Prehistoric Life/Other Extinct Creatures: Difference between revisions

Lissamphibians excluded, prehistoric amphibians are traditionally called "labyrinthodonts" or "stegocephalians", but these terms shouldn't be used today, just like "thecodonts" for basal Archosaurs or "pelycosaurs" for basal Synapsids. This because they don't indicate any natural grouping of animals, but are instead catch-all words with little scientific significance [[Science Marches On|in modern phylogenetic systematics]]. Labyrinthodonts means "labyrinth teeth", because many of these animals had convoluted, labyrinth-like internal patterns inside their teeth, but this doesn't interest us too much. Their importance was much, much greater than this and lies upon another aspect. They were, simply, the links between fish and truly terrestrial vertebrates, a keystone group for mankind's evolution. And yet, just like mammal-like "reptiles" and mesozoic mammals, they have not gained much attention in pop-culture (it seems ''only apes and monkeys'' [[Small Reference Pools|were our ancestors]] in pop-consciousness...). Their [[Did Not Do the Research|apparently]] monotonous, uninteresting appearence may have contributed to this, or rather... just [[What Measure Is a Non -Human?|our mammalian pride]] generates a sort of "denial" towards our deep origins? Anyway, basal tetrapods ''weren't'' boring, uninteresting things: anything but. They were ''very'' diversified in shape, size and ecology; as we’ll se soon.

* Sarcopterygians, aka “Lobe-finned fish”. Actually, considering these animals as ''fishes'' may appear rather arbitrary to some paleo-fans. Rather than creatures we'd normally call fish, they were a sorta middle-way between typical fish and amphibians, and many of them spent part of their life ''outside'' water, thus breaking the "fully-aquatic" criterium. They are traditionally divided in three groups: Actinists, Lungfish and Rhipidists <ref>The third term it actually in disuse: today the correct one is "basal stegocephalians & tetrapodomorphs". But if we use the latter, the pun with "actinists" [[Rule of Funny|wouldn't work anymore]]</ref>. Actinists, better-known as Coelacanths from the common name of their only <s>one</s> [[Science Marches On|two]] surviving species, are perhaps the most famous, and at the same time, the least amphibian-like: indeed, they ''were'' fully-aquatic, thus "true fish". They appeared in the Devonian Period, and were marine creatures that have remained virtually unmodified since 400 million years: but now they seriously risk to go extinct soon or later, [[Humans Are Bastards|only because]] [[What Measure Is a Non -Cute?|they are not so cute]] [[Finding Nemo|as clownfish are]]. Lungfish were a bit closer to us: they really have [[Exactly What It Says On the Tin|lungs]] for breathing air other than classic gills, appeared in the Devonian as well and specialized themselves to muddy, marshy environment with very oxygen-poor waters: that's why their lifesaving airsacs evolved. Today are the most successful missing-links between fish and land vertebrates (although less than ten species are still alive today), and yet they are less-often-mentioned than Coelacanths. Finally, "rhipidists" are an artificial assemblage of not-related lobe-finned fish. Among them were ''the ancestors of mankind'', as well as all land-living vertebrates ever existed, from [[Digimon|dinosaurs]] to [[Hamtaro (Anime)|hamsters]]. ''Eusthenopteron'' has always been the stock rhipidist, probably because of the look of its tail that recalls [[Prongs of Poseidon]]; recently, the basically identical but far bigger ''Hyneria'' has gained some notoriety thanks to [[Walking With Dinosaurs|Walking With Monsters]], portrayed as a ''[[Jaws (Film)|Jaws]]''-like [[Carnivore Confusion|villain]]. It's the ''only'' lobe-finned fish represented in that show, and [[Somewhere a Paleontologist Is Crying|with no mention at all about the role of lobe-finned fish as our-ancestors]].

* Not always [[EverythingsEverything's Even Worse With Sharks]], really. For many animal-lovers, they are among the most fascinating living things. And so is among paleo-fans. Prehistoric sharks were as diversified as modern shark are today, or rather, even more. But stop now. Things aren't always so simple as they seem. "Shark" is an ambiguous word: usually refers to ''some'' of the modern cartilaginous fish, expecially the most streamlined ones such as the Great White, but not, to say, the flattened rays and skates. But in paleontology, it usually refers to ''all'' cartilaginous fish, or at least, those belonging to the {{[http|//en.wikipedia.org/wiki/Elasmobranchii Elasmobranchian}} subgroup. The other main subgroup, the [http://en.wikipedia.org/wiki/Holocephali Holocephalians], are usually called [[Chimera Beast|Chimeras]] or, more confidentially, Rabbit-Fish. Cartilaginous fish (both sharks and chimeras) originated in the Devonian period. Chimeras have virtually not changed since then, and still retain today that mixed "shark/typical fish" appearence very common among Paleozoic fish. Sharks are often called "living fossils" because their anatomy has remained virtually unchanged since 400 million years, and yet they managed to survive the strong competiton both from the first Jurassic large sea-reptiles at first, and from the first Cretaceous ray-finned fish then.

* ''Bothriolepis'', ''Coccosteus'' and most other placoderms were small predators of invertebrates or smaller fish... but not ''Dunkleosteus''. Its name means "Dunkle's bone", but in older sources it used to be called "Dinicththys" ("fearsome fish"). But today nobody uses this name anymore. Just like the "Brontosaurus -> Apatosaurus" and "Diatryma -> Gastornis" examples, this is a pity for many long-standing paleofans: a really cool name deleted by [[Science Marches On]] and replaced by a really unexpressive one... This Devonian arthrodire was similar to ''Coccosteus'', just overgrown: 30 ft long, the size of a killer-whale, it was the largest vertebrate known so far which lived before dinosaurs. Its size is even more astounding, if you think most other Devonian armoured fishes were salmon-sized. It is one of the most famous prehistoric "leviathans" along with Megalodon, ''Liopleurodon'', ''Mosasaurus'' and ''Basilosaurus'', and was the fiercest-looking among them, thanks to its armour, and also its strange-looking teeth, [[Madness Mantra|as we'll see later]]; no surprisingly, it is a staple in those not-so-common paleobooks which show also pre-dinosaurian fauna, always described as a [[Prehistoric Monster|"monstrous killing machine"]]. Surprisingly, despite all this, ''Dunkleosteus'' has had ''very'' few apparitions in TV to date, much less than, to say, the not-so-impressive ''Elasmosaurus'' (another egregious case of [[EverythingsEverything's Better With Dinosaurs]]: OK, elasmo wasn't a dino, but lived in the same age...) Perhaps the only relevant example in recent media is [[Walking With Dinosaurs|Sea Monsters]], where ''Dunkleosteus'' was portrayed with [[Hellish Pupils|cat eyes to make it even scarier-looking]] (while most drawings show rounded, fish-like pupils), with a non-proved [[I Am a Humanitarian|cannibalistic attitude]], and, to put the cherry on the cake, its hide was ''[[Colour -Coded for Your Convenience|blood red]]''. If you have watched that show, you'll remember those strange, blade-like teeth which cut like scissors (at last, we're talking about them); these are instead [[Truth in Television]]. Only... they weren't ordinary teeth; they were ''bony plates'', the same kind of those which covered its forebody. And this is not an isolated case in the fish-world; remember we talked about sharks, and their enamel-covered, teeth-like scales? Finally we'll get it. At the start of fish evolution, scales and teeth ''were the same thing''. Then, body scales were lost by land vertebrates, never to return: the so-called reptilian "scales" are a totally different thing, just horny thickening of the skin (usually) without bony core, just like our fingernails. But ''mouth scales'' remained, and how: and they allow us to chew our meals today. Our incisors, canines, premolars and molars are, really, the only remaining fish-scales we still have. Keep this in mind, every time you go to the dentist.

* Is there anybody who has never seen those pietrified spiraled shells at least once in its life? Ammonites are probably the most iconic fossil invertebrate remains at all, thanks to their elegant shape and their extreme abundance in Mesozoic deposits, to the point they're used as index-fossils to identify Dinosaur-age-related rocks, just like Trilobites for the pre-dinosaurian ones. But wait... ammonites are ''not'' exclusive to Mesozoic! They appeared in the middle Paleozoic, but that's right, achieved their highlights in Mesozoic with kinds which are exclusive of this era: so, it works just the same. Before the first paleontologists were born, ammonites were already well-known to people, who asked themselves what the heck they are: Mother Nature's jokes, Pietrified snakes, "Ammon’s horns" (the meaning of their our-day name), or what? The very first human which understood their real nature was [[Leonardo Da Vinci]] in XVI century, but wasn't believed: we had to expect the Founder-of-Paleontology, Cuvier, after see the true fossil's nature understood at the end of the XVIII. Sometimes is heard the modern-day [http://en.wikipedia.org/wiki/Nautilus Nautilus] is the "modern ammonite": this is not true, as we'll see later: ammonites went ''totally extinct'' at the Cretaceous/Cenozoic extinction ever, the most famous victims (after real and alleged dinosaurs) of the most infamous (though [[Did Not Do the Research|not the worse]]) mass-extincion ever. Indeed, ammonites are very mysterious things, despite their abundance. We know almost nothing about the shape of their soft parts, since they don't fossilize usually: it seems, though, they were intermediate between the more basal Nautilus and the our more evolved octopusquids. Octopusquids have very complex eyes, almost identical to vertebrates, while Nautilus has one of the simplest eyes one can imagine, nothing but darkrooms without lens. And ammonites? Who knows... And their tentacles? Octopusquids have eight/ten with suckers, Nautilus more but lacking suckers. And ammonites? It seems were more nautilus-like in this respect. In drawings and models, however, expect to see Ammonites [[EverythingsEverything's Squishier With Cephalopods|with octopusquid eyes, octopusquid tentacles]] and, last but not least, octopusquid ink (while Nautilus hasn't ink at all in [[Real Life]]). Despite their fame, Ammonites are very rare things in TV. Don't expect to hear more than a single line about them -if at all. Even [[Walking With Dinosaurs]] has dedicated only a brief cameo to them, in Jurassic "Cruel Seas". Indeed, for an unexplicable reason, ammonites are usually associated with Jurassic seas, despite they were just as common in Triassic and Cretaceous.... In dinosaur books, things are a bit better: ammonites here are frequent, but... don't expect to see single kinds identified, either (unless you've a technical or semi-technical work). And don't expect to see the so-called "heteromorph" ammonites, aka strange-looking species with ''uncoiled'' shells common in Cretaceous.

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