The Shortfrilled Horned Dinosaurs

WHEN horned dinosaur remains began to be discovered in what is now Montana, they were those of the short-frilled types we know today as centrosaurines. This group includes the exotic Styracosaurus, the enigmatic Pachyrhinosaurus, and the recently discovered Einiosaurus that shows an unexpected state of horn development. I confess to a special fondness for centrosaurines. My own work in Alberta and Montana has often involved centrosaurines. In fact, part of my slender claim to paleontological legitimacy stems from my discovery and description of a new centrosaurine from Montana, which I named Avaceratops in 1986, and which occupies a place of honor in the wonderful dinosaur hall (safely away from the glare of the Tyrannosaurus) at the Academy of Natural Sciences in Philadelphia. Besides all this, the first ceratopsid dinosaur to be identified and that we still recognize today was the centrosaurine Monoclonius, named by E. D. Cope in 1876.

When Barnum Brown named Leptoceratops, the first protoceratopsid, in 1914, there was a ready yardstick of comparison because ceratopsids, especially Triceratops, were by that time well known. It is hard to imagine that there was a time when no one knew that there were dinosaurs that sported horns on their faces. It had been suspected, for instance, that the two-legged plant-eater Iguanodon had a spike on its nose. With the discovery of skeletons of Iguanodon in the coal mines of Bernissart, Belgium, in 1878, however, the 15-cm conical spike was removed from the nose and placed in its proper, if surprising, position on the thumb. There were no horned ornithopods. Clearly, having horns on the head seemed like such a good idea that, if nothing else, someone would just have to invent such an animal.

Early dinosaur discoveries in England and Europe were rather fragmentary. When Richard Owen coined the name dinosaur in 1842, no accompanying visual image was presented, because to do so would

Joseph Leidy
FIG. 5.1. Joseph Leidy (1 823- 1 89 1). (Robert Walters.)

simply entail too much speculation. The first discoveries of dinosaurs in the New World were little more auspicious. Not surprisingly, the discoveries were made in Cretaceous beds of Montana, in what we now recognize as the Judith River Formation. The geological explorer Ferdinand V. Hayden picked up a small collection of teeth in 1855 and sent them to Professor Joseph Leidy (1823-1891) at the Academy of Natural Sciences in Philadelphia (Fig. 5.1).1 Leidy, a brilliant young physician and anatomist, was one of the first scientists to make extensive use of microscopy in his research and made important contributions in many fields of natural science in addition to paleontology. He recognized Hayden's teeth as dinosaurian and in 1856 named the first American dinosaurs: Tracho-don, Troodon, Deinodon, and Paleoscincus. Unfortunately, these names have proven troublesome ever since, because the plain fact is that teeth are not a very good basis for naming dinosaurs.2 Only the name of Troodon, a nasty little meat-eater with a large brain, is still in use today. Interestingly, when we examine the vial containing the type specimen of the dubious duck-bill Trachodon mirabilis at the Academy of Natural Sciences, there are several teeth. One of these teeth is clearly that of a

Edward Drinker Cope
FIG. 5.2. Edward Drinker Cope (1840-1897). (Robert Walters.)

duck-bill, although which duck-bill we cannot say. Another tooth, less well preserved, is equally clearly that of a ceratopsid, split root and all! Thus we can trace the earliest evidence of ceratopsids to 1856.

Dinosaur science was greatly advanced with the discovery of the first good partial skeleton of a large dinosaur in 1858. The discovery came not from Europe, or from the great fossil beds of the western United States or Canada, but from Haddonfield, New Jersey, barely 10 km from Philadelphia. In Joseph Leidy's able hands, the duck-bill Hadrosaurus foulkii took form as an animal that walked on its hind legs, no longer a monster lizard but a kangaroo-like biped. Ten years later, the skeletal reconstruction of Hadrosaurus that went on display at the Academy of Natural Sciences was the first dinosaur skeleton ever exhibited anywhere in the world. Young Edward Drinker Cope (1840-1897) was enthralled by the fossil treasures of the Academy (Fig. 5.2). As a young lad of eight years, he used to spend free hours there, sketching fossil ichthyosaurs and plesiosaurs from Lyme Regis, England. Cope went abroad to study zoology and paleontology in Europe then returned to

Philadelphia to pursue his professional career. He was a brilliant man who published more than 1,400 papers in his career (and he died young!). Many of these papers were mere notes, and others contained embarrassing errors. A substantial number of his papers, however, represent fundamental insights for which paleontologists and vertebrate and invertebrate zoologists today are indebted to him. He also possessed, shall we say, an energetic personality. Many found him hard to get along with, truly an enfant terrible. He was impulsive, impetuous, and sometimes forgetful of social graces. He did not have a successful record of institutional employment, although he taught for one year at Haverford College. He also had a stormy relationship with the Academy of Natural Sciences. He was at his best when on his own; his family's wealth permitted him this luxury.

Cope began his career in fossil reptiles by describing Cretaceous specimens from New Jersey, the most important of which was an intriguing meat-eater, which he named Laelaps aquilunguis ("eagle-clawed hunting dog") in 1866. Unfortunately, the name Laelaps was already in use, and O. C. Marsh at Yale was only too happy to rename the dinosaur Dryptosaurus ("tearing lizard"), a less poetic but suitably rapacious name. In 1868, Cope described a large marine reptile, sent to Philadelphia from Kansas, as Elasmosaurus. However, in his haste, he blundered by reconstructing the head on the end of the tail—an error indelicately pointed out to him by both Marsh and Leidy, to Cope's everlasting chagrin. Soon his restless energy had brought him out west to work in the fossil beds of Kansas, Wyoming, and Colorado.

In 1872, F. B. Meek discovered bones in southwestern Wyoming, 80 km east of Green River. Cope was soon there and excavated a partial skeleton, consisting of sixteen vertebrae from the tail, sacrum, and back; two large ilia from the pelvis measuring 1.2 m in length; and some ribs. He named his specimen Agathaumas sylvestris ("great wonder of the forest") in 1872, noting that "the measurements ... of the present animal exceed those yet described from North America." He was impressed with the proximity of the bones to coal seams: "It appears that the forests that intervene between the swamps of epochs during which the coal was formed were inhabited by these huge monsters; that one of them lay down to die near the shore of probably a brackish-water inlet, and was soon covered by the thickly fallen leaves of the wood."

Cope was at a loss to explain what kind of animal this dinosaur was. He compared it to Hadrosaurus, to Dryptosaurus, and even to Cetiosaurus, concluding that "it is evidently new to our system."3 Cope was un doubtedly correct: today we can recognize the remains, which are in the collection of the American Museum of Natural History, as those of a large ceratopsid, but no skull material has ever been associated with Agathaumas, nor have further specimens of this or any other dinosaur been found in the region. The "great wonder of the forest" remains only of historical interest, as the first ceratopsid to receive its own name, but a name that falls into the dreaded category of "nomen dubium." We may guess that the animal in question was either Triceratopsor Torosaurus. These are only guesses, but they are consistent with its large size.

Cope again visited the West in 1873, and somewhere in northeastern Colorado he made a small collection of bones, which are cataloged today in the collection of the American Museum of Natural History as "fragments of horn cores, vertebrae, etc." As we have already discussed, dinosaurs were not then known to have possessed horn cores. When Cope described these materials in 1874, he failed to recognize fragments of horns as such. He did not shrink, however, from applying a name to his find, which he called Polyonax mortuarius ("master over many, dead").4 Whereas Agathaumas tantalizes, Polyonax simply clutters the literature. When John Bell Hatcher reviewed the species thirty-three years later, his scorn was little disguised:

Cope's description and figures demonstrate conclusively the extremely fragmentary and totally inadequate nature of the material upon which the genus and species were based. The fragments supposed by Cope to pertain to the ischia are now known to have been portions of the frontal horn cores. The "paleontological wastebasket" would be a fit receptacle for what remains of the type material, while the name should be dropped from the paleontological literature. It was perhaps a premonition of this which suggested to Professor Cope the specific appellation mortuarius. Unfortunately vertebrate paleontology is burdened with too many genera and species founded, as in the present instance, on fragmentary and insufficient material.5



Twice Cope failed in his quest to name a valid ceratopsid. The third time he achieved some degree of success, though it was hard won and even today does not elude controversy. Cope's first forays out west were under the escort of parties from the U.S. Geological and Geographical Survey of the Territories. By 1876, he had begun to use his favorable personal circumstances to hire his own workers. Soon he made contact with Charles Hazelius Sternberg (1850-1943), who was destined to become one of the great American dinosaur hunters of all time. The senior Sternberg, then a student at Manhattan State College in Kansas, attempted to sign on with Benjamin Mudge's expedition to the Cretaceous chalk deposits of western Kansas. Mudge had been sent to the chalk on behalf of Yale's O. C. Marsh. No positions were available when Sternberg applied, so in desperation he wrote to Cope in Philadelphia. We have the account in Sternberg's own words:

Almost with despair, I turned for help to Professor E. D. Cope, of Philadelphia, who was becoming so well known that a report of his fame had reached me at Manhattan.

I put my soul into the letter I wrote him, for this was my last chance. I told him of my love for science, and of my earnest longing to enter the chalk of western Kansas and make a collection of its wonderful fossils, no matter what it might cost me in comfort or danger. I said, however, that I was too poor to go at my own expense, and asked him to send me three hundred dollars to buy a team of ponies, a wagon, and a camp outfit... .

I was in a terrible state of suspense when I had despatched the letter, but, fortunately, the Professor responded promptly, and when I opened the envelope, a draft for three hundred dollars fell at my feet. The note which accompanied it said: "I like the style of your letter. Enclose draft. Go to work," or words to the same effect.

That letter bound me to Cope for four long years, and enabled me to endure immeasurable hardships and privations in the barren fossil fields of the West; and it has always been one of the greatest joys of my life to have known intimately in the field and shop the greatest naturalist America has produced.6

Sternberg greatly repaid the trust Cope showed in him, and the resulting collection of Late Cretaceous marine fossils provided Cope with specimens of fishes, reptiles, and birds to describe for several years. For the purpose of our narrative, however, it is events later in the summer of 1876 that hold our attention. Cope came west, arriving by rail on August 1 in Omaha, where he was met by Sternberg. Cope desired to investigate the location from which Hayden had collected the first American dinosaurs in 1855. An arduous and circuitous journey ensued, to north-central Montana via Nebraska, Utah, and Idaho. A

momentous event in American history had occurred in southern Montana just a few weeks earlier, on June 25, 1876—the Battle of Little Bighorn. Nerves were greatly ajitter, but Cope, a devout Quaker and pacifist, refused to take heed. In Fort Benton on the Missouri River, horses, a wagon, and equipment were purchased, and a cook and crew hired. Heading overland, the small band reached the badlands near the mouths of the Judith River and Dog Creek, 80 km east of Fort Benton, on August 27. Surrounding the Missouri River here were steep and forbidding riverine exposures, the likes of which Cope had never seen. Adventures included a visit by 2,000 peaceful Crow Indians and the subsequent desertion of the cook and scout; hair-raising nocturnal forays through the badlands; and a life-threatening slip down a steep slope described by Sternberg. The work was physically exhausting. Fossil remains of many animals—of both dinosaurs and other animals, including turtles, garfishes, and freshwater rays—were found. However, these were predominantly fragments or "spare parts," rather than major portions of skeletons. Sternberg recounts evidence of Cope's vivid imagination:

Every night when we returned to camp, we found that the cook had spent the whole day in cooking. Exhausted and thirsty,—we had no water to drink during the day (all the water in the Bad Lands being like a dense solution of Epsom salts),—we sat down to a supper of cakes and pies and other palatable, but indigestible, food. Then, when we went to bed, the Professor would soon have a severe attack of nightmare. Every animal of which we had found traces during the day played with him at night, tossing him into the air, kicking him, trampling upon him.

When I waked him, he would thank me cordially and lie down to another attack. Sometimes he would lose half the night in this exhausting slumber. But the next morning he would lead the party, and be the last to give up at night. I have never known a more wonderful example of the will's power over the body.7

The results of their efforts were less than spectacular. Cope left from Cow Island, 50 km downstream, on a river steamer bound for Omaha around October 15. He carried 1,700 pounds of fossils with him. Sternberg stayed on until a heavy snowfall on November 1 and then left. However, before he left, he found a significant dinosaur fossil near Cow Island that Cope described in 1889 as another species of Monoclonius.

Complete articulated dinosaur material, or even associated partial skulls and skeletons, were still a rarity in 1876. The best fossils yet known were exquisite small specimens from lithographic limestones of Germany, notably single specimens of Compsognathus and of the proto-bird Archaeopteryx. Hadrosaurus and Laelaps from New Jersey were far more complete than anything yet seen in the American West. Cope was undeterred by the quality of his specimens, and he set out quickly to describe some of his finds. When I say quickly, I mean that by October 31, 1876, scarcely two weeks after he began steaming down the Missouri, he published a fourteen-page paper in which he described four new genera and thirteen species of dinosaurs, plus seven species of turtles and fish. It may well be suspected that such an outpouring of taxonomic activity was not accompanied by mature reflection, insightful description or comparison, or even minimal illustrations—of which there were none. Furthermore, the specimens were not numbered with an accession number or museum collection number, nor were any specific locality data noted, other than that conveyed in the title of the paper: "Descriptions of some vertebrate remains from the Fort Union beds of Montana."8 These facts being the case, the reader will not be surprised to learn that the majority of taxa therein described have since been relegated to oblivion.9 One dinosaur, however, commands our attention: Monoclonius crassus.

Monoclonius crassus ("thick single-sprout") was not merely a tooth-genus. Although teeth played prominently in Cope's concept, he also included vertebrae, limb bones, and other materials in his description. Historians have complimented Cope on the elegance of his names: replete with classical allusions, grammatically well formed, and euphonious. It is all the more impressive to realize that these names were not necessarily composed in his wainscotted study—surrounded by shelves of scholarly tomes, reference works, and dictionaries—but, at least in the present instance, by the flickering light of a campfire or on the decks of a river steamer that plied the waters of a muddy river somewhere in the middle of the western wilderness of Montana.

Cope's names were not explained to his classically educated contemporaries, but we may presume that they were understood. Their meanings have suffered through the years, and the name Monoclonius is a case in point. David Lambert, for instance, in his The Dinosaur Data Book (1990), defines the name as "one horned." The late Helen Roney Sattler, in her The New Illustrated Dinosaur Dictionary (1990), carefully and correctly translates the name as "single stem," but then adds "referring to the single horn on its nose." This view has flourished since Osborn wrote Cope's biography in 1931.'° Recently, however, Benjamin S. Creisler, a classicist who is also interested in dinosaur taxonomy, did a neat and convincing job of unraveling Cope's probable intention. He interprets the name Monoclonius as a contrast with Diclonius, named immediately before Monoclonius in the same publication. Diclonius consists only of teeth, and Cope was attempting to contrast the method of tooth replacement (i.e., of sprouting) in the one dinosaur with that in the other. He compared tooth replacement in Monoclonius with that in Hadrosaurus." The sad fact is that he simply did not have enough information upon which to base his conclusions. His Monoclonius tooth was probably that of a duck-bill, not a horned dinosaur. Were this all there were to Monoclonius, it would by now simply be another of his forgotten dinosaurs, such as Dysganus or Diclonius.

Fortunately, however, Cope added further details to his description. He described the sacrum as having ten vertebrae, measuring 27 in. (69 cm) in length. Three anterior dorsal vertebrae are fused together, with a deep cup facing forward. The limb bones are said to be robust, with a femur of 22 in. (56 cm) and a tibia of 2° in. (51 cm). The forelimb was not measured but is said to be robust in contrast to that of Hadrosaurus, which certainly makes sense. The most intriguing bone is a large "episternum" or breastbone, for which he gives a length of 21 in. (53 cm). These twenty-seven lines of text conclude his description. There is no attempt either to interpret the bones or to determine what manner of animal his Monoclonius was.12

The following year, Cope expanded on his subject and included some figures for the first time. The descriptions are wordy and uninformative, and the figures of several skull elements are hard to interpret. Indeed, he wrote, "Positive determination of these elements is impracticable, as they do not resemble the corresponding bones in any animal known to me." Despite having figured a nasal horn core, Cope did not recognize that it actually was a horn! In many words he described it as L shaped (i.e., including the nasal base), massive at the base, narrowing gradually to the extremity, and roughened with grooves for blood vessels.13 It is clear enough that Cope had no concept of what kind of herbivore Monoclonius was.

The next major event in the history of horned dinosaurs was the discovery of Triceratops, whose history we discussed in Chapter 3. In 1889 Marsh named and figured a skull of Triceratops, which has since become one of the best-known dinosaurs in the world. It now became clear for the first time that horned dinosaurs were large herbivores with horns on their faces and expansive bony frills. Moreover, these were important animals in the Late Cretaceous communities of Wyoming and Montana. Cope was for the first time in a position to make some sense of his collection of Monoclonius bones from 1876. He reviewed his type species, Monoclonius crassus, and was now quite definite about it. He states that Marsh's figure "enables me to determine more exactly the affinities of several species of the family which have been in my possession for many years. The most complete specimen in my collection is that of Monoclonius crassus Cope. This includes representatives of all elements excepting the bones of the feet."

He now characterized Monoclonius as having small horns over the eyes and having an "enormously expanded parietal" with huge openings. Although he did not admit his mistake, his "episternum," or breastbone, of 1876 now had become a skull element, the parietal, which is the correct anatomical assignment. Proper placement of this element gave the skull such an improbable, even outlandish, appearance that we may forgive Cope his error. The parietal is now figured, and it is a very important specimen indeed, as we shall see presently. It resides in a basement treasure room of the American Museum of Natural History, where I have pored over it on many occasions. Cope referred to a squamosal, which he described in very general terms, but unfortunately he did not figure it. He compared pelvic and sacral bones to similar bones in Agathaumas and therefore preferred to use his name, Agathaumidae, for the family of horned herbivorous dinosaurs, consisting of Agathaumas, Polyonax, and Monoclonius. "This family is called by Marsh the Ceratopsidae; but as it is not certain that Ceratops, Marsh, is distinct from one of the genera previously named, I shall call it the Agathaumidae."14

Whatever the scientific merits of his case (and it is true that Ceratops is a poorly founded genus), it is Cope's misfortune that Agathaumas and Polyonax are forgotten genera, and his name has enjoyed no currency whatsoever. It is also Cope's misfortune that Marsh's ceratopsian genera, Triceratops and Torosaurus, are known from far more complete material than any specimen of Monoclonius discovered before 1937. Perhaps most important of all, the definitive 1907 monograph on the horned dinosaurs was a Yale production.15 As was ever the case, the victors wrote the history, and the name Ceratopsidae has served for the family of horned dinosaurs since Marsh proposed it in 1889. It is a felicitous name, and I for one am glad that it has triumphed over Agathaumidae.

Cope named three further species of Monoclonius in his 1889 paper. M. recurvicornis specimens had been figured in his 1877 paper, but he states that, "suspecting they might belong to some of the species already known," he did not name them. The "recurved horn" species consists of a pair of moderately prominent (210 mm high) orbital horns and a low, blunt nasal horn about half that height. Again Cope mentions a squamosal but does not figure it. The second species, M. spheno-cerus ("wedge horn"), was collected by Sternberg at Cow Island and is said to consist of "numerous parts of the skeleton, including parts of the skull." The most striking aspect of M. sphenocerus, and really the only one that Cope expanded on, is a very tall, straight nasal horn. It was 325 mm tall. It was as clear to Cope then as it is to us today that this nose hom is imposing. He wrote without hyperbole: "The Monoclonius sphenocerus is an animal of large size, exceeding a rhinoceros in height, and the nasal hom is the most formidable weapon I have observed in a reptile." The third species, M. fissus, has caused the fewest problems. It is based only on a single bone, which Cope misidentified as a squamo-sal. No wonder it did not resemble the squamosal of M. crassus—it was a pterygoid, and a broken one at that. It was not figured, and the species was soon ignored, as we shall do.1'

Thus was bom Monoclonius, now clearly a homed dinosaur of the Judith River Formation. Its Late Cretaceous age was established. Its name was destined to be conspicuous and important. Late in Cope's life, Osbom arranged for major parts of Cope's personal collection to be purchased by the American Museum of Natural History, which in 1895 had not yet come to prominence in dinosaur paleontology (or in any another branch of paleontology, for that matter).17 Hence, the type specimens of Monoclonius species came to reside at the American Museum, where they may be studied today. Monoclonius remained the preferred name used by Bamum Brown in his writings on homed dinosaurs from beds of Judith River age, including those collected in Alberta. (I will argue later that this usage is incorrect.)

On the other hand, the Yale camp, represented by the trio of John Bell Hatcher, O. C. Marsh, and Richard Swann Lull, had no vested interested whatsoever in preserving Cope's name. In 1907, there appeared a large, brown, folio-sized volume entitled The Ceratopsia under the authorship of these three scholars.1' As we have seen, neither Marsh (died 1899) nor Hatcher (died 1904) lived to see his triumph. The task of completing the monograph was turned over to Lull, a young professor at Yale, who did an admirable job of completing the text, modestly listing himself as editor. The book, published in 1907, is one of the most beautiful and significant tomes on dinosaurs ever published, as useful today as the day it was published.

Hatcher did not beat around the bush. He made it clear that there were serious problems with Monoclonius. The problems stem from the failure of Cope to document his finds with identifying marks (e.g., field numbers), illustrations, or locality data. Hatcher suspected, and I absolutely agree, that Cope's species are based on composite specimens rather than single individuals. That is to say, there is no evidence that he ever succeeded in finding a single specimen representing the greater part of the skeleton of one individual; rather, it is probable that the specimens he attributed to Monoclonius crassus represent a synoptic collection of elements picked up from the Missouri River badlands over the six-week period that he was there. If we knew for certain that there were only a single genus and species of horned dinosaur living at that time and place, any remains that were collected from there might justifiably be referred to that animal. However, we have no such confidence, as Marsh had in 1888 described Ceratops montanus from the same region. Although this genus is poorly founded on only two horns and an occipital condyle, the prominent horns suggest that Ceratops was a chasmosaurine, a completely different subfamily of horned dinosaurs from Monoclonius. Thus a dinosaur assembled from a collection of skeletal elements of unrelated specimens may end up being a chimaera, an animal that never existed.

Specimen numbers were applied to Cope's specimens after the fact, that is, when the bones were placed in the collections of the American Museum. Bones attributed to M. crassus are now cataloged under the number AMNH 3998. Hatcher carefully and critically described, analyzed, and figured all of the material associated with Cope's type specimen of M. crassus. He specifically included only the material that he could positively identify as pertaining to the type specimen. He was unable, for instance, to attribute any squamosal (and there were several in the collection) to M. crassus. This is unfortunate, as the squamosal is one of the most important bones in diagnosing ceratopsids.

The parietal, which forms the major expanse of the bony frill, is a beautiful bone (Fig. 5.3). Part of the right side is missing in the type of Monoclonius crassus, but as the bone is symmetrical most of the information is preserved. It is a large, fan-shaped bone with huge parietal fenestrae. It is about half a meter in length along the midline, and its width may be estimated at 830 mm. For its size, it is somewhat delicate

Tyrannosaurus Episternum
FIG. 5.3. Parietal frill: type specimen of Monoclonius crassus Cope, American Museum of Natural History. (From Hatcher et al. 1907.)

in construction, with five rather poorly defined scallops or ornaments along the edge. There are also several more or less prominent bumps on the median parietal bar between the parietal fenestrae. The back edge of the parietal is not very thick, measuring only 18 mm on the midline and 22 mm nearby. The significance of these details will become apparent later. The orbital horn described by Cope was cataloged under a separate number, and Hatcher was firmly of the opinion that it did not pertain to the type.191 agree. Thus this important detail too is wanting for Monoclonius. Hatcher described no further skull elements but proceeded to the sacrum, fused cervical vertebrae, and isolated miscellaneous vertebrae. Of the sacrum, he noted the following: "although Cope in his description has referred it to the same skeleton with the parietals and the postfrontal [sic] described above, there would seem from such general characters as size, color, degree of petrifaction, etc., to be little doubt that all three pertained to as many different individu-als."20 The alleged skeleton includes an ilium, an ischium, a shoulder girdle, a humerus, two femora, and a tibia and fibula. We know these to be ceratopsian, and all may potentially come from Monoclonius, but as there is no documented association, it is dangerous to infer one.

The material pertaining to M. recurvicornis had not been amplified since being figured by Cope in 1877 and thus still consisted only of an occipital condyle, two orbital horn cores, and a nasal horn core. Hatcher compared the orbital horn cores with those of Marsh's Ceratops montanus and advocated the transfer of Cope's species to Marsh's genus, as Ceratops recurvicornis. This step might be justified if Ceratops were regarded as a valid genus, but it too has spent most of its years in the taxonomic limbo of "nomen dubium." Thus M. recurvicornis and C. recurvicornis are equally forgotten.

M. sphenocerus is, in effect, based only on the nasal horn core and associate premaxilla. There is no sign whatever of the "numerous parts of the skeleton" to which Cope referred. It is certainly an interesting animal, and certainly a centrosaurine, but there is no compelling reason to associate it with Monoclonius. It too is in limbo. At some future date, a new find may associate a nasal horn like this one with a skull showing a full complement of diagnostic characters, including orbital horns, squamosal, and parietal. Until then, we can only speculate—an activity in which we paleontologists are not constitutionally averse to indulging from time to time.

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