Claosaurus Marsh 1890
Creators: name: Marsh, O. C.
Publisher: name: Zenodo
Year: 1892
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Reptilia
Dinosauria
Claosaurus

description: Claosaurus, Marsh, 1890.
Next in importance to the Geratopsidae of the Laramie are the Dinosaurs allied to Hadrosaurus, and, as but little is really known of the skeleton in this group, some of the important parts are here "described, and figured in Plates II and III. These are mainly from a single specimen which is in remarkable preservation; but the remains of a second individual, likewise in good condition, and in some respects more perfect, have also been used in the investigation. The species is Glaosaurus annectens, already briefly described by the writer. "
The skull will be described in a later communication. The number of vertebrae between the skull and sacrum is thirty,’ and all were found. in position. There are nine vertebrae in the sacrum, thoroughly coossified with each other. The anterior forty-five vertebrae of the tail were found in position, and in good preservation.
* This Journal, vol. xliii, p. 453, May, 1892.
The fore limbs are unusually small in comparison with the posterior, and the relative size of the two is shown on Plate II. The scapular arch presents many points of interest. The scapula is large, and so much curved that the axis of its shaft is nearly parallel to the articular faces of its lower extremity, (Plate II, figure 1, s). On the anterior margin, above the articulation for the coracoid, is a strong protuberance, with a well-defined facet, adapted to the support of the clavicle, if such a bone were present. The coracoid is very small, and is perforated by a large foramen (Plate II, figure 1, c). The two peculiar bones now generally regarded as belonging to the sternum were separate, as shown in Plate III, figure 1.
The humerus is comparatively short, and has a prominent radial crest. The radius and ulna are much elongated, the latter being longer than the humerus, and the radius about the same length. The ulna has a prominent olecranon process, and is a stouter bone than the radius. The carpal bones were quite short, and appear to have been only imperfectly ossified. The fore foot, or manus, was very long, and contained three functional digits only. The first digit was rudimentary, the second and third were nearly equal in length, the fourth was shorter and less developed, and the fifth entirely wanting, as shown in Plate II, figure 1.
In the functional digits (II, III, IV), the phalanges are elongate, thus materially lengthening the fore foot. The terminal phalanges of these digits are broad and flat, showing that they were covered with hoofs, and not with claws. The limb as a whole was thus adapted to locomotion or support, and not at all for prehension, although this might have been expected from its small size and position.
The elongation of the fore-arm and manus is a peculiar feature, especially when taken in connection with the ungulate phalanges. It may, perhaps, be explained by supposing that the animal gradually assumed a more erect position until it became essentially a biped, while the fore limbs retained in a measure their primitive function, and did not become prehensile, which was the case in some allied forms.
The pelvis is shown in Plate II, figures 2 and 3, and has already been described by the writer. Its most notable features are seen in the pubis and ischium, the former having a very large expanded prepubis, with the postpubis rudimentary, while the shaft of the ischium is greatly elongated.
The femur is long, and the shaft nearly straight. The great trochanter is well developed, while the third trochanter is large and near the middle of the shaft, as shown in Plate II, figure 2. The external condyle of the distal end is projected well backward, indicating great freedom of motion at the knee.
The tibia is shorter than the femur, and has a prominent cnemial crest. The distal end is much flattened, and the astragalus is closely adapted to it. The fibula is very straight, with its lower end flattened and closely applied to the front of the tibia. The calcaneum is large, with its concave upper surface closely fitted to the end of the fibula. Of the second row of tarsals, only a single one appears to he ossified, and that is very small and thin, and placed between the calcancum and the fourth metatarsal, nearly or quite out of sight.
The hind foot, or pes, had but three digits, the second, third, and fourth, all well developed and massive. The terminal phalanges were covered with broad hoofs. The first and fifth digits were entirely wanting.
A comparison of the limbs and feet of Claosaurus, as here described and figured, with those of three allied forms from the Jurassic, Stegosaurus, Laosaurus, and Camptosaurus, as shown on Plates IV and V, is especially instructive. These three genera have already been quite fully described and figured by the writer, but new points of interest have been made out by the recent investigation of more perfect material. The present figures will show more accurately some of the mutual relations of these early herbivorous Dinosaurs to each other, as well as to their successors in Cretaceous time. The gradual changes that can be traced from one to the other will be discussed in a later communication.
description: Published as part of Marsh, O. C., 1892, Notes on Mesozoic vertebrate fossils, pp. 171-176 in American Journal of Science 260 on pages 171-173, DOI: 10.5281/zenodo.2838842