History ScienceMarchesOn / WalkingWith

* Most [[UsefulNotes/StockDinosaursTrueDinosaurs coelurosaurs]] certainly had feathers. The several [[UsefulNotes/StockDinosaursTrueDinosaurs dromaeosaurid species]] surely had them, but in the franchise they are all shown featherless: this, rather than ScienceMarchesOn, might be interpreted more as RuleOfCool, or rather, ArtisticLicensePaleontology, since feathered non-avian dinosaurs were already known at the time; perhaps fluffy raptors would have appeared "too cute"? Another possibility is that the effects team had difficulty rendering convincing feathers. In RealLife dromeosaurids had WINGS just like their famous relative, the "ur-bird" ''[[UsefulNotes/StockDinosaursTrueDinosaurs Archaeopteryx]]''... This might be nothing compared to what is seeming to come: ''most small-sized dinosaurs'' may well have had some sort of covering. This theory was led by the discoveries of the primitive herbivore ''[[UsefulNotes/PrehistoricLife Tianyulong]]'' in China and ''Kulindadromeus'' in Russia, and further supported by [[https://www.nature.com/articles/s41559-018-0728-7 the discovery]] of feathers or feather-like filaments in two anurognathid pterosaur specimens from China: the theory is that some kind of covering was present in the last common ancestor of ''all'' dinosaurs and pterosaurs, and then it was partially lost by its largest descendants, possibly because of the [[http://en.wikipedia.org/wiki/Surface-area-to-volume_ratio#Biology surface area to volume ratio]]. Some think the "spikes" on ''[[UsefulNotes/StockDinosaursTrueDinosaurs Diplodocus]]'' have the same common origin of feathers, as well as the quill of the small herbivore ''[[UsefulNotes/PrehistoricLifeHadrosaurPredecessors Psittacosaurus]]'' and even the horny bumps lined on the back of several [[UsefulNotes/StockDinosaursTrueDinosaurs hadrosaur mummies]].

* The largest known pliosaurs were probably only around 15 metres or so at the most, and even that's pushing it for most species. As detailed in the tie-in book ''Walking with Dinosaurs: The Evidence'', the whale-sized ''Liopleurodon'' was based on an [[http://markwitton-com.blogspot.com/2020/04/in-pursuit-of-giant-pliosaurids-and.html assortment of jaw and snout fragments from Oxford Clay, as well as one vertebra around 25 cm in width housed at the Peterborough Museum]], which were interpreted at the time as stemming from pliosaurs reaching up to 18-20 meters in length (later estimates suggest that the Peterborough vertebra belongs to a specimen closer to 11-12 meters), with the main ''Liopleurodon'' of the episode being stated to be an [[BiggerIsBetter unusually large specimen]] of a species that ''on average'' reaches 18-20 meters in length. Further complicating things, some taxonomic shifting down the line transferred the largest alleged ''Liopleurodon'' remains (attributed to animals reaching 8-11 meters), such as the massive "Cumnor mandible", to the related ''Pliosaurus'', leaving ''Liopleurodon'' in the 5.5-7 meter range. Though it was still the biggest killer of its day before being replaced by (or possibly evolving into) the larger ''Pliosaurus''. Additionally, it should have a fluke on its tail, as should the ''Cryptoclidus''.

* The small size of the holotype of the megalosaur ''Eustreptospondylus oxoniensis'' (the only specimen we have of the animal) is no longer thought to be an example of island dwarfism but rather because the specimen wasn't fully grown. Furthermore, the fact that we have also discovered giant stegosaurs like ''Dacentrurus'' (one of the biggest of its kind) and even giant sauropods like ''Cetiosaurus'' in the same localities shows that the dinosaurs found in Late Jurassic Britain were just as big as their more famous American counterparts, despite the narrator's insistence that large dinosaurs were a rare sight here. Other sites, like the famous Lourinhã Formation in Portugal, further prove that large dinosaurs were in fact quite common in the European isles. Notably, the latter site revealed that the apex predator trio of ''Allosaurus'', ''Torvosaurus'', and ''Ceratosaurus'' weren't just endemic to North America but also to Portugal, along with possible fossils of ''Stegosaurus'' and the massive diplodocid ''Supersaurus''.

* The reason for ''Chalicotherium'' [[AnachronismStew showing up at the end of the Oligocene]] can be chalked up to it being used as a wastebasket taxon in the past. As it was the first chalicothere ever named, many different, often fragmentary chalicothere fossils across Eurasia and even Africa were historically placed in the genus, ranging in age from the earliest Miocene to the Mid Pleistocene (23 million to 800,000 years ago). The two largest species, the European ''Chalicotherium goldfussi'' (the type species) and Asian ''Chalicotherium brevirostris'' are only known from the Upper Miocene, and they are also the only species still confidently placed in the genus, with even ''Chalicotherium grande'', the most complete and best-researched species, being later reclassified as ''Anisodon grande''. Very fragmentary fossils belonging to smaller and more basal forms from the very Early Miocene were previously lumped into ''Chalicotherium'', "''Chalicotherium''" ''pilgrimi'' from the Bugti Hills of Pakistan, and "''Chalicotherium''" ''wetzleri'' from Western Europe, suggested that the genus showed up much earlier, but these are no longer considered members of the genus, and might not even be knuckle-walking chalicotheriines, with C. ''wetzleri'' being [[https://scholarworks.umass.edu/biology_faculty_pubs/120/ classed]] as a species of ''Metaschizotherium'' (a schizotheriine).

* The largest known pliosaurs were probably only around 12 metres or so at the most, and even that's pushing it. As detailed in the tie-in book ''Walking with Dinosaurs: The Evidence'', the whale-sized ''Liopleurodon'' was based on an [[http://markwitton-com.blogspot.com/2020/04/in-pursuit-of-giant-pliosaurids-and.html assortment of jaw and snout fragments from Oxford Clay, as well as one vertebra around 25 cm in width housed at the Peterborough Museum]], which were interpreted at the time as stemming from pliosaurs reaching up to 18-20 meters in length (later estimates suggest that the Peterborough vertebra belongs to a specimen closer to 11-12 meters), with the main ''Liopleurodon'' of the episode being stated to be an [[BiggerIsBetter unusually large specimen]] of a species that ''on average'' reaches 18-20 meters in length. Further complicating things, some taxonomic shifting down the line transferred the largest alleged ''Liopleurodon'' remains (attributed to animals reaching 8-11 meters), such as the massive "Cumnor mandible", to the related ''Pliosaurus'', leaving ''Liopleurodon'' in the 5.5-7 meter range. Though it was still the biggest killer of its day before being replaced by (or possibly evolving into) the larger ''Pliosaurus''. Additionally, it should have a fluke on its tail, as should the ''Cryptoclidus''.

* The largest known pliosaurs were probably only around 12 metres or so at the most, and even that's pushing it. As detailed in the tie-in book ''Walking with Dinosaurs: The Evidence'', the whale-sized ''Liopleurodon'' was based on an [[http://markwitton-com.blogspot.com/2020/04/in-pursuit-of-giant-pliosaurids-and.html assortment of jaw and snout fragments from Oxford Clay, as well as one vertebra around 25 cm in width housed at the Peterborough Museum]] (the latter of which turned out to have come from a sauropod), which were interpreted at the time as stemming from pliosaurs reaching up to as 20 meters in length, with the main ''Liopleurodon'' of the episode being stated to be an [[BiggerIsBetter unusually large specimen]] of a species that ''on average'' reaches 18-20 meters in length. Further complicating things, some taxonomic shifting down the line transferred the largest alleged ''Liopleurodon'' remains (attributed to animals reaching 8-11 meters), such as the massive "Cumnor mandible", to the related ''Pliosaurus'', leaving ''Liopleurodon'' in the 5.5-7 meter range. Though it was still the biggest killer of its day before being replaced by (or possibly evolving into) the larger ''Pliosaurus''. Additionally, it should have a fluke on its tail, as should the ''Cryptoclidus''.

* ''Ornithocheirus'' is shown as sexually dimorphic, with females lacking the keel-like crests. Again, this was based on a theory by David Unwin, who thought that ''Tropeognathus'' represented the male form of ''Ornithocheirus'', and that other fragmentary ornithocheirid (anhanguerid) taxa with larger and smaller crests respectively could actually represent males and females of the same species. Besides ''Tropeognathus'' being seen as a distinct genus now, this theory has largely fallen to the wayside, as it was otherwise based on fragmentary fossils that also came from various different fossil formations, so they can't confidently be identified as the same species. It's not ''impossible'' though that toothed pterosaurs exhibit sexual dimorphism, as the more distantly related ''Hamipterus'' from China is known from a large number of specimens, and the ones with larger beak crests are interpreted as adult males (though the apparent females and juveniles still aren't crestless).

* On a similar note, the idea that imagination is what distinguishes modern humans from our ancestors came from the fact that no signs of art from other human species had been found at the time. Since then, it's been found that Neanderthals carved artful objects and decorated them with pigments.

* The reason for ''Chalicotherium'' [[AnachronismStew showing up at the end of the Oligocene]] can be chalked up to it being used as a wastebasket taxon in the past. As it was the first chalicothere ever named, many different, often fragmentary chalicothere fossils across Eurasia and even Africa were historically placed in the genus, ranging in age from the earliest Miocene to the Mid Pleistocene (23 million to 800,000 years ago). The two largest species, the European ''Chalicotherium goldfussi'' (the type species) and Asian ''Chalicotherium brevirostris'' are only known from the Upper Miocene, and they are also the only species still confidently placed in the genus, with even ''Chalicotherium grande'', the most complete and best-researched species, being later reclassified as ''Anisodon grande''. Very fragmentary fossils belonging to smaller and more basal forms from the very Early Miocene were previously lumped into ''Chalicotherium'', "''Chalicotherium''" ''pilgrimi'' from the Bugti Hills of Pakistan, and "''Chalicotherium''" ''wetzleri'' from Western Europe, suggested that the genus showed up much earlier, but these are no longer considered members of the genus, and might not even be knuckle-walking chalicotheriines, with C. ''wetzleri'' being most recently classed as a species of ''Metaschizotherium'' (a schizotheriine).

* ''Proterosuchus'' is depicted as a semi-aquatic, crocodile-like swimmer. This was the traditionally held view, but more recent studies find evidence that conflicts with this idea and suggests it was a land-based predator, such as having strong, well-developed limb bones, nostrils placed on the sides of the skull rather than the top, and its fossils being known from arid environments. On the other hand, the traditional view has been upheld due to evidence from brain anatomy.

* The "American ''[[UsefulNotes/StockDinosaursTrueDinosaurs Iguanodon]]''" would probably be placed in the genus ''[[http://dx.doi.org/10.1016/j.cretres.2007.04.009 Dakotadon]]'' today. Likewise, the narrator alludes to ''Iguanodon'' being a highly successful genus that was both widely distributed and lasted for tens of millions of years, but this was due to ''Iguanodon''’s former status as a [[https://en.wikipedia.org/wiki/Wastebasket_taxon wastebasket taxon]], when any mid to large-sized ornithopod fossils from the Early to Mid Cretaceous (even if they were very fragmentary) were lumped into it. Subsequent studies, however, found that the only fossils attributable to ''Iguanodon'' come from Western Europe (Great Britain, Belgium, Germany, and Iberia) during the Barremian and early Aptian (130-122 mya), and even then, many iguanodont fossils from the Early Cretaceous of Europe have been reassigned to different genera like ''Hypselospinus'', ''Barilium'', and the aforementioned ''Mantellisaurus''.

* Studies at the time stated the saber teeth were brittle and could break when they hit bone, which actually was shown in the episode with the ''Smilodon'' only using their sabers judiciously while hunting and being very careful when eating carcasses. Later studies, however, have elaborated on this to explain their teeth weren't ''that'' brittle, and could still safely remove meat from carcasses. They could even eat much smaller bones, similar to what lions can do.

* It’s depicted as incredibly tall and lanky, with a very long neck and legs, coupled with a small head, basically resembling a 3-meter seriema. But now it’s known that giant phorusrhacids were [[https://www.researchgate.net/figure/Reproduction-of-the-skeleton-of-Paraphysornis-brasiliensis-based-on-the-holotype_fig16_26342981 stockier animals with large, ax-like heads]] used for striking down prey and it’s therefore unlikely that any terror bird reached 3 meters in height, including the largest known species, ''Kelenken guillermoi'', who is estimated to have stood between 2 and 2.5 meters tall. ''Titanis walleri'' in particular turned out to have been [[https://en.wikipedia.org/wiki/Titanis#/media/File:Life_reconstruction_of_the_terror_bird_Titanis_walleri.jpg even stockier than its closest relatives]], the polar opposite of what is shown in the episode.

* ''Megatherium'' probably wasn't as hairy as commonly portrayed, due to its large size and the fact that it lived in a warm climate. If it was shaggy as in the show, it would have overheated.
* ''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. Its design and proportions might have actually been based on smaller, more basal species, which have since been reclassified as separate genera (like ''Promacrauchenia'' and ''Huayqueriana'').

* Mammoth trunks in the show are based on their closest living relative, the Asian elephant, which only has one "finger". It is now known that mammoths had three fingers, and also that the sides of the trunk were expanded near the tip, allowing to warm it by rolling the trunk over itself.

* On a similar note, the idea that imagination is what distinguishes modern humans from our ancestors came from the fact that no signs of art from other humans species had been found. Since then, it's been found that Neanderthals carved artful objects and decorated them with pigments.

** Although a popularly depicted predator-prey relationship for a while, the idea that ''Anomalocaris'' fed upon trilobites is questionable now due to subsequent studies on the structure of its mouthparts and lack of wear suggesting that it wouldn't have been gnawing through their hard shells. More likely, ''Anomalocaris'' specialized on soft-bodied prey animals, such as worms. Previous evidence for trilobite predation, such as bite-marks and coprolites, are now considered to have come from the related dinocaridid ''Peytoia'' or giant trilobites, such as ''Redlichia''.

* The therocephalian being depicted as venomous is based on fossils of ''Euchambersia'' with possible venom gland pits in its skull and venom grooves in its teeth. However, a exceptionally well-preserved skull described in 2022 failed to find evidence of the supposed venom glands, making it possible they were actually scent glands. The venom idea remains possible, however (the venom being as incredibly potent as depicted is purely speculative though).

* A 2023 study concluded from ''Euparkeria'''s anatomy that it was not bipedal and was strictly quadrupedal, unable to rear up even for short periods because it was far too top-heavy. Barring some yet-to-be discovered genus, archosaur bipedalism must have evolved some time later during the Triassic, after the setting of the segment.

* This special portrayed the largest land animal of all time, ''[[UsefulNotes/StockDinosaursTrueDinosaurs Argentinosaurus]]'', being hunted by the largest land predator, ''[[UsefulNotes/StockDinosaursTrueDinosaurs Giganotosaurus]]''. Both have been supplanted since then: New evidence found that ''[[UsefulNotes/StockDinosaursTrueDinosaurs Spinosaurus]]'' was the biggest land predator (though it was partially aquatic), while ''Argentinosaurus'' has been surpassed in length by a specimen of ''Barosaurus'' described in 2016. (''Argentinosaurus'' is still heavier, though).[[note]]Even before ''Argentinosaurus'' was described its estimated size and weight was surpassed by those attributed to ''Amphicoelias'' and ''Bruhathkayosaurus''. However, the record size of ''Amphicoelias'' was based on a single partial vertebra that was lost shortly after it was described by Cope in 1878, and a 2018 study suggests it was actually classified as a different type of sauropod than it really was (a diplodocid versus a rebbachisaurid, which are known to have very tall vertebrae), resulting in a bloated total body length due to differing proportions(sixty metres versus thirty metres). meanwhile the estimated dimensions of ''Bruhathkayosaurus'' were never peer-reviewed and published (and since the type fossil was later lost in a moonsoon flood, no further study can be made on it) with some suggesting it was actually misidentified petrified wood. The accuracy of both original descriptions has been questioned. Evidence of other sauropod species exceeding ''Argentinosaurus'' in size still exists however.[[/note]]

* ''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 shattered their legs, even if they had enough muscle mass to propel their massive bodies so quickly.
* Like any 2000s-2010s portrayal of ''Sarcosuchus'', it’s depicted as a 12-meter giant. Those often cited estimates were originally obtained by Paul Sereno in 2001 based on the head-to-body ratio found in extant crocodilians (ranging from saltwater crocs to the gharial). But since ''Sarcosuchus'' is not a member of Crocodilia and represents a far more basal crocodylomorph, the notion that “Super Croc” had the exact same proportions as its closest living relatives has faced more and more scrutiny. Subsequent studies, using the length of the femur, have yielded a smaller size of 9-9.5 meters, and different studies, based on the width of the skull, have produced the same results. Thus it would seem that ''Sarcosuchus'' was marginally smaller than ''Deinosuchus'' (which is thought to have reached at least 10.5 meters at its largest).

* ''Leedsichthys'' would have had a more smooth head than its bone-plated portrayal in the show. As this fish is only known from numerous but very incomplete remains, there has been much confusion about its size, with early estimates suggesting it grew no larger than 9 meters, but in the 1980s, David Martill (a major consultant for WWD) calculated, based on the largest known gill baskets and using the more complete pachycormid ''Asthenocormus'' as a reference, that ''Leedsichthys'' could have possibly grown up to 27.6 meters in length. However, in 2007, the description of "Ariston" (the most complete specimen of ''Leedsichthys'' known) gave us a more accurate idea of its appearance and proportions, leading to its length being downgraded to 16.5 meters for the largest known specimens. This would make megalodon the largest known fish of all time, although ''Leedsichthys'' is still the largest known ray-finned fish ever.

* The supplementary book identifies the largest mosasaur as being ''Hainosaurus''. A number of studies since have considered ''Hainosaurus'' as being a probably synonym of ''Tylosaurus'' (on top of ''Hainosaurus'' being downsized from 17 metres to 12 metres in length, making it marginally smaller than the 13 metre long ''Mosasaurus hoffmannii'').

* The ''Argentinosaurus'' entry notes that titanosaurs are known from every continent except Antarctica; however, a titanosaur vertebrae was described from the continent (or at least, the outlying James Ross Island) in 2012.
* ''Velociraptor'' is stated to killed its prey by slashing at it with its retractable foot claws. Subsequent studies have indicated it probably couldn't slash and was more likely used for clinging to and pinning prey like modern hawks or falcons do.

* 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''/''Ornithocheirus'' in the episode is purely speculative anyway.

* The reasons for ''Chalicotherium'' showing up at the end of the Oligocene can be chalked up to it being used as a wastebasket taxon in the past. As it was the first chalicothere ever named, many different, often fragmentary chalicothere fossils across Eurasia and even Africa were historically placed in the genus, ranging in age from the earliest Miocene to the Mid Pleistocene (23 million to 800,000 years ago). The two largest species, the European ''Chalicotherium goldfussi'' (the type species) and Asian ''Chalicotherium brevirostris'' are only known from the Upper Miocene, and they are also the only species still confidently placed in the genus, with even ''Chalicotherium grande'', the most complete and best-researched species, being later reclassified as ''Anisodon grande''. Very fragmentary fossils belonging to smaller and more basal forms from the very Early Miocene were previously lumped into ''Chalicotherium'', "''Chalicotherium''" ''pilgrimi'' from the Bugti Hills of Pakistan, and "''Chalicotherium''" ''wetzleri'' from Western Europe, suggested that the genus showed up much earlier, but these are no longer considered valid members of the genus, and might not even be knuckle-walking chalicotheriines, with C. ''wetzleri'' being most recently classed as a species of ''Metaschizotherium''.

* The reasons for ''Chalicotherium'' showing up in the Late Oligocene can be chalked up to it being used as a [[https://en.wikipedia.org/wiki/Wastebasket_taxon wastebasket taxon]] in the past. The genus is known from some very complete material but all of those stem from the Late Miocene-Mid Pliocene (10-3.5 mya), with the oldest known fossils of chalicotheriines (the knuckle-walkers) stemming from the Mid Miocene (16-14 mya), while the only chalicotheres confirmed to have lived around the end of the Oligocene being the more basal schizotheriines (non-knuckle walking chalicotheres such as ''Ancylotherium'' introduced later), like ''Borissiakia'' (the best fit for “Land of Giants"). Very fragmentary fossils from the Late Oligocene-Early Miocene of Eurasia were previously lumped into ''Chalicotherium'', but those have since been deemed schizotheriines (the subgroup of chalicotheriids which did not knuckle-walk) or ''nomen dubia'', like “''Chalicotherium''” ''pilgrim'' (possibly a schizotheriine) and “''Chalicotherium''” ''wetzleri'' (now included in ''Metaschizotherium'', also a schizotheriine).

* The description of the more complete ''Gastonia'' also revealed several errors with the WWD reconstruction of ''Polacanthus'', most notably its elongated head, when ''Gastonia'''s skull is shorter and more rounded. ''Walking with Dinosaurs: The Evidence" (published in 2000) acknowledges this error, as well as the geographic displacement.

* The giant ''[[UsefulNotes/PrehistoricLifeNonDinosaurianReptiles Ornithocheirus]]'' was based on a specimen now assigned to ''[[UsefulNotes/PrehistoricLifeNonDinosaurianReptiles Tropeognathus]]''. Likewise, during the 90s it was indeed believed that the large specimen (MN 6594-V) might have had a wingspan of 11-12 meters (though those were the highest possible estimates), but it was not properly described at the time. During its final description in 2012, workers estimated its wingspan at around 8.2 to 8.7 meters, smaller than the giant featured in the episode, but still quite a massive pterosaur, second only to the giant azhdarchids. Sadly, it was lost during a subsequent museum fire, preventing any further research.
* ''Ornithocheirus'' is depicted in the episode making vast cross-continental migrations from South America to Europe due to the fact it was once thought to have lived on both continents; however, since the South American ''Ornithocheirus'' species has since been reclassified as ''Tropeognathus'', there is no longer direct evidence for it. That said, it's still possible (if speculative) that some pterosaurs migrated between continents, much like many extant birds.

* ''Polacanthus'' [[MisplacedWildlife showing up in North America]] was based on ''Hoplitosaurus marshi'', a fragmentary polacanthiine that some workers in the late '80s and '90s argued was a North American species of ''Polacanthus'', [[https://www.schweizerbart.de/papers/pala/detail/232/101114/Polacanthus_Ornithischia_Ankylosauria_a_transatlantic_armoured_dinosaur_from_the_Early_Cretaceous_of_Europe_and_North_America and was likely also inspired by then-recent news of more complete polacanthiine fossils]] being found alongside ''Utahraptor'' in the Cedar Mountain Formation of Utah. However, in 1998 (while WWD was in the middle of production), the Utah fossils were described as a distinct taxon, ''Gastonia'', and its describer James Kirkland, along with Ken Carpenter, argued against the proposed synonymy of ''Polacanthus'' and ''Hoplitosaurus'' that same year, citing that many of the anatomical similarities between them were actually plesiomorphic traits found in most early nodosaurs. Tellingly, the American cut of WWD changed the American ''Polacanthus'' into ''Gastonia''. Furthermore, a 2020 study found that only the holotype of ''Polacanthus foxii'' from the Isle of Wight could be conclusively attributed to the genus, with fossils from Iberia and other parts of Britain being deemed indeterminate polcanthiines/nodosaurs.

* The North American ''Polacanthus'' (or ''Gastonia'') 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.

* ''Leedsichthys'' would have had a more smooth head than its bone-plated portrayal in the show. Also, careful examination of its size range puts it at around 16 meters and 40 tons as opposed to 30 meters and 150 tons. This would make megalodon the largest known fish of all time, although ''Leedsichthys'' is still the largest known ray-finned fish ever.

* 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, even ''Walking with Dinosaurs: The Evidence'' admits that evidence for excessive volcanism during the Late Cretaceous is lacking and controversial, instead citing the alleged drop in saurian diversity and the possibility that a meteor impact wasn't "enough" to wipe out the non-avian dinosaurs completely to beef up the former argument. 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 crew went to great pains to film on areas of Chile with no grass. Now it is known that grass was already present in the Late Cretaceous (whether it was present in large amounts in the Hell Creek region is still unclear, however).

* A complete in depth review of the episode done in 2019 by [[Website/{{YouTube}} Ben G. Thomas]] can be found [[https://www.youtube.com/watch?v=7b2T6JXcjo4 here]]

* In 2020 [[Website/{{YouTube}} YouTubers]] Ben G. Thomas and [[WebVideo/{{TREYTheExplainer}} TREY The Explainer]] did an in depth review of the current inaccuracies and accuracies of the episode which can be found [[https://www.youtube.com/watch?v=0-jyUDp5UGg here]]

* What was thought to be evidence for "cannibalistic ''[[UsefulNotes/StockDinosaursTrueDinosaurs Coelophysis]]''" has been discredited. Some of the evidence was cannibalism was later seen as adult ''Coelophysis'' simply having died on top of juveniles, while the stomach contents of other adult ''Coelophysis'' was determined to be that of small crocodilians, not younger ''Coelophysis''. Granted, cannibalism in times of scarcity is pretty common among carnivores and is even confirmed to be the case in other theropods like ''Allosaurus'' and T. rex, so ''Coelophysis'' being cannibalistic is very plausible.

* The early long-necked dinosaur ''[[UsefulNotes/StockDinosaursTrueDinosaurs Plateosaurus]]'' could not walk on four legs.

* As the now-synonymous ''[[UsefulNotes/PrehistoricLifeOtherSmallTheropods Megapnosaurus]]'' indicates, ''Coelophysis'' was nocturnal.

* More refined radiometric dating has allowed the stratigraphic layers of the Chinle Formation to be more clearly defined, showing it stretches from about 223 to 208 million years old. ''Coelophysis'' is only definitively known from the latter end of this temporal range, so it is not actually known to have coexisted with ''Placerias'', which is from near the beginning of the stratigraphy, despite being from the same fossil formation, as more than ten million years separates the two.

* Most [[UsefulNotes/StockDinosaursTrueDinosaurs coelurosaurs]] certainly had feathers. The several [[UsefulNotes/StockDinosaursTrueDinosaurs dromaeosaurid species]] surely had them, but in the franchise they are all shown featherless: this, rather than ScienceMarchesOn, might be interpreted more as RuleOfCool, or rather, ArtisticLicensePaleontology, since feathered non-avian dinosaurs were already known at the time; perhaps fluffy raptors would have appeared "too cute"? In RealLife dromeosaurids had WINGS just like their famous relative, the "ur-bird" ''[[UsefulNotes/StockDinosaursTrueDinosaurs Archaeopteryx]]''… This might be nothing compared to what is seeming to come: ''most small-sized dinosaurs'' may well have had some sort of covering. This theory was led by the discoveries of the primitive herbivore ''[[UsefulNotes/PrehistoricLife Tianyulong]]'' in China and ''Kulindadromeus'' in Russia, and further supported by [[https://www.nature.com/articles/s41559-018-0728-7 the discovery]] of feathers or feather-like filaments in two anurognathid pterosaur specimens from China: the theory is that some kind of covering was present in the last common ancestor of ''all'' dinosaurs and pterosaurs, and then it was partially lost by its largest descendants, possibly because of the [[http://en.wikipedia.org/wiki/Surface-area-to-volume_ratio#Biology surface area to volume ratio]]. Some think the "spikes" on ''[[UsefulNotes/StockDinosaursTrueDinosaurs Diplodocus]]'' have the same common origin of feathers, as well as the quill of the small herbivore ''[[UsefulNotes/PrehistoricLifeHadrosaurPredecessors Psittacosaurus]]'' and even the horny bumps lined on the back of several [[UsefulNotes/StockDinosaursTrueDinosaurs hadrosaur mummies]].

* All the non-avian theropods have pronated hands, a position that is impossible in reality, instead they held their hands out to the sides, akin to their relatives the birds.

* The pillar-limbed croc-relative ''[[UsefulNotes/PrehistoricLifeNonDinosaurianReptiles Postosuchus]]'' was most likely a biped, or at least semi-bipedal, rather than an obligate quadruped. It would be a pursuit predator, not a slow ambush predator. However, it does rear up on its back legs in the episode for brief moments.

** The ''Placerias'' is depicted with tusks. Unlike most dicynodonts, ''Placerias'' actually had horn-like protrusions of bone projecting straight from its skull rather than tusks (technically, it also had tusks, but they're very small and hidden underneath these protrusions).

* ''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 environment 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 would later take 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''), poposaurids, 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]]).

* ''Brachiosaurus'' is no longer considered the largest land animal; the exact species of sauropod that was is not clear, one such candidate being ''Argentinosaurus'', but it wasn't ''Brachiosaurus''. The weight measurement given in the episode is also a bit higher than the maximum weight estimates considered plausible nowadays (over 70 tonnes versus less than 60 tonnes). This is likely due to weight calculation methods done on ''Giraffatitan'' (then considered a species a ''Brachiosaurus'', as noted in the companion book, which includes Africa as part of ''Brachiosaurus''' range) which are now considered to be flawed.

* Later discoveries of well-preserved sauropod skulls show that they had gums covering their teeth and a keratin covering on the end of the mouth forming into a beak-like structure. This is in stark contrast to the series depiction of sauropods with fleshy lips or exposed teeth.

* At least some ichthyosaurs could actually give birth to more than five pups at a time (up to eleven or more), and they came out head first. Most famous fossils purported to show mothers [[DeathByChildbirth dying in childbirth]] are actually of pregnant ichthyosaurs who died before birth, and the fetuses dropped out during decomposition.

* The prologue for "Death of a Dynasty" briefly mentions how tyrannosaurs never ventured into the southern landmasses and suggests that this might have been because the local abelisaurs were just as big and fearsome. This seems to be referencing a controversial idea from the '90s which proposed that southern carcharodontosaurs such as ''Giganotosaurus'' were part of the abelisaurs (later finds confirmed that they were derived allosaurs and had relatives in the north). [[note]] Also, some southern coelurosaurs such as the Brazilian ''Santanaraptor'' and Australian ''Timimus'' have been suggested to be basal tyrannosaurs, though that's very controversial due to the fragmentary nature of these taxa. [[/note]] Several fossils formerly identified as caecharodontosaurs, however, would eventually be reclassified as megaraptorids, and it turns out that the last of those were just as big as tyrannosaurs, resulting in a possible case of AccidentallyCorrectWriting.

* The prologue for "Death of a Dynasty" briefly mentions how tyrannosaurs never ventured into the southern landmasses and suggests that this might have been because the local abelisaurs were just as big and fearsome. This seems to be referencing a controversial idea from the '90s which proposed that southern carcharodontosaurs such as ''Giganotosaurus'' were part of the abelisaurs (later finds confirmed that they were derived allosaurs and had relatives in the north). [[note]] Also, some southern coelurosaurs such as the Brazilian ''Santanaraptor'' and Australian ''Timimus'' have been suggested to be basal tyrannosaurs, though that's very controversial due to the fragmentary nature of these taxa. [[/note]]