Barosaurus giganteus

Barosaurus unnamed species - Newest ultrasauropod as of 2016-2017, and probably one of the longest animals ever. Largest dinosaur currently known from currently-available known skeletal remains

Temporal range: Late Jurassic, Tithonian, ~153 Ma

Probable length: Between ~40-60 metres?
Probable mass: Between ~100-150 tonnes?

Etymology: Heavy reptile


Barosaurus was a genus of large sauropod known from the Late Jurassic Morrison Formation of North America. While Barosaurus lentus, the type species, is famed for its rearing mounted skeleton at the American Museum of Natural History, AMNH 6341, a few skeletal elements uncovered from Jensen's excavation in the Dry Mesa Quarry, formerly assigned to Supersaurus vivanae and reassigned to Barosaurus by Matt Wedel and Mike Taylor in 2016, possibly indicates a much larger species, one that may have ranked among the gigapods reaching well over 100 tonnes.

A giant cervical vertebra catalogued BYU 9024, likely the ninth in the series, is about twice as long as the corresponding cervical in AMNH 6341. It would have formed part of an immense neck probably about ~17 metres long, or longer than most brachiosaurids are tall. The whole axial column from snout to tail tip could have been well over 50 metres long in life.
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Based on 's Barosaurus. Here it is, the supersauropod Barosaurus. As assigning this specimen to Barosaurus lentus would have implied an insane level of size variation beyond even what's seen in crocodylians, birds, and pretty much every other known nonavian dinosaur, being more than 5 times as large as known adult B. lentus, I have it split into its own species. "Barosaurus giganteus" ("Gigantic heavy reptile") is just my unofficial name for it as of now.