How big did Barosaurus get?

30th August 2016

Michael P. Taylor, Department of Earth Sciences, University of Bristol, UK.
Mathew J. Wedel, College of Osteopathic Medicine of the Pacific and College of Podiatric Medicine, Western University of Health Sciences, Pomona, California, USA.

The diplodocid sauropod Barosaurus is best known from the spectacular mounted skeleton in the atrium of the American Museum of Natural History (AMNH). Apart from the disproportionately long neck it is similar in size to Diplodocus — but did Barosaurus get bigger?

BYU field jacket 3GR was collected from the Jensen/Jensen quarry, Utah, in 1966 but only recently prepared. It contains three cervical vertebrae, designated A, B and C, anterior to posterior. They belong to Barosaurus based on elongation, broad prezygapophyseal facets, "hinged" prezygapophyseal rami with dorsomedial and dorsolateral faces, narrow, posteriorly set diapophyses bearing posterior tubercles, and wing-like postzygadiapophyseal laminae. Based on spine bifurcation, vertebra C is C9–C11.

The centra of the AMNH cervicals C9–11 are 685, 737 and 775 mm long. That of vertebra C measures 1220 mm, making it 1.57–1.78 times longer. This suggests a neck length of 13.3–15.1 m based on 8.5 m for the AMNH specimen.

BYU 9024 is an even larger cervical vertebra, referred to Supersaurus but indistinguishable from C9 of Barosaurus based on the characters above. At 1370 mm in total length, it is exactly twice the length of the AMNH C9, suggesting a neck 17 m long.

Dystylosaurus has also been referred to Supersaurus. Although the holotype and only vertebra is clearly a diplodocid anterior dorsal (it has dual centroprezygapophyseal laminae, a large cotyle and "drooping" parapophyses), its tall, unsplit neural spine and pronounced ventral keel prevent assignment to any known diplodocid. It may be a valid, distinct genus.

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