Introduction
By the dawn of the 20th century, remains of giant sauropod dinosaurs were becoming quite well-known from the Western United States. The paleontologists and preparators who first worked on the bones of giants like Brontosaurus (now called Apatosaurus) and Diplodocus faced quite a challenge: how do you reconstruct the skeleton of an animal no one has ever seen, and one so gigantic that the largest modern equivalents (elephants and giraffes) are dwarfed in comparison? After carefully examining the bones, they put together sauropods that stood upright on column-like limbs, with long horizontal necks and tails.
Their work was impressively thorough: today, a century later, sauropod skeletons are mounted in much the same posture (the only obvious difference is the height at which the tail is carried). But when their work was first shown, many scientists, artists, and naturalists were unwilling to accept the idea of reptiles, much less giant ones, able to support and maneuver themselves on upright limbs. For a brief period around 1910, debates raged in lecture halls, letters columns, and the pages of scientific journals proclaiming justifications for one point of view while not-so-subtly denigrating the opposition. Indeed, the writing contains some of the most pointed barbs ever put into print by professional paleontologists, although they are typically buried among long-winded discussions of anatomical minutia.
The next volume in the HMNH online library is a perfect case in point. Dr. Oliver Hay presents a somewhat muddled argument for sprawling sauropods, based as much on his own belief in how locomotion evolved as any detailed study of the fossils. This long, rambling paper is a testament to a windier time in science, and Dr. Hay's own ability to weave an opaque collection of disparate facts around a particularly thin central argument. In the end, however, the reader is rewarded for his or her effort with a wonderful restoration of sprawling sauropods cavorting in the Jurassic muck on salamander-like limbs. For those not wishing to wait for the final installment of this article, click here (opens in a new window).
So, without further ado, the HMNH is pleased to present Part One of:
On the Manner of Locomotion of the Dinosaurs Especially Diplodocus, with Remarks on the Origin of the Birds.
By Oliver P. Hay
In a paper published some months ago (Amer. Naturalist, vol. xliii, 1908, pp. 672–681) the writer advanced the proposition that the sauropodous dinosaurs, especially Diplodocus, did not walk, as the elephants do, with the body high up from the ground and with the legs straight or nearly so, and moving in approximately perpendicular planes, but rather as do the crocodiles, with the body low down, and with the thighs standing well out from the animals sides. While I was further considering the subject I received from my friend Dr. O. Abel, of Vienna, a paper1 in which, while endorsing my views regarding the nature of the food of Diplodocus and the manner of taking it, he endeavors to show that I am in error as to the bodily pose and the manner of locomotion of the sauropods. Dr. Abel maintains that the accepted views of the way in which these animals walked is the correct one and he finds support for this view in the structure of the feet. He accepts Hatcher's opinion that Diplodocus and Brontosaurus were digitigrade and argues that therefore they walked as represented in Hatcher's restoration of the reptile. The evidences that they were digitigrade are found in the belief, probably correct, that the upper ends of the metatarsals and metacarpals were not arranged in a straight line, but in an arc of a circle; further, that the feet were entaxonic, that is, had the inner digits more strongly developed than the outer ones.
Now, it is the writer's opinion that these evidences of digitigrady will hardly stand a test. The hinder feet of the bear are certainly plantigrade and yet the metatarsals are arranged very distinctly in an arc of a circle. On the other hand, the tiger and the hyæna are digitigrade, but their metatarsals are almost in a plane. Various animals will, I think, be found to transgress Dr. Abel's rule, as one may see by looking through a collection of skeletons. Furthermore, if it is desired to see an entaxonic foot in which the metatarsals are arranged in an arc of a circle and which is nevertheless plantigrade one has only to examine the foot of the human skeleton.
FIG 1. Section through the hind foot of Testudo. X 1. ast., astralagus; met. 2, metatarsus of the second digit; ph. 1, ph. 2, first and second phalanges; t., tarsal of the second row; tib., tibia.
The writer is not disposed to deny that Diplodocus and its relatives were more or less digitigrade; but this digitigrady, through perhaps equal to that of the hinder foot of the elephant, does not prove that these reptiles walked like the elephant. The land tortoises of the genus Testudo have the feet constructed much like those of the elephant, being provided with a thick pad of skin, muscles, tendons, and connective tissue under the astragalus and the metatarsals and applying only the ungual phalanges to the ground. Nevertheless the legs of these reptiles stand out from the sides of the body as I have supposed that those of Diplodocus did. A figure (Fig. 1) is here presented showing a section made through the hind foot of T. tabulata. Unfortunately I have not been able to find or make a similar section through the hind foot of the elephant; but, to judge from various mounted skeletons and from good figures of others, one can hardly suppose that the heel is lifted farther from the ground relatively than that of the tortoise.
I grant that Dr. Abel's efforts are along a line where they are needed. Those who believe in the mammal-like gait of Diplodocus ought to give their reasons therefor. I do not assert that reasonable arguments for their view cannot be produced, but hitherto the correctness of this view has been assumed. The subject is a difficult one and needs to be studied from various points of view and by all who have the opportunity. And in studying the movements of animals one soon learns that they can assume so many positions that one may be at loss, in the case of an extinct creature, to determine which positions were the usual ones.
In the primitive condition the limbs of the Tetrapoda stand out at right angles with the body,2 and in approximately this position they are found in most Amphibia and Reptilia. When these animals are walking, the humerus and the femur move backward and forward mostly in horizontal planes. In most mammals, on the contrary, the humerus is turned backward against the thorax and the femur forward against the flank. The hand, which otherwise would be directed backward, is turned forward by the crossing of the bones of the lower arm. The movements of arm and leg are then mostly in sagittal planes. In the duckbill and the echidnas the limbs have retained the position found in most reptiles.
Now, among all the reptiles that live today there are none, except perhaps the chameleons, that have attained even an approach to the condition found among mammals.
It is evident that before the close of the Jurassic there existed both carnivorous and herbivorous dinosaurs that went about habitually on only their hind legs; but it is by no means necessary to believe that the immediate ancestors of these bipeds walked first like mammals and afterwards like birds. It is well known that certain lizards can run swiftly on their hind legs, the fore legs and tail being held free from the ground. Furthermore, as may be seen from W. Saville-Kent's figures3 the hinder limbs are not carried backward and forward in sagittal planes like those of mammals.
It seems not difficult to understand the history of the attainment of the bipedal habit among lizards and dinosaurs. When the forelegs of a quadrupedal reptile are nearly of the same length and have the same structure as the hind legs there seems to be no good reason why the animal cannot run as fast on four legs as on two. However, the hinder limbs, being nearer the center of gravity of the animal, receiving more of the weight, and being more devoted to propulsion of the body, are likely to become larger and more powerful, while the fore legs may become more or less reduced, with or without special modification for other purposes. If now a reptile whose fore legs have become relatively much shorter than the hinder ones has occasion to run with the greatest possible speed, it is likely to find that the fore legs cannot take as long steps as the hinder ones; and naturally it endeavors to get them out of the way by lifting them up in the air.
This practice would be of great advantage and would tend to become fixed. The reduced limbs might then become modified for other purposes or undergo further reduction. In the beginning, the femora would stand out from the body, giving the animal a wide tread. In time, however, the knees might be drawn closer to the flanks, the tread would become narrower and the pace more rapid. At no stage, however, would the reptile walk like a quadrupedal mammal; and no argument in favor of such a gait for Diplodocus can be deduced from bipedalism in lizards.
1 Verhandl-zool.-botan. Gessellchs. Wien, 1909, pp.117–123. Back
2 Huxley, Anat. Vert. Animals, 1872, p. 33; Flower's Osteology of the Mammalia, 1885, p. 362. Back
3 Nature, vol. 53, 1895, pp. 396–397. Back
Dr. Hay continues in Part Two.