Tyrannosaurus rex Osborn., 1905

Osborn, H. F., 1906, Tyrannosaurus, upper Cretaceous carnivorous dinosaur (second communication), Bulletin of the American Museum of Natural History 22, pp. 281-298 : 284-296

Tyrannosaurus rex Osborn.

The complete skeleton of this animal is restored on Pl. XXXIX . The height of the head in the standing position was 5.35 m. The skull was of relatively large size, of extremely robust structure. The neck was abbreviated but flexible, the cervical ribs being relatively short. In the standing position the body was balanced by the tail, only a few parts of which are known. There is little indication of much free movement between the dorsal vertebrae, the centra being of the amphiplatyan type, flat or feebly amphicoelian. The sacrals are firmly coalesced with each other and with the ilium as the centre of motion. The pubes are of extraordinary size, terminating inferiorly in an enormous peduncle. The hind limbs are provided with extremely muscular attachments, but they contain large hollow cavities and are relatively light. The feet, judging by the metatarsals and single phalanx preserved, were of huge size and provided with powerful claws.

i. THE SKULL.

The parts of the skull preserved are put in place ( Fig. 1 ) by comparison with the skull of Allosaurus ( Fig. 2 ). Our knowledge will fortunately be supplemented from a skull in the Carnegie Museum, which is perfectly preserved in the occipital region, and which, with other parts, will soon be described by Dr. W. J. Holland. In general the skull resembles that of Allosaurus , with greater massiveness and marked abbreviation, less elongate and of greater depth.

Maxillary. - The maxillaries are triangular in outline, enclosing the second antorbital foramen (2) and bounding chiefly the antorbital (1) foramen as well as the maxillo-premaxillary (3) foramen. The surface is convex, roughened, and pitted with numerous open canals and foramina, which are arranged in rows parallel with the dental series. Anteriorly and superiorly the lines of union with the premaxillaries, nasals, and prefrontals are distinguishable. On the inner side the dental alveoli extend downward into triangular plates which do not touch each other but are continuous with the walls separating the teeth and evidently functioned in their reinforcement. The maximum length of the maxillary is 690 mm.; its greatest depth, 410 mm. Twelve teeth constitute the maxillary series. There was certainly one and possibly two small teeth in the premaxillary making thirteen to fourteen altogether. The maxillary teeth are ovate in

cross section. Nos. 1 and 2 of the maxillary series are of smaller size; Nos. 4, 5, and 6 are the largest of the series; the remainder diminish rapidly to No. 12, which was greatly reduced, judging from its small alveolus.

Prefrontal. -This massive ¬-shaped bone is formed by the union of two bars surmounted by the supraorbital protuberances as in Allosaurus. On the inner surface of the descending bar is a thin transverse plate separating the orbit from the antorbital fenestra. The length of the antero-posterior bar is 340 mm., of the vertical bar 350 mm.

Palatine.-A pair of thin flat plates( Amer.Mus. No. 5866 )probably represent these elements, the main body of the plate extending forward and ending in an obtuse point which articulated with the maxillary, while a smaller process projected backward to unite with the pterygoids. The measurements are: length 355, width 225 mm.

Squamosal. -The squlamosal exhibits a decided contrast with that.of Allosaurus in the presence of the horizontal bar(possibly homologous with the depressed bar in Allosaurus ) which appears to project forward into the latero-temporal fenestra; below this bar is a rough border for union with the quadrato-jugal; its proximal end is deeply incised, apparently for the stapedial canal;. A somewhat similar bar in Allosaurus extends downward and forward. The superior groove for the reception of the projecting process of the postorbito-frontal, the roughened area for the attachment of the paroccipital, the posteroinferior attachment of the paroccipital, and the inferior articular area for the quadrate, can be made out clearly.

Dentary. - The dentaries of both rami with nearly all the teeth finely preserved are shown in both specimens; the exterior surface is pitted by vascular foramina. The symphysial union was ligamentous. The dentary deepens decidedly below its junction with the surangular.

There are thirteen teeth in each jaw of the type of Tyrannosaurus , and thirteen on one and fourteen on the other side in the jaws of Amer. Mus. No. 5866 (type of Dynamosaurus ). The teeth are large, with the transverse exceeding the antero-posterior diameter, and points recurved. The anterior tooth, as in the four anterior teeth of Allosaurus and some of the anterior teeth of Deinodon , has a subtriangular form and is of greatly inferior size; the edges divide the tooth unequally into an anterior convex face representing two-thirds of its surface, and a posterior concave face. The second to fifth teeth are the largest of the series. The sixth to the thirteenth decrease gradually, so that the thirteenth could scarcely have been functional. As in Allosaurus the serrate edges do not equally divide any of the crowns, and change according to the position of the teeth; the anterior serrated edge gradually shifts forwards from the inner side to the anterior border of the tooth. In Allosaurus the teeth are more compressed transversely, as is the case also in the Judith River Deinodon . As in the maxillaries the inner border of the alveoli is strengthened by triangular dentary plates; at their base is a deep canal parallel to the alveoli. The dental foramen opens beneath the eighth tooth. In front of this, extending nearly the entire length of the dentary is an open shallow canal. Measurements: extreme length of dentary, 850; depth at middle section, 155; largest tooth, 125 mm. Surangular. - The. surangular is a broad plate, with an arched dorsal coronoid border overhanging the concave inner surface. Contracting posteriorly a heavy inner process expands to form the anterior buttress of the articular; just in front of this is the large foramen homologous with that in Allosaurus and Hatteria . The measurements are: length 610, extreme depth 260.

2. THE VERTEBRAL COLUMN.

The vertebral formula cannot be given precisely. It is estimated in the restoration ( Plate XXXIX ) that there were twenty-three presacrals, as in Allosaurus . The characters of most of the vertebrae can be precisely ascertained from the types of Tyrannosaurus and Dynamosaurus .

Cervicals. -The cervicals in No. 5866 were found partly articulated and in position ( Fig. 3 ).

Some uncertainty exists as regards the atlas-axis complex, because the vertebra interpreted as the axis ( Fig. 2 ), which in Allosaurus lacks the odontoid process and is firmly coalesced with the axis, fails to show evidence of the sutural union between the lower portion of the centrum and the supposed hypocentrum.

The vertebra interpreted as the axis is extremely abbreviate as compared with that of Allosaurus ; possibly because of partial crushing; it bore a slender two-headed rib, which is preserved.

The atlas is positivelv determined with its very shallow concavity for the cranial condyle (c), with attachment areas for the neural arches (nph), with a definite articulation posteriorly for the hypocentrum of the axis (hy), and with a postero-superior concave surface for articulation of the odontoid.

Cervicals 3-9.- Of the cervical series Nos. 2 and 3 were in position, No. 4 was found in a separate block, Nos. 5- 11 with the neural spines of Nos. 12, 13, were found articulated. The hypocentrum of the axis exhibits a plane anterior face with a roughened posterior face for close union with the centrum in the third vertebra. These cervicals are distinguished by: (1) broad depressed neural spines ( Fig. 4 ), (2) gently opisthocoelous centra, (3) relatively short ribs which change from slender bars in C1-C3 into somewhat broadened triangular plates as preserved in C8 and C9, (4) the centra broad and short, deeply excavated laterally. The posterior faces are distinctly but gently concave, while the natural convexity of the anterior faces appears to have been altered by crushing.

In Allosaurus the cervicals are relatively elongate, more deeply opisthocoelous, with relatively narrow, erect neural spines, and more elongate ribs.

Cervico-dorsals, Nos. 10- 11. -In these transitional vertebrae, which in Allosaurus have the same relations as in Hatteria , the space between the capitulum and tuberculum rapidly widens and it is provisionally inferred ( Pl. XXXIX ) that the ribs were more of the dorsal type, as in Allosaurus , but were not connected by cartilaginous ribs with the sternum. The faces of the centra are more plane, passing into the amphiplatyan type of the dorsals. The neural spines are narrower and more elevated.

Dorsals Nos. 12-23.-We proceed on the supposition that there were eleven dorsals, the most anterior of which supported the sternum (see Plate XXXIX ). Portions of several are preserved in the two specimens, as indicated by shading in the restoration ( Pl. XXXIX ). These vertebrae are characterized by high, stout spines, with rugose areas for ligamentous attachment, rather abbreviate centra excavated laterally by deep pits which. almost completely traverse the centrum from the opposite sides. The zygopophyses are gradually approximated until in the posterior dorsals they form the characteristic wedge-shaped union, but apparently without hyposphen. The articular surfaces of the centra are partly amphiplatyan, with a characteristic slight anterior concavity in the upper portion of the face below the neural canal, similar to the same surfaces in Allosaurus .

I1906.] Obr,Trnoars 8

Sacrals.-The sacrum is completely preserved in the type of Tyrannosaurus , consisting of five vertebrae with closely coalesced neural spines forming a continuous plate with three fenestrations between S2 and S5. The centrum of S1 was less firmly united than the others and was found entirely detached in the matrix, whereas the centra of S2 and S3 were most firmly coalesced and appear to correspond with the primary sacrum. The centrum of S4 is also firmly united. Viewed from the front sacrals 2 and 3 are wedge-shaped, narrowing inferiorly, while S1 is vertically extended, and S5 is more vertically oval. S1 exhibits a broad rugose attachment area facing downward for articulation with the horizontal transverse plate of the ilium, whereas S2-5 exhibit rugose areas facing outward, that of S5 being greatly expanded.

Table of Measurements.

Vertebral Measurements of No. 5866 .

	Height of vertebra including spine mm.	Transverse width of centrum mm.	Antero-posterior length of centrum mm.
Atlas H. C.		130	65
Axis	445	145	100 without hypocentr.
3	435	140	100
4	375	155	120
5	390	165	115
6	390	165	120
7	435	175	110
8	430	180	125
9	460	175	100
10	490	165	110
11	500	180	100

Vertebral Measurements of No. 973, Type.

18	580	225	130
19	600	240	145
2
23		270	170

Sacrum of No. 973, Type .

mm.

Length of centra antero-posteriorly 940

Length of spines antero-posteriorly 1000

Height of spines and centrum, anterior 740

Height of spines and centrum, posterior 630

Transverse width of anterior centrum 270 Transverse width of posterior centrum 235

3. SHOULDER GIRDLE AND HUMERUS.

With the type specimen ( No. 973 ) are preserved the left humerus and right scapula, which indicate that the shoulder girdle and fore limb were even more reduced than in Allosaurus .

Scapula.-The scapula has the same general contour as that of Allosaurus but exhibits a more expanded inferior plate for attachment with the coracoid; as shown in Fig. 6 , it is actually larger, but compared with the size of Tyrannosaurus as a wlole it is relatively smaller than in Allosaurus . The measurements are: length of scapula 950, length of coracoid attachment 320 mm.

Humerus. -The humerus is so small that grave doubts were entertained as to its association with this animal. These were finally set aside for three reasons: (1) the humerus is hollow, proving that it belonged to one of the Theropoda; (2) the head of the humerus fits into the glenoid cavity of the scapula; (3) while absurdly reduced as -compared with the femur ( Fig. 8 ) it nevertheless is provided with very stout muscular attachments, a powerful deltoid ridge, which proves that it served some function, possibly that of a grasping organ in copulation.

4. PELVIC GIRDLE AND HIND LIMB.

Ilium. -The ilium has the same elongate form as in Allosaurus with a similar general contour, but with still more compact union

with the sacrum. An important distinction is the broad plate which extends forward on the inner -side of the ilium from the level of the pubic peduncle, especially for attachment with the first sacral vertebra; this is absent in Allosaurus . A wide plate extends backward and inward above the ischiadic peduncle for attachment with the processes of S4-5; this is present in Allosaurus . The measurements are as follows:

mm.

Extreme length ....... ...............

1515 Height above middle of acetabulum... 530

Height above pubic peduncle. 770

Width of acetabulum. 590 Ischium.-As noted above, the ischium is in progress of reduction inferiorly. Below the junction with the ischiadic peduncle of the ilium ( Fig 7 ) and with the posterior peduncle of the pubis it sends forwards a hook-like process and backwards a process, and then contracts into a long, round, diminishing bar, which united with the opposite ischium for the last 320 millimeters of its length but was not

coössifled. The 'extreme distal end is missing but there is no evidence of an expanded foot. The measurements are:

mm

Length 1110

Across peduncles ..... 360

Length of acetabulum boundary. T 160

Pubes. -The pubes are preserved complete in the type of Tyranno- saurus. They are massive bones with the proximal iliac articulations set closer together than in Allosaurus . They are separated below the junction with the ilium by an elliptical opening equal to one-third of their length; they are then united for a short distance; the middle sections again separate; the distal third is again firmly united and expands anteriorly and posteriorly into the broad foot ( Fig. 7 ) Femur. -The femur is relatively larger than that of Allosaurus but resembles it somewhat closely in form and in the areas of muscular attachment. The greater trochanter has relatively a greater

development. The articular head of the femur is clearly defined;

a very characteristic feature is that when placed in the acetabulum the planes of the articular head are set at an angle of 45̊ to the axis of the vertebral column, proving that the femora at the distal extrem- ities were approximated, bringing the hind feet close together at the ground. The petrified bone is remarkably light for its size, weighing only 180 lbs. when cleaned of all matrix; seventeen inches of the middle portion of the sllaft is hollow, containing a cavity ( Fig. 10 ) four inches in diameter. The total length is 1300 mm.; the mid-diameter of the shaft is 180; the diameter of the head, 200, the greatest transverse width of the condyles, 340 mm.

Tibia. -The tibia is relatively larger than that of Allosaurus but with similar contours and similar attachments; twenty-five inches of the shaft is hollow, with a cavity two to three inches in diameter. The total length is 1140 mm. or 160 mm. less than that of the femur. Pes. -The pes is composed of three very elongate and massive metatarsals exhibiting a more powerful and less mobile arrangement of the metatarsals, because they show sutural attachments but not actual coalescence in the middle portion of the shaft, as represented in Fig. 11 . Mts. III was considerably the longest and largest of the series and firmly buttressed between II and IV; the distal ends of Mts. II and IV turn outward. Mts. I was evidently composed of proximal and distal osseous segments as in Allosaurus; of these only the distal segment is preserved, indicating a retroverted, birdlike position of the claw. The chief measurements are as follows:

Mts. II, length. " IV " ........ " III width of distal end mm.

615

600

140

5. THE THORAX.

Ribs. - A considerable number of thoracic ribs are preserved with No. 5866 , but they have not as yet been fully worked out. The general form is represented in Pl. XXXIX . The probabilities are that the ribs extended back beneath the anterior crest of the ilium as in Allosaurus and in the Sauropoda.

Abdominal ribs. - One of the most surprising characters discovered in this fossil is the presence of an abdominal series of ribs, consist-

ing of double-pointed central ribs and single-pointed short lateral ribs, as in Sphenodon . As shown in Fig. 12 the ribs are asymmetrical and sometimes double. They mostly exhibit a double anterior and posterior rough surface attachment to the preceding and succeeding ribs. The median arched part of the rib extended forward and the free ends pointed backward.

6. THE DERMAL ARMOR. Many dermal plates were found with the individual No. 5866

originally described as Dynamosaurus ; they were used in defining Dynamosaurus . Some doubt as to their association with this carnivorous Dinosaur is caused by the presence of a fragment of a frill of Triceratops and a portion of the jaw of an Iguanodont. These plates were, however, found with ribs that can certainly be assigned to the carnivorous Dinosaur, because they exhibit no resemblances to the ribs of the Sauropoda or Iguanodontia. The plates are irregular in form and size, ranging from half an inch to six inches in length, the small ones rounded and the larger ones flattened with sometimes a raised central ridge curved to form part of the dermal line or crest. The largest plates are about half an inch thick.

Despite the evidence cited above it is difficult to imagine why this carnivorous Dinosaur should be protected by any form of dermal armature, unless possibly against attacks by members of its own family.

Figures

Fig. 1. Skull of Tryrannosaurus. d, dentary; sur, surangular; sq, squamosal; prf,prefrontal; o, orbit; na, anterior nares; 1, 2, 3, antorbital openings. Dotted outlines arefrom Allosaurus.

Fig. 2. Skull of Allosaurus in the American Museum of Natural History. To same scale as the skull of Tyrannosaurus.

Fig. 3. Cervical vertebrm of Tyrannosaurus.,Amer. Mus. No. 5866. hypocentrum of atlas; nph, neuropophysis; 2 supposed axis with its hypocentium; od, odontoid; 3, 9 remaining cervicals; r8, r9, ribs found attached to ribs, 8-9, 1-011, cervico-dorsals; c, capitular facet; t, tubercular facets.

Fig. 6. B Scapula of Tyrannosaurus. A Scapula of Allosaurus.

Fig. 7. Pelvis of Tyrannosaurus. Amer. Mus. No. 73.

Fig. 8. Humerus of Tyrannosaurus. Amer. Mus. No. 972. To same scale as femur (Fig. 9). a, external view; b, posterior view.

Fig. 10. Section of femur of Tyrannosaurus. Amer. Mus. No. 973.

Fig. 11. Right pes of Tyrannosaurus. Amer. Mus. No. 973

Fig. 12. Abdominal ribs of Tyrannosaurus. Amer. Mus. Nos. 973 and 5881.

PLATE XXXIX. RESTORATION OF TYRANNOSAURUS REX. From the type skeleton, Amer. Mus. No. 973. Many of the vertebrae belong to No. 5866.

Fig. 4. Anterior view of mid-cervical vertebra, Amer. Mus No. 5866