Achillobator Perle, Norell & Clark, 1999
Achillobator Perle, Norell & Clark, 1999 "Achilles (tendon) hero"
a-KIL-o-BAH-tor (Gr. Akhilles (mythical Greek hero whose only vulnerable spot
was his heel; his name is associated with the tendon that runs along the heel bone)
+ Mongolian bator "hero") (m) alluding to the powerful Achilles tendon [tendo calcaneus]
that must have existed along the "heel" on the second phalanx of dromaeosaurs,
for attachment of the large flexor muscle that permitted slashing blows from the huge claw
on the second toe: "The penultimate phalange of the second digit [in Achillobator]
is massive with a hypertrophied postero-ventral heel, which probably served as the
insertion area of the flexor of the digit tendon." Achillobator is known from
a fragmentary partial associated skeleton (Holotype: FR.MNUFR-15
(Mongolian National University, Ulaan Baatar)), consisting of a left maxilla,
left femur and tibia, left metatarsals III and IV, right ilium, pubis, and ischium,
isolated phalanges from the feet and hands, tooth fragments, isolated caudal vertebrae,
and fragments of ribs; collected in 1989 at Burkhant, southwest of the village of Dzun Bayan,
near Khongli Tsav, Southeast Gobi Desert, Mongolia, in the Late Cretaceous
(Late Santonian/Early Campanian) Bayan Shireh Formation. The fragmentary maxilla (upper jaw)
bone indicates Achillobator had a large skull "similar in proportion to carnosaurs."
The pubis is long and robust, with a foot-like distal expansion similar to "carnosaurs";
the pubis is also oriented much more forward than in typical dromaeosaurs,
which have an opisthopubic, or backward-pointing pubic bone.
The surprising combination of a primitive "carnosaur"-like pelvis with a raptor-like toe-claw
sets Achillobator apart from other known dromaeosaurs. The formal description of
Achillobator was published by the National Museum of Mongolia based on an extremely
preliminary manuscript without the knowledge of the junior authors
(Mark Norell and James Clark).
This incomplete scholarly process poses problems for some details and conclusions found
in the original paper. Burnham, Derstler, Currie, Bakker, Zhou and Ostrom (2000), in their
description of Bambiraptor, suggest that the taxon may be based on "upon of mixture
of bones from two or more actual species," with only the pedal unguals being identifiable as
dromaeosaurid material, while "the ilium, ischium, maxilla, and caudal vertebrae share no
unique features with the Dromaeosauridae."
Type Species: Achillobator giganticus [ji-GAN-ti-kuhs] Perle, Norell & Clark, 1999
"gigantic," to indicate its very large size for a dromaeosaurid--the proportions of its femur
(50.5 cm long compared to around 30 cm in Deinonychus) and other bones suggest it was
likely at least a third to twice as large as Deinonychus, perhaps up to 6 m (20 ft.)
long with a 13 cm long slashing claw. The original description suggests Achillobator
was "three times as large as Deinonychus," but this estimate appears to be an error.
Theropoda Maniraptora Dromaeosauridae Late Cretaceous (Santonian/Campanian)
Mongolia [added 5/2000]
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