Theropod gaping jaws

Adam Khor

T-Rex had a stronger bite but Allosaurus had a relatively bigger gape.

https://www.washingtonpost.com/national/health-science/which-dino-had-the-biggest-scariest-mouth-hint-it-wasnt-t-rex/2015/11/09/955fbd2c-834d-11e5-9afb-0c971f713d0c_story.html

Linnaeus

Hello Adam,

I have suggested, on another palaeontology forum, that the exceptionally wide gaping jaws of Allosaurus were useful for tearing off larger chunks of prey. These jaws, although amply equiped with fearsome, razor-sharp teeth, would have served more as hinged shears than as daggers. Allosaurs had hungry nestlings to feed, and needed to bring them food: good red meat. I am of the opinion that Allosaurus, after making the kill, would eat whatever it could on the spot, then shear off sizeable sections of meat with those immense jaws; this hearty "take-out" meal would have been personally delivered to the wee Allies waiting back at the nest.

Adam Khor

It's a cute picture but I don´t think there's any convincing evidence that Allosaurus took care of its young thus far. Looking at the skeletons of juvenile allosaurs they look like they could take good care of themselves (although I have never seen a true hatchling or very young infant tbh).

Linnaeus

Hi Adam,

It seems to me that, the more advanced faunal species become, the more helpless are their newborn offspring. Just-hatched insects, fish, crustaceans etc. are quite capable of fending for themselves.

Not always, tho. Take burying beetles- both parents actually take care of their offspring, feeding them with regurgitated carrion kind of what like one would expect from a bird. The larvae of bees, wasps and other social insects are pretty helpless too. As for fish, there's plenty of them that take care of their young (amazingly, some are capable of counting their numerous offspring to keep track of them). I can´t think about any crustaceans that care for their young but I wouldn´t be surprised if there were a number of them.

Baby amphibians apparently do not require parental care.

Again, there's exceptions- the African bullfrog male is a very dedicated father, closely keeping an eye on his tadpoles. There's poisonous frogs in South America that seek secluded "pools" for their tadpoles and then feed them constantly, like you would feed a pet fish. And caecilians not only care for their young, they feed them with their own skin.

But once we enter into the world of reptiles...most particularly prehistoric reptiles...matters change. Very young dinosaurs, before they learned to hunt and become familiar with their environment, were probably as helpless and vulnerable as week-old kittens. Their senses were most likely underdevoloped at that age; what is more, being so small and unable to run fast, they would have been easy prey for predators WITHOUT SOME KIND OF PARENTAL PROTECTION AND CARE, at least until they achieved an age sufficient to take care of themselves.

While we do know through fossil finds that some herbivorous dinosaurs (such as Maiasaura or Massospondylus) were indeed born underdeveloped and unable to fend for themselves, dinosaurs are a large and diverse group that lasted over 160 million years on Earth (without counting birds). We just can´t assume that because a few known dinosaurs cared for their young, then all dinosaurs did.
The evidence is particularly scant for theropods; we know some of them did incubate their eggs which is a kind of parental care, but just how much time they dedicated to their young after they hatched is a whole different matter. Many reptiles today care for their eggs but then leave their young to fend for themselves- this includes crocodilians, which are the dinosaurs' closest living relatives. This is rarer in birds- an example would be the megapode, which is born with flight feathers and is able to fly at one day of age. But if you looks at modern birds, the ones that are born most helpless are the ones from species that nest on trees, and are therefore safe from most ground-bound predators. Land birds tend to be much more precocial. Since large dinosaurs were obviously not nesting on trees, I'd venture precocial young were much more common than they are amongst modern birds.

And the known juveniles of theropods seem to support this. Take a look at the youngest known T-Rex specimen, MOR 6625 otherwise known as Chomper:





So it wasn´t a newborn but it does give us an idea of what a baby T-Rex looked like. Its skull and jaws are almost identical to those of adults of much smaller theropod species. And we know that young T-Rex had much longer legs and more slender bodies than their parents:




These are not the proportions of a "cute" baby animal that needs to inspire an adult's protective instincts. It was already a killing machine; able to run fast and catch smaller animals with ease. Chances are high T-Rex did not spend much time in the nest. Newborn T-Rex are believed to have been 45 cm long or so; the adults were 13 meters long and weighed up to 9-10 tons. The size difference is just insane. I wouldn´t be surprised if the baby T-Rex were hyperprecocial and just ran out of the nest almost as soon as they hatched, ready to terrorize bugs and lizards and other small fry.

Compare the proportions of the T-Rex above with those of baby Maiasaura and Massospondylus (some of the few dinosaurs for which there's good evidence of post-hatching parental care). They look a lot more like baby birds and mammals, with huge eyes and round heads.

But even these fierce carnivores mated (some perhaps for life), and produced wee offspring for which their instinct, if nothing else, may have inspired care and attention.

Again, we have no evidence taht they mated for life. I'm sure many of them did, but we don´t know which ones or how common it was.

I may be a just sentimental elderly lady

For some reason I assumed you were a guy until now :B

, but I tend to see each reptile or mammal as a marvellous being with feelings, emotions, the capacity for loyalty, responsibility, immense courage and...oh yes...love. Even the dinosaurs. Birds, the dinos' direct discendants which are not so different from them after all, all famous for the tender, untiring care they give to their young. And pet birds can be among the most affectionate of companions.

It is hard to generalize when it comes to such large groups of animals. I'm sure there were indeed some great parents amongst dinosaurs, as well as others that to our eyes wouldn´t be so great. We need more fossils... or a time machine.

Linnaeus

You've made some good observations, Adam. In the case of parental care among animal classes, I was speaking mostly of generalities. You brought out some interesting exceptions. Well, for every rule there is at least one exception.

Today's hyper-urbanized world has eliminated huge areas of jungles, forests and uninhabited land. There are fewer wild carnivores today than ever before, and far less danger to herbivores, which are increasingly concentrated on farms. But the entire Mesozoic was teeming with ferocious beasts. It was probably the most perilous epoch of all. T-Rex at two years of age may have been a seasoned killer; yet even he hatched as a spindly-legged morsel, probably capable of nothing more than waiting for mum to place some meat into his tiny gaping jaws. ALL living creatures go through a period of babyhood. In some species it's lengthy, in others brief; but all are born as wee critters, not full-grown prodigies like Athena springing in perfect adult glory from the head of Zeus. My assertion is simply that most animals, from reptiles up, require SOME parental care. How much depends on the individual species.

Yes, I'm a lady. An invalid whose love for prehistory keeps me alive. An eccentric amateur palaeontologist from Italy. I've chosen the nickname Linnaeus because that splendid scientist, the Father of Classification, is my hero. I stubbornly refuse to accept modern cladistics which would lump all descendants, offshoots, distant cousins and possible relatives together in an unnatural clade. I agree completely that birds are directly descended from certain feathered dinosaurs; but nothing in the world will ever convince me that birds ARE dinosaurs. More of this argument will be forthcoming...

Adam Khor

Linnaeus wrote: »

It was probably the most perilous epoch of all. T-Rex at two years of age may have been a seasoned killer; yet even he hatched as a spindly-legged morsel, probably capable of nothing more than waiting for mum to place some meat into his tiny gaping jaws.

I'm not so sure about this. Yes, it probably was born a spindly-legged morsel, but it was a spindly-legged morsel with lots of sharp teeth and everything seems to suggest it could run quite fast. Being small would not necessarily preclude it from being an acomplished hunter; after all, it wouldn´t be chasing after Edmontosaurus and Triceratops, but rather go after lizards and insects and small mammals. And since they apparently grew insanely fast (gaining over 2 kg per day at one point of its development), they wouldn´t even be that small and vulnerable for too long.

If you look at modern day reptiles, most of them are actually very well equipped to survive on their own. Newborn snakes are born with all their predatory instincts and sharp senses, and the venomous ones are already capable of delivering a precise and deadly bite from the moment they hatch. Hell, people have been bitten by snakes that weren´t even fully out of the egg yet.
Same goes for crocodilians; ready to swim and snap from the very beginning. And although some crocodilians do offer a degree of maternal care (by helping their babies climb out of the nest, and even carrying them to the water in their jaws), they really can´t keep an eye on them at all times once they're in the water. The babies have to fend by themselves, and hunt their own food. Yes, many die of starvation or eaten by larger animals, but this is why reptiles lay many eggs; at least one or two are bound to make it. What little we know about dinosaur reproductive habits suggests they too lay many eggs per nest.

Linnaeus wrote: »

ALL living creatures go through a period of babyhood. In some species it's lengthy, in others brief; but all are born as wee critters, not full-grown prodigies like Athena springing in perfect adult glory from the head of Zeus. My assertion is simply that most animals, from reptiles up, require SOME parental care. How much depends on the individual species.

Agreed, but babyhood is different for every animal. A newborn lion is utterly helpless; a newborn cobra can kill you. Regarding T. rex, since we don´t have any nests or eggs or complete hatchling skeletons, it is difficult to know whether they'd be more like lions or cobras. Honestly I have some trouble seeing a 13 meter long, 9-10 ton adult tyrannosaur feeding a bunch of 45 cm long critters without having some sort of accident. The size difference would be just insane. Crocodilians today care for their young to an extent but usually don´t feed them.

Like you said, of course, there are exceptions to every rule. I found this video of a mother crocodile allowing her young to feed on a piece of meat she's holding. Keep in mind, however, that these crocodiles are captive, so this is probably not a behavior you'd see in the wild, and also that the baby crocs are already quite big (nothing like the size difference you'd see between an adult T. rex and her newborn babies).

Linnaeus wrote: »

Yes, I'm a lady. An invalid whose love for prehistory keeps me alive. An eccentric amateur palaeontologist from Italy. I've chosen the nickname Linnaeus because that splendid scientist, the Father of Classification, is my hero. I stubbornly refuse to accept modern cladistics which would lump all descendants, offshoots, distant cousins and possible relatives together in an unnatural clade.

I have a fondness for Linnaean classification as well, if only because it's the one my father taught me as a child. Any given day he would randomly name an animal and I had to give him the full classification from Kingdom to species. I kind of saw it like a game.

Ziphius

Linnaeus wrote: »

Yes, I'm a lady. An invalid whose love for prehistory keeps me alive. An eccentric amateur palaeontologist from Italy. I've chosen the nickname Linnaeus because that splendid scientist, the Father of Classification, is my hero. I stubbornly refuse to accept modern cladistics which would lump all descendants, offshoots, distant cousins and possible relatives together in an unnatural clade. I agree completely that birds are directly descended from certain feathered dinosaurs; but nothing in the world will ever convince me that birds ARE dinosaurs. More of this argument will be forthcoming...

What are your criteria for distinguishing bird from non-bird?

Linnaeus

Hello Ziphius,

I would like to speak briefly here about class and clade.

Science should be...indeed, MUST be...precise in its concepts and definitions. The traditional Linnean method of classification provides such precision by placing life forms in well-defined families and classes. Cladistics, on the other hand, tends to cloud over the distinctions and particular unique features between families, classes and species, assigning faunal types to overly broad, often arbitrary mega-groups solely on the basis of supposed "family ties". Thus, birds, the direct discendants of theropods, are considered to be, cladistically speaking, highly derived dinosaurs. But by the same "logic", we might claim that mammals are simply highly derived reptiles, reptiles are advanced amphibians, amphibians just smarter fish with legs, and so on all the way back to the amoeba, which would be our remote clade-cousin too. Or we could just call ourselves hairless apes, according to cladistic principles.

But this hazy, all-inclusive cladistic practice ignores the fundamental principle of evolution, which is that species change, improve, become DIFFERENT and more specialized over time. One class is generated from another, by an evolutionary process which may be gradual or rapid but which always eventually produces new life forms, significantly different from that which went before.

Thus birds, as direct discendants of feathered dinosaurs, have retained certain features of these theropods, yet have evolved sufficiently away from the reptiles to merit a new class and classification: Aves, not super-modernized dinosaurs.

The drawing line which separates birdlike theropods from true birds may be extremely fine; but, for the sake of scientific precision, it is essential to identify it. For several years, I have been conducting specialized research on avian evolution. I am of the opinion that Iberomesornis is the earliest genuine bird of primitive type (Enantiornithes). Adam recently sent me some priceless info concerning a recently discovered creature called Archaeornithura meemannae, which seems to represent the earliest known bird of modern type (Ornithuromorpha). So we are getting closer all the time to identifying the elusive "missing link", which would be on the borderline between theropod and bird (a transitional creature, perhaps something similar to Rahonavis but earlier).

I am sending a very interesting article which sets forth, briefly, the main structural and physiological traits which distinguish birds from reptiles.

www.es.ucsc.edu/...0527%20BIRDS/08-0527%20...

Linnaeus

Hi Adam,

Once again, you have brought out some valid points. Thanks for telling me about the behavioural patterns of several species.

The infant T-Rex, still "in diapers", surely had sharp teeth and claws (so do newborn kittens; but at that age, do they deliberately use them for aggressive purposes?) He may not have had predatory instincts, right away, except maybe to snap up some lizards or insects that were scurrying by (as you suggested). I believe that T-Rex as a hatchling would not have known how to hunt properly: not unless he had been born with a highly-developed instinct, as some creatures possess (snakes and others that you mentioned). Let us remember that young birds must LEARN to fly; predators of many species LEARN to hunt; and it is their parents who teach them this. Another essential part of a young creature's education is getting to know its environment, learning how to identify the odours of foes and to avoid danger. Babies of all the higher species observe the behaviour of adults and acquire knowledge from this. They also need to gain practical experience.

I maintain that it's important to determine what is the proportion of instinct and acquired knowledge in animal behaviour.

Adam Khor

Linnaeus wrote: »

The infant T-Rex, still "in diapers", surely had sharp teeth and claws (so do newborn kittens; but at that age, do they deliberately use them for aggressive purposes?)

Technically cats are born toothless. They also can´t see and are really uncoordinated. Again, it is impossible to know if they're a good analogue to a newborn T. rex without having a hatchling fossil, but I would personally doubt it. In many ways non-avian dinosaurs resemble crocodilians; I suspect newborn T. rex was a lot more capable than a newborn kitten.

Linnaeus wrote: »

He may not have had predatory instincts, right away, except maybe to snap up some lizards or insects that were scurrying by (as you suggested).

I don´t see why snapping at lizards or insects wouldn´t count as fully-developed predatory instincts. Baby crocodiles start out snapping at aquatic bugs, tadpoles, diminutive fish etc. As they grow their prey grows, but the instincts remain the same.

Linnaeus wrote: »

Let us remember that young birds must LEARN to fly; predators of many species LEARN to hunt; and it is their parents who teach them this. Another essential part of a young creature's education is getting to know its environment, learning how to identify the odours of foes and to avoid danger. Babies of all the higher species observe the behaviour of adults and acquire knowledge from this. They also need to gain practical experience.

Yes, but most flying birds are born altricial (helpless and even featherless in many cases), and the adults dedicate a lot more time to their "education" so to speak. If T. rex was hyperprecocial, more like crocodilians or the megapode, then its parents wouldn´t really teach it anything; megapodes can fly without anyone teaching them. I honestly think this makes more sense for T. rex due to the size difference; it would've been completely unable to take on the prey its parents would hunt. By force it had to specialize on different prey.
As for gaining practical experience, this does not necessarily require adult supervision; baby crocodiles will snap at anything that moves, including twigs and floating leaves, but quickly learn what is food and what is not, all by themselves.

Linnaeus wrote: »

I maintain that it's important to determine what is the proportion of instinct and acquired knowledge in animal behaviour.

If only we could measure this from fossils... alas, we aren´t even sure when it comes to living creatures.

Linnaeus

Kittens are born toothless? I seem to remember that a little cousin of mine once roughly picked up a very small kitten, and got sharply nipped for it.

The main problem with understanding prehistoric animal behaviour is that we weren't there to observe it. Mere fossils can only tell, or rather hint at, part of the story. We must also take into consideration that each creature, even within one particular species, was an individual, and some parents may have felt more sense of responsibility than others: for example, one mother Maiasaur might have defended her hatchlings to the death, another might have chosen to save her own hide by running away.

Yes, a time machine would be useful for revealing the many secrets of the past.

Adam Khor

Then that kitten was at least three weeks old.

Yes of course there would be individual variation- but if we go there, we may as well stop discussing a species' general behavior altogether.