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Re: Tyrannosaurs



In a message dated 95-08-21 18:39:17 EDT, jshields@iol.ie (James Shields)
writes:

>>                Tarbosaurus
>>                  Tarbosaurus efremovi
>
>Whatever happened to Tarbosaurus bataar?
>
>James Shields
>
>

Here is a relevant excerpt from part 1 of my review of Tyrannosauridae for
_Dino-Frontline_ (as usual, italics deleted by the Clipboard):

        The Sino-Swedish Paleontological Expeditions of 1927-31 to the Gobi in 
China
turned up some nondescript tyrannosaurid material, some of which was
described by Anders Birger Bohlin in 1953 and referred to Prodeinodon (under
the misspelled name Deinodon mongoliensis). But it was not until after World
War II that the Gobi yielded its first bonanza of tyrannosaurid specimens,
including excellent, nearly complete skulls and skeletons of what seemed to
be several new species. In 1946, the Paleontological Institute of the Soviet
Academy of Sciences (Akademia Nauk) negotiated with the Mongolian People's
Republic to send expeditions to the Gobi to search for fossils. Under the
overall supervision of Academician Yuri Alexandrovich Orlov, the expeditions
of 1946-1949 were led by renowned paleontologist and science-fiction writer
Ivan Antonovich Efremov. Among the scientists accompanying Efremov were
paleontologists Anatoly Konstantinovich Rozhdestvensky and Evgenii
Alexandrovich Maleev (the two e's in his last name are pronounced separately:
Ma-LAY-ev), and geologist Nestor Ivanovich Novozhilov, all of whom became
connected in some way with the tyrannosaurids discovered on the expeditions.
        The first expedition, during the summer of 1946, was mainly for
reconnaissance, to prospect for sites where interesting fossils might be
uncovered. These were found all over the southeastern Gobi, but especially in
the Nemegt Basin, a depression about 40 by 100 km in area encompassing
sediments laid down in a large delta by slowly moving streams about 70
million years ago, early in the Maastrichtian stage of the Late Cretaceous
epoch. It was on this reconnaissance expedition that the huge partial skull
and vertebrae of a gigantic tyrannosaurid were unearthed. It was a
spectacular discovery: the first good tyrannosaurid specimen to be found in
Asia.
        There was no follow-up expedition in 1947; instead, plans were made for 
a
much better-equipped expedition for the following year. That famous 1948
expedition was a cooperative affair, involving not just Soviet
paleontologists but also interested Mongolian and Chinese scientists. The
Soviet government furnished GAZ cars, ZIL trucks, and excavating equipment.
On March 18, 1948 a convoy comprising at least 30 people left Ulan Bator, the
Mongolian capital, headed south. But it was not until its arrival in the
Nemegt Basin that the expedition found more good tyrannosaurid material. On
May 9, field technician J. Eaglon came across a ten-meter-long skeleton,
nearly complete, in red sandstone of what are now known as the Upper Nemegt
Beds. The expedition promptly called it "Eaglon's skeleton." It was the first
of seven more or less complete tyrannosaurid skeletons of various sizes
brought back to Moscow by the expeditions of 1948 and 1949. In addition,
partial skulls, fragmentary skeletons, isolated bones, and scattered teeth of
tyrannosaurids almost too numerous to count were exhumed. Considering the
rarity of tyrannosaurids in North America [not any more: Ed. Note], this was
a real windfall.
        The richness of dinosaur bones of all kinds in the Nemegt Basin made it
difficult to explore and prospect other areas; the expedition's time was
largely consumed excavating skeletons found there. Three particularly
productive sites are known as Nemegt, Altan Ula, and Tsagan Ula; Altan Ula is
also called the "Dragons' Tomb," where seven virtually complete skeletons of
the duckbilled dinosaur Saurolophus angustirostris and three of the seven
tyrannosaurid skeletons were unearthed.
        After the third and final Academy of Sciences expedition in 1949, the 
work
of describing the Gobi dinosaurs fell to Maleev. In two brief papers in 1955,
in consecutive issues of the Proceedings ["Doklady"] of the USSR Academy of
Sciences, he established one new genus and four new species for the
tyrannosaurids. In his initial paper, he described the 1946 specimen (PIN
551-1), with a skull (were it complete) slightly larger than that of AMNH
5027, as the holotype of the new species Tyrannosaurus bataar (the trivial
name derives from the Mongolian for "hero" or "warrior"; Figure 26). The
other three taxa were described in his second paper: Tarbosaurus efremovi
("Efremov's frightening lizard") for a nearly complete skeleton about 10-12
meters long (PIN 551-2; Figure 27); Gorgosaurus lancinator ("shredder" or
"one who tears to pieces") for a skull and associated fragmentary postcranial
remains of an animal about 9 meters long (PIN 553-1; Figure 28); and
Gorgosaurus novojilovi (honoring geologist Novozhilov) for an incomplete
skull and associated fairly complete skeleton about 6 meters long (PIN 552-2;
Figure 29). I have as yet been unable to determine whether "Eaglon's
skeleton" actually became the holotype specimen of Tarbosaurus efremovi.
        Unfortunately, Maleev's descriptions were too brief to individually
characterize his different species. Most of the characters he listed apply to
tyrannosaurids in general: They describe the family as a whole rather than
the family's members, and serve only to establish the skeletons as
tyrannosaurids. All things considered, if you read between the lines, it
seems as if he simply separated the species by size. The smallest skulls and
skeletons were classified in the genus Gorgosaurus and the largest in
Tyrannosaurus. And the new genus Tarbosaurus, into which most of the
Mongolian specimens fell, he created for those specimens too big for
Gorgosaurus and too small for Tyrannosaurus. Had Daspletosaurus already been
described, perhaps he would have used that genus instead of creating
Tarbosaurus! Maleev should not be faulted for this; he was merely carrying on
in the tradition of the classical studies of large theropods.
        Maleev died in 1966 before he could finish the more thorough 
descriptions of
the Gobi tyrannosaurids he was working on. His monograph, never completed,
was eventually prepared for publication in incomplete form by Rozhdestvensky
and his student, Sergei Mikhailovich Kurzanov, who completed the tables of
measurements. Primarily a bone-by-bone osteology of Tarbosaurus efremovi, the
paper appeared posthumously in 1974 in the first volume of the Transactions
["Trudy"] of the Joint Soviet-Mongolian Paleontological Expeditions. It is
the single most important paper yet published on the Gobi tyrannosaurids.
        Well before Maleev's monograph appeared, however, Rozhdestvensky had
reanalyzed Maleev's tyrannosaurid taxonomy. In 1965, he suggested that Maleev
had multiplied the number of species unnecessarily. What Maleev had taken as
different species, asserted Rozhdestvensky, were simply growth stages of a
single Nemegt tyrannosaurid species. Thus, Tyrannosaurus bataar represented a
large, aged adult almost 15 meters long; Tarbosaurus efremovi represented a
younger adult about 80% fully grown; Gorgosaurus lancinator was a 60%-grown
subadult; and Gorgosaurus novojilovi was a 40%-grown juvenile. All belonged
to the same species, for which the trivial name bataar had priority, of a
distinct genus, for which the name Tarbosaurus was available. Thus the
species Tarbosaurus bataar was born.
        Rozhdestvensky applied this idea not just to tyrannosaurids but to many
other closely related, sympatric ("having the same homeland") dinosaur genera
and species. But in the absence of statistically meaningful samples, and
except for obviously juvenile skeletal features such as small, poorly
ossified bones, there is no foolproof way to distinguish growth stages of a
single species from a series of closely related species of different sizes.
For example, both lions and leopards live together on the plains of eastern
Africa. If one were a paleontologist of the distant future examining
fossilized African lion and leopard skeletons, could one determine that two
species of big cats had existed, or would one fall into the error of thinking
that leopards were merely subadult lions? It is not an easy problem to solve,
and I do not think we have yet reached any firm answers for the dinosaurs
Rozhdestvensky dealt with.
        For years, paleontologists accepted Rozhdestvensky's very reasonable
conclusion that there was only one large tyrannosaurid genus from the Nemegt
Basin. As a result, even though only one specimen has ever been described of
a truly Tyrannosaurus-size individual--the holotype of Tyrannosaurus bataar
itself--and most specimens fall into the 10-12-meter size range of
Tarbosaurus efremovi, the adult length of "Tarbosaurus bataar" is almost
universally quoted as 14 to 15 meters. The problem that has thus arisen is to
explain why most of the known specimens, from many different Nemegt
localities, represent "young" individuals.
        Recently paleontologists began to suspect that the smallest species,
Gorgosaurus novojilovi, represented a genus separate from the other
tarbosaurs. In 1992, Carpenter pointed out several minor but important
differences from Tyrannosaurus bataar and named the new genus Maleevosaurus.
Carpenter then followed Paul (in Predatory Dinosaurs of the World; 1988) in
resurrecting Maleev's original species Tyrannosaurus bataar for the other
specimens referred to Tarbosaurus. He found only very minor, species-level
differences between the largest Asian and North American tyrannosaurids.
        In preparing this review, I reexamined the characters that might define
Tyrannosaurus and the various Mongolian species, and I have come to a
different opinion. First of all, Maleev was partly correct; there are indeed
more than just two tyrannosaurid species among the material found in the
Nemegt Basin. There are at least three: the largest, about 14-15 meters long,
named Tyrannosaurus bataar; a smaller, more lightly built form about 10-12
meters long, named Tarbosaurus efremovi; and the smallest, the 6-meter-long
Maleevosaurus novojilovi. The largest form actually represents a genus
distinct from both Tyrannosaurus and Tarbosaurus. In Box 1 [unpublished in
_Dino-Frontline_--Ed. Note], I call this new genus Jenghizkhan, celebrating
the great Mongol conqueror whose empire stretched across Asia from China to
Europe during the 12th century. As far as I know, Jenghizkhan bataar was the
largest and most imposing Asian tyrannosaurid.
        The genus Tarbosaurus seems to be afflicted with the lion-leopard 
problem.
For example, the type specimen of Gorgosaurus lancinator, generally referred
to Tarbosaurus bataar, is indeed a juvenile, as Rozhdestvensky stated. But it
is a 60%-grown Jenghizkhan bataar, not a Tarbosaurus efremovi. I also suspect
that one or two of the 10-to-12-meter individuals, maybe more, presently
referred to Tarbosaurus may on reexamination turn out to be subadults of
Jenghizkhan. It is diabolically unfortunate that the majority of Gobi
tyrannosaurid specimens have never been illustrated in print or even
identified with specimen numbers. So even when one can study a clear
photograph in an exhibition guidebook or some other publication, one does not
know whether one is looking at the holotype, the paratype, a referred
specimen, or a restored plaster cast. There is not one accessibly published
dorsal view of the skull of any Gobi tyrannosaurid, even in Maleev's 1974
monograph! All views are lateral or oblique, making it difficult to assess
the extent to which certain skull characters are expressed. I have more to
say about this situation in part 2 of this review.
        The type specimens of Tyrannosaurus bataar and Gorgosaurus lancinator 
are
displayed under glass at the Academy of Sciences' paleontological museum in
Moscow. The holotype (PIN 551-2) and paratype (PIN 552-1) skeletons of
Tarbosaurus efremovi were originally mounted in tandem at the same museum,
the first time that two large tyrannosaurid skeletons had ever been displayed
together in a single hall. As with the New York and Carnegie Tyrannosaurus
rex skeletons, the actual fossil skulls were too heavy to be mounted;
instead, lightweight wooden replicas were carved by the museum's preparators.
The smaller type skeleton of Maleevosaurus novojilovi was prepared as a free
mount, with missing parts restored in plaster as if it were a young
Tarbosaurus (which it is not). Since the 1950s, one of the two large
skeletons (I don't know which) was returned to Mongolia for permanent display
at the Ulan Bator Museum of Natural History, but it was eventually replaced
in Moscow, either by another skeleton or by a full cast. Specimens of
juvenile tyrannosaurids are also on display at Ulan Bator. I have seen one
photograph of an extremely juvenile Gobi tyrannosaurid (probably a
Tarbosaurus efremovi), but I do not know where that specimen is housed. [If
you know any of this information, I'd like to hear from you!--Ed. Note.]
        The postwar Soviet expeditions were followed up in the 1960s by the 
Joint
Polish-Mongolian expeditions, which discovered at least six more
tyrannosaurid skeletons. No papers detailing these finds, with measurements,
ever appeared. Some skeletons were identified by quarry sites in a geological
paper by Riszard Gradzinski in 1970; one particularly complete individual
about 10 meters long, called Tsagan Khushu #2, has been cast in its entirety
and is apparently available to museums outside Warsaw, Poland and Ulan Bator.
Significantly, Gradzinski refers to the tyrannosaurids as Tarbosaurus sp., as
if more than one species might be identifiable among the known material.
        One of Mongolia's foremost vertebrate paleontologists is Rinchen 
Barsbold,
who has become the leading expert on the theropods large and small of the
Gobi. His doctoral dissertation on these dinosaurs was published in 1983 as
volume 19 of the Transactions of the Joint Soviet-Mongolian Paleontological
Expeditions. But tyrannosaurids occupy only three or four of the 117 pages
that comprise the volume; only one skull (GI 100/59) is illustrated, in a
tiny figure on page 8. The picture is too small for me to be certain, but
there is a decent chance the skull belongs to a Jenghizkhan rather than a
Tarbosaurus. Tyrannosaurus bataar, Gorgosaurus lancinator, and Gorgosaurus
novojilovi are not even mentioned. It seems as if, despite the demise of
Communism, information about Mongolian tyrannosaurids remains a state secret.

I'd be happy to post the description of Jenghizkhan from Box 1 if anyone
wants it.

Verbose George