My backgound is mainly Entomology. The classification of juvenile insects is practically a different field of study. I can only imagine the problems we’d have if insects were known only from the fossil record.
maybe we in the alternate universe would discover a caterpillar transforming in a caccoon one day and the caterpillar fans would scream at the scientists making them dubious
The same thing is also true for extinct cephalopods like Ammonoids and Nautiloids. Their shells are made up of multiple chambers separated by septae. During the growth of the individual, more chambers are added to the shell. However in some specimens the early chambers are not preserved. The first (larval) part of the shell is called a Protoconch and is a very important feature for taxonomy, but it's often missing. It's also hard to tell if the specimen has already reached adulthood, because many species of cephalopods just keep growing their whole life. That's why nowadays there are sometimes giant squids and octopuses that can be far larger than the average. Some Ammonites like the genera Prolobites and Nautiloids like the Oncoceratids would constrict the opening of their last chamber to a small slit, so we can tell that they had stopped growing, but most species didn't to this. So while the largest found Ammonite Parapuzosia seppenradensis was "only" 2.5 m in diameter, there might have been far larger individuals. Then there is also the phenomenon of so called Microconch and Macroconch specimens of Ammonites, where the same species has a small and a large shell form. The big ones are postulated to be the females, because they would need more room to store eggs.
The idea seems both plausible and elegant. Even if it turns out to be wrong, or to account for only a few compsignathids, this is the type of suggestion that leads to a deeper understanding of the animals and ecosystems.
Very unsurprising. Jack Horner suggested this a while ago, but now they are expanding the theory to include other dinos apparently. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-kQa11RMCeSI.html
This is a cautious approach to certain mysteries. The broad concept that many taxa are misclassified juveniles has been suggested before, particularly amongst the ceratopsians. (Horner et al). This could be the start of a major reclassification amongst therapods. Time marches on, as they say.
The problem is complicated by lack of carcharodontid and megalosaurid growth stages. Hard to know precisely how hatchling anatomy differed from adults. Even with tyrannosaurs, for which there is more age-specific material, it's not clear which of the group's adult traits juveniles had or lacked. All adult tyrannosaurs possess several unique features, including a small premaxilla with D-shaped “incisor”-like teeth, fused nasals, extreme pneumaticity in the skull roof and lower jaws, a pronounced, verticle muscle attachment ridge on the ilium and an elevated femoral head. A Compie with a verticle iliac ridge could be confidently assigned to Tyrannosauroidea. My guess is that a feature like that would appear even in hatchlings. Similar distinquishing traits exist for other coelurosaurs, plus their fellow tetanuran megalosaurs and carnosaurs, but often without good development sequences. I'm still willing to accept a valid Compie clade, with perhaps wrongly assigned juvenile and dwarf adult members of other tetanuran groups.
Possibly, but consider the huge changes in many reptiles and birds as they grow to accommodate larger muscles and display structures, such as the incredible difference in head and body shape between baby and mature adult iguanas. Such a bone ridge could easily have been a structural adaptation that develops as needed to support the muscles layering on. Bones fuse, change, and grow throughout an animal’s life cycle, if only we could watch one mature… or if everything grew like giraffes. Baby= just tiny adult. 😅
@@danielled8665 You have a point, but even the youngest known tyrannosauroids have at least a protoridge. It might be the most diagnostic trait of the clade. But hatchlings, maybe not.
@@MechaShadowV2 That may be true, but you're basing that comparison on the external physical view of the lizard. When talking about (for the most part) just bone structure its easy to see how the classification can get muddled - especially as we have no true blueprint for how most dinosaurs changed through their age.
Compies: **act like land piranhas in JP2 instead of being small fox-like predators hunting lizards and small mammals** _"Allosaurus had never seen such bullshit before."_
This look at juveniles vs adult sizes is very important; compare the difference between a hatchling Asian Green Water Dragon to an adult, the difference is so dramatic you wouldn’t think they were the same species. Also compare a baby emu to an adult. I’ve also been reading about the possibility of different ages of the same species growing and changing to fill different ecological niches as they go through their lifespan, and the possibility of large sauropods laying such an insane number of eggs that baby sauropods could basically feed an ecosystem of predators on their own. After all, egg size is limited by surface area, so even a jumbo jet sized Dino couldn’t lay eggs much bigger than a football.
Comodo dragons do something similar. Their children are very small compared to them and they can climb trees. They fill that nieche and move on to the apex nieche once they grow up and lose the ability to climb.
As I recall, there is a deep sea fish, that for nearly a century, was considered two separate species. Only females had benn discovered of the one, and only males of the other. They were so different in size, shape, and feeding styles nobody imagined a connection. Then someone did genetic studies and the two species were suddenly recognized as one.
I don' think compsognathidea is a completely dubious group, as Sinocalliopteryx has at least one adult to represent it, and Sinosauropteryx had two well preserved eggs where the oviducts would've been. Still, Juravenator and Sciurumimus being juveniles megalosaurs is interesting.
Not much different than the offspring of large reptiles and a few birds of today. That is why we generally don’t find small turtle species together with large ones in the same ecosystem, unless they differ very much in body plan and lifestyle.
Some turtle species switch diets nearly completely iirc. Some switch from being nearly completely carnivores to herbivores and vice versa. If we just got a snap shot of those today we’d probably think they were different species, as that’s not super common.
Jurrassic park the lost world (no2) List says ~60 compies on the island. They encounter instead ~60 assorted giant therapods that have grown up. I mean it fits the theme of: 'don't screw around with things you don't understand' very very well.
In the context of the (1st) book that's an awesome idea! Compies play a bigger role in the plot and the book is themed more around catastrophic human misunderstandings of genetics. The book has a stronger tone of: *these are not truly* _dinosaurs_ *these are* _genetic nightmare hybrids._ The pressure of two (relatively) large rexes roaming the island might trigger the groups of compies to swarm in an effort to out-compete each other to rival the rexes by adulthood. We could imagine this antagonizing the rexes. Perhaps sexual dimorphism is the actual explanation of the "juvenile" rex and they are a mating pair. This might cause a pheremonal feedback-loop creating a breeding pressure-cooker for all the predators on the island. Maybe that's why the compies behaved differently on the mainland. That, combined with unexpected traits through hybridization with frogs or whatever could explain the lack of feathers on these compies, which might dramatically impact their behavior.
I think it's absolutely nuts how much within-species ontogenetic niche partitioning there was in the Mesozoic- so many r-selected large animals, totally alien to how large animals (mammals) have done things for the Cenozoic..
and to what degree was parental care, at least of hatchlings like modern alligators, a thing? Was it something that became more prevalent as the Cretaceous unfolded and that's why basal tetanurans went extinct? So many fascinating questions it opens about the ecology of the Mesozoic
This is what interests me about dinosaurs. No matter what we figure out or speculate, we won't know for certain, and the mystery, the unlimited "what ifs," are just wonderful. What if this separate dinosaur is just a juvenile of this other dinosaur? What if the growth of one dinosaur makes them change so drastically they seem like separate species? How did they hunt/eat, what do we think they looked like. I love dinosaurs
Ontogeny is something that needs more attention in the paleo-space. Ever since the Pachycephalosaurus situation I’ve wondered what animals could turn out to be the babies of other ones.
I'm sure some of them are. Some - but not all. Why wouldn't there be dinosaurs that were smaller? At the same time, it's important to understand growth stages of large theropods - and there just isn't enough information so far to understand what those were. We DO know it took years to reach full adult size.
Actually, if true, it would make sense that very few dinosaurs are small and meant to stay small. Just like how the roles of medium sized predators are filled by half-grown large sized dinosaurs, if the role of small predatorial dinosaur is being filled by the hatchling of larger dinosaurs,, it makes sense that there wouldn't be hardly any truly small predatorial dinosaurs. It would simply create too much competition for prey, and the chances that the hatchlings of the larger dinosaurs would outconpete them is far too great. However if operating under the assumption that they are all hatchlings, suddenly it makes sense. Ecological niches can only exist so long as the population of that niche is not overburdened by resource limitation. It makes more sense that the niche is filled by hatchlings of the larger species we know of than to assume that the hatchlings of the larger species coexist in perpetual competition with an entire class of species that are designed to stay the same size as a hatchling of a larger species. I would pose that the ones who are truly small to stay small are in the extreme minority.
@MechaShadowV2 we do see it today; where are the small species of crocodilians? Smallest is a dwarf caiman and it is still nowhere near as small as a hatchling alligator. They lay a large number of eggs, and their babies fill the "small sized crocodilian" niche, and the mid sized crocodilian niche.
My first thought on learning that the juveniles of large dinosaurs filled ecological niches that would instead be filled by other species in mammal-dominated ecosystems was that perhaps this is what made them the most vulnerable to mass extinction? If a handful of species are filling many critical spots on the food chain, it makes it a lot easier for the whole thing to collapse, right?
These cute, fluffy renderings are probably more accurate. These animals probably had alot more soft tissue and feathers and their faces were probably more rounded and less boney. It's fun to imagine skeletal, lizard skin theropods for our horror films, but reality is probably much cuter.
I imagine there were likely varieties of large theropod exterior appearances based on their native environment. Some likely looked more like big bird and others like my my bearded dragon. My bearded dragon exists after all and has scales.
I absolutely fuckin hate it when scientists say "we must be careful with this new hypothesis" as if the original idea was anything more than an untested hypothesis, that being "out of egg = adult". They need to defend and give evidence for compys being adults.
This is very exciting, there will be changes coming regardless of if the new classifications of the three species mentioned are accepted. Very compelling, it sounds like fun agonizing over Fossils and discovering possible a missing juvenile stages. It's like sorting puzzle pieces ! I love it!!!!
This is an interesting idea, definitely worth looking further into👍. i saw a program featuring the hypothesis of Draco-Rex being a young Paci. and it was really interesting, it explains alot about the features and how they would have changed over the aging of the dinosaur. i think it might have been in the Dino Revolution or Dinosaur Revolution series made like 10 or 12 years ago? 😳 wholly Crap. Has it already been 10 or 12 years since the first time i saw that? Oh dear🤦♂️. 😅
From what I found, if compsognathus itself was a juvenile it’s most likely torvosaurus because they had a very similar range and timeline, and torvosaurus is a megalosaurid, just like other dinosaurs described as adult forms of some compsognathids, but it could still be an undiscovered species or even it’s own thing
There really needs to be a tough little handbook of juvenile theropods with tons of illustrations of characteristics. Little bi-pedal dino fossil, check the manual, woo-lah, a baby allosaur.
I'm not sure how people missed this and seem to have assume most specimens are adults. Of course juveniles are not only smaller but have other anatomical differences. There is a word for this but I'm drawing a blank right now (anatomical traits of juvenile animals)
well it's hard to know what consistutes an adult and juvenile dinosaur since we don't have non-avian dinosaurs alive to examine, the only reason this is being addressed now is because we have built enough of a foundation and knowledge on dinosaurs that we can go back and check to see if our previous conclusions were wrong or based on now inaccurate information, this is just he process of science, you almost never get things exactly right the first time.
I have some curiosity regarding your drawing of a Compsignathid with an egg. That egg size does not appear to be oversized considering the egg sizes of many other small reptiles )lizards, snakes etc. Considering say the alligator which lays equal size eggs over its whole life span during which it may double in size - I tend to think that the egg laying may not have been only within the adult (allosaurus etc) and the Compsignathids were a reproductive stage of the larger therapods just not producing the same number of eggs. Does this seem to be possible to anybody else? With the inclusion that egg laying is not as demanding on the 'mother' as carrying live young would be.
The Nanotyrannus was clearly NOT a juvenile T. rex. It had more teeth and bigger forearms (in real size, not by proportion) than any of the known T. rex specimens including Sue. How could a baby T. rex have lesser teeth and smaller arms when it grew up?
Btw, I wish the field would use "shoulder height" or "stick measure" instead of meaningless measures like "length". Because it gives a much bigger idea of how big something really is.
This is the Paleontology version of Baby Dinosaurs hiding in a Trench Coat to see an R-Rated movie and the New Dinosaur species names are the names they put on their fake IDs. . . . Even if I am a sucker for dinos who happen to be smol. My favorite thing about Stegouros Elengassen is the guy being the size of a dog.
It seems like a pretty plausible and well thought out hypothesis, I would like to see what his peers say on the matter as more research is done to see whether he is right or wrong.
Nano Tyranis has been found to have a fully fused skull and longer arms than an adult Trex. So either there were mutant T rexes or more likely they were their own species
Is the concept of a fully fused skull even present in dinosaurs? As far as I know that's a mammal only thing, to facilitate birth, but egg laying animals dont have that issue.
Thank you very much for sharing this! BTW what theropod skeleton is shown in 12:2 ( I'm guessing Torvosaurus or Dryptosaurus)? To me, those teeth look as if they had fallen a good part out of their sockets, post mortem - or were these really thus long in life? .
The idea has merit to it, that's for sure. I'm curious to hear more of it. Though I certainly wonder what it means for compsognathus itself [my personal fav dino]
The only ones I'd consider "safe" (definitely not hatchlings) are Sinocalliopteryx, Sinosauropteryx, and Ubirajara, as all three has evidence of adulthood in at least one fossil. Compsognathus is still on the potential hypothetical chopping block of being just a hatchling of something else.
@@Specogecko I hate to be the actually guy But uhh, this guy wasn't making it up, It was instead made up by Jack horner. Who also made the T-rex was scavenger and Nanotyrannus. Also the guy who helped find the Maiasaura. (I think) while I'm not a big fan of him, he's fine sometimes and this is one of the times I agree with him I mean how likely is it that 3 pachycephalosaurus type dinosaurs lived in the same place at the same time.
@@stevetheheadcrab7110 I'm not a huge dinosaur expert but aren't there sites where multiple Spinosaurs are found? More generally, I know there are loads of sites with two sauropods, though that's a bit more general.
The thing is, the process of fossilization all but destroys organic matter. Practically speaking, the bones are turned to stone. And such a process also often destroys evidence of, for example, growth plates. It's hard to tell if a bone is mature when it's technically made of compressed minerals and not actually bone.
Happily given like, and humorous or insightful comment, for the Almighty Algorithm, here. 👋😊 Watching many of these in a row, and doing other things, so you get a copypasta. _~shrug~_
Typical science. I've seen the video of the remains of the nantyranus in the "dueling dinos" pair, and saw their comparison of that tyranosaur's forelimbs with recognized adult T-Rex forelimbs that were half the size. Can you name a single animal that is not parasitic, whose body parts shrink as they grow larger? If not, the alternative would be the "sub-adult tyranosaur" of that discovery would grow into and adult so much larger than any known individual of that species as to beg the question of whether it was its own separate species in its own right. This is where "science" fails. Because humans are involved, and money, true discovery is discarded in favor of established reputations and politics.
Can't all this be proven or disproven by checking the number of "rings " in the cross section of the compsignathid bones , thus confirming if the animal is a juvenile or not?
While it is cool how we're slowly learning how dinosaurs truly looked , I can't help but feel a little sad. I grew up thinking about how cool dinosaurs looked, only to learn years later that they're actually completely different. Like the spino, or the rex, two of which I always saw as sorta rivals.
If the French specimen of Composgnathus longipes indeed be an adult, then Genus Composgnathus at least contains small dinosaurs, with some or all not the juveniles of larger theropods. There should be other such genera in its family. But it's also likely that some specimens assigned to Family Composgnathidae are indeed juveniles of bigger tetanurans. The smaller European islands of the Late Jurassic might not have been able to support large theropods.
Even if Composgnathus is known from valid, small adult specimens it could have been a island dwarf of one of the larger groups like the carnosaurs. Hopefully more research will lead to less "mays" and "mights" about them.
@@chimerasuchus That's a plausible hypothesis. Cau's methodology might be able to resolve whether candidates are juvenile or dwarf megalosaurs or carnosaurs, rather than, as previously thought, small when adult coelurosaurs. It could be that feathers are more general among at least theropods, but that coelurosaurs retained more plumage as adults, thanks to smaller size. Some big ones however also were feathery.
With the big dinosaurs, of course their hatchlings and juveniles filled a totally different ecological niche. And of course these hatchlings and juveniles would have heavily competed with smaller dinosaur species. One could even argue that there was hardly a niche for smaller species as the many hatchlings of the large species filled all the niches during their growth.
They are more niches available for small predators than larger ones, so the offspring of the bigger theropods would have still been strictly in the minority. On the other hand, adult medium sized theropods were much rarer than in mammal-dominated ecosystems.
Now, more or less, accidentally find the skeleton of a suspected, previously unknown, juvenile 'Habsburg' male .. in Chicago .... then - Identify, classify, and call it: science. Ah! the joys of studying bones etc. Don't mock; well, not too much anyway (getting that Habsburg bit 'right' may just be a matter of guesswork, and rest on entirely coincidental or extraneous data, stuff like that happens). Keep up the great work, btw.
I liked them as land piranhas. Oh well. It's a fictional movie from my childhood anyway. Crosses Procompsinagthus off and writes reason as "Misidentified as a unique Dinosaur species when in fact they may have been the offspring of larger theropods." Sigh. Reality bites, but it's Reality.
Diplodocus were born from an egg the size of a football, and grew up to fit the length of a baseball field, that's a HUGE transformation to undergo. Dinosaurs, just like birds, undergo big transformations when they grow. So a compy being the juvenile version of a much bigger carnivore is completely plausible
2:16 looks so damn cuddly. That’s the one with known colors, and it just had to look like some lizard in a raccoon costume.🤣 I can imagine getting it as a “tiny dino” pet, then it would grow large enough to hunt down our neighbors. Too bad they’re all dead. Time to feel sad about random stuff like this...😢🥀
I think this is highly plausible, I mean a hatchling T-Rex had a long way to go before it reaches max size, yet at even just 2 meters tall it would be a huge predator in today’s times. Must’ve been a bloodbath back then...
They actually proved the micro Rex thing I believe, its arms were larger than an adult tyrannosaur. According to the video I watched, I'm not gonna pretend like I actually know
If you have an interesting theory that some are misclassified, you should be testing it on those most likely for the claim to hold true. It wasn't a direct claim that no compsignatid was real, just that some accidentally got misclassified. Now that his first hypothesis sounds reasonable, it's important to try and find for which others it holds true. Finding a compsignatid that clearly lacks juvenile traits, or trying to sort the family in "juvenile traits" and "lacking juvenile traits" could further solidify the proof. It almost solves to many problems to not be true.
wow this is really incredible ! I just don't know the skulls are so small and gracile on the compy's the adult carnosaurs and just massive comparably. I just can't see a snout in a small skull growing that much and becoming that much more robust. it's really a mystery
So compsognathidae could be the ugly ducklings turning out to be swans, eh? Very interesting theory, thank you for informing about it. ...would it be very rude to ask you to check out a video or two on Latin pronunciation? I got most of what you were saying, but some names I had to wait to see written.
As a kid, this theory was quite the possiblity. It isn't due to its size making it seem likely to be a juvenile but its distribution to be found where larger theropods are found and it being related to or in some cases cannot be properly classified. Before Horner stated something similar to Torosaurus and Triceratops, some dinosaurs already looked to be the younger or immature stage of another previously known dinosaur. I wonder how many other archosaurs are in a similar situation.
