakidae (Houndsharks) yes, 2+ RL spp
=>=> (Order Lamniformes) = Mackerel Sharks]
(This is a small order, with only 17 species currently extant on RL-Earth, but those are all large sharks and mostly active predators ? at least some of whom have some capability to manage their body temperature, which lets them operate in reasonably cold water ? such as the Great White Shark, the Mako, and the Thresher Shark species: We probably have several species from this order in the surrounding oceans, and as at least occasional visitors to the warmer sections of our coastal waters?)
Family Alopiidae [= Thresher sharks]temp & tropical oceans
Family Cetorhinidae [= Basking Shark]N/A
Family Lamnidae [= Mackerel, or White, Sharks]
Family Megachasmidae [= megamouth shark] (in the deeps, scarce, maybe belongs in Basking Shark family)
Family Mitsukurinidae [= Goblin Shark] (deep water, 1 species, need to look)
Family Odontaspididae [= Sand Sharks] (warm or temperate coastal waters worldwide except eastern Pacific, so probably present hereunless we have an endemic alternative)
Family Pseudocarchariidae (crocodile shark) [1 species in RL, tropical] N/A
=> (Superorder Squalomorphii)
=>=> Order Heptanchiselachiformes [= Seven-gilled sharks]
=>=>=> Family Heptanchiselachidae * [= Seven-gills]
=>=>=> Family Caecaselachidae [= Blind Sharks]
(Most modern sharks have only five pairs of gill slits each, with the only extant species that retain the more ?primitive? conditions of either six or seven pairs being the few members of the orders Hexanchiformes [2species @ 6 pairs, 2 species @ 7 pairs] and Chlamydoselachiformes [2 species, @ 6 pairs] which also share some ?primitive? traits. It was originally thought that the Blind Sharks of our region?s seas [a trio of deep-water species, whose name comes from the fact that they have only vestigial eyes] belonged either with the other seven-gilled sharks in the first of those orders or with the six-gilled Frilled Sharks ? to which they are morphologically otherwise very similar, and whose ecological role is similar to theirs ? in the latter order: Molecular studies carried out in recent years, however, suggest that they are actually a ?basal? group with regard to the Squalomorphii as a whole or even to the entire Neoselachiian division?)
=>=> (Order Hexanchiformes) [=Cow Sharks]
[This order of ?primitive? sharks now contains only a handful of species, all of them normally found only in deep water, on RL-Earth; We might have some of them in our own region?s waters, too, but I don?t know whether anybody has actually looked thoroughly enough to be certain either way. Possibly we just have more species of the preceding order, instead.)
Hexanchidae
=>=> (Order Chlamydoselachiformes) [= Frilled Sharks]
[This order is absent from our region?s waters: we have an endemic order of sharks, with a comparable ecological role, instead]
Chlamydoselachidae
=>=> (Order Squaliformes) [= Dogfish sharks]
(This is a large order, and although most of its members on RL-Earth are relatively small it does include some larger predators.)
=>=>=> Family Boreoselachidae
=>=>=>=>Boreoselachus somnosus [= ?Arctic Shark?]
(This is our region?s ecological counterpart to RL-Earth?s ?Greenland Shark?, although that species belongs to the order Orectolobiformes instead. Like its counterpart it is one of only a few Shark species that spends much time in really cold water, and is a relatively slow swimmer in whose diet the carcasses of land animals that have been washed into the sea after dying in or near rivers play a major role.)
=>=> (Family Centrophoridae) [= Gulper Sharks] ()
=>=> (Family Dalatiidae) [= Kitefin Sharks] ()
=>=> (Family Echinorhinidae) [= Bramble Sharks] ()
=>=> (Family Etmopteridae) [= Lantern Sharks] ()
=>=> (Family Oxynotidae) [= Rough Sharks] ()
=>=> (Family Somniosidae) [= Sleeper Sharks] ()
=>=> (Family Squalidae) [= Dogfish Sharks] ()
=>=>=> Family Parasqualidae [= Dogfish sharks] ()
=>=> (Order Squatiniformes) [= Angel Sharks] [possibly present in the warmer sections of the region?s seawaters]
Squatinidae
=>=> (Order Pristiophoriformes) [= Sawsharks] [possibly, but not probably, present in the warmer sections of the region?s seawaters]
Pristiophoridae
(Infra-class Batoidea) [= Rays, Skates, and Sawfish]
=>=> (Order Torpediniformes) [= Electric Rays] [probably present in the warmer sections of the region?s seawaters & maybe in some rivers]
=>=> (Order Pristiformes) [= Sawfishes] [possibly present in the warmer sections of the region?s seawaters & maybe also in some rivers]
=>=> (Order Rajiformes) [= Skates and relatives] [probably present, widspread and fairly abundant]
=>=> (Order Myliobatiformes) [= Stingrays and relatives] [probably present in the warmer sections of the region?s seawaters & maybe in some rivers]
Class Chondrichthyes ('Cartilaginous Fish'): Subclass Holocephali ('Chimaeras', or 'Ratfish')
(This is another ?ancient? group for which I suspect most if not all of the Idu region?s native species are endemic; native genera might be endemic too, but probably all higher levels of classification are shared with the RL-Earth species? It is also another group whose surviving members rarely come to people?s attention, and that I therefore consider a low priority for developing in more detail?)
Sub-class Elasmobranchii (Sharks and Rays)
(The waters of the Idu region probably contain representatives from most of the major groups from this Class that have surviving members on RL-Earth, although those families and orders whose RL ranges are basically just tropical might come to us only as occasional visitors to the region?s more southerly waters. [Also, if you accept my suggestions, the ecological niches as large plankton-feeders which the Whale Shark & Basking Shark fill in RL will be occupied here by species of ?primitive? ?bony fish? ? close relatives of the Sturgeon ? instead?]It seems likely to me that oceanic genera and species, especially the types that reach the greatest sizes,are more likely to be shared between the two worlds than are either the smaller oceanic types or the [more localised] coastal types. If the larger types present ever included Carcharodon megalodon, the largest shark that is known to us from RL-Earth fossils, then it also seems probable to me that this became extinct in both Earths at about the same time ? around the end of the Pliocene, c. 2.5 million years ago ? and for the same reason which is thought to have been the fact that the whales which had been one of its main food sources shifted to spending a lot of their time in polar waters too cold for this species.)
(The RL-Earth members of this sub-class, excluding those that became extinct during or before the ?K/T Event? at the end of the ?Age of the Dinosaurs?, fall into the following orders_)
(Infraclass Euselachii)
? (Division Hybodonta) *
=> ? (Order Hybodontiformes) *
=>=> Family Potamoselachidae *
(On RL-Earth this order, which had already lost its formerly dominant role among sharks in the seas but still retained a role in freshwater ecosystems, apparently was among the groups of organisms that became extinct during the Cretaceous / Palaeogene transition at the end of the ?Age of the Dinosaurs?. However in the Idu this one endemic family of river-dwelling sharks which survived at least until the end of the Palaeocene epoch [although it has become extinct by now ...])
(Infraclass Euselachii)
(Division Neoselachii) [= modern sharks]
=> (Superorder Galeomorphi)
=>=> (Order Heterodontiformes) [= Bullhead Sharks]
(This is a small order of sharks whose current range on RL-Earth is tropical & subtropical: We probably don?t have any of them in our region?s waters.)
=>=>=> (Family Heterodontidae)[N/A]
=>=> (Order Orectolobiformes) [= Carpet Sharks]
(The current range of this order on RL-Earth is tropical and temperate, but centres on the Indo-Pacific region with which we have had little contact: therefore, again, we probably don?t have any of them in our region?s waters.)
=>=>=> (Family Brachaeluridae = Blind Shark, Bluegrey Carpet Shark)[N/A]
=>=>=> (Family Ginglymostomatidae = (Nurse sharks [widespread enough in RL that they could be in our warmer waters]
=>=>=> (Family Hemiscylliidae = Bamboo, Longtail Carpet, &Epaulette, Sharks) [N/A]
=>=>=> (Family Orectolobidae = Wobbegong sharks [Indo-Pacific, one species to Japan?]
=>=>=> (Family Parascylliidae = Collared Carpet Sharks) [N/A]
=>=>=> (Family Rhincodontidae = Whale Shark [N/A)
=>=>=> (Family Stegostomatidae = Zebra Sharks [N/A]
=>=> (Order Carcharhiniformes) [= Ground Sharks]
(This is currently the largest order of sharks in RL; Many of the species within it are relatively small as sharks go, for example the ?Catsharks?, but it also contains two families of large sharks as well: These are the ?Requiem Sharks? [including such well-known species as the Tiger Shark, Blue Shark, Blacktip Sharks, and Bull Shark] and the ?Hammerhead Sharks?. We almost certainly have a number of species from this order present ? at least sometimes ? within our region?s waters?)
=>=>=> (Family Carcharhinidae) [= Requiem Sharks]
=>=>=>=>Carcharhinus iapetusi = ?Iapetic, or Iduan, Bull Shark?
(This is a distinct species from, although closely related to, C. leucas which is the ?Bull Shark? of RL-Earth: Evidently a population of either the latter species itself or a common ancestor of the two arrived here long enough ago for speciation to have occurred, because we now have a fairly new population of the RL form as well ? among the ?Amazonian? additions to Malabra?s fauna ? and where the two types meet they do not interbreed.).
?Hemigaleidae (Weasel sharks): The Atlantic Weasel Shark is the only one likely to reach us from RL
?Leptochariidae (Barbeled houndshark) [monospecific, tropical] N/A
?Proscylliidae (Finback catsharks)yes, at least in warmer waters
?Pseudotriakidae (False catsharks) yes, 1 of 4+ species is worldwide [in the deeps]
?Scyliorhinidae (Catsharks) yes
?Sphyrnidae (Hammerhead sharks) yes, some species' ranges extend into into warm temperate waters [at least?]
?Triakidae (Houndsharks) yes, 2+ RL spp
=>=> (Order Lamniformes) = Mackerel Sharks]
(This is a small order, with only 17 species currently extant on RL-Earth, but those are all large sharks and mostly active predators ? at least some of whom have some capability to manage their body temperature, which lets them operate in reasonably cold water ? such as the Great White Shark, the Mako, and the Thresher Shark species: We probably have several species from this order in the surrounding oceans, and as at least occasional visitors to the warmer sections of our coastal waters?)
Family Alopiidae [= Thresher sharks]temp & tropical oceans
Family Cetorhinidae [= Basking Shark]N/A
Family Lamnidae [= Mackerel, or White, Sharks]
Family Megachasmidae [= megamouth shark] (in the deeps, scarce, maybe belongs in Basking Shark family)
Family Mitsukurinidae [= Goblin Shark] (deep water, 1 species, need to look)
Family Odontaspididae [= Sand Sharks] (warm or temperate coastal waters worldwide except eastern Pacific, so probably present hereunless we have an endemic alternative)
Family Pseudocarchariidae (crocodile shark) [1 species in RL, tropical] N/A
=> (Superorder Squalomorphii)
=>=> Order Heptanchiselachiformes [= Seven-gilled sharks]
=>=>=> Family Heptanchiselachidae * [= Seven-gills]
=>=>=> Family Caecaselachidae [= Blind Sharks]
(Most modern sharks have only five pairs of gill slits each, with the only extant species that retain the more ?primitive? conditions of either six or seven pairs being the few members of the orders Hexanchiformes [2species @ 6 pairs, 2 species @ 7 pairs] and Chlamydoselachiformes [2 species, @ 6 pairs] which also share some ?primitive? traits. It was originally thought that the Blind Sharks of our region?s seas [a trio of deep-water species, whose name comes from the fact that they have only vestigial eyes] belonged either with the other seven-gilled sharks in the first of those orders or with the six-gilled Frilled Sharks ? to which they are morphologically otherwise very similar, and whose ecological role is similar to theirs ? in the latter order: Molecular studies carried out in recent years, however, suggest that they are actually a ?basal? group with regard to the Squalomorphii as a whole or even to the entire Neoselachiian division?)
=>=> (Order Hexanchiformes) [=Cow Sharks]
[This order of ?primitive? sharks now contains only a handful of species, all of them normally found only in deep water, on RL-Earth; We might have some of them in our own region?s waters, too, but I don?t know whether anybody has actually looked thoroughly enough to be certain either way. Possibly we just have more species of the preceding order, instead.)
Hexanchidae
=>=> (Order Chlamydoselachiformes) [= Frilled Sharks]
[This order is absent from our region?s waters: we have an endemic order of sharks, with a comparable ecological role, instead]
Chlamydoselachidae
=>=> (Order Squaliformes) [= Dogfish sharks]
(This is a large order, and although most of its members on RL-Earth are relatively small it does include some larger predators.)
=>=>=> Family Boreoselachidae
=>=>=>=>Boreoselachus somnosus [= ?Arctic Shark?]
(This is our region?s ecological counterpart to RL-Earth?s ?Greenland Shark?, although that species belongs to the order Orectolobiformes instead. Like its counterpart it is one of only a few Shark species that spends much time in really cold water, and is a relatively slow swimmer in whose diet the carcasses of land animals that have been washed into the sea after dying in or near rivers play a major role.)
=>=> (Family Centrophoridae) [= Gulper Sharks] ()
=>=> (Family Dalatiidae) [= Kitefin Sharks] ()
=>=> (Family Echinorhinidae) [= Bramble Sharks] ()
=>=> (Family Etmopteridae) [= Lantern Sharks] ()
=>=> (Family Oxynotidae) [= Rough Sharks] ()
=>=> (Family Somniosidae) [= Sleeper Sharks] ()
=>=> (Family Squalidae) [= Dogfish Sharks] ()
=>=>=> Family Parasqualidae [= Dogfish sharks] ()
=>=> (Order Squatiniformes) [= Angel Sharks] [possibly present in the warmer sections of the region?s seawaters]
Squatinidae
=>=> (Order Pristiophoriformes) [= Sawsharks] [possibly, but not probably, present in the warmer sections of the region?s seawaters]
Pristiophoridae
(Infra-class Batoidea) [= Rays, Skates, and Sawfish]
=>=> (Order Torpediniformes) [= Electric Rays] [probably present in the warmer sections of the region?s seawaters & maybe in some rivers]
=>=> (Order Pristiformes) [= Sawfishes] [possibly present in the warmer sections of the region?s seawaters & maybe also in some rivers]
=>=> (Order Rajiformes) [= Skates and relatives] [probably present, widspread and fairly abundant]
=>=> (Order Myliobatiformes) [= Stingrays and relatives] [probably present in the warmer sections of the region?s seawaters & maybe in some rivers]
Class Chondrichthyes ('Cartilaginous Fish'): Subclass Holocephali ('Chimaeras', or 'Ratfish')
(This is another ?ancient? group for which I suspect most if not all of the Idu region?s native species are endemic; native genera might be endemic too, but probably all higher levels of classification are shared with the RL-Earth species? It is also another group whose surviving members rarely come to people?s attention, and that I therefore consider a low priority for developing in more detail?)