Torosaurusa Bull Lizard

In among the steady stream of Triceratops skulls that John Bell Hatcher was sending east to Yale in 1891 were a pair of ringers: two very large skulls that clearly were not the same as the others. The skulls were found less than 2 km apart in southeastern Wyoming. Marsh was on to them right away. By September 1891, he had described them as two species of Torosaurus. The name is an interesting one. It is often construed as "the bull lizard" ("El Toro") in reference to the very large size of the skulls. It may have been a clever pun on Marsh's part. The Greek root of the name refers to perforation, presumably of the crest. In 1891 Marsh had just named Sterrholophus ("solid crest"), which we regard as simply Triceratops. Torosaurus with its parietal fenestrae presented a great contrast to Triceratops. In the plausible interpretation of classicist Ben Creisler, the name Torosaurus ("perforated lizard") simply forms a contrast with solid-crested Triceratops.

The first species, the more perfect of the two skulls, was Torosaurus latus ("wide"), in which Marsh observed for the first time parietal fenestrae. This feature is familiar to us, with the benefit of one hundred years' experience, but for Marsh, Triceratops was the only point of reference, the only other horned dinosaur besides Torosaurus. To Marsh, the parietal crest of Torosaurus was not complete because of these holes. But to us, with our broader perspective, the reverse is true—Triceratops is very unusual in lacking parietal fenestrae. He found the crest thin and light, but very broad and flat, lacking any kind of median ridge. The highly distinctive squamosal of Torosaurus is strikingly long and rather narrow, with a free border unadorned by scallops, bumps, or epoccipitals. Its length exceeds 1.2 m! The nasal horn core is rather short and compressed, and the postorbital horn cores, though incomplete, seem less robust than those of Triceratops. Initially Marsh described Torosaurus as "earlier and less specialized" than Triceratops, but this is erroneous as the two were contemporaries.

In the same paper, Marsh described a second species, Torosaurus gladius ("sword," in reference to the shape of the squamosal, resembling the blade of a sword). The squamosal measured 1.4 m in this specimen, and the postorbital horn cores stood about 70 cm high. The parietal was quite well preserved in the second specimen.1 In January 1892, Marsh elucidated his description with illustrations of the two skulls, the second of which measured nearly 1.7 m across the parietal crest. A peculiarity of this specimen is that the postorbital horn cores are situated caudal to the eye socket, rather than above it. These erect horns are 68 cm high. The crest measures more than half the length of the skull: nearly 1.6 m in length. These enormous animals had truly long frills.2 Hatcher gave the total length of the skull of T. latus as 2.2 m and estimated the length of T. gladius at 2.35 m, but the width of the occipital condyle was a modest 85 mm.3 It was, however, incompletely fused. It is a rather frightening thought that the gigantic skull of Torosaurus gladius was that of an immature animal, with further potential for growth!

Regrettably, Torosaurus has remained a rare and rather poorly known horned dinosaur. More than fifty years passed until the next specimen came to light, this time in northwestern South Dakota, roughly 300 km northeast of the Triceratops beds of Wyoming. The well-preserved specimen was discovered by E. H. Colbert, leading a field party for the Academy of Natural Sciences of Philadelphia in 1944. Colbert and James Bump described the specimen in 1947. Colbert is the most beloved of American dinosaur paleontologists, the elder statesman of our field. His books on the subject inspired me during my formative years—too long ago to admit. For much of his career he was associated

Torosaurus Skull
FIG. 4.1. Torosaurus latus skull at the Academy of Natural Sciences, Philadelphia. (Robert Walters after Colbert and Bump 1947.)

with the American Museum of Natural History in New York. During the years of World War II, however, he was permitted to supplement his meager salary by spending one day per week curating fossils at the Academy of Natural Sciences in Philadelphia. This arrangement benefited both parties significantly.

The skull that was collected, prepared, and exhibited at the Academy of Natural Sciences is clearly Torosaurus latus, as Colbert and Bump recognized. The new specimen is much smaller than the Yale specimens and measures 1.6 m in length, with an occipital condyle of 95 mm in diameter. The postorbital horn cores, at 38 cm in height, are about half as high as those of T. gladius (Fig. 4.1). They also are inclined forward at 45°, rather than being erect as in the Yale specimens. The nasal horn core, as in the other two specimens, is low and blunt. Details of the parietal fenestrae that were not accessible in the type specimen of T. latus are made clear. The fenestrae are very large, occupying about half of the frill. Marsh thought that the parietal fenestra in T. latus contacted the squamosal, but the better preservation of the Philadelphia specimen strongly suggests that Marsh was mistaken. The squa-mosal in the new specimen measures a paltry 79 cm in length.

Rather than describing the new specimen as yet another species, Colbert and Bump took the opposite tack. Instead, they compared all three skulls and concluded that they represent but a single species, Torosaurus latus. They attributed the differences to growth and also hinted at sexual variation but did not come right out with it.41 applaud the modernity of their reasoning, and, rushing in where angels fear to tread, I will go one step further. I will suggest that the two Yale specimens are males, with erect, divergent horns, and that the Philadelphia specimen is a female, with procumbent, parallel horns. The analogy with Lehman's interpretation of sex differences in Triceratops is clear. In fact, Lehman and I both agree that the Philadelphia specimen is a female and that Torosaurus gladius is a male (he believes that the type specimen of T. latus is a female). The striking contrast is between the smallest specimen, which has a fused occipital condyle and is close to its maximum size, and the largest specimen, which has an unfused condyle and thus has significant potential for further growth.

Other reports of Torosaurus have been sporadic, based on disarticulated material or partial skulls. Fossils from the North Horn Formation of Utah were described in 1946 by Charles Gilmore as Arrhinoceratops utahensis' In 1976, Douglas Lawson suggested that these fossils be transferred to Torosaurus utahensis. Lawson also claimed, on the basis of his interpretation of certain fragmentary parietals, that Torosaurus was present in the Big Bend region of Texas.' Today we are inclined to include T. utahensis in Torosaurus latus unless compelling reasons (i.e., adequate fossil material) emerge. Tim Tokaryk in 1986 described a frill of a Torosaurus from Saskatchewan. This specimen measures 1.62 m in breadth across the back of the frill, only about 5 percent smaller than the larger Yale specimen. It has unusually wide squamosals, each of which has an opening in it. Tokaryk's report does an important service in documenting the geographic range of the giant ceratopsid.7 Parties from the Milwaukee Public Museum working in eastern Montana in 1981 recovered a partial skull of Torosaurus and an incomplete skeleton. The skull is of very large size, and the find is enhanced by a superbly preserved right front leg, the significance of which is discussed in Chapter 9.'

CHASMOSAURUS—THE CHASM LIZARD

In Alberta, the Red Deer River arises as a babbling, glacier-fed brook in the ice-sculpted Rocky Mountains, crosses aspen parkland, then slashes southeastward across the rolling shortgrass prairies. As it does so, it furrows deeply through sediments that record the last eleven million years of dinosaur time. Its brown waters eventually carry soil the dinosaurs once tread upon into Hudson Bay, half a continent away (Map 4.1). In steep riverine badlands adjacent to the Red Deer, explor-

Hudson Bay Badlands

• Pac hy rhino saurus ©Avaceratops

0 Triceratops V Brachycerato ps

• Leptoceratops • Einiosaurus VMontanoceratops A Achelousaurus OTorosaurus GDTorosaurus and Triceratops OAnchiceratops, Arrhinoceratops, & Pachyrhinosaurus ACentrosaurus, Styracosaurus, & Chasmosaurus

•Chasmosaurus, Ce ntr osaurus, & Monoclonius

• Pac hy rhino saurus ©Avaceratops

0 Triceratops V Brachycerato ps

• Leptoceratops • Einiosaurus VMontanoceratops A Achelousaurus OTorosaurus GDTorosaurus and Triceratops OAnchiceratops, Arrhinoceratops, & Pachyrhinosaurus ACentrosaurus, Styracosaurus, & Chasmosaurus

•Chasmosaurus, Ce ntr osaurus, & Monoclonius

MAP 4.1. Homed dinosaur localities, northern Great Plains.

ing Canadian geologists and paleontologists from the Geological Survey of Canada in Ottawa uncovered evidence of dinosaurs beginning in the 1870s. George Dawson, Joseph B. Tyrrell, Thomas Chesmer Weston, and Lawrence M. Lambe began to make the first discoveries of Canadian dinosaurs, albeit of a rather fragmentary and tantalizing nature. It is a little ironic that the first important dinosaur fossil found in Alberta, collected by Tyrrell near Drumheller in 1884, was eventually described and named Albertosaurus sarcophagus ("Alberta lizard, eater of flesh") by Osborn in New York in 1905. Alerted to the existence of dinosaurs in Alberta, the Survey continued its efforts. In 1888 and again in 1889, Weston explored the Red Deer River by boat, but he lacked the technical skills to collect significant fossils. Lambe, also using a boat, was more successful. He worked the exposures of the "Belly River series" (Judith River Formation) between Berry Creek and Dead Lodge Canyon in 1897, 1898, and 1901. His success in the field was not brilliant, but he was the first Canadian to study dinosaur fossils, initially with Osborn but soon on his own. No complete skulls or skeletons of dinosaurs had yet been found here.

In their diffident, Canadian way, dinosaur studies north of the border did not begin in earnest until 1902, with the publication by Lawrence M. Lambe (1863-1919) of an important monograph entitled "On Ver-tebrata of the Mid-Cretaceous of the North West Territory." The publication is a well-illustrated presentation of extensive faunal remains from one of the rich fossil localities of the world, the Judith River Formation of Alberta along the Red Deer River. We now know these beds to date from about 74 to 76 Ma, that is some six to eleven million years older than the Triceratops beds of Wyoming, Montana, and Alberta. The fossils include dinosaurs and nondinosaurian reptiles. Unfortunately, the dinosaur materials Lambe had at his disposal then were largely disarticulated, no complete skulls yet having been found. Lambe named three species of Monoclonius: M. dawsoni, M. belli, and M. canadensis.' None has actually turned out to be Monoclonius. The first specimen, M. dawsoni, belongs to the short-frilled Centrosaurus apertus, whom we shall meet in the next chapter. Barnum Brown began collecting skulls and skeletons in Alberta in 1910 and was followed there in 1912 by the Steinbergs, employed in the service of the Geological Survey of Canada. Thus by 1913 Lambe began to have high-quality specimens at his disposal. It was quickly clear to him that Monoclonius belli, which he had established on the basis of a fragmentary parietal, was a completely different dinosaur from Monoclonius.

By January 1914, Lambe had published a preliminary paper presenting a diagnosis of Protorosaurus belli. He expressed it as follows:

Skull large, broadly triangular in superior aspect, with an abbreviated facial portion and a greatly expanded posterior crest ending squarely behind. Coalesced parietals forming a slender frame-work enclosing large subtriangular fontanelles. Squamosals very long and narrow with a scalloped free border. Epoccipitals present. Supraorbital horn-core small, upright. Orbit small. Supratemporal fossae not greatly developed. Body covered with non-imbricating plate-like, and tubercle-like scales.10

This diagnosis is very trenchant. However, the rest of the paper does not follow in the same vein. There are no figures of the skull, but there are four very interesting plates showing fossilized skin patterns associated with the specimen. No measurements are given. (What does "large" mean? This dinosaur was certainly not large compared to Tri-ceratops or Torosaurus.) The paper makes scant reference to a specific specimen. Lambe's comments deal principally with the relationship of his animal to Marsh's Torosaurus. In 1902, Lambe had expressed the opinion that his Monoclonius belli was "probably ancestral to such later forms as Torosaurus latus and T. gladius of Marsh, from the Laramie of Wyoming."11 In 1914 he crowed, "This belief is strengthened by the discovery during the past summer of a skull, with most of the skeleton, of one individual of this species at the type locality." He clearly and not unreasonably believed that "its affinities are with Torosaurus, Marsh, to which it apparently leads in a direct line of descent, and from which it differs by well-marked primitive characters." The name Protorosaurus ("before Torosaurus") expressed this belief succinctly. He was refreshingly explicit about the characters he considered primitive. These were smaller size, greater length of the face, retention of a scalloped free margin of the squamosal, greater size of the parietal fenestrae, smaller supraorbital horn cores, and erect rather than procumbent horn cores.12 A more satisfactory paper followed the next month (February 1914). It figured the skull with lateral and dorsal photographs, making it evident that the front of the otherwise exquisite skull was missing (Fig. 4.2). In addition, an important matter was cleared up. Lambe now realized that the name Protorosaurus was already in use for a Permian reptile from Europe. He thus substituted the name Chasmosaurus ("chasm lizard"), explaining that "The new name has reference to the openings in the skull, more particularly to the great size of the intra-parietal fontanelles." He noted that the front part of the skull "had gone to pieces through weathering," but that the frill was "in a particularly excellent state of preservation." Lambe was impressed by the length of the frill, 25 percent longer than the rest of the skull, and the narrowness of the face. The frill is flat, slightly wider than it is long, and has the form of a triangle, apex forward, base directed caudally. The squamo-sals are like long isosceles triangles, broad toward the front of the skull and tapering backward to reach very nearly the rear edge of the parietal. In this regard, the squamosals of Chasmosaurus are very much like those of Torosaurus, and very much unlike those of Triceratops. There are seven epoccipitals on the right squamosal, eight on the left, plus a large one on the lateral corners of the parietal. The squamosals measure 86 cm in length. The parietal also contrasts greatly with that of Triceratops.

Chasmosaurus Kaiseni
FIG. 4.2. Chasmosaurus belli, American Museum of Natural History, (a) Lateral view, (b) dorsal view. (From Dodson and Currie 1990. Donna Sloan. Courtesy of the University of California Press.)

The fenestrae in Chasmosaurus are enormous, so that the caudal half of the frill is reduced to a slender but strong T-shaped framework, completely unlike the solid, saddle-shaped parietal of Triceratops. The horn cores are not at all impressive. Only the postorbital horn cores are preserved, and these are erect, low, conical structures about 90 mm high, situated immediately above the eye sockets. They are a far cry from the half-meter-long horns of Triceratops and Torosaurus. Lambe estimated the length of the skull of Chasmosaurus belli at 1.65 m. The breadth of the frill is 106 cm.13

In 1915 Lambe published an important monograph on horned dinosaurs, the diversity of which had doubled in the few years since the publication of the Hatcher, Marsh, and Lull monument of 1907. The ostensible purpose of this paper was to deal with the third of his three species of 1902, Monoclonius canadensis ("from Canada"). This specimen was in fact the best of the three that he named as separate species on that occasion. It consisted of a right squamosal, jugal, postorbital, and dentary of moderate size. In 1902, no mention was made of a nasal, but by 1915 a right nasal had joined the skull. Lambe did not have a new specimen to elucidate his type, but he did have a much better grasp on the structure of ceratopsid skulls. He believed that his species did not fall into any described genus. He thus erected a new genus to receive his species, which he named Eoceratops canadensis, the "dawn horned face from Canada." Whereas he believed that Chasmosaurus was ancestral to Torosaurus, he drew comparisons between Eoceratops and Tricera-tops, although allowing the difference that the former had parietal fenestrae.

Eoceratops seems to be small and compact, with a deep skull as Lambe restored it. The squamosal measures 58 cm in length and is rather broad at 36 cm. There are six gentle scallops along the free edge, dying out caudally. The postorbital horn core is erect, a tall 216 mm high, and curves gently backward. The low, blunt nasal horn core is particularly interesting, consisting only of the right half. It thus is clearly formed by separate left and right nasals, fusing later in life. Moreover, there is a scooped, crescentic "gouge" at the base of the right nasal with an apparently separate bone suture into the horn core. Lambe described this as a separate bone, which he named the "epinasal.""

Lambe believed the orientation of the horn cores, especially the postorbital horn cores, to be very important in ceratopsian taxonomy. He wrote:

From our present knowledge of the horn-cores of the Ceratopsidae their curvature, or the direction of their growth, is constant in any species. In individuals of the same species there is remarkably little variation in the curvature or direction of growth of both the supraorbital and the nasal horn-cores Differences of size occur, no doubt due to age and possibly to sex, but apparently the growth of a horn-core is in a definite direction, forward, upward, or backward, and also with inward or outward curvature in the case of brow-homs, according to the genus and species to which the individual belongs.

Lambe rejected the synonymy of Eoceratops with Chasmosaurus belli on account of the difference in the postorbital horn cores.

Lambe compared all of the known ceratopsids and recognized three groups, which he formally designated as subfamilies of the Ceratopsi-

dae: the Eoceratopsinae, Centrosaurinae, and Chasmosaurinae. The first subfamily consisted of Eoceratops, Anchiceratops, Diceratops, and Triceratops, characterized by trends of large brow horns increasing in size; persistently small nasal horn; broadly triangular squamosal; and parietal fontanelle closing. The second subfamily, the Centrosaurinae, consisted of Centrosaurus, Styracosaurus, and Brachyceratops. These cera-topsids are characterized by persistently small brow horns and persistently large nasal horns; small squamosal; and parietal fontanelle "diminishing." The third group consists of Chasmosaurus and Toro-saurus, which show trends of brow horns increasing; nasal horn decreasing; squamosal lengthening; and parietal fontanelle diminishing.

With regard to the frill, Lambe saw the trend as "a persistent attempt ... in all three groups to enlarge and strengthen it and to render it a more efficient means of defence by covering more of the neck and shoulders." He evidently regarded the long-frilled lineages as more highly derived, an assessment with which we will not quarrel: "A final result is reached in the Eoceratops and Chasmosaurus groups in a neck-frill of increased compactness, strength, and resisting power." Lambe also illustrated in the monograph the excellent complete skull of Chasmosaurus belli found by the Steinbergs in 1914 and provided a photograph of a recently found, large and superb skull of Centrosaurus apertus}5

History has not looked favorably on the genus Eoceratops nor on the subfamily Eoceratopsinae. Thomas Lehman, in the most comprehensive study of the Chasmosaurinae, regards Eoceratops as a species of Chasmosaurus, C. canadensis.'6 The genera contained within the subfamily are similarly regarded as chasmosaurines. We shall return to a discussion of C. canadensis later. Lambe did not return to the subject of horned dinosaurs during the few years left in his lifetime.

In 1920, George Sternberg, collecting for the University of Alberta in the Judith River Formation of the Red Deer Valley, found a fairly small ceratopsid skull. Charles W. Gilmore described it in 1923 and referred the specimen to Eoceratops canadensis. He estimated the skull to have been about 1.2 m long, although this is possibly a little too generous. It is well preserved, except that it is missing the back half of the frill. The nasal horn core is prominent but blunt, showing no trace of division into left and right halves. The postorbital horn cores are strongly procumbent and measure 170 mm in height. As in Lambe's specimen, they are concave caudally. The squamosal is broad (28 cm), but its length cannot be estimated. It shows epoccipitals, which are lacking in the

Ottawa specimen.17 Lull in his 1933 monograph was not convinced that the Alberta specimen was distinct from Chasmosaurus, although he referred it to a different species, as discussed later in this chapter.18

Reconstructing Chasmosaurus

Charles Mortram Sternberg (1885-1981) was one of C. H. Sternberg's three sons. All three lads came to Alberta with their dad in 1912. C. H. Sternberg left Canada in 1916 to resume his career in the United States as a commercial fossil collector. George Sternberg, the oldest of the three brothers, left Canada in 1923. Levi Sternberg joined the technical staff of the Royal Ontario Museum and lived in Toronto until the end of his life (1976). Charlie remained in Ottawa for the rest of his life. Lambe, his mentor in Ottawa, died suddenly in 1919, and Charlie assumed his duties as museum scientist as well as technician.

For a person with a high school degree (from that misty, bygone era when even elementary schools still taught a great deal), Charlie Sternberg had a distinguished career as a paleontologist. His first paper appeared in 1921, supplementing Lambe's study of the ankylosaur Panoplosaurus, and his publications continued to appear until 1970, even though he nominally retired in 1950. He described numerous Canadian dinosaurs. As was the style in those days, he did not engage in rapturous flights of speculative fancy, but his papers have stood the test of time very well. His descriptions and interpretations were reliable, and this term is intended as high praise. No published study of Canadian dinosaurs is possible to this today without citing one or another of Sternberg's papers. One of the great thrills of my young professional life (or to be honest, my preprofessional life) was meeting CM., as we called him, when he would visit the old paleo labs of the National Museum of Canada, where I worked as a student during the summer of 1967.

Following Lambe's death in 1919, C. M. Sternberg assumed the role of director of the paleontology enterprise of the Geological Survey of Canada and soon began publishing. One of his early papers was on the description of a patch of skin impression associated with the skeleton of Chasmosaurus belli that he had collected in 1913.19 Two years later he wrote a paper describing a lovely exhibit at the National Museum of Canada of a pair of C. belli skeletons mounted side by side. (Fig 4.3). Sternberg noted that although horned dinosaurs were well known to the public, as most museums of the world had the skull of one or another, skeletons were very rare (Fig. 4.4). The two specimens were the

Chasmosaurus Skull
FIG. 4.3. Chasmosaurusbelli, Canadian Museum of Nature, Ottawa. This exquisite skull belongs to one of the pair mounted by C. M. Sternberg. (Photo by Peter Dodson.)
Centrosaurinae
FIG. 4.4. Skeletal reconstruction of Chasmosaurus belli, (a) Lateral view, (b) dorsal view. (Gregory S. Paul.)

first group of horned dinosaurs ever mounted. One (NMC 2245) was collected 5 km downstream from Steveville in 1913, the other (NMC 2280) some 10 km downstream from the first in 1914. In addition to the skull, the first specimen included a vertebral column complete up to the twenty-fourth vertebra of the tail, pectoral and pelvic girdles, humeri, one ulna, femora, one tibia and fibula, and some foot bones. The vertebral column of the second skeleton was complete to the pelvis and included the pelvis and shoulder girdle. Apart from both humeri and a portion of one femur, the limbs were missing. Missing parts were restored in plaster. One striking if unquantified feature of the two skeletons is that the bones of one (NMC 2245) are much lighter in construction than those of the other. Sternberg not only attributed the difference in the otherwise very similar specimens to sexual dimorphism, he also posited that the larger one was the female.

Sternberg noted the difficulty he encountered in mounting the shoulder joint, owing to the lateral offset of the head of the humerus. He expressed very clearly the dilemma that every mounter of ceratopsid skeletons has faced: "Consequently the only way the limb could be posed, so the head of the humerus fitted into the glenoid cavity was to place the humerus at almost right angles to the perpendicular. This made the animal very low in front and extremely bow-legged. The humerus placed in this position made a very much better articulation with the ulna and radius than could be gained otherwise." As Sternberg realized, "such a pose does not suggest speed but rather an animal which waddled along with a swaying motion." Our modern aesthetic sensitivity finds this pose somewhat offensive. Today we try to mount ceratopsids with the forelimbs as elevated as possible, but attempts to restore these animals as greyhound-like racers reside more easily in the two-dimensional world of canvas and acrylic than they do in the three-dimensional world of plaster and welder's rod. We will return to this issue in the final chapter.

Sternberg presented an extensive list of measurements of both specimens. As restored, one skeleton (NMC 2245) measures 4.93 m in length, the other (NMC 2280) 4.95 m in length. The skull of the former measures 1.68 m in length, that of the latter 1.65 m in length. NMC 2245 is 1.5 m in height at the pelvis, with a femur length of 75 cm and a tibia length of 53 cm.20 The two Ottawa specimens of Chasmosaurus belli made a striking exhibit. Although the specimens are no longer exhibited in Ottawa, casts of these skeletons may be seen in Philadelphia at the Academy of Natural Sciences and at the Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta.

More Species of Chasmosaurus

For a comparative neophyte in academic paleontology, C. M. Sternberg made a surprisingly cheeky comment that subtly "dissed" his late mentor when in his 1927 paper he stated, "the brow horns vary in length, and it is questionable whether their size or length has any generic or specific significance. The horn itself was probably much longer than the bony core."21 Although these are words to live by, few chose to live by them, and new specimens soon became new species. Other specimens of Chasmosaurus belli were collected from the Steve-ville badlands of Alberta and were recognized as such. In his compilation of 1933, Lull recognized a number of such specimens in Ottawa,

FIG. 4.5. Chasmosauruskaiseni, American Museum of Natural History. (From Dodson and Currie 1990. Donna Sloan. Courtesy of the University of California Press.)

Toronto, New York, and New Haven. For instance, the beautiful skull of American Museum of Natural History (AMNH) 5402 is photographed, and Yale Peabody Museum 2016 illustrated in ventral view. However, a skull that Barnum Brown collected in 1913 seemed in some respects to stand apart from the normal range of variation. This fine skull, AMNH 5401, measures 1.52 m in length, by no stretch of the imagination a large skull. The frill is only 82 cm wide across the back. However, it has a pair of very tall, procumbent postorbital horn cores that measure 370 mm in length, recurved as in all other specimens of Chasmosaurus. The rostrum in front of the external nostril is strikingly long and low. In 1933, Barnum Brown described this specimen as Chasmosaurus kaiseni, honoring his associate Peter Kaisen (Fig. 4.5). Brown did consider the possibility that this skull was Ceratops, Marsh's genus from the Judith River Formation of Montana that was based on a pair of horn cores and an occipital condyle. However, he wisely decided to refer it to the well-characterized genus Chasmosaurus.22 The University of Alberta specimen of Eoceratops is in Lull's judgment better referred to Chasmosaurus kaiseni as a sexual variant, presumably a female, according to Lull.

Lull, in his 1933 monograph, named another species, Chasmosaurus brevirostris ("short rostrum"), on the basis of a skull at the Royal Ontario Museum collected by the University of Toronto in 1926 (Fig. 4.6). Lull characterized C. brevirostris as follows:

This species conforms to belli, except that the muzzle is very short and deep, more as in Monoclonius, and the nasal horn is large and curves somewhat backward, although inclined forward at the base. The brow

FIG. 4.6. Chasmosaurus brevirostris, Royal Ontario Museum. (From Dodson and Currie 1990. Donna Sloan. Courtesy of the University of California Press.)

horns are like the nasal but smaller. The last epoccipital on the squamosal is markedly larger than in any other specimen. .. . There were nine epoccipitals borne on the squamosal.23

This is a large skull, approximately 1.8 m in length. Not mentioned in the description is a prominent opening in the left squamosal. This skull really does have a short, deep face, almost antithetical to that described in C. kaiseni.

Finally C. M. Sternberg got into the act himself. In 1940 he described Chasmosaurus russelli (honoring L. S. Russell, who became one of Canada's most distinguished native sons in paleontology). The skull was collected in 1938 by Russell for the Geological Survey of Canada and came from the Manyberries region of extreme southeastern Alberta, not far from the Montana border. Sternberg designated a second skull as a paratype. This skull, collected in 1928, came from the Red Deer River Valley 5 km south of Steveville. A third skull was collected in 1937 from the Manyberries region, and a fourth specimen consisted of a partial parietal collected in 1935 from a locality along the South Saskatchewan River some 100 km east of Steveville. The type specimen is a large skull, measuring 1.94 m in greatest length. The nasal horn core is described as massive but the postorbital horn cores are lacking. In addition, the squamosal shows poorly developed scallops along the free edge. The caudal bar of the parietal, rather than being T shaped as in C. belli, is Y shaped. Sternberg described it as "deeply indented" or "deeply emar-ginate." The parietal does not bear epoccipitals as it does in C. belli. Several limb bones were found with the paratype. These reinforce the idea that C. russelli was a large animal. The humerus measures 71 cm and the tibia 61 cm.24 The comparable measurements in C. belli are 51 cm and 53.5 cm. If C. belli measures 4.9 m in length, C. russelli may measure between 5.7 and 6.9 m in length. Although the latter figure is surely excessive, it does indicate that this animal was unusual for a horned dinosaur of Judithian age.

Matters rested there for many years. As described previously, the trend in more recent years has been to look for ways to consolidate species, not to name more. No one is more sensitive to that trend than Thomas Lehman, who completed his Ph.D. at the University of Texas in 1985 under the supervision of Warm Langston, Jr. Lehman, now a professor of geoscience at Texas Tech University in Lubbock, published an important paper in 1990 in which he demonstrated rational ways to reduce oversplit taxonomy of chasmosaurines and to group species together in meaningful ways. Nonetheless, he too has contributed to the taxonomic history of the genus Chasmosaurus by naming a new species. The status of the Texas Chasmosaurus somehow seems less ambiguous than that of the multiple species from Alberta, because the geographic separation of more than 2,000 km makes biological sense of a distinct species.

In 1938, a withering depression seared dustbowl-dry landscapes throughout the American West. Franklin D. Roosevelt, determined to get the nation back to work, had established the Works Progress Administration, widely known as the WPA. Labor-intensive projects of staggering variety were carried out. Yet few were as unusual—or took place in such a forbidding (albeit austerely beautiful) landscape—as that supervised by Professor William Strain of the College of Mines and Metallurgy in El Paso. The crew under his supervision excavated three dinosaur bonebeds near the Rio Grande that separates Texas from Mexico, in an area of West Texas that is now Big Bend National Park. The bones came from the Aguja (phonetically the; is an h) Formation of Late Cretaceous age, roughly equivalent in age to the Judith River Formation of Alberta. Lehman interpreted the sediments as representing deltaic interdistributary marshes, that is to say, swamps. One deposit contained 342 identifiable bones, more than 70 percent of which belonged to the same species of ceratopsid, which Lehman named Chasmosaurus mariscalensis ("named for Mariscal Mountain, in the southern part of Big Bend National Park, near the type locality") (Plate II). The specimens reposed unstudied at El Paso for nearly fifty years, until Lehman became interested. The collection is quite marvel ous, consisting as it does of a large number of disarticulated specimens of Chasmosaurus of small to large size, including both skull and skeletal bones.

Lehman systematically described all identifiable elements of the skeleton. A number of elements are unrepresented in the collection, including the rostral bone and the nasal bone, so the form of the nasal horn core was speculative. Postorbital horn cores, of which there are eleven, are among the most abundantly represented elements in the collection. These range from 140 mm to 350 mm in height and are generally erect. As in all specimens of Chasmosaurus, they are recurved, that is, concave backward. Lehman noted subtle differences among them, notably that some are quite erect, whereas others are slightly procumbent and also diverge laterally. He posited that the erect horn cores were those of males and that the less vertical ones were those of females. There are four braincases in the collection. The smallest occipital condyle measures 41 mm in diameter and is unfused, showing all three separate bones that contribute to its formation; the largest measures 70 mm in diameter.

Regrettably, the parietal is poorly represented, but one fragment that includes both the median bar and part of the caudal border shows the Y shape seen in C. russelli. Lehman speculated that there were epoccipi-tals on the parietal, unlike in C. russelli, because there are swellings that may represent points of attachment for these elements. Fortunately, squamosals are well represented, although they are somewhat fragmentary in condition. Lehman reported that they are triangular as in the general form of chasmosaurine squamosals, but that they are relatively short and broad, more so than in other forms of Chasmosaurus—in fact, more so than in other chasmosaurines except for Triceratops, Toro-saurus utahensis, and Anchiceratops. He believed that the squamosal of C. mariscalensis did not change shape or elongate significantly during growth. There are six or seven coarse scallops on the squamosal, expressed as epoccipitals in mature specimens. This number is low compared to other specimens of Chasmosaurus. He tentatively suggested that differences in the epoccipitals (broader squamosals with rounder, blunter scallops versus more slender squamosals with more pointed epoccipitals) might have a sexual basis. Five maxillae that range in length from 258 mm to 452 mm show that the number of teeth in the upper jaw increases from twenty to twenty-eight during the phase of growth represented.

Of the postcranial skeletal elements, the best represented are humeri (thirteen), femora (seventeen), and tibiae (fourteen), all robust, well-

constructed bones. Humeri range from 352 mm to 545 mm in length, femora from 355 to 713 mm, and tibiae from 389 to 556 mm. The general consistency in the size spread of all elements encourages the interpretation that the deposit contains the disarticulated remains of just a few individuals rather than the water-transported remains of bones gathered some distance upstream and deposited willy-nilly, like driftwood upon a beach. We can go further, using the wonderful reference specimen of Chasmosaurus, C. belli (NMC 2245), which is 4.93 m long and has these measurements: humerus 508 mm, femur 749 mm, tibia 533 mm. We can make the following estimates for C. mariscalensis:

Small Large

Humerus

Femur

Tibia

Bone Length (mm)

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  • thomas
    Has a dinosaur fossil ever been found in el paso texas?
    8 years ago

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