Dynamosaurus imperiosus, Osborn, 1905

Osborn, H. F., 1905, Tyrannosaurus and other Cretaceous carnivorous dinosaurs, Bulletin of the American Museum of Natural History 21, pp. 259-265 : 263-264

Dynamosaurus imperiosus gen. et sp. nov.

Type. — Numerous dermal plates and many parts of the skeleton. Collection of 1900, American Museum No. 5866, from Seven Mile Creek, six miles north of Cheyenne River, Weston County, Wyoming. The type of this skeleton was found by the American Museum expedition of 1900 under Mr. Barnum Brown, whose preliminary report was as follows: “ It consists of lower jaws, having that large foramen characteristic of Ceratosaurus , serrated teeth of uneven height joined by cartilage, not anchylosed. Concavo-concave and plano-concave vertebrae of lumbar-dorsal region are deeply excavated on sides and bottom rising to plane surface in region of canal; extremely hollow and as in Morosaurus not having spines and transverse processes united to centra. Sacral vertebrae 3? Post-sacral vertebrae, of which seven were embedded in stone matrix, show plano-plano surfaces. Transverse processes united to centra. Nature of cervical vertebrae not determined. Ribs large, not greatly curved in dorsal region, tapering gradually to those of cervical region. But few chevrons were found, those of extreme length in proportion to size of vertebrae. ”

Generic characters. — Carnivorous dinosaurs with twelve to fifteen mandibular teeth of rounded to flattened form. Anterior truncate teeth reduced or wanting. Irregular bony plates developed on the back or sides of the body. Alveolar partitions between the mandibular teeth extending upward into triangular plates on the inner sides of the jaws above the borders of dentaries.

Specific characters. — Twelve to thirteen mandibular teeth.

This animal is distinguished by the presence of superficial bony dermal plates which extended either along the dorsal or side lines of the body, by the reduction of the number of teeth, by the apparent absence of truncated anterior teeth, by the rounded rather than lenticular form of the teeth, by the presence of a row of triangular upgrowths of the dental alveoli on the inner sides of the jaws. In Deinodon there will probably be found a larger number of teeth, and some of the anterior teeth of the jaw will be found to be truncated and serrate posteriorly as in Allosaurus .

Dentition. — The species D. imperiosus appears to be distinguished by the presence of from twelve to thirteen mandibular teeth. The inner view of the mandibular ramus ( Fig. 1 ) exhibits a small anterior alveolus for a vestigial tooth followed by twelve fully functional teeth, behind which there is another partially closed alveolus; thus there appear to have been two reduced and twelve functional teeth. The dentition is not homodont, every tooth differing slightly in its section and in the position of the serrate edges, also in size. The third functional tooth from the front is apparently the largest, the measurements of the crown being a. p. 43, tr. 33, vert. 82 mm. The last functional tooth is decidedly smaller, the crown measuring a. p. 19, tr. 11, vert. 15 mm.

Jaws. — Between the teeth are a series of triangular osseous plates, which appear to be upward continuations of the alveolar walls which separate at the base from the edge of the dentary.

Figures

Fig. 2. Inner surface of the left lower jaw of the type specimen of Dynamosaurus imperiosus. 1/8 nat. size.