Horseshoe Crabs: NOT Living Fossils

Horseshoe crabs are often considered living fossils, but that ignores large parts of their fossil record. While certainly their basic body plan hasn't undergone as much change as those of other organisms, that's not to say they're unchanged for millions of years.
Read some papers on this topic:
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www.nature.com...
www.researchga...
www.ncbi.nlm.n...
onlinelibrary...../doi/10.1111/pala.12220
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[@HuckleberryHim]

Love that bedbug just chilling on the top left of the graphic at 2:48. He's not a mite, he's not an arachnid, he's not even a chelicerate. But nobody's noticed, and at this point he's too afraid to say anything.

[@talroitberg5913]

Good catch. I was going to point out that Uropygi look like this ( upload.wikimedia.org/wikipedia/commons/thumb/3/34/Mastigoproctus_giganteus_0004_L.D..jpg/640px-Mastigoproctus_giganteus_0004_L.D..jpg ) and the graphic at 2:48 has Amblypygi twice by mistake, but that feels like a small correction relative to the bedbug.

[@1TakoyakiStore]

I always thought of the term as just applying to a body plan of a group of animals being relatively unchanged and not having anything to do with genetic variance. Like if the average person sees a tadpole shrimp they would likely refer to it as a living fossil because of the apparent similarities to horseshoe crabs. The way you're referring to the term seems to be that it only applies if an animal living today is of the same species as one we have a fossil of (which is difficult if not impossible to prove). Honestly I don't think it's appropriate for "living fossil" to be a scientific term (maybe in Gars but that's a whole other conversation). And then there's the literal interpretation of living fossil, which interestingly enough are our teeth. The same process of minerals replacing biological matter that constitutes fossils occurs as plaque buildup in our teeth if we haven't been brushing consistently, and this happens when our teeth are alive. But with all that being said, why argue over the term "living fossil" for horseshoe crabs when they are neither crabs or horseshoes? Seems like that would need to change first before we start getting upset over the phrase in question.

[@42ZaphodB42]

So aren't modern crocodiles! They literally evolved at the end of the cretaceous. If crocodiles are living fossils, so should birds be.

[@onehairybuddha]

Ducks go back to the Cretaceous too I believe. I might start calling them living fossils!

[@42ZaphodB42]

@@onehairybuddha modern bird lineages evolved in the late cretaceous, thats right and the group itself in the late jurassic.

[@nefelpitou]

I kinda feel like the opposition to the term living fossil is a bit of pedantry here. I don't think anyone was ever using it as a serious scientific term, and the criticism that seems to be made against the term seems to be based on an argument that no one is making; like I've never heard anyone use the term to claim that horseshoe crabs have existed literally forever , completely unchanged, rather the claim that they are living fossils is based on the living examples extremely close visual resemblance to very ancient fossils (while there are xiphosurans from the Mesozoic that don't look identical to modern ones, there are plenty that are so close from even the Triassic that they could be easily mistaken for a modern species by even someone familiar with the animals ). I feel like the argument that "actually modern horseshoe crabs aren't living fossils because they only look nearly identical to animals from 250 million years ago, but look somewhat different from ones that lived 400 million years ago, isn't really very convincing. The better argument , I feel like, is that there are actually a lot of different lineages of invertebrates that have maintained a high degree of morphological similarity to Mesozoic or even Paleozoic forms, it's just a lot of these animals are either more mundane (for instance bivalves, I'm only really familiar with arthropod taxonomy so if you gave me a bivalve fossil my only guess would be "sometime in the last 450 million years maybe?" ) or more obscure and uninteresting (i.e priapulids) to the average person, so they don't really think about them in the same way. The idea of what is or isn't considered a living fossil has more to do with vibes, then their actual antiquity or resemblance to ancestors and I think that's a more salient critique of the term

[@dankykongmax2786]

You must not be aware of Young Earth Creationists

[@WeebishSwed]

​@@dankykongmax2786I think that's why it is sorta important to point out how they aren't the same, and that they have changed over time. Creationists love to use Living Fossils as proof of creation after all. I do think it is still fun to use as a term, but also important to know the differences.

[@flydrop8822]

This makes me wonder, is there an effective way to measure how much an organism has changed anatomically in comparison to an ancestor? And then compare that to another organism of the same period, with an ancestor of the same period as the other one, and therefore be able to tell which organism changed the most? It seems like this is something that is very intuitive, yet there doesn't seem to be much real studies about it and everything related to this is just informal conversations rather than scientific analysis. I think a lot could be learned from analysing how organisms evolved over time in comparison to each other, maybe even making predictions about their ancestral lineages as well as their descendants.

[@pseudolullus]

You would be surprised, as the exact argument of an almost literally unchanged animal has been made about gars (the fish) this year. I take it with a big grain of salt, as they claim that the genetic clock in gars has been pretty much stopped and not just their phenotype. So there is kind of a debate right now. @•flydrop882 Yes, we can use morphometric analyses to quantify body shapes/relative proportions and compare them, for instance.

[@haseo8244]

It’s like no one is talking about top snails either. Around since Ordovician era as well too.

[@Goddot]

I saw the fossil at 1:50 irl! It's in the Senkenberg Museum in Frankfurt, they have a fantastic fossil collection.

[@myrmeciagulosa1267]

You have one of the best T-shirts I've ever seen. There are eurypterida on it, it's so cool.

[@RaptorChatter]

Hopefully we'll be getting to making more at scale to sell

[@Irobert1115HD]

@@RaptorChatter i think darwin coined the term for species where he couldnt explain why they looked like species that looked like species from the fossil record.

[@DeRien8]

Love your eurypterid shirt! Small note, I do marine science research and camps with kids, and there are several locations in New Jersey where we find horseshoe crabs in brackish tidal waters in the lower reaches of rivers

[@RaptorChatter]

Didn't realize that even modern ones do that, neat!

[@CITADEL5]

Excellent presentation. Packed with information about horseshoe crabs and their ancestral forms. Also you get directly to your subject without wasting time with unrelated or personal information. Thank you. You have a new subscriber.

[@RaptorChatter]

Great to hear!

[@gattycroc8073]

I made a comment on another video talking how Mesozoic Temnospondyls and Cenozoic Notosuchians where sort of living fossils for their time but of course all things change through time. Koolasuchus differed a lot from other Temnospondyls and the last Notosuchians that lived during the Miocene changed a lot since the rest went extinct.

[@HuckleberryHim]

It's crazy that you showed an animation of solifugid feeding at 3:30, I literally just watched General Apathy's newest video in Jordan and he has super close shots of one eating and, wow... I never knew they did that. Was as horrifying as it was fascinating. An animation can't do it justice, it was straight out of an alien horror movie

[@RaptorChatter]

I remember poking one with the end of a pencil when I was 7 or so, and being horrified and then so intrigued. From my view I saw the 80s Predator jaws try and bite a pencil eraser. Great animals.

[@entity_unknown_]

Mawsonia is living in the deepest part of the great lakes and in the Loch Ness

[@jplaystrueskate]

Why do you think so

[@f.u.m.o.5669]

This is trolling. This has to be trolling.

[@technopoptart]

@@jplaystrueskate cryptid memes

[@mscottjohnson3424]

Biology teacher here. The term "Living Fossil" isn't a hard scientific classification. As this video states, all species are in a constant state of genetic drift, meaning that even organisms alive today that superficially look very similar to very old organisms in the fossil record are, certainly, genetically quite different from their ancient ancestors. While "living fossil" was historically used to describe extant (currently living) species that closely resemble their relatives in the fossil record, it's more commonly used by biologists today to describe an extant clade (a group of species that includes a single common ancestor and all of its descendents) that represents a formerly much larger clade of which the few (or one) extant species is the only survivor, and for which the latest common ancestor between it and its closest living relatives was quite distant, usually at the phylum, class, or order level of taxonomy. A good example is the Turatara, a reptile that is the only living species of the order Rhynchocephalia, meaning it is more distantly related to every other extant reptile than every other extant reptile is to any other extant reptile. Turtles and crocodiles are pretty distantly related, but they are still more closely related than either is to the turatara. Turataras look, superficially, like lizards, though lizards are more closely related to crocodiles, turtles, and even birds than they are to turataras. Turataras are living fossils because Rhynchocephalians used to be quite abundant during the mesozoic, but have all gone extinct except for the turatara. It is the only living member of a once large and diverse group of reptiles that is not closely related to any other currently living group of reptiles. Monotremes, the egg-laying mammals, of Australia could also be considered living fossils. At some point, all mammals laid eggs, but now one small clade is the only group left. This does not mean that current monotremes look a lot like early mammals, but they represent an extremely distant lineage that has all but gone extinct. All mammals, even marsupials, are more closely related to each other than any are to monotremes. Horseshoe crabs could be considered living fossils because they are the only extant members of the order of arthropods called Xiphosura. As the video stated, their closest living relatives are the arachnids (a diverse extant clade) and the sea spiders (not spiders at all, as the video stated), but their common ancestor lived during the Cambrian, and they share only a subphylum. This means that the horseshoe crabs are, by far, more distantly related to any other extant arthropod than monotremes are to any other extant mammals and tuataras are to any other extant reptile (including birds). I would call horseshoe crabs living fossils, not because of their resemblance to their ancient ancestors, but because they are only remaining family of an order of arthropods that split off from the phylum hundreds of millions of years ago. The fact that the Xiphosura used to be far more abundant and diverse, but now only the horseshoe crabs still exist, is what makes them a living fossil in my book. tl;dr The term "living fossil" is no longer used to describe a species that superficially looks very similar to its ancient ancestors, but rather to small groups of species that are only very distantly related to any other currently living organisms, and/or who represent the only living members of a formerly much larger and more diverse group.

[@Dondash08]

O_O This is a teacher...

[@whome9842]

Thank you! "Living fossil" sounded silly to me. I used to ask myself "How can you claim it is unchanged just because it is similar to some ancient species?" "Sometimes similar creatures are actually different species to the point it require an specialist or even genetic testing to tell them apart, sometimes different populations of the same species might look very different (dogs for example)." Your definition makes much more sense.

[@42ZaphodB42]

@@mscottjohnson3424 Birds represent the only family of dinosauria and their only relatives are the crocodiles. All the birds relatives diverged at the beginning of the triassic. By your example, theyd be living fossils - which is silly

[@densamme1752]

I could have bought your argument for the tuatara but horseshoe crabs is a family not a single type who survived multiple mass dying episodes

[@42ZaphodB42]

@@densamme1752 Not even that. Tuatara is just the only species that's left. And it's still a "modern" species of sphenodont. Tuatara diverged from its closest living relatives exactly at the same time that the birds did, which I explained. So if tuatara is a living fossil, birds are aswell.

[@nyeti7759]

Really enjoyed the video - I didn't know much about horseshoe crabs before except that, well, they're living fossils. It sounds like their situation is more like that of crocodilians. The ones we have today have a general body plan and lifestyle that were also present among their distant ancestors, but they're only part of a formerly much more diverse group.

[@Tuishimi]

This was a good statement about "living fossils"... over time nothing stays the same, even if they LOOK the same. At the same time it makes me sad, because I like that phrase. :D

[@daubert4892]

This kind of evolutionary stasis can be called stabilomorphism if you don’t want to use the words ‘living fossil’

[@robrice7246]

Would the terms Lazarus taxon & Lazarus species work for some of the so called "Living Fossils"?

[@patreekotime4578]

I think it's also considered an outdated, nonsensical term.

[@Lightman0359]

@robrice7246 no need for an arbitrary aesthetic category. Species are either extant or extinct. Seeing the context of Lazaus, it could possibly be used for species that were either completely extinct and brought back through cloning, or functionally extinct (gone from the wild or from a specific habitat) and brought back through captive breeding and release programs. However, in both of those cases endangered is a better term until they repopulate enough to be removed from protection.

[@RaptorChatter]

Lazarus taxa are still pretty reasonable, as it's any representative of a group which wasn't known to have survived so long. Chimerarachne as a sister group to spiders is a great example, as the group isn't around now, but there is a multi-hundreds of million year gap separating it, from its closest relative.

[@timkbirchico8542]

we need to drop the biblical references when naming processes. most people dont know the lazarus story anyway.

[@patreekotime4578]

@@timkbirchico8542 Yeah I would argue it's kind of a useless name anyway. It basically just means "we havent found a continuous fossil record connecting this animal to a similar older animal". I think it's just as nonsensical as living fossil.

[@BlackReaper0]

Wow, sea spiders looks interesting.

[@syafiqjabar]

They have organs in their legs

[@joeshmoe8345]

Thanks a bunch for sharing this with us Big Dog!

[@klasa3gplaterka5]

There is a guy in Netherlands and You are the favourite KZbinr of him

[@RaptorChatter]

There is at least on person from the Netherlands on the discord, so maybe the same person.

[@robrice7246]

12:42 Are their body plans just very successful for their environmental niche (hence why people like to make that false claim of them being "unchanged", despite the fact that evolution will find ways to experiment or build off that basic body plan to resemble something very different)?

[@patreekotime4578]

It's probably more useful to think of it like convergent evolution. The same way that similar environmental pressures allow two very different animals to eventually look (vaguely) similar, so similar environmental pressures may allow the same group of animals to retain (vaguely) similar traits. All traits that result in another generation are "successful", so it's also not really useful to talk about more or less successful traits. We also have no way of knowing how many anatomical or behavior differences between these animals are not preserved in the fossil record. So the appearance of similarities may just be bias in what is preserved.

[@thedarkmasterthedarkmaster]

I get that it's not 100 percent accurate but I must admit the backlash against living fossils as a term is kinda silly

[@RaptorChatter]

A lot of the criticism for it is coming from an educator standpoint. It gets a bit tiring to explain how "living fossils" aren't a good term for academic discussions, and paints a very simplistic view of certain animals, despite them having been around just as long as the lineage which led to any other modern organism has.

[@davewalter1216]

Love your eurypterid shirt, but I don't know where you got that chart (well, yes I do - you credit 'Animalfact'), but the "Mites (Acariformes)" is illustrated by a bedbug (insect - 3 pairs of legs and antennae - and definitely a bedbug) and the leftmost Uropygi is just another Amblypygi as far as I can see. I suppose I shouldn't complain, at least the chart doesn't mash the two not closely related superorders of mites together, but a picture of a red velvet mite, spider mite, or other common Acariformes is not that hard to find. Anyway, if you revise this presentation, you should go for a better showcase for the extant chelicerates.

[@tuxuhds6955]

Horseshoe Crabs are living fossils and Pluto is a planet. THERE!

[@Dondash08]

I agree with this 100%. Even if creatures look the same, it has changed. Mentally, internally, physically. Nothing is the same as it was thousands of years ago.

[@dalailarose1596]

Did you say "glown" instead of "glowed"? I don't hate it 😊

[@RaptorChatter]

All languages are made up, and you got the point, so I think it's perfectly fine

[@Stegosaurus.Stenops]

Raptor Chatter video detected

[@Iwatch2019cartoonsobsessively]

That voicecrack at 0:56

[@5hape5hift3r]

Genetics shows horseshoe crabs to actually be quite deep in the arachnid family tree. So they aren't stem chelecerates

[@RaptorChatter]

Or, alternatively, they are the sister group to arachnids, as they lack most of the distinctive arachnid traits. There's a lot of debate about this still, and I tend to support the James Lamsdell phylogenies.

[@5hape5hift3r]

@@RaptorChatter genetics tends to be stronger evidence for the actual evolutionary tree, in the 2019 paper they looked into this due to many previous genetics studies keep resolving Xiphosura inside the arachnid tree. they used the most genetic data ever used, and used multiple methods, and even tried accounting for long branch attraction by excluding some genetic data, all trees showed Xiphosura as inside the arachnid tree, and most trees resolved them as sister to Ricinulei.

[@IC1101-Capinatator]

@@5hape5hift3r…But yet another paper disproved that in favour of them being more basal again. www.ncbi.nlm.nih.gov/pmc/articles/PMC6534568/

[@5hape5hift3r]

@@IC1101-Capinatator interesting

[@JamieLevin-b8b]

To me, this is like telling a kid that Santa doesn’t exist😢😢😢😂

[@ferengiprofiteer9145]

On one extreme, no two individual lifeforms are the same. (Well, maybe clones:) But, it helps us understand and discuss if we draw distinctions, hence taxonomy. Arguably, every generation is a hybrid of the previous generation, so not the same. Splitting hairs about defining the nonscientific term "living fossil" is rearranging deck chairs, isn't it? What's the ado about?

[@Grand_History]

A living fossil should be any organism that is representative of its ancestors enough that you can learn a lot about extinct ecosystems from the one living organism. If you can learn about the past from a living animal, that would make it a living fossil

[@robertjackson1813]

Please tell me how to have that shirt or else im hunting y down for it

[@RaptorChatter]

We will hopefully be selling them in the future, just been super busy, so no good timeline for it yet.

[@AsherHamilton-m6z]

I live in new England and see horseshoe crabs all the time there my favorite animals

[@chaosopher23]

Atlantic horseshoe crabs live in brackish water. Narragansett Bay is always loaded with them. They're harmless, but curious and pesky... they will come and visit while I dig clams, and try to crawl on me.

[@Alte.Kameraden]

2:58 the mite on the top left corner isn't a mite but a bed bug. Not even related to mites. xD

[@graphite2786]

It's a very bad graphic - besides bedbug ( insect) representing the mite there is also 2 pictures of Amblypygi whipspiders, one over Amblypygi and one over Uropygi, the whipscorpions & vinagroons

[@RaptorChatter]

Apologies, I must have totally spaced that graphic. We have had a lot happen over the week of editing, so just a simple space out when watching it back over.

[@RaptorChatter]

Apologies, I must have totally spaced that graphic. We have had a lot happen over the week of editing, so just a simple space out when watching it back over.

[@graphite2786]

@@RaptorChatter You are totally forgiven, mistakes happen

[@AntoekneeDE]

Living fossils do exist, my father-in-law for instance 😂 I take the point that suggesting an organism is unchanged from its ancestors or their relatives isn’t accurate, but it is interesting to see a morphology that has in very general terms remained a successful format over time in many different environments, and retained by a lineage as opposed to convergent evolution in less related groups recurrently reaching similar solutions to the similar problems. On the subject of long lasting morphology, the platypus can’t get enough love, I believe that would be another creature that could sometimes be referred to as a living fossil by some but also one where it is believed it’s morphologically similar ancestors didn’t use the same parts of the water column. My pedantry in this case would be that they are referred to as primitive mammals because them split from the rest of extant mammals likely somewhere in the early Jurassic and retain ancestral traits such as cervical ribs, sclerotic rings, egg laying of course, and the whole down stairs one hole business, but the reality is they’ve also been evolving ever since; they didn’t just split off from therians and multituberculates and hit the brakes on evolution, over time they retain what works and change what doesn’t or else don’t survive

[@GreenPoint_one]

So like crayfish today horseshoes were freshwater inhabitans :3

[@2l84t]

More impressive than the Trilobite in many ways.

[@danielmalinen6337]

I have understood a living fossil to mean an animal whose close relatives / kind have long-term fossil records. Or at least this is how it has been explained to me before and told that, for example, a hedgehog is a living fossil.

[@dylanbarnes9195]

I own a living trilobite...its a pill bug named jessie

[@zungaloca]

I truly believe evolution rate is different depending

[@GreenPoint_one]

For me they are still special animals :3

[@vincentx2850]

That is one killer shirt!

[@joakos1122]

thats super nitpicky, for everyday people they are living fossils and rightfully so. so many similarities of even birds and dinosaurs they are all windows into the past though obviously not the full picture

[@scottsvt9104]

It’s a living fossil just like crocodiles and alligators. They remain relatively unchanged. Some scientists may argue over one minuscule part of the fossil is different but not really. It’s mostly opinion based anyways. The entire field of paleontology is mostly opinion based.

[@imthestarman7531]

I love your shirt dude, can I ask where you got it?

[@RaptorChatter]

We had it made ourselves. With any luck we'll be able to sell them in the future, but no exact timeline for that. Lots of life stuff popping up.

[@cjalexanderjr8811]

Pet stores advertise Triops longicaudatus as “living fossils.”

[@RaptorChatter]

Yep, and they're wrong, but it sells.

[@unnamed9858]

yo where'd you get that allosaurus diagram looks sick

[@RaptorChatter]

Dinosaur National Monument!

[@secondbeamship]

What are the closest modern relatives of Trilobites?

[@RaptorChatter]

Hard to say for sure. Based on my Agnostus video, I would say they're probably the sister group to Pancrustacea, which includes crustaceans and insects and a few other groups. Unfortunately they diversified so quickly that we don't really have a super solid record of their earliest forms. The fossil record goes from no trilobites to very obviously trilobites with no middle ground.

[@JcoleMc]

I think segemented worms would be the closest

[@jaggerbushOG]

Those things are so creepy.

[@RenaMoonn]

Oh hey, i'm expanding the wiki page of these guys!

[@RaptorChatter]

Love my wiki editors. Especially on paleo content where there's so many citations

[@RenaMoonn]

@@RaptorChatterI’ve only edited the page that includes living horseshoe crabs, but for what I’ve seen from paleowiki… yeah, it’s a lot of reading. I’ve significantly expanded the article though, so while I don’t have to do too much reading, I have to do a LOT of writing (it’s kinda tiring)

[@RaptorChatter]

I do know James Lamsdell should be working on the new Treatise of Invertebrate Paleontology chapters on horseshoe crabs, so hopefully a good bit more in the future.

[@dennismason3740]

Paleoz are nerds? Imma trekker since 1966, not a warsian as John Williams hurts my bones and yes, I do better compositions.

[@posticusmaximus1739]

Not Crabs either!

[@aarnijarvelainen8499]

Nor horses or shoes

[@IcefloeProductions-qv2qg]

Semantics

[@Eloraurora]

This is sounding like crocodiles, a little. Fossils similar to what we have today, but also a lot more varied forms that have died out.

[@RiddleBoxBree]

I approve of the new wall art

[@connordarvall8482]

5:39 It sticks out like a horseshoe crab in a freshwater environment!

[@haraya_manawari]

I think the term just gives them more appeal and intrigue

[@robloggia]

What ever benefit fluorescence may have had, it certainly makes them much easier to find in the house.

[@RaptorChatter]

Retrospectively I should have had a UV light whenever I walked through the house in high school. Found 2-3 a month in the summer late at night. Never got stung by those ones fortunately.

[@vinniepeterss]

❤❤

[@DanDaFreakinMan]

I think the term is more for the noobs to describe creatures that visually look identical to their past counterparts. As a noob myself I can't tell the difference between even the alive horseshoe crab species apart so as far as I know they are all the same, including the fossilized ones.

[@011keepers]

New background art!?

[@TheDanEdwards]

The term "living fossil" should never be used. It's just a sensationalist term intended to grab attention.

[@thesjkexperience]

It sort of applies to some humans? 😂. Otherwise, agree! Always shocked by scientists who like “settled science “.

[@YoshiMario69]

Jist like objects running basic apps being called SMART devices, and now specialized apps being calles ARTIFICIAL INTELLIGENCE.

[@thesjkexperience]

@@YoshiMario69 Smart = well featured. It’s America, you know what the marketing department is going to do . Selling the sizzle, not the steak 🫣🤣

[@YoshiMario69]

@@thesjkexperience ´murica, who markets for the entire freaking world. Even in Mexico we can´t escape your bull crap haha

[@vinniepeterss]

😮😮

[@slizgi86]

The whole "living fossil" name is just a popular science clickbait talk. It is impossible that organism don't evolve even slightly within big amount of time.

[@Crocy]

Hello fellow fish 😛

[@catherinehubbard1167]

Love that tasteful and terrific eurypterid shirt!

[@RaptorChatter]

Hopefully we'll be selling them in the future! But lots of life stuff, so slow on doing that.

[@hypanusamericanus9058]

1:47 That's so sad 😭

[@pw6447]

Cool shirt.

[@Erikuzuma]

*Covers ears* I can't hear you la la la la!

[@casualsleepingdragon8501]

Creationist: that sign can't stop me because i can't read

[@FakeSugarVillain]

I just think they look a little bit silly

[@RaptorChatter]

Very silly for sure.