Time Of The Titans: We're unsure about Stegosaurs using their plates to frighten predators, but it's cooler showing them this way; the same thing about the symbiotic behaviour in the tiny pterosaur called Anurognathus.
Also note that this episode (placed in Late Jurassic North America) is the most Stock Dinosaurs-filled of the six of WWD: we can see the largest/most striking animals of each subgroup, but not their smaller relatives just because aren't spectacular enough (with the notable exception of an unnamed small bipedal herbivore similar to Othnielia). We can see Allosaurus but not the smaller, horned Ceratosaurus (very common in old films but very rare in modern TV); Diplodocus and Brachiosaurus but not Camarasaurusnote Camarasaurus was the most common dinosaur of that habitat and was huge like its relatives, but since it didn't bear any record in length, height or weight, it was probably judged as "not cool enough"; the iconic Stegosaurus shows up while Iguanodon's relative Camptosaurus is absent being not so impressive-looking (never mind Camptosaurus was probably the main prey of Allosaurus), and the robustly built Ornitholestes instead of the slenderer Coelurus (although the latter appears in the book).
The "Ballad of Big Al" (also placed in the same habitat) had the possibility to add more non-stock animals as well, but producers decided instead to add only one dino, a stock one (and how!): Apatosaurus aka Brontosaurus.
Cruel Sea: Liopleurodon was not that big (50 tons and 50 ft seem more reasonable measures than 150 tons and 80 ft), nor was the largest carnivorous animal ever lived. The narrator tries to handwave it mentioning that it was an unusually large specimen, not to mention extremely old, over one-hundred years in age.
To be fair, there is fragmentary evidence of very large Liopleurodons or similar giant Pliosaurs implying they may have grown up to 70 ft.
Finally, primitive cartilaginous fish (generally called "sharks" in paleontology, but not related with modern sharks) shown with appearence and behaviour of actual modern-day sharks, with the one in the show resembling a bit like "horned Great Whites".
Giant Of The Skies: Ornithocheirus wasn't the largest pterosaur ever, and like Liopleurodon it wasn't that big anyway as shown in the program (best estimates say a wingspan of 20 ft, while other pterosaurs reached 50 ft). We can also add the Zerg Rush -like full bird attack against the old gigantic pterosaur.
And then, among Early Cretaceous dromeosaurids, the 18ft long Utahraptor was preferred to the much smaller Deinonychus, despite the former is far less-known scientifically than the latter. It's interesting though, that WWD Utahraptors are portrayed with the body and skull design Deinonychus was thought to have: thus Deinonychuswas represented in the show in an indirect way (much like the Jurassic Park "velociraptors"), but this time is justified, since we don't know how Utahraptor's head looked since its skull has never been discovered except for the very end of its snout).
Spirits Of The Ice Forest: This is the most speculative of the six episode of WWD, because dinosaurs from Cretaceous Australia are poorly-known compared to those from other habitats. One may add that all the animals portrayed seem more or less oversized in respect to their Real Life counterparts.
The Iguanodon relative Muttaburrasaurus with air sacs for making loud sounds: this one is a classic (but not demonstrated) theory regarding some iguanodontians and hadrosaurs like Edmontosaurus and Saurolophus because of the shape of their skull.
Death Of A Dynasty: Dromaeosaurus living alongside T. rex. It may be considered an example of Rule of Cool since dromaeosaurid remains coming from that period are very scanty, while those of the better-known but less dramatic relative Troodon are much more complete (however Prehistoric Park averted it showing the latter in the small predator role).
And, obviously, T. rex getting more than half the time, while the herbivorous ceratopsians, hadrosaurs and ankylosaurs have only minor roles (and most "small" dinosaurs from that habitat, such as ornithomimids, pachycephalosaurs & thescelosaurids, are totally missing, although ornithomimids do appear later in Prehistoric Park).
It's interesting, though, that T. rex and Ceratopsians do not battle this time (don't worry, they'll fight each other in Prehistoric Park...)
However in the companion book, a Tyrannosaurus does bring down a wounded Torosaurus (in the series, it survives and the rex is shown eating a Triceratops).
Weirdly inverted with Quetzalcoatlus; even if it wasn't known as a giant stork-like pteroaur note although this suggestion for their habits had been around since at least the early 90's, so they could easily have opted for that if they wanted to be "edgy", at the time it was commonly depicted as a giant vulture/marabou like scavenger. Instead, they opted for an Ornithocheirus like fish eater (nevermind that it lived inland and was found nowhere near the coast, as the episode implied it was a vagrant from the sea), not even dignifying it with a mention of it's status as the second largest flying animal that ever lived.
Though it was mentioned in the narration as a "13-meter giant", so it's possible that the writers simply felt that having to add onto that the explicit statement that it was the largest flying vertebrate ever would just be insulting the viewer's intelligence.
Walking With Beasts:
New Dawn: Carnivorous giant ants....just that. We don't know if they were really that voracious or even if they were carnivorous at all.
Other example is the whale-ancestor Ambulocetus portrayed just like modern Nile Crocodiles are in most documentaries, feeding only upon land mammals, while in Real Life it probably ate mostly fish (just like Nile crocodiles).
Whale Killer: Basilosaurus throwing a shark in the air just like orcas do with seals. And 60 tons seem too much for this very long but slender cetacean (perhaps 20 tons is a more reasonable measure).
Land Of Giants: Among the several Hyaenodon species of different size (from a small dog to a large cow), the largest of them all was chosen. And the boar-related entelodonts having huge mouths and capable to open them as much as hippos are... while most drawings show them with smallish, pig-like mouths instead. Finally "bear-dogs" (only distant relatives of modern canids) acting just like actual dogs.
Which might make the last example an aversion, as the bear-dog species depicted is of the smaller, dog-like kind, rather than the nowadays more famous, bear-sized variety.
Next Of Kin: Deinotherium entering in "musth" and chasing all the Australopithecus they meet just like modern elephants; however, deinotheres weren't elephants at all, just distant relatives (as much as we are related to baboons) and we have no proof about such a behaviour. Again, like hyenodonts, only the largest species of Deinotherium show up (the smaller one weren't bigger than modern elephants).
Sabre Tooth: Smilodon roaring just like lions (only felids pertaining to the modern genus Panthera can roar thanks to their specialized larynxes), and showing the same let's-kill-all-the-cubs behaviour typical of modern lions. But the most awesome example is the giant sloth Megatherium stealing a carcass to Smilodons and killing one of them in the process.
Prehistoric Park repeats the trope showing again roaring Smilodons.
About roaring Smilodons according to recent evidence, yes, they could.
Subverted/inverted in Prehistoric Park; here the male mammoth does charge Nigel and the huge rhino Elasmotherium which flees immediately (despite Elasmotherium weighs 5 tons as much as a male mammoth and has probably more chances to win a fight against the latter, being faster and more agile).
Walking With Monsters: Actually, this one might as well be named "Walking With Rule of Cool", it's filled with it from start to finish. Not counting the "Theia" hypothesis about the Moon's birth presented as fact, we have:
Cambrian Period: Anomalocaris fighting each other without any apparent reason, and the tiny vertebrate-ancestor Haikhouichthys scavenging the flesh of the loser Anomalocaris just like modern hagfish and lampreys; note Modern jawless vertebrates such as lampreys and hagfish are very specialized animals, while Hakhouichthys, being a very early animal, was more likely a filter-feeder, see Prehistoric Life. Also, the only true Cambrian invertebrate shown is, naturally, the first superpredator Anomalocaris (The others are generic trilobites.
Silurian Period: Armoured fish Cephalaspis portrayed as a tireless migrant despite it was a bad swimmer in Real Life (and depicted so just a moment before during the Brontoscorpio's chase); not to mention that scorpion which moults onto land instead of into water (with a high risk to get dehydratated...). Also Brontoscorpio being shown instead of the more classic-but-smaller Palaeophonus to represent the passage from water to land among arthropods.
Devonian Period: Always-screeching protoamphibian Hynerpeton (shaped upon the iconic Ichthyostega) that lays eggs with the same look of a frog's eggs; and primitive cartilaginous fish which look like a modern shark (as seen before in Cruel Sea). Also the Hyneria being used instead of the iconic Eusthenopteron to represent the transition from fish to amphbians because it's larger.
Carboniferous Period: The most Rule of Cool-filled of all: Arthropleura rearing just like a cobra to frighten enemies, and the giant anthracosaurian amphibian impaling the "giant millipede" after the fight. And giant spiders with black venom (Real Life spiders have colourless, water-looking poison) and apparently laughing sadistically upon its victims before destroying the nest of the tiny protoreptile Petrolacosaurus (with the narrator saying "ARTHROPODS ARE BACK!").
Early Permian Period: The rival female Dimetrodon chooses to lay her eggs just over another Dimetrodon nest despite all the endless room available... Interesting that Dimetrodonts are represented in a strong Komodo Dragon-like fashion in this show, despite being mammal relatives (and correctly shown with mammal-like skin instead of scaly, at last). Not to mention the Dimetrodont which sprays dung over the camera and the babies which dive themselves in dung to repel the (alleged) cannibalistic adults...
Late Permian Period: The Gorgonopsid shown is the largest member of its family (most relatives were much smaller than the near-reptile Scutosaurus which appears as its prey); the Diictodons playing a sort of Wack-a-mole with the gorgonopsid; the giant amphibian labirhynthodont which produces a "cocoon" just like modern lungfishes (there is no proof of this); and it seems there are too many Gorgonopsids that manage to survive around such a small lake almost empty of food...
Early Triassic Period: The herbivorous stem-mammal Lystrosaurus and the croc-like chasmatosaurs behaving just like modern wildebeest and Nile crocodiles; another stem-mammal, the carnivorous therocephalian, with a venom so powerful that "it's several times more lethal that a black mamba's" (we don't know even if it was venomous at all).
Sea Monsters plays it straight more than any other Walking With continuation: but it may be a bit more justified this time, since the purpose of this program was just showing "the most dangerous prehistoric marine wildlife".
However it's worth noting that the stock sea reptile Elasmosaurus shows up accurately at last, with relatively stiff necks (and not snake- or swan-like as seen in almost every other portrait).
Related to the Sea Monsters example above, the Land of Giants special also details Nigel Marven's efforts to track down the largest of all the dinosaurs and the biggest land predator ever: Argentinosaurus and Giganotosaurus, respectively. We get to see a whole pack of Giganotosaurus bring down a small Argentinosaurus, but if this wasn't cool enough for the viewers, they included a scene of Nigel's plane flying alongside a (still oversized) Ornithocheirus, and as the icing on the cake, included the gigantic crocodilian Sarcosuchus. Naturally, recent studies indicate Giganotosaurus wasn't the largest carnivorous dinosaur, and there may have been bigger dinosaurs than Argentinosaurus, but at the time it was made, they were considered record-holders.
Fragile? A fossil has been found of a Tarbosaurus with a fractured skull, probably by a therizinosaur claw or an ankylosaur tail club (it's in the hands of a private collector, though)
Talking about the "largest theropod" argument: if a complete Therizinosaurus skeleton is discovered in the future it could become the real largest theropod: thanks to its bulky body, it was perhaps heavier than the modern "biggest one", the sail-backed Spinosaurus (made famous by Jurassic Park III). But don't forget the equally impressive giant ornithomimid Deinocheirus: if its forelimbs were proportionate to the body, it might result as long as Spinosaurus and perhaps even taller than it. Let's see the awesome concurrence: both Deinocheirus and Therizinosaurus were large herbivorous (at least omnivorous in the case of Deinocheirus) theropods which dispute the record of the "longest forelimbs" among bipedal dinos; both are rather mysterious, since they are mainly known just from their forelimbs which once lead to the belief that they were predators even more powerful than T. rex; and both lived in the same habitat, were described in the same country (Mongolia) and entered the dinosaur list in the same period (the 1970's)! It will be awesome to see a Therizinosaurus vs Deinocheirus fight; or, alternatively, Deinocheirus vs Tarbosaurus.
A herd of Diplodocus mowing down a group of small predatory Coelurus with their spiky necks.
The Allosaurus-scene in the small canyon involves more predators (although the Allosaurus attack from the end is missing).
While in the series, the giant pterosaur Quetzalcoatlus just catches a fish, eats it, and then flies away, in the book, the poor thing is mangled and pulled into the lake by a bunch of giant crocs Deinosuchus.
And perhaps the most violent scene of all: the Ankylosaurus (who is a mother this time) isn't satisfied with "just" breaking the leg and messing up the internal organs of the T. rex... it brings her down to the ground, and continues to bash the T. rex's head with its clubbed-tail into a bloody mess... in front of their kids. The Tyrannosaurus chicks later drink the blood of their mother.
The Chased By Dinosaurs specials with Nigel Marven play this pretty straight by only showing the "cool" animals (especially Giganotosaurus, Argentinosaurus, and Therizinosaurus despite the latter probably being a relatively rare animal in its ecosystem), but it's more justified than most examples in the franchise since most of the time Nigel is specifically looking for the most Badass prehistoric animals, and probably chooses to go to places where he's more likely to find them.