Name: Amphicoelias ‭(‬Double hollow‭)‬.
Phonetic: Am-fee-see-le-as.
Named By: Edward Drinker Cope‭ ‬-‭ ‬1878.
Synonyms: Amphicoelias latus.
Classification: Chordata,‭ ‬Reptilia,‭ ‬Dinosauria,‭ ‬Saurischia,‭ ‬Sauropodomorpha,‭ ‬Sauropoda,‭ ‬Diplodocoidea.
Species: A.‭ ‬altus‭ (‬type‭)‬,‭ ‬A.‭ ‬fragillimus.
Diet: Herbivore.
Size: Uncertain due to lack of and subsequent loss of remains,‭ ‬but estimated between‭ ‬40‭ ‬and‭ ‬60‭ ‬meters long.
Known locations: USA,‭ ‬Colorado.
Time period: Kimmeridgian to Tithonian of the Jurassic.
Fossil representation: Fragmentary and isolated remains,‭ ‬original fossils are now lost.

       Amphicoelias is a contender for possibly the biggest dinosaur ever known.‭ ‬Unfortunately as with most such claims there are a lot of ifs,‭ ‬buts and maybes to consider before awarding Amphicoelias the title of biggest dinosaur and possibly even vertebrate.‭ ‬The controversy about Amphicoelias begins back with the original description of a vertebrae and femur that were first described by Edward Drinker Cope back in‭ ‬1878.‭ ‬The vertebrae,‭ ‬though incomplete,‭ ‬was believed to have been as large as‭ ‬2.4‭ ‬meters high when compared with other more complete genera.‭ ‬The femur was also huge,‭ ‬but accurate descriptions have not survived to today and estimates for this vary,‭ ‬though it was also unusually big.‭ ‬Unfortunately neither of these bones is available for study because they‭ ‬have mysteriously disappeared,‭ ‬either mislaid or crumbled away from lack of preservation techniques being applied.‭
       Large dinosaurs are almost never preserved whole because they are simply too big to be buried in time to be protected from scavengers and the effects of environmental erosion,‭ ‬which also explained why fossils for Amphicoelias have been so rare.‭ ‬So,‭ ‬in order to accurately reconstruct Amphicoelias,‭ ‬the surviving description of the original fossils has had to be compared with similar genera that are more complete.‭ ‬Here,‭ ‬the sauropod Diplodocus is thought to be the closest match for Amphicoelias,‭ ‬but here there is another problem.‭ ‬Amphicoelias and Diplodocus appear to be so similar that some palaeontologists have questioned if they should be separate genera or actually the same.‭ ‬Features that were once thought to be exclusive to Amphicoelias have now been seen in some specimens of Diplodocus meaning that the line between these two dinosaurs is now more blurry than ever,‭ ‬but without the original Amphicoelias fossils to check against,‭ ‬we can never know for certain.
       Using Diplodocus as a body stand in and scaling it up so that the bones match up to the known elements of Amphicoelias yields startling results.‭ ‬The length estimates for Amphicoelias can range as high as the sixty meters long mark,‭ ‬and if these are correct,‭ ‬Amphicoelias would not only be the longest dinosaur,‭ ‬but the longest vertebrate known to ever live on this planet.‭ ‬This would be almost twice as long as the length of the current‭ ‘‬popular‭’ ‬biggest dinosaur Argentinosaurus‭ (‬which also is known from very incomplete remains‭)‬.
       Weight estimates for Amphicoelias are much harder to establish,‭ ‬but again,‭ ‬using Diplodocus as a stand in and scaling it up to the size of Amphicoelias yields a colossal estimate of just over one hundred and twenty-two tonnes,‭ ‬heavier even than estimates Argentinosaurus.‭ ‬If correct then Amphicoelias would‭ ‬only‭ ‬be beaten by a blue whale in terms of weight,‭ ‬but might still be the heaviest vertebrate known to live on land.‭ ‬The only potential rival to that claim would be another sauropod called Bruhathkayosaurus,‭ ‬however as you might suspect,‭ ‬this sauropod is also only known from incomplete remains,‭ ‬with a deal of controversy surrounding them.
       The fossils of Amphicoelias were originally believed to have been recovered from the mid Cretaceous era Dakota Formation,‭ ‬but later analysis and study of nearby fauna discoveries has now led to the realisation that they were more likely recovered from the late Jurassic era Morrison Formation.‭ ‬Other sauropods from this formation include the aforementioned Diplodocus as well as Apatosaurus,‭ ‬Brachiosaurus and Camarasaurus.‭ ‬Stegosaurs such as Stegosaurus and Hesperosaurus,‭ ‬nodosaurs and ankylosaurs such as Gargoyleosaurus and Mymoorapelta as well as ornithopods like Dryosaurus and Camptosaurus are also known from the same Formation as Amphicoelias.
       Potential predatory threats to Amphicoelias may have come from theropod dinosaurs such as Allosaurus,‭ ‬Saurophaganax,‭ ‬Torvosaurus,‭ ‬Ceratosaurus and Elaphrosaurus.‭ ‬It is uncertain what kind of threat if any that these dinosaurs could have posed a fully grown adult Amphicoelias,‭ ‬but smaller juveniles would have always been in danger.

Further reading
-‭ ‬On the Vertebrata of the Dakota Epoch of Colorado,‭ ‬Edward Drinker Cope‭ ‬-‭ ‬1878a.
-‭ ‬A new basal diplodocid species,‭ ‬Amphicoelias brontodiplodocus,‭ ‬from the Morrison Formation,‭ ‬Big Horn Basin,‭ ‬Wyoming,‭ ‬with taxonomic reevaluation of Diplodocus,‭ ‬Apatosaurus,‭ ‬and other genera,‭ ‬H.‭ ‬Galiano‭ & ‬R.‭ ‬Albersdorfer‭ ‬-‭ ‬2010.
-‭ ‬Biggest of the big:‭ ‬a critical re-evaluation of the mega-sauropod Amphicoelias fragillimus.‭" ‬In Foster,‭ ‬J.R.‭ ‬and Lucas,‭ ‬S.G.,‭ ‬eds,‭ ‬K.‭ ‬Carpenter‭ ‬-‭ ‬2006.
-‭ ‬Camarasaurus,‭ ‬Amphicoelias and other sauropods of Cope,‭ ‬H.‭ ‬F.‭ ‬Osborn‭ & ‬C.‭ ‬C.‭ ‬Mook‭ ‬-‭ ‬1921.
-‭ ‬New remains of Amphicoelias Cope‭ (‬Dinosauria:‭ ‬Sauropoda‭) ‬from the Upper Jurassic of Montana and diplodocoid phylogeny,‭ ‬J.‭ ‬A.‭ ‬Wilson‭ & ‬M.‭ ‬Smith‭ ‬-‭ ‬1996.


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