If anyone can help me out rn, it'd be appreciated. I had unexpected surprises with a bill (not even my own, it was my eldest niece's) for emergency vet treatment and had to help cover the cost. I have a kofi and paypal and do commissions (send me an ask or message me). It'll be greatly appreciated if ya'll could spare any change.
To clarify: I need to buy food for myself that I can safely eat without getting sick (feck you, body) and heating because the weather is turning cold. Anything you have to spare really will make a difference.
[kofi]
Go to paypal.me/kathryncowle0 and type in the amount. Since it’s PayPal, it's easy and secure. Don’t have a PayPal account? No worries.
If anyone can help me out rn, it'd be appreciated. I had unexpected surprises with a bill (not even my own, it was my eldest niece's) for emergency vet treatment and had to help cover the cost. I have a kofi and paypal and do commissions (send me an ask or message me). It'll be greatly appreciated if ya'll could spare any change.
Prehistoric Sharks and their role in their ecosystem? Idk if that has already been asked.
Note: I haven't gone past the Permian period with this ask. Mostly because my brain won't let me, but also because it's long as heck. Someone ask me about sharks in the age of dinosaurs as a separate ask. I’ll answer that and link it to this one, and this one there. Otherwise, I’m done xD
Well, this definitely isn’t a question that’s been asked, no, but it's certainly an interesting one! It’s also a bit of a challenge to answer because sharks have been around in some way, shape, or form for over 400 million years and that’s a lot of time for ecological change. I talked a bit about prehistoric sharks in this ask here but that was less detailed than it was an overview of shark evolution. As I noted there, sharks have been around since the Ordovician era to the modern day and that gives them far, far more wiggle time for snatching ecological niches for them to grow nice and comfy in.
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To understand the effect of prehistoric sharks in their ecosystems, we have to look at the ecosystem of each era of geological time and the sharks/shark-like species in the eras. Also, might help to understand what terms like Ordovician and Paleozoic mean so little breakdown of geological time below.
Geological time can be broken up into eras and those eras into periods. The ones we care about of the: Paleozoic era, the Mesozoic era, and the Cenozoic era.
The Paleozoic era covers time from 541.0 million years ago to 485.4 million years ago (MA) and covers six geological periods of time:
The Mesozoic era covers time from 251.902 million years ago to 66 million years ago (MA) and is broken into three geological periods:
Triassic (251.902-201.3 MA),
Jurassic (201.3-145.0 MA), and
Cretaceous (145.0-66.0 MA).
Lastly, the Cenozoic era which runs from 66 million years ago to the present day and is also separated into three periods:
Paleogene (66.0-23.03 MA),
Neogene (23.03-2.58 MA), and
Quaternary (2.58 MA to now).
I’ll be including the dates and periods throughout this answer but this is a good little breakdown if you can’t remember the order or geological eras each period belongs to. Also it helps me to organise this whole answer without going off on tangents!
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It’s important to note that most of the sharks that existed in prehistoric times died out and aren’t directly related to modern sharks and rays; thus they belong to the Chondrichthyes sub-group, the Holocephali or chimaeras. Incidentally, the only living species of the Holocephali are the Chimaeraformes, or Ghost Sharks. Aspects of shark evolution in the bizarre sharks from the Devonian, Carboniferous, and Permian periods all seem to have shown up in the Holcephali ancestors of the Chondrichthyes order: though some modern shark direct ancestors were weird, lbr.
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Anyway, lets go!. Everything else under cut bc wow long.
Paleozoic Era: 541.0-251.902 MA
Cambrian Period: 541.0-485.4 MA
I’m not really going to talk about the Cambrian era because, honestly, no shark relatives to be found, so moving on.
Ordovician Period: 485.4-443.8 MA
Running between 485.4 and 443.8 million years ago, the ecosystem of the Ordovician period consisted mostly of marine invertebrates and corals. Think, Great Reef on steroids as the general environment for the Ordovician period when sharks evolved. Sharks evolved over 450 million years ago, just before the end of the Ordovician period, surviving the first of many extinction events: the Ordovician-Silurian extinction event. From graptolites (plankton-like extinct marine creatures), trilobites (arthropods, very much look like woodlouse but bigger), brachiopods (marine creatures that had shells/lived in), to primitive fish, gastropods (snails), cephalopods (squids), and the very first conodonts (early vertebrates), sharks developed around this period as potentially toothless predators.
The evolutionary branch below shows you the evolution of vertebrates to where we reach the class Chondrichthyes (aka fish with cartilage skeletons rather than bone which includes sharks and rays). Jawed vertebrates, or Gnathostomata, evolved in the middle Ordovician era and is where the idea of fish with jaws becomes mildly terrifying for all the creatures out there at the time. Jawed fish can bite shells and crush them. The poor trilobites, brachiopods and all the rest really got unlucky when pre-cursor sharks started to show up in the Ordovician period, lol.
[source: wikipedia]
The Ordovician-Silurian extinction event likely happened when the climate changed at the end of the Ordovician period. With continental drift happening all the time, the massive super-continent of Gondwana settled over the South Pole during the Upper/Early Ordovician and had the side effect of causing glaciers to form. Massive ones. This made the oceans shallower, thus causing sea-levels to drop over time. It’s a best guess that this significant shift in climate caused a mass extinction event which saw 60% of existing marine invertebrates genera and 25% of families go completely extinct. Pre-sharks were one of those that survived.
Jaw vertebrates like Gnathostomata were a hardy bunch and we have them to thank for us being around by the way.
Silurian Period: 443.8-419.2 MA
Anyway, the climate changed for the Silurian period from 443.8 to 419.2 million years ago. Smaller continents like Laurentia and Baltica were the only other landmasses in this time, with most of the northern hemisphere being ocean (Gondwana was so big it literally covered most of the southern hemisphere hence the reason it had such an impact on the climate of the late Ordovician). A micro-continent called Avalonia broke off from the northern edge of Gondwana and drifted north. The northern continents of Laurentia, Baltica, and Avalonia, slowly collided through the late Ordovician, Silurian, and Devonian periods, turning into the supercontinent Euramerica. This resulted in the Caledonian Orogeny which was a major mountain building event: it’s here that the mountains of Scotland, Wales, the northern Appalachians and Ireland, as well as Sweden and Norway were initially formed. With such dramatic continental drift and changes in continents, it makes sense that the marine environment experienced changes as well. One of those was 60% of marine invertebrates becoming extinct and huge gaps opening in the ecological structure of the marine environment.
This is where ecological niches and species specialisation comes into play.
The landmass that would eventually become North-west America existed under a shallow ocean for most of the Silurian, allowing sunlight to reach the bottom and for marine animals to rapidly evolve. From extensive coral reefs to a more specialised jawless fish class of Agnatha, to Placoderm (armoured fish with cartilaginous skeletons), we saw a lot of changes from the Ordovician. One of the apex predators of this time were Eurypterids; a type of arthropod most likely related to horseshoe crabs. These creatures became the largest arthropods to ever have lived on earth by the time of the Devonian.
I don’t know if any of ya’ll ever watched Primeval but there’s an episode with a giant fucking scorpion/Silurian era Not Okay Insect. Yeah. That was an Eurypterid. No, I’m not happy to remember that. I love scorpions but definitely not the sea scorpion version.
So yeah, this is when sharks had jaws, but didn’t have teeth yet. They weren’t apex predators yet. Just another type of jawed fish that was able to start specialising in ways that would lead them to what we call the modern shark.
Throughout the Silurian period there were a number of minor extinctions of species like plankton and among conodonts likely from fluctuations in sea levels and radiation; solar flares maybe? But then the Silurian period ended and the Devonian began; which is where we see the first true sharks evolved.
Note: there was no ‘mass extinction’ event in the Silurian period.
Devonian Period: 419.2-358.9 MA
Following the Silurian, came the Devonian, ranging between 419.2 and 358.9 million years ago. That’s a lot of time for environmental and ecological changes to occur. Especially when you consider the super continents of Gondwana and Euramerica as well as the developing evolution of land animals that became mammals in the end.
In the Devonian, we see some really interesting shark species evolve, like the Cladoselache species of shark. The Cladoselache didn’t have dermal denticles like modern sharks or claspers. They did have gills and were torpedo-shaped, however. Whilst there is less known about Cladoselache because they did have cartilaginous skeletons rather than bone ones, the fossil records indicate that there were a relatively successful species of four-foot long sharks, existing for around 100 million years. Even though Cladoselache didn’t have dermal denticles to aid swimming, they were still fast and agile due to other evolutionary adaptations; like light-weight fins made of dentine and enamel and a blade fin in front of the dorsal fin that helped reduced water resistance/drag as it swam.
You see, in the Silurian, the Chondrichthyes class of fish come about. These were the fish with cartilage skeletons (yes, like sharks and rays nowadays). It’s from this class, which is a sub-group of the infraphylum class Gnathostomata. Within the Chondrichthyes class, we have additional sub-classes: Holocephali and Elasmobranchii. Holocephali are chimaera fish species, whilst Elasmobranchii are our sharks, skates, rays, and sawfish. So 430 million years ago, we have the class of animal that is the true precursor of our modern-day sharks. This is why, when you see any Shark Facts on the internet, sharks are usually listed as over 400 million years old.
Back in 2020, a new species of shark was discovered to have existed in the Devonian period, named: Ferromirum Oukherbouchi.
[image source: sci-news.com]
It was a type of symmoriiformes shark, which existed from about 382 million years ago to the early Cretaceous about 280 million years ago. Ferromirum Oukherbouchi existed around 365 million years ago in the Late Devonian, was around 13 inches long, had large eyes and a specialised jaw capable of rotating outwards and down since the lower jaw wasn’t fused in the middle. This adaptation made it easier for Ferromirum Oukherbouchi to impale prey with their teeth, then, rotating their jaws back into alignment, they were able to swallow the prey more effectively when the jaws closed fully.
Think Predator face from Alive vs Predator lmao.
With this method of catching prey, Ferromirum Oukherbouchi probably engaged in suction feeding, where sea water entered the mouth when the jaws opened quite literally like pulling the plug from a drain and seeing the water rush down the drain; closing the jaws then was like putting the plug back in. Throughout the Paleozocia era (Cambrian to Permian: 541.0 to 251.902 million years ago), this sort of jaw joint was really common and likely very effective for predators and prey alike. Of course, with more teeth and better replacement of said teeth, that kind of jaw joint became obsolete over time and is why we have modern sharks and rays with complex jaws and (in the case of sharks) lots of pointy teeth.
The Devonian period ended with another mass extinction where much of the marine life in the oceans went extinct. For those species that survived, and the ones that evolved after, a whole new world had opened up (yes, I meant the pun), and this is where we see the first True Sharks show up in the fossil record. This extinction event occurred around 372 million years ago and saw 50% of all genera (species) become extinct. Then, on top of this, 359 million years ago (less than 20 million years after the major extinction of 50% of all species), another extinction event occurred (called the Hangenberg event) which led to the Carboniferous period of geological time to begin.
Carboniferous Period: 358.9-298.9 MA
After the Devonian we have the Carboniferous period from 358.9 to 298.9 million years ago when the prehistoric shark order Xenacanthida appears in the fossil record. This shark order likely grew up to 5 metres in length, with large serrated spines on their back from the neck and with teeth very distinct to the group. This order of prehistoric shark was present in almost all forms of water: freshwater, shallows, and swamps. Of the Xenacanthida order, some of the most notable genera are Orthacanthus and Xenacanthus.
Orthancanthus were apex predators in freshwater swamps and bayous in what became Europe and Modern America. At nearly 3 metres and teeth that were serrated, it's understandable they were apex predators. As a species, Orthancanthus were also cannibalistic, preying on younger Orthacanthus when possible. Below are: 1) fossilised teeth of Orthancanthus which were round, like a bullet, but also serrated and very good at piercing armour, scales, bone etc; 2) a pencil sketch of Orthancanthus Seckenbergianus.
[image source: wikipedia]
[image source: wikipedia]
Interestingly, there is evidence of a purely predator-prey relationship between Orthancanthus and another species of shark: Triodus (a Xenacanthidan genus of shark). Triodus were freshwater sharks that lived from the Carboniferous to the Triassic, and honestly deserved better than to be forever chowed on by their bigger cousin. As it is, Orthancanthus as a group seemed capable of ontogenetic adaptations: a theory called ontogenetic niche theory, suggests that individual creatures may change their behaviours or diet to enable their continued existence and not suffer from things like poor growth. It means that Orthancanthus was a very successful predator and also adaptive to its environment; likely partly why it was such a successful species for so long.
[image source: wikipedia]
Xenacanthidan sharks were separated into five genus: Xenacanthus, Triodus, Plicatodus, Wurdigneria, and Mooreodontus. Interestingly, Xenacanthidan sharks became less and less diverse throughout their existence until they went extinct in the Triassic period.
Xenacanthus sharks were only around 1 metre long and never more than 2 metres; which is likely why Orthancanthus species were able to prey on Triodus. The dorsal fin of Xenacanthus was more like the fin of an eel, running all the way along the back of the body and likely suggests Xenacanthus swam similarly to eels. They may also have had a venomous spike that protruded from the back of their head (probably for protective reasons since the back of the head is a vulnerable spot) and with teeth that were v-shaped rather than like a bullet as with Orthancanthus, it's likely that Xenacanthus feed on crustaceans and scaled fish.
It’s interesting that two closely related orders—Orthancanthus and Xenacanthus—had such different appearances and even diets. Kind of like modern sharks and rays hmm…
Anyway, moving on.
Permian Period: 298.9-251.902 MA
To the last period of the Palezoic era (from 541.0 to 251.902 million years ago), we reach the Permian period. The Permian period ran from 298.9 to 251.902 million years ago and is when Pangaea formed. Pangaea was a supercontinent that quite literally caused immense climate and environmental chaos because of how big it was. The northern part of the continent was victim to intense heat all year round and extreme fluctuations between dry and wet conditions throughout the year. The southern part of the continent was buried under ice caps and bitterly cold.
Synechodontiformes order sharks showed up in the fossil record during the Permian period and existed well into the Paleogene period over 200 million years later. That’s a pretty decent showing for an order of sharks, not gonna lie. Anyway, this order of sharks were a branch of Neoselachii: the group of Elasmobranchii/Neoselachii (cartilaginous fish that includes modern sharks and rays). Synechodontiformes were originally believed to be polyphyletic (a group containing the common ancestor species but not all of the descendent species of the common ancestor) but are actually monophyletic; aka all of the descendants of the common ancestor are part of the group.
Toxoprion, of the Heliocoprionidae family, are part of a subclass of Chondrichyhtes called Holocephali. Holocephali fossils show up from the Devonian and show that they began to split off from Elasmobranchii around 421 million years ago. Most of the shark-fish from this subclass had features that were part of the main elasmobranch in the Paleozoic era; though the extant (living) species of Holocephali show that the features aren’t as useful for apex predators today as they might have been. With long tails that are thin, they used their large pectoral fins for movement, had no stomach (the guts were just stomach and intestines combined) and small mouths for better feeding on molluscs and invertebrates on the seafloor. Now, back when there were shallow oceans, that sort of thing was useful. Nowadays, with deep oceans and the lack of light down on the seafloor, it’s not quite as beneficial. But considering the changes in climate and such, it’s interesting to know that such features still exist in a (now) non-related cousin to the modern shark and are still useful to said cousin. The holocephalian species Dwykaselachus was studied and determined that the early members of the holocephalian group still had features we’d consider ‘shark-like’ over 280 million years ago. Anyway. Toxoprion and other Helicoprionidae all had weird bottom jaws. You might have heard of a shark with a circular saw kind of mouth; yeah, that was real. Toxoprion was one of them.
[image source: wikipedia]
[image source: natgeo]
This just in: evolution is weird.
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Now, I’m not going to lie, my brain is kind of dying now from having to dig so much for references and image sources and I’m kind of at the point where I want to scream at the void about sharks and weird evolution.
So, I’m going to call it quits here with sharks and shark-like fish cousins just for my sake. I can talk more about shark evolution and the effects they had but, honestly, for a single species (or lots of species of the same core branch), the effect sharks have had and still do have on ecological habitats is so varied… there’s too much to cover unless I want to write an actual 10k paper about sharks and… honestly, no thanks. This is already 3k and I hadn’t even reached the Triassic period. Gods.
If you are talking about dolphins they used to be wolf like creatures that due to scarcity of food they had to hunt in water so they slowly evolved into water mammals, dolphins still have claw bones but they are unnecessary and dolphins will get rid of them with time and will develop abilities to breath under water
It’s important to mention that we now know dolphins will probably never need to develop true water breathing, because the fact that they breathe air from the surface is actually an ADVANTAGE for them. They get more oxygen at once than an animal with gills and it permits a much higher, more energized activity level for longer periods of time.
They are murderous monsters empowered by their access to the forbidden air
BONNETHEAD IS AN OMNIVORE SHARK, RESEARCHERS FOUND
What an animal consumes and what an animal digests and assimilates for energetic demands are not always synonymous. Sharks, accepted as carnivores, have guts that are presumed to be well suited for a high-protein diet. However, the bonnethead shark (Sphyrna tiburo), an abundant shark commonly found in seagrass habitats, has been previously shown to consume copious amounts of seagrass, flowering marine plant that forms subsea meadows in some coastal waters in the Gulf of Mexico, as in other parts of the world. And now, is considered the first known plant-eating shark. The finding were published in the journal Proceedings of the Royal Society.
The bonnethead shark is an abundant shark species in shallow waters of the Eastern Pacific, the Western Atlantic, and the Gulf of Mexico, where they feed on seagrass and small crustaceans, snails and other fishes, and according to researchers, in natural conditions, up to 62.1% of gut content mass is seagrass. Because a large percentage of the diet is seagrass, conserving seagrass beds is vital to the hammerhead shark family and other marine life.
Photo: bonnethead shark in Bahia State, Brazil, by José Amorim Reis-Filho.
Reference (Open Access): Leigh et al., 2018. Seagrass digestion by a notorious ‘carnivore’. Proc. R. Soc. B.
