History ScienceMarchesOn / WalkingWith

* The episode depicts ''Anatotitan/Edmontosaurus'' as being considerably smaller than ''Tyrannosaurus'', but newer fossils indicate it was actually much larger, with specimens such as MOR 1142 and MOR 1609 suggesting lengths of over fifteen metres and possibly up to fifteen tonnes for some adults, far out-weighing the biggest ''T. rex''.

* The generic dromaeosaur goes unnamed in the episode because, at the time, there wasn't a named dromaeosaur taxon that was sympatric with T. rex, though supplementary material calls it ''Dromaeosaurus'', as isolated teeth known from Hell Creek and adjacent sites had previously been tentatively attributed to it and ''Saurornitholestes'', but both are only known from the previous Campanian age. Post-2013, there are now three named dromaeosaurs that coexisted with T. rex (the giant ''Dakotaraptor'', the small ''Acheroraptor'', and the midsized ''Dineobellator'', with the last one being from New Mexico). Furthermore, we now know that ''Dromaeosaurus'' had a rather deep, robust skull armed with strong jaws, and the same is true for ''Saurornitholestes '' ([[https://twitter.com/DavidEvans_ROM/status/1405155294540357637/photo/1 though it wasn't known until a well-preserved skull was found in 2014]]), in contrast to the ''Deinonychhus''-like skull shown here (on account of it being a PaletteSwap of the ''Utahraptor'', itself based entirely on ''Deinonychus''). It has even been suggested that the former two were more reliant on their heads for killing than the contemporary Asian velociraptorines (though they would have still used their feet and talons).

* The generic raptor is simply identified as a "dromaeosaur", because at the time, there wasn't a named dromaeosaur species that was known to have existed alongside ''Tyrannosaurus''; now there are known to be at least three (''Dakotaraptor'', ''Acheroraptor'', and ''Dineobellator'', with the last one being from New Mexico).

* The ''Muttaburrasaurus'' are shown as facultative bipeds similar to ''Iguanodon'', but later research indicates that they were obligate bipeds and much more primitive in form. They're also depicted with thumb spikes, but shortly before the show premiered, the description of ''Muttaburrasaurus'' was revised after no evidence was found for any.

* ''Postosuchus'' and ''Placerias'' are both depicted as sluggish and ungainly relics from a bygone age that are destined to be supplanted by the "superior" dinosaurs (not unlike how we used to view [[DumbDinos dinosaurs]] themselves back in the early to mid-20th century in relation to mammals), who are framed as being more versatile, fleet-footed and have the unique gift of bipedalism. Suffice to say, none of that is true, as all terrestrial Triassic tetrapods were just as agile, sophisticated, and well-adapted to their enviroment as early dinosaurs and most of them likely died out as a result of the [[https://en.wikipedia.org/wiki/Triassic%E2%80%93Jurassic_extinction_event Triassic-Jurassic mass extinction]], which also allowed dinosaurs to take over ([[HistoryRepeats in the same way mammals took over thanks to the K-T mass extinction]])[[note]]The narration by Creator/KennethBranagh does mention the Triassic-Jurassic extinction during the credits, mostly glossing over it by stating how the dinosaurs have continued to evolve[[/note]], and bipedalism wasn’t unique to dinosaurs, as several other contemporary archosaurs, such as rauisuchids (including ''Postosuchus''), proposaurids, and shuvosaurids were also bipedal and shared many other morphological similarities to true dinosaurs (the last of which looked [[https://en.wikipedia.org/wiki/Effigia#/media/File:Effigia_BW.jpg nigh-identical to dinosaur]] [[https://en.wikipedia.org/wiki/Shuvosaurus#/media/File:Shuvosaurus_BW.jpg to the untrained eye]]).

* ''Allosaurus'' was generally not as huge as depicted here, as most adult specimens are around 8-9 meters in length, not 12 meters. This may have resulted from confusion with a close relative called ''Saurophaganax maximus'' which actually did grow to 10.5-12 meters and 4-5 tons. However, some scientists do consider the two to be the same animal (although still as a separate species, ''Allosaurus maximus'', as opposed to the species most are familiar with, ''Allosaurus fragilis''). That said, fossils of giant allosaurs (including the giant ''Allosaurus amplexus'' as well as ''Saurophaganax'') are incredibly rare at Morrison and usually very fragmentary while the mid-sized ''Allosaurus fragilis'' is much more common, to the point of being the best documented of all macropredatory theropods. This also implies that the giant variety was a rare sight, which would make sense, as the large apex predator in any given ecosystem is bound to be rarer compared to the smaller mesocarnivores. So [[BiggerIsBetter showcasing the larger species in favor of the smaller one]] is more RuleOfCool rather than an accurate reflection of reality. ''The Ballad of Big Al'' does somewhat fix this issue, by emphasizing that gigantic specimens of ''Allosaurus'' are indeed a rare sight, but presents it as being due to most ''Allosaurus'' not living long enough to reach their adult size instead of being a case of species diversity and/or size variation within a species, as relatively few specimens in any given species reach their maximum potential size even if they live long lives.

* The episode depicts the European ''Anurognathus'' in North America and interacting with otherwise North American animals. This is probably because the actual pterosaur fossils of the Morrison Formation are pretty terrible. However, the genus ''Mesadactylus'' was tentatively classified as an anurognathid in 2007, so they could have used that instead of ''Anurognathus'' nowadays.

** The holotype hails from the Irdin Manha Formation, which turned out to be Mid Eocene in age (44-40 mya), not Late Eocene (39-34 mya), meaning it would not have been a contemporary of ''Embolotherium''. The apex predators of Late Eocene Asia would have been hyaenodonts and entelodonts (like the ones seen in "Land of Giants").

* ''Argentinosaurus'' would have looked different than the ''Saltasaurus''-like design in the show; giant titanosaurs are now known to have longer necks and upright-slanted postures similar to ''Brachiosaurus''.

* Any and all shots of pterosaurs taking off bipedally became inaccurate after it was discovered that they launched quadrupedally. The documentary also avoids showing the large pterosaurs taking off almost entirely, because at the time it was uncertain how such large flying animals could lift up from the ground. It's now known that they probably pushed off their front limbs to vault themselves into the air.

* ''Giganotosaurus'' is portrayed as briefly being able to chase a speeding car and suggested in supplementary material as being able to reach speeds of over thirty miles per hour. Later bio-mechanical studies on the running speeds of large theropods found it would have been impossible for them to run at high speeds, or possibly even run at all (that is, having a stride where both feet are off the ground at the same time for most of the stride) because they were so heavy their footfalls would have broken their legs, even if they had enough muscle mass to propel their massive bodies so quickly.

* ''Liopleurodon'' is identified as the largest carnivorous reptile to have ever lived. Aside from the aforementioned revisions about pliosaur size, just one year after the series premiered a gigantic Triassic ichthyosaur was described known as ''Shonisaurus sikanniensis'' (although it's sometimes considered a species of ''Shastasaurus'') which, at 21 metres in length, was far larger than any pliosaur or mosasaur. Fragmentary fossils of related animals suggest even larger sizes, possibly up to 26 metres in length, about the same size as the ''Liopleurodon'' is as depicted in the series. Although, since it was toothless and dolphin-like in shape, it wouldn't have been quite as fearsome-looking as a pliosaur or mosasaur.
* A number of mosasaur fossils have been found with shark like tail impressions (one long fin, one short fin). These fossils, and various other arguments, suggest that most or all mosasaurs would have looked more fishlike than the ones shown on the show. This, combined with the fact that it was warm-blooded, would have made it an even faster, more active hunter and give it access to polar regions.
* The largest mosasaurs probably didn't get as large in reality as they were portrayed because of this, as they would have had a more compact body shape. Lengths of between forty and fifty feet are considered more likely for the largest mosasaurs such as ''Mosasaurus'' or ''Tylosaurus''.

* ''Macrauchenia patachonica'' was actually a [[https://en.wikipedia.org/wiki/Macrauchenia#/media/File:Macrauchenia_wiki.png very imposing animal]], [[https://blogs.scientificamerican.com/laelaps/what-in-the-world-was-macrauchenia/ similar in size to a moose but more stocky in build]], weighing up to a ton, in contrast to the rather dainty animal depicted in the episode.

!!'''Reptile's Beginnings'''

* The ''Allosaurus'' is portrayed with an unusually short and blunt skull, but this is because the design is based on the ''Allosaurus'' neotype, USNM 4734, which had a rather poorly preserved skull that was distorted in the fossilization process, rendering it shorter and more rounded. It's now recognized that this was in error, but not before the error was repeated in ''The Ballad of Big Al'' (complete with the skull's smaller secondary crest ridges). Together, the shortened skull and the mistake of placing the horns over the eyes instead of in front almost make the ''Allosaurus'' look like a long-armed ''Carnotaurus''.

* Geologists now place the end of the Oligocene at 23 million years ago, instead of 25.

* The North American ''Polacanthus'' is now seen as a separate taxon, ''Hoplitosaurus''. The line that ''Polacanthus'' are "often found around ''Iguanodon'' herds" might have been alluding to the fact that that the former was at the time a minor wastebasket taxon, with several different nodosaurid fossils from throughout the United Kingdom, Spain, and (in ''Hoplitosaurus''' case) North America attributed to it. However, a 2020 study found that only the holotype could be conclusively attributed to ''Polacanthus'', and all other European fossils were too scrappy to conclusively classify.

* ''Elasmosaurus'' is stated to have also inhabited Russia and Japan, but these species are now considered to be either indeterminate elasmosaurid species for the former and classified as ''Futabasaurus'' in 2006 for the latter.

* * The cast of the episode wouldn't have all been contemporaries in real life. ''Therizinosaurus'', ''Tarbosaurus'', ''Mononykus'', and ''Saurolophus'' all come from the mid Maastrichtian Nemegt Formation (which gets namedropped by Nigel, meaning it's the episode's setting), which overlies the early Maastrichtian Barun Goyot Formation, and it, in turn, overlies the late Campanian Djadochta Formation (which houses ''Velociraptor'' and ''Protoceratops''). To complicate matters, velociraptorine and protoceratopsid fossils from the intermediary Barun Goyot Formation have subsequently been reassigned to separate genera (''Kuru'' and ''Shri'', and ''Bagaceratops'' respectively), which widened the age gap. Nemegt did house a medium-sized dromaeosaur (and possible velociraptorine) called ''Adasaurus'', but no protoceratopsid fossils are known from the site. Furthermore, Nemegt and Djadochta turned out to be quite different biomes, with the former being an alluvial plain and thriving with large dinosaurs, while the latter was more arid and desert-like (complete with sand dunes), and mainly housed small dinosaurs.
* Feather issues aside, ''Velociraptor'' was likely nocturnal.

* The episode uses the interpretation that crested and crestless ornithocheirids were respectively males and females (even suggesting the keel-like crest of "males" allowed them a different style of fishing from the crestless females). This was a pet hypothesis from the series' pterosaur consultant, David Unwin, but the idea does not have much weight behind it nowadays, primarily because there's no real evidence for it beyond speculation. The sexual dimorphism seen in ''Tropeognathus''/''Ornithcheirus'' in the episode is purely speculative anyway.

While ''Walking With Dinosaurs'' was generally accurate for when it was made, it is over two decades old now. New evidence regarding behavior, color and other details are always emerging. So, there are inaccuracies.

** The ''Elasmosaurus'' model has aged rather poorly, suffering from severe shrinkwrapping, which gives it a very bulbous head and skinny neck, along with an overly rotund body, while later reconstructions show it as a much more streamlined and hydrodynamic animal. It's also given a length of 50 feet, but that is likely an overestimate, as the largest known elasmosaurids likely didn't grow longer than 40 feet and taxonomic shuffling later placed the largest Niobrara specimens in the genus ''Styxosaurus'' (previously treated as a synonym of ''Elasmosaurus'' by some), leaving ''Elasmosaurus'' at a more modest 35 feet (its incomplete holotype is the only specimen that can confidently be assigned to ''Elasmosaurus'').

* The episode sets the tone that even before the asteroid arrives, dinosaurs are already doing poorly due to increased global volcanism poisoning the environment with toxic fumes, and the meteor is more like the straw that broke the camel's back. However, this stance on dinosaur mass extinction is highly contentious, and many newer studies indicate evidence for a drop in end-Cretaceous dinosaur diversity brought on by mass volcanism is inconclusive at best. Notably, few other dinosaur documentaries even mention it. The next prevailing view is that an impact event was indeed the primary reason for their extinction and they were doing very well beforehand, [[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6842625/ which is]] [[https://www.science.org/doi/10.1126/science.aay5055 currently the]] [[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7382232/ majority held view]].

* The ''Hyaenodon'' is described as being “as big as a rhino”, but no known hyaenodont approached the size of even the smallest extant rhino (the Sumatran rhino, which can still reach a whopping 800 kg). The largest known hyeanodont is ''Megistotherium osteothlastes'', with an estimated weight of 500 kg, but it lived in Early-Mid Miocene Africa, not Late Oligocene Asia. The largest species of ''Hyaenodon'' proper, ''Hyeanodon gigas'' (only known from teeth and jaw fragments), is estimated to have weighed 250-378 kg, about the size of a tiger. The exaggerated size was likely based on outdated methods used for calculating the body weight of hyaenodonts, based on the proportions of modern carnivorans. This failed to take into account their unique proportions compared to modern carnivores (specifically their proportionally larger heads), leading to overestimates.