What ’s your pet dinosaur ? If you say “ pterodactyl ” , then oof – we ’ve flummox bad word . The same goes for anybody who went for a plesiosaur : they were n’t dinosaur , and neither were their fell crony .
“ You may intend that an beast is a dinosaur because it ’s with child and scaly , ” paleontologist Danny Barta , then a PhD Candidate at the Richard Gilder Graduate School , American Museum of Natural History , in a2018 videofrom the Museum . “ But these trait evolve much earlier in evolutionary history . ”
These are far from the only case of thing you may have thought were dinos , but actually are n’t . So , who else qualifies ?
Artist’s rendition of Aigialosaurus bucchichi, a basal mosasauroidImage Credit: FunkMonk (Michael B. H.), viaWikimedia Commons(CC BY-SA 3.0)
Pteranodons and Pterosaurs
Yes , we know – they ’re one of the most famous types of prehistoric creature out there ; one of the Big Four you determine of as a kid ( alongsideTyrannosaurus rex , Triceratops , andStegosaurus , of class ) ; heck , they ’re literally five out of the six main theatrical role inDinosaur Train . But no : Pteranodons – and their cousins , pterosaur – are not , in fact , dinosaur .
“ dinosaur and pterosaurs separate from one another nearly 250 million twelvemonth ago , ” explained Barta . “ 250 million years ago is really a long time geologically , ” he added , “ so dinosaurs and pterosaurs , while they may be close cousins in an evolutionary good sense , are really quite widely separate . ”
An disposed comparison might be humans and chimpanzee . We share a common antecedent , and we ’re middling tight related – but still , we ’re definitely not the same thing .
Artist’s impression of Dimetrodon gigashomogenesImage Credit: Nobu Tamura,spinops.blogspot.com,paleoexhibit.blogspot.com, viaWikimedia COmmons(CC BY-SA 4.0)
There are measurable physiologic differences separating the two clades : dinosaurs , notably , have a fix in their hip socket and a summit along their upper arm , while pterosaurs do n’t ; pterosaurs , conversely , have a super - prospicient 4th finger that supports their annex – like a bat – while dinos not only lacked this buttended to recede digitsthe further through clip they survived .
But “ just because flying reptile are n’t dinosaurs does n’t make them any less awing , ” Barta point out . “ They ruled the skies for over a hundred and fifty million years , and I think that ’s really cool . ”
Mosasaurs
Okay , come on now : this one not only has “ saur ” decently there in the name , but it ’s also a lead attraction in Jurassic World ( the repair ) and the bomber ofJurassicWorld(the film ) .
But , alas , the mosasaurs were not dinosaur . As with plesiosaurs , the biggest game show is its habitat : “ With the elision of some hiss , for lesson penguin , dinosaur lived on nation , not in the ocean , ” points out theNatural History Museum , London .
That ’s not the only feature that disqualify the mosasaurs from dinodom , though . dinosaur “ had an good stance , with leg vertical to their body , ” the Museum explains – “ this is the chief feature that sets dinosaur aside from other reptilian . ” As aquatic , swim reptiles , mosasaurs had fins , or flippers , or at well little flappy leggies that hang out on either side of their body like a crocodile ’s .
Fossilized skeleton of Deinosuchus, in Natural History Museum of Utah, Salt Lake CityImage Credit: Daderot viaWikimedia Commons(Public Domain)
Then there ’s the issue of … well , result . dinosaur laid eggs ; mosasaurs did n’t . They were quite the mish - mash of features from a modern - day view , really : they were scaly , like lizards , but most likely ardent - blooded ; they lived in the water , but breathed air rather than through gills – and , very unusually for a reptilian , theygave nascence to live young .
So , if not dinosaur , then what ? Well , one way to remember about it is this : while the dinosaurs – or at least , the therapods – evolved downinto birds , mosasaurs are most likely related to today ’s snakes or monitor lizard .
Dimetrodons
This one is n’t so immediately recognizable , which is a shame , because it ’s doing its best . The genusDimetrodonwas liberal – potentially over 2 meters ( 6.6 foot ) in length , depending on species – scaly ; ate “ basically whatever they desire , ” Kirstin Brink , a palaeontologist and paleontologist at the University of Manitoba in Canada , toldDiscover Magazinelast year ; and just look at that sail !
ButDimetrodonspecies were not dinosaur – in fact , the extinction of these huge predators actuallypredatesthe dinosaurs by around60 millionyears . That may be why it ’s still such a mystery to advanced expert : its sail , for example , is “ decidedly puzzling , ” Brink said , and even its classification is “ still a routine of a mess . ”
What we do roll in the hay , though , is thatDimetrodonspecies weren’tjustnot - dinosaur – they were in reality more close related to mammals than other dinosaurs . “ We are really closer related toDimetrodonthan any other reptilian is , ” Brink enjoin Discover .
Is this the weirdest animal to ever exist?Image Credit: Emma Finley-Jacob
Now , to be clear , the animals in all likelihood were n’t the ascendant of modern mammals : they were what ’s known as synapsid – a radical thattodayconsists only of mammals , but that ’s just becauseeverything else in the family tree pall out .
outdoors of its genealogy , though , perhaps you could see a few other telltale sign thatDimetrodondoesn’t go in the dinosaur group . First up , there ’s that leg locating : squat and sprawl , not just and underneath , like dinosaur . ascertain the skull , and you ’ll see a single pickle behind the optic socket – a humble clew , but an important one , since dinosaur “ had two holes behind the eye socket , ” the Natural History Museum , London explicate , with “ enceinte , strong jaw muscles [ that ] went through the holes to attach directly to the top of the skull . ”
Crocodilians
They ’re big , scaly , chilling , and magnificently have been around since just about the morning of time . So surely , crocs and alligators are dinosaurs , right ?
Nope ! Like Pteranodons , these reptiles branched away before the dinosaurs really became dinosaurs at all – in fact , they ’re further off , genealogically speak , than Pteranodons are from the dinosaur ( and of course , with their sprawling leg view , they do n’t qualify as dinosaur disregarding of when they split off ) .
Now , we may think of crocs and alligator as scary mofos today , but naturereallydidn’t mess around back in the Cretaceous period . TakeDeinosuchus , for example – the name literally means “ terrible crocodile ” , and that ’s credibly becauseit wassome 10 meters ( 33 feet ) in duration , weigh up to five tonnes , and had a bite forcepotentially more than six timesas strong as a modern saltwater crocodile .
It ’s not surprising , then , that experts think this mega - dilelikely chowed downon real dinosaurs – even quite large 1 , like the nine - time - recollective , four - t Kritosaurus , whomit subsist alongsidein what is now Texas .
And if the crocodilians have a motto , it ’s manifestly “ if it ai n’t break , do n’t set it ” . Not only do today ’s crocs calculate virtually superposable to their ancient ancestors – albeit littler – but they also likely hunt the same way , using “ death rolls ” that wereperfected some 80 million old age agoby great - great - grandmaDeinosuchus .
Tanystropheus
Tanystropheuswas a weird lookin ’ creature : 6 meters ( 20 feet ) long from nose to tip , andmore than halfof it was neck .
It was , Stephan Spiekman , a paleontologist at the University of Zurich , enjoin theNew York Timesin 2020 , “ one of the most problematical animals that ever lived . ”
“ How could this brute even breathe or swallow ? ” he said . “ And then there is the evolutionary query : Why on ground did this beast germinate this ridiculously long neck ? ”
Now , Tanystropheushas essentially been baffling paleontologists ever since it was first described back in 1852 . At first , its neck was so farseeing as to convert its finder that it was actually two animal instead of one . Then , people think those stretched - out cervical vertebrae must have supported a wing membrane , and classify it as a pterosaur . But even when they were go it so wildly incorrect , the experts all agree on one thing : Tanystropheuswasn’t a dinosaur .
So why not ? After all , it ’s scaly , ancient , and – at least some of the time , potentially – a country animal ( most potential it wasat the very least semi - aquatic , if not mostly aquatic ) .
On the other hand , it lacks the upright legs of a dinosaur – once again , we ’ve got a waddler on our hands . They also live a tad too betimes to well be a dinosaur , hang out in the middle Triassic rather than the dino flush of the Jurassic and Cretaceous eras .
Mostly , though , Tanystropheusis just in the wrong part of the evolutionary tree diagram . They ’re descend from a dissimilar line from dinosaurs – think mankind vs emulator ; pteranodons vs dinosaur ; justeven furtherback than that .
Still , it was “ quite successful in evolutionary terms , endure for at least 10 million old age and happen in what is now Europe , the Middle East , China , North America , and perchance South America , ” Spiekman pronounce in a 2023statement .
That was despite its ridiculous neck , which Spiekman and co-worker had found was undoubtedly a weak point for the fauna : an inspection of some fossils ofTanystropheusheads and necks – justthe head and neck , brutally end before the trunk as if ripped in two – let on clear bite gull at the interruption , suggest a vulture had gone directly for the neck in its hunt for a tasty meal .
Ah , well . “ Evolution is a game of trade - offs , ” Spiekman said . “ The reward of have a long neck opening clearly outweighed the risk of being direct by a predator for a very long time . ”
