The American Naturalist, Vol. 12, No. 8. (Aug. 1878), pp. 563–564.
A new species of Amphicœlias.—I have recently received from my indefatigable friend, Mr. O. W. Lucas, the almost entire neural arch of the vertebra of the largest saurian I have yet seen. It was found in the Dakota formation of Colorado, near Canyon city, in the same bed that has thus far produced the known species of Camarasaurus, Amphicœlias, Hypsirophus, etc. In the extreme tenuity of all its parts, this vertebra exceeds those of this type already described, so that much care was requisite to secure its preservation. It exhibits the general characteristics of the genus Amphicœlias, in the hyposphen, antero-posteriorly placed neural spine, and elevated diapophysis for the rib articulation. The diapophyses are compressed and supported by a superior and inferior, and anterior and posterior, thin buttresses, separated by deep cavities. As compared with Amphicœlias altus, this reptile differs in the greater elevation and attenuation of the neural spine, as well as its different form; also in the generally more laminar character of its buttresses and walls The double rib of the anterior border of the spine of the A. altus is here represented by two laminæ which extend on each side, so as to give a horizontal section of the spine a T shape. The posterior zygapophyses have less lateral expanse than A. altus, but they continue as horizontal laminæ with a deep cavity above and below: their superior surfaces contract into two ridges, which are separated by a deep groove. These ridges, unlike the anterior ones, approximate to each other closely on the border of the spine. The summit of the spine is wanting. The measurements are: total elevation of neural arch, preserved, 1500 m.; elevation of posterior zygapophyses, 585; transverse expanse of posterior zygapophyses, 190; vertical diameter of base of diapophysis, 390. These figures show that the total elevation of this vertebra, when complete, was not less than six feet, and probably more.
Posterior dorsal vertebra of Amphicœlias fragillimus.
Since in A. altus and C. supremus the length of the femur is twice the elevation of the dorsal vertebra, we may surmise that the length of the femur of this animal was twelve feet, but this is of course not a necessary consequence of our present knowledge. But so far as the vertebræ are concerned the following rule is without exception among the Saurians of the Dakota epoch: It is, that the size of the vertebra is in direct proportion to the attenuation of its walls. This latter character, as seen in this and other species, resembles nothing so much as what is seen in deep sea fishes, as Alepidosaurus, etc., and suggests that these beasts may have walked in deep water and browsed on precipitous shores.
The species above described may be called Amphicœlias fragillimus. The dimensions of its vertebræ much exceed those of any known land animal.—E. D. Cope.