Daspletosaurus, Russell, 1970
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persistent identifier |
https://treatment.plazi.org/id/03E3C818-545C-5320-FF09-C9C53639F851 |
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treatment provided by |
Jeremy |
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scientific name |
Daspletosaurus |
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gen. nov. |
Albertosaurus libratus ( Lambe 1914)
Gorgosaurus libratus Lambe 1914 , p. 13
Gorgosaurus sternbergi Matthew and Brown 1923, p. 7 Distribution
Oldman Formation, near Steveville, Alberta.
Referred specimens
* NMC 8782 incomplete manus and pes, fragments from hind limbs (3 miles south of Steveville, upper half of beds).
* AMNH 5423 jaw fragments, four caudal vertebrae, fragments of pelvis, left hind limb (Little Sandhill Creek basin).
NMC 2270 maxilla.
NMC 12063 maxilla.
ROM 4591 nasals ( east side of coulee, at Denhart, Alberta).
AMNH 5664 (type of G. sternbergi) nearly complete skeleton (quarry 54 of Sternberg 1950).
USNM 12814 nearly complete skeleton, lacking tail (Little Sandhill Creek basin).
* NMC 2250 ilium.
ROM 1422 fragmentary skull.
ROM 1237 skeleton, lacking presacral vertebrae and right hind limb (quarry 21 of Sternberg 1950 UA 10 skull, several presacral vertebrae and ribs, right humerus, left metatarsus (quarry 48 of Sternberg 1950 AMNH 5432 left maxilla, left tibia-metatarsus and some phalanges of pes (quarry 59 of Sternberg 1950).
).
NMC 11593 pelvis, hind limbs, base of tail (quarry 50 of Sternberg 1950).
ROM 683 maxillae.
ROM 436 left premaxilla and maxilla.
ROM 1247 palatal elements.
AMNH 5336 skull (quarry 57 of Sternberg 1950).
AMNH 5458 skull and nearly complete skeleton (Little Sandhill Creek basin).
NMC 2120 (type of G. libratus ) nearly complete skeleton (quarry 36 of Sternberg 1950).
NMC 2193 surangular.
FMNH PR 308 skull and skeleton, lacking hind limbs and tail (Little Sandhill Creek basin).
NMC 11814 braincase.
Diagnosis
Length of dentary tooth row 71 per cent of length of fourth metatarsal (USNM 12814?, NMC 2120). In adult animals (NMC 2120) combined length of scapula-coracoid greater than that of femur. In adult animals (AMNH 5458, NMC 2120), combined length of tibia and astragalus 95 per cent of that of femur.
Comments
Gorgosaurus Sternberg /, with the most complete skeleton known of a North American tyrannosaur as its type, was characterized by Matthew and Brown (1923: 7) as follows: "It is of smaller size and more slender proportions that in G. libratus . The jaws are much less massive and the muzzle is more slender, the maxilla more elongate and shallow, the orbital fenestra more circular. The tibia is considerably longer than the femur." Gilmore (1946: 3) suggested that the apparent slenderness of the muzzle in the type was caused by crushing, and Rozhdestvensky (1965) has demonstrated that the tibia /femur ratio decreases during growth in tyrannosaurs { Tarbosaurus ).
Matthew and Brown (1923: 7) were aware of the possibility that these characters might be due to the juvenility of the type specimen, noting that the pelvic elements were not co-ossified. The sutures between the bones of the skull roof are widely open, and there is nothing in the morphology of the specimen to suggest that it is not an A. libratus approximately two-thirds grown. Interestmgly, the supraoccipital alae of the parietals are only about one-fourth as large as in adults, indicating that these crests become more powerfully developed with maturity.
Rozhdestvensky's ( 1965) important studies of growth changes in the limb proportions of Tarbosaurus require that North American material be examined for similar growth effects. Although articulated remains of juvenile tyrannosaurs are far from being the commonest of fossils, a barely adequate sample of halfgrown to adult specimens of /I. libratus is available, from which some impression may be gained of allometric growth in the species.
Six specimens of A. lihratus from the badlands of the Oldman Formation near Steveville, Alberta, have been examined for changes in bodily proportions correlating with the size of the animal. The smallest individual of the series AMNH 5423 was considered as possibly referable to A. libratus because the lengths of the tibia and metatarsus continue the same trends seen in larger specimens of the species, because Albertosaurus is three times as abundant as Daspletosaurus in this area of outcrop of the Oldman Formation, and because only adult specimens of the latter genus have so far been found here. The other five specimens (AMNH 5664, USNM 12814, NMC 11593, AMNH 5458, NMC 2120) have been assigned to A. libratus on the basis of their skeletal anatomy { see diagnoses). The precise horizon from which each of these specimens was collected is known in only three cases, although dinosaurian fossils are restricted to an approximately 200- foot vertical interval in the area ( Sternberg 1950). In view of the great resemblance oï A. sarcophagus from the younger Edmonton Formation to A. libratus , it is improbable that allometric changes would be obscured by evolutionary changes over a stratigraphie interval of this magnitude.
The length of the femur was arbitrarily chosen as a standard to which the lengths of other skeletal structures in a specimen were compared {see Table 1). The allometric changes are apparent when the lengths of the skeletal structures are expressed as a percentage of the femur length and plotted against femur length on a graph. These data, although based on a minimal number of measurements, seem to indicate that as the animal increases in size from half-grown to fully mature, the presacral vertebral column, ribs, scapula-coracoid, pubis, and ischium increase more rapidly in length than does the femur; the skull, sacrum, humerus, and radius-ulna grow at approximately the same rate; and the caudal vertebral column, manus, tibia, metatarsus, and pes grow at a slower rate. These relative rates of growth appear to be rather constant, although in the case of the combined length of the tibia-astragalus the rate of increase is slow, relative to that of the femur, until the animal attains the size of USNM 12814, when the growth rate abruptly changes to equal that of the femur.
'
The comparative changes in the proportions of skeletal structures may have been of the same general magnitude during the earlier, more rapid stages of growth. Assuming that this was true, it would be possible to estimate the relative bodily proportions of a very young (hatchling) Albertosawus libratus . For a femur length of 100 mm, the lengths of the following structures were estimated graphically as follows: skull 88 mm, presacral vertebral column 210 mm, sacrum 70 mm. anterior twenty-four caudal vertebrae 390 mm, scapula-coracoid 63 mm, humerus 26 mm, ulna 20 mm, manus 48 mm, second metacarpal 7 mm, ilium 100 mm, pubis 68 mm, ischium 54 mm, circumference of femur 28 mm, tibia-astragalus 140 mm, metatarsal three 85 mm, third digit of pes 56 mm.
Using these figures as a guide, an attempt has been made to reconstruct the skeleton of a hatchling tyrannosaur. The adult morphology of A. libratus has been modified by reducing the development of muscle scars and tuberosities, and the number of teeth in the jaws and by increasing the size of the orbit. The ungual phalanges of the manus and pes are shown, as in a very immature specimen (NMC 8782), referred to A. libratus because the first ungual of the manus, unlike in Daspletosaurus , is strongly curved. The lengths of the ribs are entirely conjectural, as the increase in rib length is apparently too rapid in more mature individuals to have been sustained throughout the ontogeny of the animal. It is hoped that this reconstruction ( Figure 3) will serve both as an estimation of the actual appearance of a very young specimen of A. libratus , and as a means of focusing attention on misinterpretations unknowingly incorporated into it.
Albertosaurus sarcophagus Osborn 1 905
Laelaps incrassatus. Cope 1892, p. 240
Dryptosaurus incrassatus, Lambe 1904, p. 6
Albertosaurus sarcophagus Osborn 1905 , p. 265
Albertosaurus arctunguis Parks 1928, p. 7
Distribution
Lower Edmonton Formation, Red Deer River, Alberta.
Referred Specimens
NMC 5601 (paratype of A. sarcophagus ) skull and lower jaws, fragments of sacral vertebrae and ilium, distal end of tibia with astragalus, fourth metatarsal, three ungual phalanges of pes (sec.?, tp. 33, rge. 22, W. 4th mer., east bank of Red Deer River, Member B of Edmonton Formation).
AMNH 5222 scattered skull (sec. 12?, tp. 33, rge. 22, W. 4th mer., 150 feet above east bank of Red Deer River, Member B of Edmonton Formation).
ROM 807 (type of ^4. arctunguis) sacrum and adjacent vertebrae, left scapulacoracoid and forelimb, left half of pelvic girdle and associated hind limb (sec. 27 or 34, tp. 30, rge. 21, W. 4th mer., 100 feet above west bank of Red Deer River, Member A of Edmonton Formation).
NMC 5600 (type of A. sarcophagus ) palatal region of skull, braincase and lower jaws (sec. 11?, tp. 29, rge. 21, W. 4th mer., approximately 100 feet above Red Deer River, along Kneehills Creek, Member A of Edmonton Formation).
? NMC 2196 scapula-coracoid, abdominal ribs (sec. 35?, tp. 28, rge. 20, W. 4th mer., west bank of Red Deer River, Member A of Edmonton Formation).
Diagnosis
Length of dentary tooth row 65 per cent of length of fourth metatarsal (NMC 5601). In adult animals (ROM 807, if the distal end of the scapula has not been broken off) combined length of the scapula-coracoid about 80 per cent of that of femur. In adult animals (ROM 807) combined length of tibia and astragalus equal to (or slightly greater than) that of femur.
Comments
In defining Albertosaurus arctunguis. Parks (1928: 5-7) stressed the dissimilarities between the distal end of the fourth metatarsal of his specimen (ROM 807) and that of the paratype of A. sarcophagus (NMC 5601). The slightly pathologic condition of this portion of the latter element, as Parks himself noted ( 1928: 7), accounts for some of the differences, while the remainder are due to the fact that the posteroexternal edge of the distal articulating surface has been broken off, which Parks failed to recognize. The ungual phalanges associated with NMC 5601, considered by Parks as belonging to the manus, actually belong to the pes. Altogether, it is not possible to separate the type of A. arctunguis from the type and paratype of ^. sarcophagus on morphological grounds, and the great resemblance of each of these specimens to the corresponding region of the skeleton of A. libratus argues convincingly for their inclusion within a single species.
In addition to the characters noted in the diagnosis, the forelimb of ROM 807 seems to be slightly shorter than in A. libratus (NMC 2120), and the pubis is slightly larger than in the latter specimen {see Parks 1928: 12, 20, 23). A. sarcophagus occurs in both member A and B of the lower Edmonton Formation ( Russell and Chamney 1967: 10, 12). It is unfortunate that the species is not known from more complete material.
In tyrannosaurs, the bone beneath the brain stem gives the appearance of being solid. However, this region of the skull is almost entirely filled with large sinuses, which are separated from one another only by thin walls. Fenestrae, through which these sinuses communicate with the surface of the bone, have occasionally been confused with openings for nerve or blood vessel conduits {see for example Lambe 1904: pi. 7, fig. 15; Gilmore 1946: 10). A reconstruct tion of the ventral part of the braincase in Albertosaurus is presented here ( Figure 4), based primarily on a partial dissection of the braincase of NMC 5600 { A. sarcophagus ), with the parasphenoidal area restored from ROM 1237 { A. libratus ). The large sinuses located in the parasphenoid rostrum and ventral part of the basisphenoid are seen in sagittal section. Dotted lines show the approximate extent of the latter sinus and two other sinus systems on either side of the cranial midline. The fenestrae linking each sinus system with the exterior are indicated by arrows; the arrow labelled " X " passed through the fenestra draining the sinus system in the paroccipital process. The more dorsal sinus systems are partly subdivided by thin webs of bone, which would probably exhibit a high degree of variability in diflFerent individuals.
In Tyrannosaurus (AMNH 5117), and also in AUosaurus ( Osborn 1912: figs. 9-10), there is a foramen in the basisphenoid near the anteroventral edge of the laterosphenoid, which Osborn identified as the ventroposterior opening of the carotid canal. Although the distal part of the canal was not observed in NMC 5600, a small foramen in the pituitary fossa may mark its anterior termination. Behind this is another foramen, which may have contained the sixth nerve.
Neither the posterior course of the canal leading to the latter foramen nor the point of penetration of the sixth nerve into the floor of the medullary cavity was identified in this specimen. Not shown in Figure 4 are the conduits for nerves X to XII, which lie in the bone immediately ventrolateral to the medullary cavity and emerge on the occipital face of the skull in three foramina situated beside the neck of the occipital condyle. A small rod of bone, measuring 30 mm between its broken ends and 2.5 mm in diameter, was found in the matrix between the broken right quadrate and paroccipital process in NMC 5600. No doubt it is the stapes.
It should be noted that in tyrannosaurs the median elements of the dermal skull roof are solidly sutured to each other and to the braincase below. This rigidity, coupled with the structural weakness of the basipterygoid processes, absolutely precludes any possibility of normal kinetic movement in the skull. Perhaps the diarthroid joint between the quadrate and squamosal, loose overlapping of the basipterygoid processes by the pterygoids, and split nature of the posterior part of the palate would allow some displacement of the temporal muscle mass in a medial direction. In similar fashion, the loose dorsal and posterior contacts of the jugal and quadratojugal, in combination with a vertically flexible antorbital lacrimal bar, may have allowed some displacement of the temporal muscle mass in a lateral direction. It is probable, however, that these suites of structures operated in an entirely passive manner, in response to the struggles of a massive prey held between the jaws. Even movements of the postulated kind must have been very limited, serving only to prevent the breakage of bones within the skull.
Genus Daspletosaurus new
Daspletosaurus torosus new species *
Distribution
Oldman Formation, near Steveville, Alberta, except where noted.
.
Type
NMC 8506 skull and skeleton, lacking hind limbs (quarry 88 of Sternberg 1905).
Paratype
AMNH 5438 sacrum and adjacent thoracic and caudal vertebrae, pelvis, right femur, left tibia and second metatarsal ( Little Sandhill Creek basin).
Referred Specimens
NMC 350 left hind Hmb (sec. 31, tp. 20, rge. II, W. 4th mer.).
AMNH 5346 maxilla (Little Sandhill Creek basin).
UA 11 right femur and fourth metatarsal.
NMC 11594 incomplete, weathered skull and lower jaws (Oldman Formation, near Manyberries, Alberta: near centre NW.;!: sec. 36, tp.l, rge. 6, W. 4th mer., about 30 feet below prairie rim or 3,285 feet above sea level).
BMNH R4863 premaxilla, maxilla, dentary.
Diagnosis
Premaxilla does not contact nasal below external naris. Maxillary teeth large, not greatly reduced posteriorly. Anteriormost antorbital fenestra within maxilla minute, hardly visible in lateral aspect, first antorbital fenestra nearly as high as long. Nasals slightly constricted between lacrimals, invaded posteriorly on either side by long slender tongue of frontal. Frontal broadly exposed on skull roof, lacks deep vertical cleft above orbit. Prefrontal broadly exposed dorsally between nasal, lacrimal, and frontal. Lacrimal ' horn' triangular in lateral aspect, with apex centred above antorbital ramus of bone; exceeds postorbital ' horn' in development. Anteroexternal edge of antorbital ramus of lacrimal is not continued across lateral surface of jugal. Ventral process of extopterygoid inflated, with large ventrally opening sinus; jugular process of bone also inflated. Angular terminates posteriorly beneath centre of surangular foramen.
Ventral opening of main basisphenoid sinus situated on midline of skull, behind transverse wall linking basipterygoid processes. Optic fenestra not bridged medially by presphenoid. Exits for cranial nerves III and IV contained in single pit on anterior surface of laterosphenoid. Exit for cranial nerve Vi situated on lateral surface of laterosphenoid.
Neural spine of fourth cervical vertebra much larger than that of fifth. Neural spine of fifth cervical distally pointed, that of sixth cervical smaller and sharply pointed. Presacral vertebrae tend to be shorter and higher than in Albertosaurus ; basal caudal vertebrae diminish less rapidly in size posteriorly than in latter species.
In adults length of humerus estimated to equal 38 per cent of that of femur, forelimb powerfully developed relative to that of Albertosaurus . Anterodistal condyle of metacarpal I reduced, causing first digit to diverge distally from second. First phalanx of digit II robust in adults. Dorsal edge of ungual of digit I passes through arc of about 90 degrees.
Anterior blade of ilium covers diapophysis of twelfth thoracic vertebra. In adults circumference of femur equal to 38 to 41 per cent of length of femur. In comparison with Albertosaurus specimens of similar femur length, presacral vertebral column is much shorter, thoracic ribs are slightly longer, forelimb is longer, ilium and sacrum are longer, and metatarsus is slightly shorter.
Comments
The type specimen of D. torosus was collected by C. M. Sternberg late in the 1921 field season. As is usual in large theropod specimens, the head and anterior part of the vertebral column were pulled dorsoposteriorly toward the pelvis before the animal was buried. Although the hind limbs and many of the more distal caudal vertebrae were lost and although the remainder of the skeleton was partly scattered, the specimen is generally very complete and very well preserved. Sternberg's field notes indicate that at the time the specimen was collected he thought it belonged to an undescribed species of Gorgosaurus or to a new genus. Photographs of the skeleton in situ have been published by Sternberg (1945: 191; 1946: pi. 15; 1966: fig. 9), and of the skull by Sternberg (1945: 191; 1946: pi. 6; 1966: fig. 17).
Daspletosaums attained approximately the same length (28-30 feet) as its contemporary Albertosawus. However, the body, which measured 1,350 mm (53 inches) through the widest point of the thoracic region in NMC 8506, and the base of the tail are much heavier than in Albertosaurus , and the hips and hind limbs are also more powerfully developed. The forelimb, although small, is relatively larger than in any other known tyrannosaur. Interestingly, with the exception of NMC 350, which is subadult, only fully grown specimens of Daspletosaums have so far been collected from the Oldman Formation, while remains of one-half to three-quarters grown albertosaurs are relatively not uncommon in these sediments. The simultaneous existence of these two large carnosaurs indicates the presence in the fauna of two écologie niches to accommodate them. As the endocranial cavities of both forms are quite small, it might be expected that differences in their gross morphology would rather accurately express their behavioural differences. Perhaps the more powerfully constructed daspletosaurs preyed on ceratopsians, and the more fleet albertosaurs were better suited to subsist on hadrosaurs. Albertosaurs and hadrosaurs are indeed correspondingly more abundant in the Oldman fauna than are daspletosaurs and ceratopsians.
The reconstruction of Daspletosaums torosus ( Figure 9) is based principally on the type skeleton (NMC 8506) and the hind limb of the paratype (AMNH 5438). Restored parts include the last two phalanges of the second digit of the manus, acetabular area of the ischium, posterior tip of the pubic boot, all of the metatarsals except the second, the entire pes, and caudal vertebrae 12-14, 18, 19, 21, 22, 26, 28-30, 32, and 36-37. The hind limbs of NMC 350 and NMC 11594 were consulted in drawing elements missing in this region of the type and paratype. Cervical and thoracic ribs are preserved on one side or the other throughout the presacral series of NMC 8506. In the reconstruction they are drawn as seen in lateral aspect, causing the ribs of the posterior thoracic region, which curve away from the vertebrae at a high angle, to appear unusually short. The solid line representing the ventral limit of the body was obtained by projecting the curvature of the anterior thoracic ribs to the midline of the body and by extending this line back to the anteroventral tip of the pubic boot. The abdominal ribs are not shown in the reconstruction.
The dental formula of D. torosus , as indicated by cranial material referred to the species, is: premaxillary teeth 4, maxillary teeth 14 or 15, dentary teeth 15 or 16. There are 11| to 15 serrations per 5 mm on the carinae of the marginal teeth, the serrations being coarsest near the centre of the jaws.
The palate is disarticulated but exceptionally well preserved in NMC 8506 {see Figure 8). The vomers are fused together anteriorly dividing posteriorly into two thin vertical sheets of bone. A vertical anterior ala from the pterygoid broadly underlaps each of these vomerine processes. However, the pterygoids do not meet each other on the midline of the skull, nor do they contact the ventral part of the ascending processes of the palatines (the same relations exist in the palate of A. libratus , see AMNH negative number 37883, taken of USNM 12814). In Albertosawus {see NMC 5600; Gilmore 1946: 11) and probably also in Daspletosaums (NMC 8506) the upper edges of the anterior pterygoid alae loosely but widely contact the upper edge of these palatine processes, with the result that each half of the tyrannosaur palate is separated from the opposite half as far anteriorly as the middle of the vomers. The anterodorsal tip of the ascending process of the palatine is firmly applied to the external dorsoposterior corner of the vomer in D. torosus (NMC 8506) and perhaps also in Albertosawus (AMNH 5336?; Gilmore 1946: 11).
Distribution
Member B of Edmonton Formation, near ScoUard, Alberta.
Referred Specimen
NMC 11315 scattered cranial elements, abdominal ribs, left forelimb, pelvis and hind limbs ( SW. \ sec. 20, tp. 34, rge. 21, W. 4th mer., 150 feet above south bank of Red Deer River).
Comments
NMC 11315 represents the remains of a slightly more than half-grown tyrannosaur. It is referred to Daspletosaurus because the humerus, radius-ulna, ilium, and circumference of the femur are longer relative to the length of the femur than would be expected in an Albertosaurus of similar femur length. The claw of the first digit of the manus seems less recurved than in the latter genus. The specimen shows that Daspletosaurus probably underwent the same ontogenetic changes in limb proportions as did Albertosaurus . The foot is very similar to that of Albertosaurus , although the metatarsus is slightly shorter than in similarly sized specimens of this genus.
Tyrannosaur humeri are very infrequently found, and of the two Daspletosaurus specimens where it is preserved, the distal end of one (NMC 8506) is pathologic. Similarly, of five specimens of A. libratus where a humerus is preserved, in two of them (UA 10, FMNH PR308) the bone has also been damaged in life. This is an unusually high incidence of damage and suggests that the small forelimbs were often crushed by the weight of the massive bodies of these reptiles.
Genus Tyrannosaurus Osborn 1 905 , p. 259
Type species: Tyrannosaurus rex
Diagnosis { See Osborn 1906, 1912, 1917; Matthew and Brown 1923)
Premaxilla contacts nasal below external naris. Maxillary teeth relatively larger than in Daspletosaurus . Anteriormost antorbital fenestra within maxilla not visible in lateral aspect, first antorbital fenestra slightly higher than long. Nasals narrowly constricted between lacrimals. Frontal essentially limited to anteromedial wall of supratemporal fenestra, only small rim of bone reaches dorsal surface of skull. Prefrontal exposed dorsally between lacrimal and frontal. Lacrimal ' horn' represented by conical inflation not interrupting dorsal profile of skull. Postorbital ' horn' or rugose area well developed. Anteroexternal edge of antorbital ramus of lacrimal not continued across lateral surface of jugal. Ventral process of ectopterygoid inflated with very large, ventrally opening sinus. Angular terminates posteriorly behind surangular foramen.
Ventral openings of main basisphenoid sinus situated on either side of midline of skull, dorsomedial to each basipterygoid process. Vertical plate of presphenoid contacts orbitosphenoid and narrow suboptic bridge of laterosphenoid, separating optic fenestra into two openings. Cranial nerves III and IV open into single pit ventrolateral to optic fenestra. Exit for cranial nerve Vi situated close to anterolateral edge of laterosphenoid, but not so close as in Albertosaurus .
Neural spines of fourth and fifth cervical vertebrae subequal, rather narrow in lateral aspect. Neural spine of fifth cervical distally pointed, that of sixth vertebra smaller and sharply pointed. In adults length of humerus equal to about 28 per cent of that of femur. Anterior blade of ilium does not cover diapophysis of twelfth thoracic vertebra. In adults circumference of femur approximately equal to 41 per cent of length of femur. Bodily proportions generally as in Daspletosaurus , although adult specimens about 25 per cent larger, humerus more reduced and ilium longer than in this genus.
Distribution
Upper Edmonton Formation, Alberta.
Referred Specimens
NMC 9950 phalanx of pes (7 miles east of Huxley, centre sec. 10, tp. 34, rge. 22, W. 4th mer., about 170 feet above Kneehills Tuff").
NMC 9554 fragment of cervical centrum (20 feet below and 200 yards south of locality for NMC 9950).
Comments
The presence of Tyrannosaurus in Lance equivalent upper Edmonton strata has been noted several times {see Sternberg 1949; L. S. Russell 1964; Langston 1965). This record is based primarily on a badly eroded and shattered skeleton observed by Sternberg in 1946, weathering out of a fractured concretion high on the face of a cliff". Langston revisited the locality in 1960 and collected a phalanx, noting that the skeleton was even more badly damaged than when Sternberg discovered it, and that little of it still remained in situ.
The phalanx (NMC 9950) is the fourth one of the fourth toe and measures 53 mm in length and about 80 mm across its distal articulation. Hence it is larger and broader than the corresponding element in Albertosaurus and Daspletosaurus . Unfortunately only the first phalanx of the fourth toe is known in Tyrannosaurus ( Osborn 1906: fig. 11). This bone is relatively broader than in any known Oldman or Edmonton form, and by analogy it seems probable that the above fourth phalanx may indeed belong to Tyrannosaurus . The vertebra (NMC 9554) is generically indeterminate.
TYRANNOSAURS NOT KNOWN TO OCCUR IN CANADA
Albertosaurus lancensis ( Gilmore)
Gilmore (1946) has described the skull of a small carnivorous dinosaur from the Lance Formation of eastern Montana. The skull is quite different from that of Tyrannosaurus and Gilmore founded a new species on it, correctly referring it to Gorgosaurus {= Albertosaurus ). Although the skull is only half as long as that of a fully grown A. libratus , the sutures between the bones of the skull roof are tightly interlocking, and some have been obscured through intergrowth; the supraoccipital alae of the parietals are well developed, and a clearly formed tuberosity is present on the ventral border of the jugal ( Gilmore 1946). The opposite conditions prevail in the skull of AMNH 5664, a specimen of A. libratus of comparable size. The skull of A. lancensis is therefore probably from a fully grown individual, and its small size may be characteristic of the species.
Albertosaurus lancensis further differs from A. libratus and A. sarcophagus (AMNH 5222) in that the frontals meet on the midline throughout their entire length, while in the latter two species these elements are separated anteriorly by a small wedge of bone from the nasals. The frontals are not so deeply cleft above the orbits as is the case in A. libratus and A. sarcophagus . Gilmore (1946: 6) suggested that the prefrontal may be rather well exposed on the skull roof, unlike in the more ancient species of the genus. Otherwise the skulls of the three forms are quite similar.
This species is known from the remains of at least seven individuals collected by the Palaeontological Institute of the Academy of Sciences of the U. S. S.R. ( Maleyev 1955 ^?, 1955c) and six more collected by the Polish-Mongolian Palaeontological Expedition ( Kielan-Jaworowska 1967), all from the Nemegt basin in strata that may be approximately Edmontonian {see L. S. Russell 1963) in age. The form has not yet been thoroughly described, although it has been the subject of several brief reports {see Introduction) and a cast of the skull of one specimen (NMC 10422) was available for study through an exchange with the Palaeontological Institute. Tarbosaurus seems to be most closely allied to Tyrannosaurus . It differs from this genus in that the nasals are not quite so constricted between the lacrimals, the frontals do have some dorsal expression ( but not so much as in Albertosaurus or Daspletosaurus ), the surangular foramen is small, and adult animals are smaller than adult specimens of Tyrannosaurus . (I am indebted to Dr. A. K. Rozhdestvensky for the above information on the morphology of Tarbosaurus .)
TABLES OF MEASUREMENTS
AU measurements are expressed in millimetres. The lengths of the phalanges were measured between the lateral edges of the anterior and posterior articular surfaces, along the horizontal midline of the bone.
MEASUREMENTS USNM 12814 Albeitosaurus libratus
{ see also Table 1)
Length lower dentition 352
DORSAL RIBS (tubercuium to end):
LENGTHS OF PHALANGES OF PES:
3 4 5 Right Pes 1 2
digit 1 87 - digit 2 141 94 131* digit 3 157 98 97 115* digit 4 103 72 71 - -
For measurements of the type oï A. libratus , see Lambe (1917). For measurements of specimens of this species in the American Museum of Natural History, see Matthew and Brown (1923)
VERTEBRAE
MEASUREMENTS NMC 11593 Albeitosaiiriis libraliis
{ see Table 1):
LENGTH OF ELEMENTS IN RIGHT PES:
LENGTH OF ELEMENTS IN LEFT PES:
CAUDAL VERTEBRAE:
MEASUREMENTS NMC 8506 Daspletosaums torosus DORSAL RIBS:
FORELIMBS:
MANUS:
PELVIS:
MEASUREMENTS NMC 8506 Daspletosaurus torosus CERVICAL VERTEBRAE:
DORSAL VERTEBRAE:
CAUDAL VERTEBRAE: MEASUREMENTS AMNH 5438 Daspletosaums torosus VERTEBRAE:
Caudals
PELVIS: length of ilium
1096 HIND LIMB: MEASUREMENTS UA 11 Daspletosaurus torosus HIND LIMB: MEASUREMENTS NMC 11315 Daspletosaimis ci. D. torosus SKULL height of quadrate
:
164 FORELIMB: MANUS: PELVIS AND HIND LIMB: LENGTH OF ELEMENTS IN LEFT PES: References
.
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( 1946). A new carnivorous dinosaur from the Lance Formation of Montana. Smithsonian Miscellaneous Collections 106 ( 13): 1-19.
Hay, O. p. ( 1908). On certain genera and species of carnivorous dinosaurs, with special reference to Ceratosaunis nasicornis Marsh. United States National Museum Proceedings 35 ( 1648): 351-366.
Huene, F. von ( 1932). Die fossile Reptil-Ordnung Saurischia, ihre Entwicklung und Geschichte. Monographien zur Géologie und Palae- ontologie 4: 1-361.
Kielan-Jaworowska, Z. ( 1967). Les résultats des expéditions paléontologiques polonomongoles (1963- 1965) dans le Désert de Gobi et Mongolie occidentale. Colloques Internationaux du Centre National de la Recherche Scientifique, numéro 163, Problèmes actuels de paléontologie: 419- 25.
Lambe, L. m. ( 1904). On Diyptosaurus incrassatus (Cope), from the Edmonton Series of the North West Territory. Geological Survey of Canada, Contributions to Canadian Palaeontology 3: 1-27.
( 1914). On a new genus and species of carnivorous dinosaur from the Belly River Formation of Alberta, with a description of the skull of Stephanosaurus marginatus from the same horizon. Ottawa Naturalist 28: 13-20.
( 1917). The Cretaceous theropodous dinosaur Gorgosaunis. Geological Survey of Canada Memoir 100: 1-84.
Langston, W., jr. ( 1965). Pre-Cenozoic vertebrate paleontology in Alberta: its past and future. In Vertebrate paleontology in Alberta, University of Alberta, Edmonton, p. 9- 31.
Leidy, J. ( 1857). Notices of remains of extinct reptiles and fishes, discovered by Dr. F. V. Hayden in the bad lands of the Judith River, Nebraska Territory. Academy of Natural Sciences of Philadelphia Proceedings 8: 72-73.
( 1860). Extinct Vertebrata from the Judith River and Great Lignite Formation of Nebraska. American Philosophical Society Transactions n. s. 1 1: 139-154.
Maleyev, E. a. ( 1955 «). Carnivorous dinosaurs of Mongolia (in Russian). Priroda June 1955: 112-115.
( 19556). Gigantic carnivorous dinosaurs of Mongolia (in Russian). Dokladi Akademii Nauk S.S.S.R. 104 ( 4): 634- 637.
( 1955 c). New carnivorous dinosaurs from the upper Cretaceous of Mongolia (in Russian). Dokladi Akademii Nauk S.S.S.R. 104 ( 5): 779-782.
( 1964). Family Deinodontidae (in Russian). //; Rozhdestvensky, A. K. and L. P. Tatarinov, Ocnovi Paleontologii 12: 538-540.
Marsh, O. C. ( 1890). Additional characters of the Ceratopsidae, with notice of new Cretaceous dinosaurs. American Journal of Science (third series) 39: 418-426.
Matthew, W. D., and B. Brown ( 1922). The family Deinodontidae, with notice of a new genus from the Cretaceous of Alberta. American Museum of Natural History Bulletin 46: 367-385.
( 1923). Preliminary notices of skeletons and skulls of Deinodontidae from the Cretaceous of Alberta. American Museum of Natural History Novitates 89: 1-10.
OSBORN, H. F. ( 1905). Tyrannosaurus and other Cretaceous carnivorous dinosaurs. American Museum of Natural History Bulletin 21: 259-265.
( 1906). Tyrannosaurus, upper Cretaceous carnivorous dinosaur (second communication). American Museum of Natural History Bulletin 22: 281-296.
( 1912). Crania of Tyrannosaurus and Allosaurus. American Museum of Natural History Mémoires (n. s.) 1: 1-30.
( 1913). Tyrannosaurus ^ restoration and model of the skeleton. American Museum of Natural History Bulletin 32: 91-92 ( 1917). Skeletal adaptations of Ornitholestes, Struthiomimus, Tyrannosaurus. American Museum of Natural History Bulletin 35: 733-771 Parks, W. A. ( 1928). Albertosaurus arc (unguis, a new species of therapodous dinosaur from the Edmonton Formation of Alberta. University of Toronto Studies, Geological Series 25: 1-42.
Rozhdestvensky, A. K. ( 1965). Growth changes in Asian dinosaurs and some problems of their taxonomy. Paleontologicheskii Zhurnal 1965 ( 3): 95-109.
Russell, D. A. ( 1967). A census of dinosaur specimens collected in western Canada. National Museum of Canada Natural History Paper 36: 1-13.
, and T. Potter Chamney ( 1967). Notes on the bio-stratigraphy of dinosaurian and microfossil faunas in the Edmonton Formation (Cretaceous) Alberta. National Museum of Canada Natural History Paper 35: 1-22.
Russell, L. S. ( 1964). Cretaceous non-marine faunas of northwestern North America. Royal Ontario Museum, Life Sciences Contribution 61: 1-24.
Sternberg, C. M. ( 1945). Canadian dinosaurs. Canadian Geographical Journal 30: 186-199.
( 1946). Canadian dinosaurs. National Museum of Canada Bulletin 103: 1-20.
( 1949). The Edmonton fauna and description of a new Triceratops from the Upper Edmonton Member. National Museum of Canada Bulletin 113: 33-46.
( 1950). Map 969 A Steveville west of the fourth meridian, notes on fossil localities. Geological Survey of Canada.
( 1966). Canadian dinosaurs. National Museum of Canada Bulletin 103 (second edition): 1-28.
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Plate I.
Plate II
Plate III Plate IV
'
).
Albertosaurus sarcophagus Osborn 1 905
Laelaps incrassatus. Cope 1892, p. 240
Dryptosaurus incrassatus, Lambe 1904, p. 6
Albertosaurus sarcophagus Osborn 1905 , p. 265
Albertosaurus arctunguis Parks 1928, p. 7
Distribution
Lower Edmonton Formation, Red Deer River, Alberta.
Referred Specimens
NMC 5601 (paratype of A. sarcophagus ) skull and lower jaws, fragments of sacral vertebrae and ilium, distal end of tibia with astragalus, fourth metatarsal, three ungual phalanges of pes (sec.?, tp. 33, rge. 22, W. 4th mer., east bank of Red Deer River, Member B of Edmonton Formation).
AMNH 5222 scattered skull (sec. 12?, tp. 33, rge. 22, W. 4th mer., 150 feet above east bank of Red Deer River, Member B of Edmonton Formation).
ROM 807 (type of ^4. arctunguis) sacrum and adjacent vertebrae, left scapulacoracoid and forelimb, left half of pelvic girdle and associated hind limb (sec. 27 or 34, tp. 30, rge. 21, W. 4th mer., 100 feet above west bank of Red Deer River, Member A of Edmonton Formation).
NMC 5600 (type of A. sarcophagus ) palatal region of skull, braincase and lower jaws (sec. 11?, tp. 29, rge. 21, W. 4th mer., approximately 100 feet above Red Deer River, along Kneehills Creek, Member A of Edmonton Formation).
? NMC 2196 scapula-coracoid, abdominal ribs (sec. 35?, tp. 28, rge. 20, W. 4th mer., west bank of Red Deer River, Member A of Edmonton Formation).
Diagnosis
Length of dentary tooth row 65 per cent of length of fourth metatarsal (NMC 5601). In adult animals (ROM 807, if the distal end of the scapula has not been broken off) combined length of the scapula-coracoid about 80 per cent of that of femur. In adult animals (ROM 807) combined length of tibia and astragalus equal to (or slightly greater than) that of femur.
Comments
In defining Albertosaurus arctunguis. Parks (1928: 5-7) stressed the dissimilarities between the distal end of the fourth metatarsal of his specimen (ROM 807) and that of the paratype of A. sarcophagus (NMC 5601). The slightly pathologic condition of this portion of the latter element, as Parks himself noted ( 1928: 7), accounts for some of the differences, while the remainder are due to the fact that the posteroexternal edge of the distal articulating surface has been broken off, which Parks failed to recognize. The ungual phalanges associated with NMC 5601, considered by Parks as belonging to the manus, actually belong to the pes. Altogether, it is not possible to separate the type of A. arctunguis from the type and paratype of ^. sarcophagus on morphological grounds, and the great resemblance of each of these specimens to the corresponding region of the skeleton of A. libratus argues convincingly for their inclusion within a single species.
In addition to the characters noted in the diagnosis, the forelimb of ROM 807 seems to be slightly shorter than in A. libratus (NMC 2120), and the pubis is slightly larger than in the latter specimen {see Parks 1928: 12, 20, 23). A. sarcophagus occurs in both member A and B of the lower Edmonton Formation ( Russell and Chamney 1967: 10, 12). It is unfortunate that the species is not known from more complete material.
In tyrannosaurs, the bone beneath the brain stem gives the appearance of being solid. However, this region of the skull is almost entirely filled with large sinuses, which are separated from one another only by thin walls. Fenestrae, through which these sinuses communicate with the surface of the bone, have occasionally been confused with openings for nerve or blood vessel conduits {see for example Lambe 1904: pi. 7, fig. 15; Gilmore 1946: 10). A reconstruct tion of the ventral part of the braincase in Albertosaurus is presented here ( Figure 4), based primarily on a partial dissection of the braincase of NMC 5600 { A. sarcophagus ), with the parasphenoidal area restored from ROM 1237 { A. libratus ). The large sinuses located in the parasphenoid rostrum and ventral part of the basisphenoid are seen in sagittal section. Dotted lines show the approximate extent of the latter sinus and two other sinus systems on either side of the cranial midline. The fenestrae linking each sinus system with the exterior are indicated by arrows; the arrow labelled " X " passed through the fenestra draining the sinus system in the paroccipital process. The more dorsal sinus systems are partly subdivided by thin webs of bone, which would probably exhibit a high degree of variability in diflFerent individuals.
In Tyrannosaurus (AMNH 5117), and also in AUosaurus ( Osborn 1912: figs. 9-10), there is a foramen in the basisphenoid near the anteroventral edge of the laterosphenoid, which Osborn identified as the ventroposterior opening of the carotid canal. Although the distal part of the canal was not observed in NMC 5600, a small foramen in the pituitary fossa may mark its anterior termination. Behind this is another foramen, which may have contained the sixth nerve.
Neither the posterior course of the canal leading to the latter foramen nor the point of penetration of the sixth nerve into the floor of the medullary cavity was identified in this specimen. Not shown in Figure 4 are the conduits for nerves X to XII, which lie in the bone immediately ventrolateral to the medullary cavity and emerge on the occipital face of the skull in three foramina situated beside the neck of the occipital condyle. A small rod of bone, measuring 30 mm between its broken ends and 2.5 mm in diameter, was found in the matrix between the broken right quadrate and paroccipital process in NMC 5600. No doubt it is the stapes.
It should be noted that in tyrannosaurs the median elements of the dermal skull roof are solidly sutured to each other and to the braincase below. This rigidity, coupled with the structural weakness of the basipterygoid processes, absolutely precludes any possibility of normal kinetic movement in the skull. Perhaps the diarthroid joint between the quadrate and squamosal, loose overlapping of the basipterygoid processes by the pterygoids, and split nature of the posterior part of the palate would allow some displacement of the temporal muscle mass in a medial direction. In similar fashion, the loose dorsal and posterior contacts of the jugal and quadratojugal, in combination with a vertically flexible antorbital lacrimal bar, may have allowed some displacement of the temporal muscle mass in a lateral direction. It is probable, however, that these suites of structures operated in an entirely passive manner, in response to the struggles of a massive prey held between the jaws. Even movements of the postulated kind must have been very limited, serving only to prevent the breakage of bones within the skull.
Genus Daspletosaurus new
Daspletosaurus torosus new species *
Distribution
Oldman Formation, near Steveville, Alberta, except where noted.
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Type
NMC 8506 skull and skeleton, lacking hind limbs (quarry 88 of Sternberg 1905).
Paratype
AMNH 5438 sacrum and adjacent thoracic and caudal vertebrae, pelvis, right femur, left tibia and second metatarsal ( Little Sandhill Creek basin).
Referred Specimens
NMC 350 left hind Hmb (sec. 31, tp. 20, rge. II, W. 4th mer.).
AMNH 5346 maxilla (Little Sandhill Creek basin).
UA 11 right femur and fourth metatarsal.
NMC 11594 incomplete, weathered skull and lower jaws (Oldman Formation, near Manyberries, Alberta: near centre NW.;!: sec. 36, tp.l, rge. 6, W. 4th mer., about 30 feet below prairie rim or 3,285 feet above sea level).
BMNH R4863 premaxilla, maxilla, dentary.
Diagnosis
Premaxilla does not contact nasal below external naris. Maxillary teeth large, not greatly reduced posteriorly. Anteriormost antorbital fenestra within maxilla minute, hardly visible in lateral aspect, first antorbital fenestra nearly as high as long. Nasals slightly constricted between lacrimals, invaded posteriorly on either side by long slender tongue of frontal. Frontal broadly exposed on skull roof, lacks deep vertical cleft above orbit. Prefrontal broadly exposed dorsally between nasal, lacrimal, and frontal. Lacrimal ' horn' triangular in lateral aspect, with apex centred above antorbital ramus of bone; exceeds postorbital ' horn' in development. Anteroexternal edge of antorbital ramus of lacrimal is not continued across lateral surface of jugal. Ventral process of extopterygoid inflated, with large ventrally opening sinus; jugular process of bone also inflated. Angular terminates posteriorly beneath centre of surangular foramen.
Ventral opening of main basisphenoid sinus situated on midline of skull, behind transverse wall linking basipterygoid processes. Optic fenestra not bridged medially by presphenoid. Exits for cranial nerves III and IV contained in single pit on anterior surface of laterosphenoid. Exit for cranial nerve Vi situated on lateral surface of laterosphenoid.
Neural spine of fourth cervical vertebra much larger than that of fifth. Neural spine of fifth cervical distally pointed, that of sixth cervical smaller and sharply pointed. Presacral vertebrae tend to be shorter and higher than in Albertosaurus ; basal caudal vertebrae diminish less rapidly in size posteriorly than in latter species.
In adults length of humerus estimated to equal 38 per cent of that of femur, forelimb powerfully developed relative to that of Albertosaurus . Anterodistal condyle of metacarpal I reduced, causing first digit to diverge distally from second. First phalanx of digit II robust in adults. Dorsal edge of ungual of digit I passes through arc of about 90 degrees.
Anterior blade of ilium covers diapophysis of twelfth thoracic vertebra. In adults circumference of femur equal to 38 to 41 per cent of length of femur. In comparison with Albertosaurus specimens of similar femur length, presacral vertebral column is much shorter, thoracic ribs are slightly longer, forelimb is longer, ilium and sacrum are longer, and metatarsus is slightly shorter.
Comments
The type specimen of D. torosus was collected by C. M. Sternberg late in the 1921 field season. As is usual in large theropod specimens, the head and anterior part of the vertebral column were pulled dorsoposteriorly toward the pelvis before the animal was buried. Although the hind limbs and many of the more distal caudal vertebrae were lost and although the remainder of the skeleton was partly scattered, the specimen is generally very complete and very well preserved. Sternberg's field notes indicate that at the time the specimen was collected he thought it belonged to an undescribed species of Gorgosaurus or to a new genus. Photographs of the skeleton in situ have been published by Sternberg (1945: 191; 1946: pi. 15; 1966: fig. 9), and of the skull by Sternberg (1945: 191; 1946: pi. 6; 1966: fig. 17).
Daspletosaums attained approximately the same length (28-30 feet) as its contemporary Albertosawus. However, the body, which measured 1,350 mm (53 inches) through the widest point of the thoracic region in NMC 8506, and the base of the tail are much heavier than in Albertosaurus , and the hips and hind limbs are also more powerfully developed. The forelimb, although small, is relatively larger than in any other known tyrannosaur. Interestingly, with the exception of NMC 350, which is subadult, only fully grown specimens of Daspletosaums have so far been collected from the Oldman Formation, while remains of one-half to three-quarters grown albertosaurs are relatively not uncommon in these sediments. The simultaneous existence of these two large carnosaurs indicates the presence in the fauna of two écologie niches to accommodate them. As the endocranial cavities of both forms are quite small, it might be expected that differences in their gross morphology would rather accurately express their behavioural differences. Perhaps the more powerfully constructed daspletosaurs preyed on ceratopsians, and the more fleet albertosaurs were better suited to subsist on hadrosaurs. Albertosaurs and hadrosaurs are indeed correspondingly more abundant in the Oldman fauna than are daspletosaurs and ceratopsians.
The reconstruction of Daspletosaums torosus ( Figure 9) is based principally on the type skeleton (NMC 8506) and the hind limb of the paratype (AMNH 5438). Restored parts include the last two phalanges of the second digit of the manus, acetabular area of the ischium, posterior tip of the pubic boot, all of the metatarsals except the second, the entire pes, and caudal vertebrae 12-14, 18, 19, 21, 22, 26, 28-30, 32, and 36-37. The hind limbs of NMC 350 and NMC 11594 were consulted in drawing elements missing in this region of the type and paratype. Cervical and thoracic ribs are preserved on one side or the other throughout the presacral series of NMC 8506. In the reconstruction they are drawn as seen in lateral aspect, causing the ribs of the posterior thoracic region, which curve away from the vertebrae at a high angle, to appear unusually short. The solid line representing the ventral limit of the body was obtained by projecting the curvature of the anterior thoracic ribs to the midline of the body and by extending this line back to the anteroventral tip of the pubic boot. The abdominal ribs are not shown in the reconstruction.
The dental formula of D. torosus , as indicated by cranial material referred to the species, is: premaxillary teeth 4, maxillary teeth 14 or 15, dentary teeth 15 or 16. There are 11| to 15 serrations per 5 mm on the carinae of the marginal teeth, the serrations being coarsest near the centre of the jaws.
The palate is disarticulated but exceptionally well preserved in NMC 8506 {see Figure 8). The vomers are fused together anteriorly dividing posteriorly into two thin vertical sheets of bone. A vertical anterior ala from the pterygoid broadly underlaps each of these vomerine processes. However, the pterygoids do not meet each other on the midline of the skull, nor do they contact the ventral part of the ascending processes of the palatines (the same relations exist in the palate of A. libratus , see AMNH negative number 37883, taken of USNM 12814). In Albertosawus {see NMC 5600; Gilmore 1946: 11) and probably also in Daspletosaums (NMC 8506) the upper edges of the anterior pterygoid alae loosely but widely contact the upper edge of these palatine processes, with the result that each half of the tyrannosaur palate is separated from the opposite half as far anteriorly as the middle of the vomers. The anterodorsal tip of the ascending process of the palatine is firmly applied to the external dorsoposterior corner of the vomer in D. torosus (NMC 8506) and perhaps also in Albertosawus (AMNH 5336?; Gilmore 1946: 11).
Distribution
Member B of Edmonton Formation, near ScoUard, Alberta.
Referred Specimen
NMC 11315 scattered cranial elements, abdominal ribs, left forelimb, pelvis and hind limbs ( SW. \ sec. 20, tp. 34, rge. 21, W. 4th mer., 150 feet above south bank of Red Deer River).
Comments
NMC 11315 represents the remains of a slightly more than half-grown tyrannosaur. It is referred to Daspletosaurus because the humerus, radius-ulna, ilium, and circumference of the femur are longer relative to the length of the femur than would be expected in an Albertosaurus of similar femur length. The claw of the first digit of the manus seems less recurved than in the latter genus. The specimen shows that Daspletosaurus probably underwent the same ontogenetic changes in limb proportions as did Albertosaurus . The foot is very similar to that of Albertosaurus , although the metatarsus is slightly shorter than in similarly sized specimens of this genus.
Tyrannosaur humeri are very infrequently found, and of the two Daspletosaurus specimens where it is preserved, the distal end of one (NMC 8506) is pathologic. Similarly, of five specimens of A. libratus where a humerus is preserved, in two of them (UA 10, FMNH PR308) the bone has also been damaged in life. This is an unusually high incidence of damage and suggests that the small forelimbs were often crushed by the weight of the massive bodies of these reptiles.
Genus Tyrannosaurus Osborn 1 905 , p. 259
Type species: Tyrannosaurus rex
Diagnosis { See Osborn 1906, 1912, 1917; Matthew and Brown 1923)
Premaxilla contacts nasal below external naris. Maxillary teeth relatively larger than in Daspletosaurus . Anteriormost antorbital fenestra within maxilla not visible in lateral aspect, first antorbital fenestra slightly higher than long. Nasals narrowly constricted between lacrimals. Frontal essentially limited to anteromedial wall of supratemporal fenestra, only small rim of bone reaches dorsal surface of skull. Prefrontal exposed dorsally between lacrimal and frontal. Lacrimal ' horn' represented by conical inflation not interrupting dorsal profile of skull. Postorbital ' horn' or rugose area well developed. Anteroexternal edge of antorbital ramus of lacrimal not continued across lateral surface of jugal. Ventral process of ectopterygoid inflated with very large, ventrally opening sinus. Angular terminates posteriorly behind surangular foramen.
Ventral openings of main basisphenoid sinus situated on either side of midline of skull, dorsomedial to each basipterygoid process. Vertical plate of presphenoid contacts orbitosphenoid and narrow suboptic bridge of laterosphenoid, separating optic fenestra into two openings. Cranial nerves III and IV open into single pit ventrolateral to optic fenestra. Exit for cranial nerve Vi situated close to anterolateral edge of laterosphenoid, but not so close as in Albertosaurus .
Neural spines of fourth and fifth cervical vertebrae subequal, rather narrow in lateral aspect. Neural spine of fifth cervical distally pointed, that of sixth vertebra smaller and sharply pointed. In adults length of humerus equal to about 28 per cent of that of femur. Anterior blade of ilium does not cover diapophysis of twelfth thoracic vertebra. In adults circumference of femur approximately equal to 41 per cent of length of femur. Bodily proportions generally as in Daspletosaurus , although adult specimens about 25 per cent larger, humerus more reduced and ilium longer than in this genus.
Distribution
Upper Edmonton Formation, Alberta.
Referred Specimens
NMC 9950 phalanx of pes (7 miles east of Huxley, centre sec. 10, tp. 34, rge. 22, W. 4th mer., about 170 feet above Kneehills Tuff").
NMC 9554 fragment of cervical centrum (20 feet below and 200 yards south of locality for NMC 9950).
Comments
The presence of Tyrannosaurus in Lance equivalent upper Edmonton strata has been noted several times {see Sternberg 1949; L. S. Russell 1964; Langston 1965). This record is based primarily on a badly eroded and shattered skeleton observed by Sternberg in 1946, weathering out of a fractured concretion high on the face of a cliff". Langston revisited the locality in 1960 and collected a phalanx, noting that the skeleton was even more badly damaged than when Sternberg discovered it, and that little of it still remained in situ.
The phalanx (NMC 9950) is the fourth one of the fourth toe and measures 53 mm in length and about 80 mm across its distal articulation. Hence it is larger and broader than the corresponding element in Albertosaurus and Daspletosaurus . Unfortunately only the first phalanx of the fourth toe is known in Tyrannosaurus ( Osborn 1906: fig. 11). This bone is relatively broader than in any known Oldman or Edmonton form, and by analogy it seems probable that the above fourth phalanx may indeed belong to Tyrannosaurus . The vertebra (NMC 9554) is generically indeterminate.
Albertosaurus lancensis ( Gilmore)
Gilmore (1946) has described the skull of a small carnivorous dinosaur from the Lance Formation of eastern Montana. The skull is quite different from that of Tyrannosaurus and Gilmore founded a new species on it, correctly referring it to Gorgosaurus {= Albertosaurus ). Although the skull is only half as long as that of a fully grown A. libratus , the sutures between the bones of the skull roof are tightly interlocking, and some have been obscured through intergrowth; the supraoccipital alae of the parietals are well developed, and a clearly formed tuberosity is present on the ventral border of the jugal ( Gilmore 1946). The opposite conditions prevail in the skull of AMNH 5664, a specimen of A. libratus of comparable size. The skull of A. lancensis is therefore probably from a fully grown individual, and its small size may be characteristic of the species.
Albertosaurus lancensis further differs from A. libratus and A. sarcophagus (AMNH 5222) in that the frontals meet on the midline throughout their entire length, while in the latter two species these elements are separated anteriorly by a small wedge of bone from the nasals. The frontals are not so deeply cleft above the orbits as is the case in A. libratus and A. sarcophagus . Gilmore (1946: 6) suggested that the prefrontal may be rather well exposed on the skull roof, unlike in the more ancient species of the genus. Otherwise the skulls of the three forms are quite similar.
This species is known from the remains of at least seven individuals collected by the Palaeontological Institute of the Academy of Sciences of the U. S. S.R. ( Maleyev 1955 ^?, 1955c) and six more collected by the Polish-Mongolian Palaeontological Expedition ( Kielan-Jaworowska 1967), all from the Nemegt basin in strata that may be approximately Edmontonian {see L. S. Russell 1963) in age. The form has not yet been thoroughly described, although it has been the subject of several brief reports {see Introduction) and a cast of the skull of one specimen (NMC 10422) was available for study through an exchange with the Palaeontological Institute. Tarbosaurus seems to be most closely allied to Tyrannosaurus . It differs from this genus in that the nasals are not quite so constricted between the lacrimals, the frontals do have some dorsal expression ( but not so much as in Albertosaurus or Daspletosaurus ), the surangular foramen is small, and adult animals are smaller than adult specimens of Tyrannosaurus . (I am indebted to Dr. A. K. Rozhdestvensky for the above information on the morphology of Tarbosaurus .)
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.