“ These Alamosaurs are a hundred feet long, and weigh some 80 tonnes. They are the largest dinosaurs on the continent. So huge that no predator can tackle them. ”
Alamosaurus (Ojo Alamo lizard) is a genus of titanosaurian sauropod dinosaur that lived in various parts of southwest USA, 70 - 66 million years ago, during the Maastrichtian stage of the Late Cretaceous Period.
Size comparison of several specimens of Alamosaurus
Alamosaurus is one of the largest known sauropods of North America. Standing at least 11 meters (36 feet) tall, 30.5 meters (100 feet) long, and weighing 38 - 80 metric tons (42 - 88 short tons),[PhP 1][4][5][DN 1] it rivals the size of the biggest sauropods like Argentinosaurus, which lived in Argentina, South America around 97 - 92 million years ago.
In a 2009 study, it was believed that only smaller titanosaurs like Saltasaurus and Ampelosaurus had osteoderms on their backs, with armored titanosaurs being 60 - 70% smaller than unarmored ones, hence, they likely evolved these bony plates, scutes, and bulbs in order to compensate for their smaller size. The study outright names Alamosaurus as one of the unarmored sauropods to further support its conclusion.[8] However, a discovery in 2015 confirmed that Alamosaurus actually bore osteoderms on its back (the largest of which come in the form of the "ellipsoid morphotype" or "bulb" type), proving that even the largest known sauropods may have had bony plates, and that the absence of osteoderms on sauropod fossils is not necessarily evidence that they did not possess this armor, as these osteoderms may eventually turn up in subsequent discoveries.[6] Given how size alone is enough to protect a fully-grown healthy adult Alamosaurus, it is possible that the osteoderms of the species are either evolutionary leftovers from smaller ancestors that had more need for armor, or served as secondary defenses for those that are yet to grow to a tremendous size, as it may have taken Alamosaurus approximately 45 years to reach a mass of 32 metric tons (35.3 short tons), gaining a maximum of one metric ton (1.1 short tons) a year,[7] leaving younger individuals vulnerable for a considerably long time, justifying the need for osteoderms, which appear to remain on the animal for the rest of its life, even when it no longer has a need for them. As a sauropod, Alamosaurus is believed to have a long lifespan, with one individual in North America stated to be at least 70 years old.[PhP 1]
Alamosaurus appears in the first segment of North America, which shows a herd of them traveling by the coast of the Western Interior Seaway. A 70 year-old member of the herd eventually collapses and succumbs to old age, and its corpse becomes the subject of dispute for carnivores that came to scavenge the carcass, from troodontids and T. rex to a pair of Quetzalcoatlus. Alamosaurus, along with the other titanosaurs of the series, are also the subject of the Prehistoric Planet: Uncovered segment "How Did Dinosaurs Get So Big?"
“ The coast of the vast, inland sea that almost splits North America in half. Here in the south, as the tide falls, giants are drawn to the shoreline. ”
Alamosaurus lived 70 - 66 million years ago in the Javelina, Black Peaks, and El Picacho Formations in Texas, the Ojo Alamo Formation in New Mexico, and the North Horn Formation in Utah, USA,[1] alongside animals like Quetzalcoatlus and Tyrannosaurus. It is believed that the regions it inhabited were semi-arid inland plains. While Alamosaurus appears to be mostly confined to the southwestern areas of the US, indeterminate titanosaur remains have supposedly been found in the Evanston Formation in Wyoming, though more recent studies are unable to confirm that these fossils are indeed those of Alamosaurus.[2][3]
Origin[]
Most North American dinosaur species are known to have come to and from Asia. Alamosaurus is peculiar in that it is the only known sauropod in North America after 30 million years of complete sauropod absence. Hence, the mysterious origin of Alamosaurus is a significant aspect of it, subject to continuous debate.
One theory is that the species (or at the very least, its ancestors) immigrated from South America on the same land bridge that hadrosaurs traveled to reach South America, though this theory is challenged by the fact that the "bridge" between North and South America may not have been a single, unbroken strip of land, but a series of islands, thus making the crossing of the sauropods problematic, with their large size making island rafting a less-feasible means of reaching North America.[9]
The alternate theory points to an Asian origin instead, given the close relationship of Alamosaurus with Opisthocoelicaudia of Mongolia, though this does not take into account that Alamosaurus is also closely related to Pellegrinisaurus of Argentina, that the land bridge of Beringia (which connects Asia and North America) would have been inhospitable to titanosaurs due to the being closer to the poles, and that there are no traces of Late Cretaceous sauropods in Northern Laramidia (since if Alamosaurus or its ancestors came from Asia, the titanosaur would have passed through areas near or within the more northern areas of Laramidia like the Hell Creek, Lance, and Scollard Formations, leaving behind a population of subspecies or something that evolves into another, distinct sauropod species).[10]
The third theory, the idea that sauropods that lived in North America for the past 30 million years prior Alamosaurus were simply not preserved well, is considered unlikely. As of 2021, the belief that Alamosaurus (or its ancestors) immigrated from South America is the most supported theory, currently considered as the only viable explanation of their existence on the southern end of Laramidia.[10]
Social Behavior[]
“ Some live to a great age. This male is around 70 years old. Many in the herd are likely to be his offspring. But his long life is now coming to an end. His immense body is beginning to fail him. He may not survive the night. ”
Alamosaurus is depicted traveling in herds that consist of related individuals, offspring of some of the older members. Given how sauropods were likely not as complex as birds (with some species, like crows and magpies, even holding what appears to be funerals)[11] or elephants (which possess greater brain-to-body ratios and also mourn their dead),[12] these family ties do not seem to matter the herd's members. When one of them succumbs to old age and dies, the rest of the herd continues on with their migration with not a glance back, prioritizing their journey and search for resources.
References[]
General[]
↑ 1.01.1Weishampel, David B; et al. (2004). "Dinosaur distribution (Late Cretaceous, North America)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 574-588
