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Re: Tyrannosaurs



In a message dated 95-08-25 08:14:07 EDT, Blaise Considine writes:

>I'd like to express my appreciation for your joining (or de-lurking) on 
>this list. I've found your posts to be extremely informative. I'd enjoy 
>reading your description of Jenghizkhan, provided you allow me the 
>opportunity to ask you questions if the description is too "scientific".
>
>

Okay, here it is, with accessory graphics removed:

Box 1: Description of Jenghizkhan

Linnaean hierarchy:
Paraclass Reptilia
 Parasubclass Diapsida
  Parainfraclass Archosauria
   Parasuperorder Theropodomorpha
    Paraorder Theropoda
     Suborder Tyrannosauria nov.
      Family Tyrannosauridae
       Subfamily Tyrannosaurinae
        Paratribe Tarbosaurini nov.
         Genus Jenghizkhan nov.
          Type species Jenghizkhan bataar (Maleev, 1955) n. comb.

Synonyms of type species:
        Tyrannosaurus bataar Maleev, 1955
        Tarbosaurus bataar (Maleev, 1955) Rozhdestvensky, 1965
        Tyrannosaurus (Tyrannosaurus) bataar (Maleev, 1955) Paul, 1988
        Gorgosaurus lancinator Maleev, 1955
        Aublysodon lancinator (Maleev, 1955) Charig, 1967
        Deinodon lancinator (Maleev, 1955) Kuhn, 1965

        Etymology: Latinized version of the name of the Mongol tyrant Genghis 
Khan,
who ruled an empire extending from Europe to China during the late 12th and
early 13th centuries A.D., in reference to the presumed ecological role of
this dinosaur as the top predator of its domain.

        Holotype specimen of type species: PIN 5511 (figure above; scale bar = 
10
cm; some of the dorsoventral crushing of the original specimen "repaired" by
artist Tracy Lee Ford [deleted from Clipboard--Ed. Note]), an incomplete
skull including both frontals, parietals, nasals, lacrimals, postorbitals,
jugals, maxillae, and dentaries; maxillary and dentary teeth; occiput with
partial braincase; and at least four associated vertebrae (cervicals 3 and 4
and dorsals 3 and 4, figured on next page at left [deleted from
Clipboard--Ed. Note]); as described by Maleev (1955). Presently at the
Paleontological Institute of the Russian Academy of Sciences in Moscow.

        Type locality and horizon: Nemegt Formation, southern Mongolia. More
specific locality information is not yet available. Discovered on the 1946
(first) Russian Academy of Sciences paleontological expedition to Mongolia.

        Diagnosis: The genus Jenghizkhan differs from other members of the 
paratribe
Tarbosaurini in its larger size (overall adult length about 14 meters) and
its massively constructed, rugose vertical skull elements, namely, the
postorbital-jugal bar and lacrimal-jugal bar. In Tarbosaurus efremovi these
vertical elements are relatively slender, with quite smooth external
surfaces. In Jenghizkhan, the lacrimal and postorbital meet above the orbit
to create a continuous circumorbital flange from approximately the middle of
the vertical ramus of the lacrimal around to the suborbital tuberosity
("postorbital bar") on the vertical ramus of the postorbital. The frontal is
thereby excluded from the orbital rim, although a notch may be present at the
dorsal apex where the lacrimal rugosity contacts the postorbital rugosity. In
Tarbosaurus efremovi and most other tyrannosaurids, the frontal remains part
of the orbital rim as a well-defined notch or discontinuity in the
circumorbital surface, separating the lacrimal from the postorbital. These
characters are probably not age-related, since they are present in the
holotype juvenile skull of Gorgosaurus lancinator.

        Jenghizkhan has the tallest neural arches relative to centrum diameter 
of
any tarbosaurinid (ratio about 2:1 in Tarbosaurus efremovi holotype dorsal 4,
but almost 3:1 in Jenghizkhan bataar holotype dorsal 4: even greater than in
the corresponding element of Tyrannosaurus rex; see figures on next page
[deleted from Clipboard--Ed. Note]). The anterior dorsal vertebrae have
pointed neural spines in lateral view, and very deep pneumatic hollows and
sharply defined laminae in ventral surfaces of transverse processes.
Parapophyses are very well developed, although this may indeed be due to the
maturity of the holotype individual. Tall neural arches are probably not
age-related, since they are already apparent in a small tarbosaurinid
skeleton mounted for display in the museum in Ulan Bator next to an adult
Tarbosaurus efremovi.

        Jenghizkhan is distinguished from Tyrannosaurus by the greater relative
length and slenderness of the muzzle and dentaries, and by the significantly
greater dentary tooth count: Jenghizkhan shows 1516 dentary teeth, of which
the first is of comparable size to the ones following, whereas the holotype
of Tyrannosaurus rex shows only 13, of which the first is very small. The
maxillary and dentary teeth of Jenghizkhan are as a rule more laterally
compressed than the thick teeth of Tyrannosaurus. In Tyrannosaurus, the
suborbital tuberosity appears as a pendant "postorbital bar," but it is not
pendant in any figured specimen of Jenghizkhan or Tarbosaurus. It is
difficult to estimate the width of the occiput of the Jenghizkhan bataar
holotype skull from photographs (no clear posterior or dorsal views have ever
been published), but although wide it seems to be considerably less so than
the widely flaring occiput of Tyrannosaurus (AMNH 5027). The occipital
condyle seems to be directed posteriorly, not posteroventrally as in
Tyrannosaurus.

        Referred specimens: Holotype partial skull and associated postcranial
remains (PIN 5531) of Gorgosaurus lancinator Maleev, 1955, here considered
to be a 60%-grown Jenghizkhan bataar individual. A few specimens referred to
the species Tarbosaurus bataar and/or Tarbosaurus efremovi illustrated in
various publications and exhibition guidebooks are clearly referable to
Jenghizkhan bataar, mainly as subadult individuals, but their specimen
numbers remain unavailable. One of these is the juvenile tarbosaurinid at
Ulan Bator noted under Diagnosis above.

Referred species:
        ?Jenghizkhan luanchuanensis (Dong, 1979) n. comb., formerly 
Tyrannosaurus
luanchuanensis Dong, 1979 and Tarbosaurus luanchuanensis (Dong, 1979)
Olshevsky, 1991, based on five large teeth from the Qiuba Formation of
Luanchuan County, Henan Province, China.

        Discussion: See appropriate sections in text of parts 1 and 2 of this
review. Systematics and relationships of the suborder Tyrannosauria, family
Tyrannosauridae, parasubfamily Shanshanosaurinae, subfamily Tyrannosaurinae,
tribe Alioramini, paratribe Tarbosaurini, paratribe Albertosaurini, and tribe
Tyrannosaurini are discussed in part 2.