Maleevosaurus novojilovi ( Maleev) 1955, 1992

Carpenter, K., 1992, Tyrannosaurids (Dinosauria) of Asia and North America, Aspects of Nonmarine Cretaceous Geology, Beijing: China Ocean Press, pp. 250-268 : 256-257

Maleevosaurus novojilovi ( Maleev) 1955 b

Figs. 2C , 5C

— Gorgosaurus novojilovi Maleev 1955b

Holotype:

PIN 552-2 partial skull and skeleton.

Diagnosis.. (Cranial) Maxillary fenestra small; pro-maxillary fenestra not visible laterally; antorbital fenestra proportionally very large,and much longer than high; lacrymal horn moderately developed, not rugose; postorbital not very rugose; lower ramus of maxilla low and slender; jugal slender resulting in a very large orbit; dentary slender. (Postcranial) Cervical neural spines tall, not as reduced as in other tyrannosaurids. Acromion process of scapula virtually non-existant. Ischium has a very pronounced spur-like obturator process, and distally, the shaft curves downward. Metatarsal IV does not overlap metatarsal III at midshaft, nor does metatarsal III have much of an overlap of metatarsal II at midshaft.

Stratigraphic and Palaeobiogeographic Distribution: Nemegt Formation,Mongolian People’s Republic.

Discussion: That Maleevosaurus is a tyrannosaurid is indicated by the slightly opisthocoelous cervical centra, didactyl manus, anteroposteriorly compressed, broad cervicals,well developed anterior foot of the pubis,and broad and tall ascending process of the astragulus. Originally, the holotype of Maleevosaurus was one of four species of tyrannosaurid named by Maleev from Mongolia. He had named it Gorgosaurus novojilovi ( Maleev, 1955b) ,but because of its small size (femur length 560 mm), Rozhdestvensky (1965) considered it a juvenile Tarbosaurus (= Tyrannosaurus ) bataar . Gradzinski and others ( 1977) and Osmolska (1980) noted that the third metatarsal was considerably more slender than in T. bataar ,and doubted that this was a juvenile character. They referred to the specimen as ’Gorgosaurus’ novojilovi .

In order to determine if ’Gorgosaurus’ novojilovi is a juvenile T. bataar , comparisons were made to the similarities and differences between an adult and juvenile Albertosaurus libratus . These were AMNH 5458,with a femur length of 1025 mm,and AMNH 5664, with a femur length of 700 mm. Comparisons were also made to a growth series of skulls of T. bataar ( Fig. 4 ).

In the juvenile Albertosaurus , the lacrymal horn is already well developed and the jugal proportionally large. In T. bataar , there is also no change in development of the lacrymal horn and in size of the jugal. Therefore, the moderately developed lacrymal horn and the slenderness of the jugal in ‘ G.’ novojilovi are not considered juvenile features. Furthermore, no change occurs in the relative size of the antorbital fenestra in T. bataar from juvenile to adult, indicating that the large size of the antorbital fenestra in ‘ G.’ novojilovi is also not a juvenile feature. However, contrary to Gradzinski and others ( 1977) and Osmolska (1980),it is possible that the slenderness of the third metatarsal is a juvenile character,as this metatarsal is considerably more slender in the juvenile Albertosaurus than in the adult. It is possible, however, that this is not the case in the Tyrannosaurus specimens available to Gradzinski and others and Osmolska,but their observations have not yet been published.

It is clear from the above analysis, that except for possibly the slenderness of the third metatarsal, ‘ G. ’ novojilovi is not a juvenile T. bataar . Furthermore, ‘G. ’ novojilovi cannot be referred to the genus Albertosaurus (= Gorgosaurus ),nor to any other known genus of tyrannosaurid because of the large size of the antorbital fenestra, slenderness of the jugal, the very well developed obturator process, and sharply downward curved ischium. For this reason,it is best to assign ‘Gorgosaurus’ novojilovi to a new genus, Maleevosaurus .

Although it is possible that the holotype of Maleevosaurus novojilovi is a juvenile, based on its small size, the neural arches are fused to their centra, and the calcaneum to the astragulus. This suggests that Maleevosaurus is a small tyrannosaurid.

Figures

Figure 2. Comparison of tyrannosaurid skulls: A- Tyrannosaurus rex AMNH 5027 (modified from Osborn, 1912); B - Tyrannosaurus bataar holotype PIN 551 - 1, with missing areas restored after PIN 551 - 3 and GI SPS 100 / 59 (from photographs, Maleev, 1974 and Barsbold, 1983); C- Maleevosaurus novojilovi holotype PIN 552 - 2 (modified from Maleev, 1974); D-Albertosaurus sarcophagus AMNH 5222, with lower jaws based on NMC 5600 and NMC 5601 (modified from photographs and Lambe, 1904); E - Albertosaurus libratus (modified from Russell, 1970); F-? Albertosaurus lancensis holotype CMNH 7541, composite of the left and right side (modified from photographs); G - Daspletosaurus torosus (modified from Russell, 1970 and photographs of NMC 8506). All drawn to scale; scale beneath Tyrannosaurus rex = 10 cm

Figure 4. Growth series for skulls of Tarbosaurus bataar: A-PIN 551 - 1 (holotype) with missing areas reconstructed from PIN 551 - 3 and GI SPS 100 / 59 (from photographs, Maleev, 1974, and Barsbold 1980); B-PIN 551 - 3 (holotype of Tyrannosaurus bataar) (from photographs and Maleev, 1974; the posterior margins of the squamosal and quadratojugal are apparently incomplete or curved away from the viewer, hence the different shape of these bones compared to the other skulls); C-GI SPS 100 / 59 (modified from Barsbold, 1980); D-PIN 552 - 2 (holotype of Gorgosaurus lancinator) (modified from Maleev, 1974). All skulls to scale; scale under A = 10 cm

Figure 5. Comparison of tyrannosaurid skeletons: A - Tyrannosaurus rex (based on drawings and photographs of AMNH 5027 and CM 9380); B - Tyrannosaurus bataar (based on photographs of PIN 552 - 1, a young adult); C- Maleevosaurus novojilovi (modified from Maleev, 1974); D- Albertosaurus sarcophagus (skeleton based on photographs and drawings of ROM 807, with the skull based on photographs and drawings of AMNH 5222, NMC 5600 and NMC 5601); E- Albertosaurus libratus (skeleton modified from Lambe, 1914, and skull modified from Russell, 1970); F- Daspletosaurus torosus (modified from Russell, 1970). All drawn to scale; height of scale beneath Tyrannosaurus rex tail = 1 m