Brachytrachelopan

Chapter • Meet the dinosaur

Overview

Brachytrachelopan mesai was a small sauropod that breaks nearly every rule we associate with long-necked dinosaurs. It reached roughly 9–11 metres in length and probably weighed somewhere between four and ten tonnes, but its most striking feature is the neck: about 40 percent shorter than that of its close relative Dicraeosaurus, and the shortest neck known in any sauropod. The cervical vertebrae were short and stout, carrying tall neural spines that leaned forward and anchored powerful neck and shoulder muscles. The vertebral column curved gently downwards along the neck, so the head was naturally held low, roughly one to two metres above the ground. The animal walked on four column-like legs and carried its tail clear of the ground. Because only a single incomplete skeleton is known, much of its behaviour remains guesswork. No skull material has been found, so the feeding apparatus must be reconstructed from other dicraeosaurids, which had narrow snouts with slender, pencil-like teeth set at the front of the jaws. With the head fixed at a low level, Brachytrachelopan could sweep its muzzle in an arc through shrubs and ferns, cropping plant material at one to three metres — precisely the browsing zone that, in Jurassic South America, was not being exploited by taller sauropods. Researchers have suggested that the absence of stegosaurs from South American faunas may have opened this low-browsing niche. Its diet was entirely plant-based: conifer shoots, ginkgophytes, cycads, ferns and seed ferns. Like all sauropods it did not chew, instead swallowing bulk vegetation and relying on slow fermentation in a capacious gut. A short neck is a short lever, which made the head quicker and easier to move precisely, while the tall neural spines suggest a stiff but extremely strong neck. Whether that strength was also used in display or shoving contests between individuals is a hypothesis, not an established fact. The discovery story is unusually charming. A shepherd named Daniel Mesa was searching for a lost sheep in the hills near Cerro Cóndor in Chubut Province, Argentine Patagonia, when he noticed bones weathering out of the rock. The skeleton, from the Late Jurassic Cañadón Calcáreo Formation, was excavated and described in 2005 by Oliver Rauhut, Kristian Remes, Regina Fechner, Gerardo Cladera and Pablo Puerta. The name means roughly "short-necked shepherd god", from Greek brachys (short), trachelos (neck) and the pastoral god Pan, while the species name mesai honours its finder. The holotype (MPEF-PV 1716) includes cervical and dorsal vertebrae, the sacrum, parts of the pelvis and a femur, but no skull and no tail.

Chapter • Where it lived

Habitat

Brachytrachelopan lived in the Late Jurassic, roughly 150–145 million years ago, in what is now Chubut Province in Argentine Patagonia. The single known skeleton comes from the Cañadón Calcáreo Formation near the village of Cerro Cóndor, a sequence of river and lake deposits. The setting was a semi-open floodplain crossed by meandering rivers, with seasonal dry spells and a flora of conifers, ginkgophytes, cycads and dense ground cover of ferns — exactly the low vegetation a short-necked browser could exploit.

Chapter • Wild behavior

Behavior & Ecology

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Chapter • Scientific place

Taxonomy