Take a moment to think about the appearance  of a modern bird – like a parrot, or something  

similar. We know these animals have relatively  thick bodies, feathery coats, unique patterns,  

and varying colors. Now, let’s look at a  parrot’s skeleton. You’ll notice that based  

on the bones alone, these birds seem like  they’d have long, slender frames — yet the  

layers of skin and feather coverings make  them look quite different than their gaunt  

skeletal structures might suggest. And this exact  phenomenon presents a practical challenge when it  

comes to reconstructing accurate depictions of  dinosaurs. An increasing number of soft tissue  

discoveries have suggested that many (though not  all) species of dinosaurs possessed more feathers,  

layers of fat, and other unusual details than one  might assume based on the outdated depictions many  

of us grew up with. The challenge of capturing  the forgotten peculiarities of dinosaurs is at  

the center of “All Yesterdays,” a book written and  illustrated in part by C.M. Koseman — whose work  

you may recognize from his other most famous book  “All Tomorrows.” The 2012 speculative paleo-art  

book All Yesterdays was created not just by  Kosemen, however, but also Darren Naish — an  

expert paleontologist and author, and John Conway:  a skilled paleo-artist. These three are brilliant,  

and I have links to where you can follow and  support them in this video’s description.  

Not long ago, I covered a section of this book  titled “All Todays,” in which the authors imagine  

what might happen if, millions of years into  the future, clueless alien scientists tried  

to create depictions of long extinct organisms  based solely on the fossil record — with pretty  

hilarious results. But I can’t emphasize enough  that, despite misconceptions to the contrary,  

All Yesterdays isn’t trying to belittle the field  of paleontology with these images — or suggest  

modern scientists are similarly clueless  when it comes to reconstructing dinosaurs.  

Paleoart has come a long way, thanks in part  to the efforts of these creators. The three  

authors — all of whom are deeply involved in  the paleontology community themselves — make  

it clear that modern paleontologists aren’t  just blindly interpreting fossils — but also  

making great strides in integrating studies of  feather impressions and soft tissue preservation  

to gain complete pictures of what these incredible  creatures might have looked like. However,  

there are still, of course, a diversity of  fascinating unknowns when it comes to dinosaurs,  

and All Yesterdays explores how speculation  — as long as it’s cautiously grounded in  

science — can both help and even play a vital  role in showcasing the intriguing possibilities  

of how dinosaurs might have looked and behaved.  All Yesterdays stresses a balance between caution  

and speculation, always pointing out that  many of the reconstructions within the pages  

might be completely off the mark. That’s just  the nature of speculation. With that said,  

let’s get started, and imagine what unique aspects  of dinosaurs may not show up in the fossil record.  

The first out-of-the-norm reconstruction of  a dinosaur All Yesterdays explores is of a  

Carnotaurus, drawn at a unique angle by John  Conway. While the bull-horned predators are  

usually depicted from the side, here, the authors  depict the animal head on — drawing attention to  

just how strange the animal looks — with its arms  stuck out to the sides in a bizarre display. The  

idea behind the strange spectacle comes from the  animal’s skeleton, which shows the animal had  

stunted, ineffectual arms — yet possessed unique  shoulders which would have allowed the animals to  

spread these arms out sideways in a way utterly  dissimilar to other large predatory dinosaurs,  

and seemed to serve no practical purpose. So,  the authors imagine the arms on Carnotaurus (and  

the related Majungasaurus, pictured here in C.M.  Koseman’s one of a kind style) were waved about  

in mating or territorial displays, potentially  alongside bright colors — not unlike many birds  

today. A bizarre concept to be sure, but not  altogether improbable given the available  

paleontological data. Of course, dinosaur colors  might have also gone in the opposite direction.  

Can you see the Majungasaurs in this image?  How about now? Here, the authors explore the  

possibility that some dinosaurs might have  had appearances which supported camouflage  

and mimicry: bending into the natural features of  the environment much like a modern stick-bug. Now,  

it’s usually smaller animals, not predators like  Majungasaurs, which employ camouflage. But some  

large modern predators’ body patterns, like the  tiger’s distinctive stripes which allow them to  

blend into tall grasses, do help them ambush prey.  So, it’s possible certain dinosaurs might have had  

similar camouflaged appearances. Here’s another  recreation which, at first, might be difficult to  

see. This is All Yesterday’s speculative concept  for a Plesiosauria, portraying the animal with  

impressive camouflage. Strange though this might  seem to anyone familiar with traditional portrays  

of Plesiosauria, the modern oceans are swarming  with remarkable forms of mimicry. Just look at the  

incredible appearance of something like a leafy  seadragon, and you’ll start to understand just how  

incredible past ocean life might have looked. Now,  the authors aren’t actually making a scientific  

assertion that this was what all Plesiosauria  (which for the record, weren’t actually dinosaurs,  

but adjacent marine reptiles) looked like.  Most Plesiosauria likely had smooth skin  

for better hydrodynamics, but it’s not impossible  some branches tried an ambush approach which may  

have favored better camouflage. An interesting  possibility for sure. Back on land, here’s a  

quite heavily feathered speculative reinvention  of a Therizinosaurus. The Therizinosaurus looks  

quite menacing based on its skeleton alone,  thanks to the animal’s absurdly long claws,  

which in the past excited artists and caused them  to make an overly-deadly looking animal — despite  

the fact the animal wasn’t a predator. The thick  layer of feathers certainly makes the animal look  

less frightening, and quite different from  their skeletal appearance. If you compare the  

gaunt skeleton of say, an owl, however, to the  quite different shape of the actual bird, you  

could start to see how such a difference between  skeleton and body size isn’t too crazy a concept.  

Therizinosaurus skeletons also have wide hips, so  it’s been theorized they have sizeable physiques.  

Beyond proto-feathers, All Yesterdays also  explores the hypothetical that some dinosaurs,  

like Heterodontosaurus, might have had defensive,  quill like structures — not unlike the defense of  

the modern porcupine. Seem hard to believe?  Well, a recent exceptionally well-preserved  

specimen of the early ceratopsian Psittacosaurus  was found with bristle-like quills on its tail.  

The Psittacosaurus is actually one of the most  completely reconstructed dinosaurs, and its  

appearance is certainly not tame. Paleontologists  don’t think the bristles on its tail were for  

self-defense, but it’s certainly possible some  geneses like Heterodontosaurus — which we also  

now know had some kind of spike-like dermal quills  — could have used their bristles for self-defense.  

Going further into hypothetical territory  regarding proto-feathers, the authors imagine  

a group of Leaellynasaura Amicagraphica as rotund  furballs quite different from the popular notion  

of a ‘dinosaur.’ Far from fanciful speculation,  however, the authors’ recreation is based on  

evidence that the Leaellynasaura lived in a  near-polar region, and almost certainly had  

to endure sub-zero temperatures. While one might  look at such a reconstruction and think it looks  

too adorable for a dinosaur, The Authors point  out the hesitancy around depicting dinosaurs as  

‘cute’ is a potentially an overly-limiting  one. Also incorporated into this design,  

Leaellynasaura tails were almost three times as  long as their body, for reasons paleontologists  

aren’t quite certain of. All Yesterdays depicts  their tails as strange, flagpole-like tools  

for social displays. While easy to dismiss this  concept as overly-speculative, the authors point  

out that while it’s certainly unlikely, it’s only  so much weirder than what you might see anywhere  

else in nature. But appearance is only one half of  the speculative puzzle when it comes to dinosaurs.  

The authors observe that various unique behaviors  likely weren’t preserved in the fossil record.  

Just think about the mating dances of birds  of paradise, the unique calls of whales,  

or even something as simple as the dung rolling  of Dung Beetles. All of these behaviors are huge  

parts of what gives these animals their identity,  and yet most of them could never be understood  

from remains alone. And it stands to reason  some dinosaurs might have had behaviors which  

fall into the same category. Here’s an intriguing  speculative example of the Elasmosaurus, marine  

reptiles which aren’t actually dinosaurs, behaving  in a highly unusual manner. Here, the authors  

invent a scenario where the Elasmosaurus lunge  out of the depths and wave their necks — competing  

to prove who is the strongest. Older art of  Elasmosaurus sometimes shows them holding their  

necks above the water’s surface with ease, but  modern paleontology has proven these animals had  

heavy bones and dense necks, which could only be  lifted out of the water with significant effort.  

So, the authors imagine these animals exerting  such strain as a form of social competition.  

Of course, this is absolutely and unapologetically  speculative, yet equivalently remarkable behavior  

is likely lost somewhere in our past. In a similar  vein of speculative thought, here the authors  

imagine Protoceratops engaging in a behavior  there’s no direct evidence for in the slightest.  

And yet, certain breeds of goats also climb  trees, a strange-looking behavior you wouldn’t  

guess the hooved mammals would engage in based on  its body plan alone. It’s something like this sort  

of unexpected conduct which might be absent in the  fossil record. (and yes, these modern goats? They  

are not a hoax—they truly hang out in trees.) On  the subject of dinosaurs doing things they’re not  

known for, playing is certainly a significant  example. Instead of showing a dinosaur striking  

a pose or getting attacked by a predator, this  recreation shows a Carmarasaurus grandis enjoying  

a simple roll in the mud. Speculative though this  might seem, almost all living animals engage in  

some form of play —both larger mammals, but also  various species of birds, reptiles, and even fish  

take part in behavior for no other practical  reason that it seems to be fun. So dinosaurs,  

even if they’re sometimes thought of creatures  that lived in constant battle with each other,  

almost certainly engaged in play too. And here at  the end is an image which, despite its simplicity,  

is one of the hardest to process. It’s showing a  t-rex just sleeping — but so much of our classic  

perception of the creature is of a roaring  monster with its jaws agape ready to strike,  

that we forget the tyrannosaurus is also…  just an animal. And animals sleep — especially  

hunting animals, who need to conserve energy and  therefore spend a considerable amount of time  

resting. It’s not certain if T rex’s slept  on their sides or not — but it’s still an  

intriguing image that gets the viewer to think of  the animal as more than just a machine of death.  

Ultimately, science and speculation aren’t  concepts in opposition to each other.  

All paleontological art of long-extinct creatures  is speculative to some degree, and thinking about  

interesting — albeit unusual — possibilities,  can help us appreciate all we know — and don’t  

know — about these remarkable animals from the  distant past. And that’s the end of our glimpse  

at the intriguing “All Yesterdays.” If you liked  this content, please consider supporting Kosemen,  

Naish, and Conway’s work by purchasing  a copy of the book — and by patronizing  

their other works and social media, which as  always you can find in the links below. Also,  

thanks for watching. If you enjoyed this entry,  please lend your support and like, subscribe,  

and hit the notification icon to stay up to date  on all things Curious. See you in the next video.