Achillobator

Chapter • Meet the dinosaur

Overview

Achillobator was one of the largest raptor-type dinosaurs ever found, a member of the family Dromaeosauridae that also includes Velociraptor and Deinonychus. At roughly 4.5–6 metres long and an estimated 250–400 kilograms, it was built far more heavily than its smaller cousins. The skeleton shows a stocky body, a strikingly robust pelvis, powerful hind limbs and a stiffened tail carried straight out behind the animal as a counterbalance — never dragged along the ground. Each foot bore the enlarged, sickle-shaped claw on the second toe that is the signature of the group, held raised clear of the ground while walking. No feathers were preserved with the fossil, but because close relatives such as Velociraptor, Zhenyuanlong and Microraptor have been found with clear feather impressions, modern reconstructions show Achillobator as fully feathered, with long vaned feathers along the arms and a fan at the tail tip. Its behaviour is harder to pin down, because only a single incomplete skeleton is known. The short, muscular hind limbs and unusually broad hips point to an animal built for power and stability rather than long pursuits. Many researchers think large dromaeosaurids used their arms and sickle claws to grip and pin struggling prey while biting, much as hawks and eagles hold prey against the ground today. The pelvis of Achillobator, in which the pubis points more forward and downward than in other dromaeosaurids, remains one of the most debated features of the whole genus. Achillobator was a pure meat-eater in a landscape it shared with slow, armoured Talarurus, the plant-eating Gobihadros, the strange long-clawed therizinosaurs Segnosaurus and Erlikosaurus, and the tyrannosauroid Alectrosaurus. Its teeth are recurved and serrated, ideal for slicing through flesh and tendon. It most likely hunted medium-sized herbivores, and like almost all predators it would also have scavenged carcasses and taken smaller animals when the chance arose. The fossil — a partial skeleton including jaw fragments, vertebrae, the pelvis and bones from both the fore- and hind limbs — was collected in the Bayan Shireh Formation of southeastern Mongolia during a joint Mongolian–American expedition. The animal was named in 1999 by the Mongolian palaeontologist Altangerel Perle together with Mark Norell and James Clark. The name blends the Greek hero Achilles, referring to the massive attachment for the Achilles tendon on the heel bone, with the Mongolian word baatar, "hero"; the species name giganticus refers to its size. The original description appeared as a hastily produced preliminary paper, which led some workers to suspect for years that the material might be a chimaera of more than one animal. Later study has supported it as a single, genuinely heavily built predator.

Chapter • Where it lived

Habitat

Achillobator lived during the Late Cretaceous, roughly 96–89 million years ago, in what is now southeastern Mongolia. The holotype comes from the Bayan Shireh Formation at Burkhant, Dornogovi Province. The setting was a semi-arid inland region of floodplains, meandering river channels, seasonal lakes and open ground — considerably wetter than the great dune fields preserved in later Cretaceous rocks of the Gobi. Its neighbours included the armoured Talarurus, the hadrosauriform Gobihadros, the therizinosaurs Segnosaurus and Erlikosaurus, and the predatory Alectrosaurus.

Chapter • Wild behavior

Behavior & Ecology

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Chapter • Scientific place

Taxonomy