Alamosaurus

The one‭ ‘‬fact‭’ ‬that is often presented for *Alamosaurus* is that it is named after the Alamo,‭ ‬the famous mission in San Antonia that was the site for one of the most important battles in the Texas Revolution.‭ ‬However this is completely false and the truth of the matter is that the first *Alamosaurus* remains which were found in New Mexico were so named because they came from the Ojo Alamo Formation.
*Alamosaurus* was a reasonably large titanosaur,‭ ‬the most common group of more advanced sauropod dinosaurs that were the most common during the Cretaceous.‭ ‬A complete adult specimen

of *Alamosaurus* continues to prove elusive,‭ ‬although this is a common problem for most large dinosaurs in general.‭ ‬Juveniles however are often more complete because their smaller bodies are more easily covered by sediment,‭ ‬and comparison of juvenile fossils with those of adults has led to estimates of around twenty meters long,‭ ‬give or take a meter or two,‭ ‬for adult *Alamosaurus*.‭ ‬A skull of *Alamosaurus* is also currently unknown,‭ ‬although associated teeth are quite slender,‭ ‬possibly for snipping at tree tops.‭ *‬Alamosaurus* also seems to have lacked the osteoderm armour‭ (‬bony plates that grew in the skin‭) ‬that is known to be present in many other titanosaurs since out of all the known *Alamosaurus* remains,‭ ‬no osteoderms have yet been found.
       More importantly,‭ ‬the presence of *Alamosaurus* in the south western portions of the United States is proof that the sauropods had not disappeared completely from North America during the Cretaceous.‭ ‬Sauropods however are usually associated with dryer and higher up landscapes,‭ ‬and these areas do not seem to have been that abundant,‭ ‬due mainly to the Western interior Seaway submerging most of the central portions of North America.‭ ‬As such it is quite conceivable that the distribution of sauropods like with most animals is down to the availability of suitable habitat.
       How *Alamosaurus* came to live within the United States at the end of the Cretaceous is a question that has caused some confusion for some since for a long time the popular conception of sauropods was that they mostly disappeared from North America at the end of‭ ‬the‭ ‬Jurassic.‭ ‬This idea is based upon the observation that fossils of sauropods were more common in North America at the end of the Jurassic,‭ ‬but seem to have been replaced by ornithischians like hadrosaurs and later on ceratopsian dinosaurs during the Cretaceous.‭ ‬However the saying that absence of evidence is not necessarily evidence of absence is commonly used in palaeontology,‭ ‬and slowly but surely Cretaceous age sauropods are slowly but surely being discovered in North America with examples including *Astrodon*,‭ *‬Sauroposeidon‭* ‬and *Cedarosaurus* amongst others.‭ ‬Slowly,‭ ‬Cretaceous sauropod‭ (‬or rather more specifically titanosaur‭) ‬genera are coming together to help complete a picture of the dinosaurian fauna of North American ecosystems where titanosaur sauropods are actually still quite common,‭ ‬although still perhaps not as common as their late Jurassic ancestors.
       There are too alternative theories concerning how *Alamosaurus* came to live in North America.‭ ‬One is a direct Asian origin where *Alamosaurus* or immediate ancestors to it crossed the Bering Strait land bridge and spread down to the south-western regions where the habitat may have remained more suitable for a stable and permanent population.‭ ‬This is‭ ‬in‭ ‬part supported by the placement of *Alamosaurus* within the Opisthocoelicaudiinae group of titanosaurs,‭ ‬the type genus of which,‭ *‬Opisthocoelicaudia*,‭ ‬is currently only known from Asia.‭ ‬However this group also sits within the Saltasauridae and *Alamosaurus* is seen to have a lot of similarities with the type genus of this group,‭ *‬Saltasaurus*.‭ ‬This has led to speculation of a South American origin for *Alamosaurus*,‭ ‬although the main problem here is that South America is thought to have been separated from North America during the Cretaceous by ocean.‭ ‬Additionally other strictly South American dinosaurs such as the abelisaur theropods are still not known in North America,‭ ‬and vice versa,‭ ‬North American dinosaurs like tyrannosaurs are not known in South America.‭
       Altogether the arguments for a South American origin are not that convincing,‭ ‬but one possibility that may explain these similarities is convergent evolution.‭ ‬This is simply where two animals‭ (‬or in this case dinosaurs‭) ‬that are separated by time and/or geography find themselves in the same survival conditions and so physically change to carry near identical adaptations for coping with their survival requirements.‭ ‬This principal has been observed countless times,‭ ‬and where the animals share a common ancestor and similar biology,‭ ‬the similarity is just the more likely to occur.
       Dinosaur art and popular fiction often depicts life and death struggles between large theropods such as tyrannosaurs and long necked sauropods.‭ ‬As stated above this was long thought unlikely to have happened in North America,‭ ‬but *Alamosaurus‭* ‬did live in North America at a time that saw large tyrannosaurs such as *Daspletosaurus* and *Bistahieversor* roaming the land in search of prey.‭ ‬A fully grown *Alamosaurus* may still have been too much of a challenge for these dinosaurs,‭ ‬but a smaller juvenile would have certainly been within their predatory scope.‭ ‬Other dinosaurs that *Alamosaurus* shared its habitat with include the ceratopsian dinosaur *Torosaurus* and the hadrosaur *Edmontosaurus*.‭ ‬Additionally it would have also been possible to see the giant pterosaur *Quetzalcoatlus* soaring through the skies of the time.