678 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



The calcaneum. — The tuberosity is rather long and very 

 rugous at its distal end, and with a much flattened shaft which 

 is about one-half as wide as long. The calcaneum bears facets 

 for articulation with the cuboid, the astragalus, and on its 

 upper outer face a small one for the articulation with the 

 fibula. 



The calcaneo-astragalar facet is somewhat saddle-shaped, its 

 fore-and-aft axis being a reversed curve, first concave, then con- 

 vex. The sustentacular facet, however, is deeply concave, the 

 transverse axis curving through an arc of 90°, while the fore-and- 

 aft axis is straight. Below there is but one facet, the calcaneo- 

 cuboid, somewhat semilunar in shape, extending about half the 

 width of the bone. Except for the articulation with the fibula, 

 tliere is little evidence of movement between the calcaneum 

 and the adjoining bones. 



The astragalus presents a beautiful hourglass-sliaped astrag- 

 alotibial facet, bearing on its outer face a clearly defined fibula 

 facet. The range of flexion and extension in the tibiotarsal 

 joint is considerable. Distally two facets are indicated, that 

 for the navicular being by far the larger and somewhat flat- 

 tened, and with a small, prominent, downwardly projecting 

 process, which effectually limits anj' fore-and-aft motion. A 

 prominent ridge divides the two facets, that for the cuboid 

 being an elongated triangle, first convex and then concave 

 from before backward. 



The navicular is very flat and presents two distal facets, that 

 for the ectocuneiform being the larger and somewhat triangular 

 in shape, while that of the mesocuneiform is semilunar, the 

 line of demarcation between the two being almost straight. 



The cuboid has a thickness equal to that of the navicular and 

 ectocuneiform combined and exhibits proximally two contig- 

 uous facets, the lesser for the calcaneum and the greater for the 

 astragalus. Distally there are two facets, the external, the area 

 of which is about four times the greater, being for metatarsal 

 4. This is somewhat saddle-shaped, while the other, that of 

 metatarsal 3, is nearly flat. 



The ectocuneiform is absent in the right pes, though present in 

 the left, being rej^laced in the former by that of another indi- 

 vidual. It articulates distally with metatarsals 3 and 2, though 

 the latter articulation almost fades out anteriorly, broadening 

 as one goes to the rear. This is markedly different from most 

 titanothere feet which the author has seen, in wliicli a wide line 

 of contact is indicated on the face of the tarsus. There is, 

 however, no possibility of contact between the miesocuneiform 

 and metatarsal 3, as the former articulate distally with meta- 

 tarsal 2 only. 



The whole pes is remarkably rigid when compared wath the 

 manus, as there is little indication of any intertarsal movement, 

 none between the tarsus and the median metatarsal, and no 

 lateral and but little fore-and-aft play between the tarsus and 

 the lateral metatarsals. 



The principal dimensions of the pes are: 



Millimeters 



Width of astragalar facet. 105 



Length of calcaneum . 208 



Width of the distal row of tarsals 140 



Height, astragalus to proximal end of the 



third metatarsal 108 



Length of the third metatarsal 205 



Conclusion 



The general proportions of the skeleton would indicate a 

 huge animal, 7 feet 4 inches in height to the withers and some- 

 thing over 12 feet in length, somewhat rhinoceros-like in aspect, 

 but with more massive, pillar-like limbs, which, as Professor 

 Osborn has shown, are correlated with great weight. The 

 extreme flexibility of the carpus seems to indicate an elephant- 

 like habit of kneeling on the wrists when rising and lying down. 



The creature was hardly adult, as indicated by the unossified 

 vertebral epiphyses, though probably of full stature, and it 

 indicated a form in the middle stage of evolution. 



The numerous resemblances in both the skull and 

 the skeleton of Diplodonus tyleri to Brontops robustus 

 strengthen the conclusion that the Diplodonus phylum 

 is an offshoot of the Brontops phylum. The resem- 

 blances extend to the principal measurements of the 

 skull and skeleton in the end members of the two 

 genera. The chief differences are seen in the wider 

 and more specialized manus of Brontops rohustus and 

 in its longer femur. (Gregory.) 



SUBFAMILY MENODONTINAE 



Ailops Marsh 



Two very incomplete skeletons are associated with 

 skulls of the genus Ailops, one in the Field Museum 

 at Chicago referred to Ailops marshi, the other in the 

 British Museum (Natural History) referred to Ailops 

 crassicornisf. This meager material has so far 

 yielded but few clear generic characters of the post- 

 cranial skeleton; it merely indicates that the smaller 

 species of Ailops have short limbs as compared with 

 both Brontops rohustus and Menodus trigonoceras. 



Ailops marshi 



An incomplete skeleton in the Field Museum (No. 

 P6900) comprises six dorsal vertebrae, 21 caudals, 

 part of the pelvis, and much of the limbs. The skull 

 of this specimen is described on page 514. This 

 skeleton as mounted in the Field Museum, under the 

 direction of Dr. E. S. Riggs, is figured below. 



Vertebrae. — The dorsals are strongly opisthocoelous. 

 The centra measure from 48 to 50 millimeters on the 

 midventral line. The 21 caudals measure 111 milli- 

 meters in length, the .tail being relatively long. The 

 midcaudals increase in length; the posterior caudals 

 diminish, as shown by the following measurements: 



Fore limh. — The height of the fore limb at the 

 shoulder is estimated at 1,285 millimeters. 



The right scapula is nearly complete, except at the 

 top. Its height is estimated at 500 millimeters, as 

 compared with 690 in Brontops robustus and 640 in 

 Menodus trigonoceras. 



The humerus measures 425 millimeters from the 

 head to the distal trochlea as compared with 615 in 

 Brontops robustus (type) and 557 in Menodus trigo- 

 noceras. The crest of the great tuberosity is mod- 

 erately developed, much lower than in B. robustus; it 

 is continued antero-internally into the usual incurved 



