Dinosaur Brachytrachelopan mesai, of Late Jurassic, Argentina!
In a clade known for their long necks, Brachytrachelopan mesai is known for having the shortest neck. This (comparatively) small sauropod comes from a family of oddball sauropods with already shorter-than-average necks, Dicraeosauridae, known best for the famous sail-necked Amargasaurus and Bajadasaurus. Even though Brachytrachelopan was the smallest of its family, with the shortest neck, it was still a large animal, at 10–11 metres (33–36 ft) in length and 5 metric tons (5.5 short tons) in body mass. Brachytrachelopan’s shorter neck was likely an adaptation for lower browsing, allowing it to occupy a niche similar to iguanodontian ornithopods, which seemed to be absent from Late Jurassic Gondwana. Likewise, while North America at the time was abundant with iguanodontians, they lacked Dicraeosaurids. The two clades may have been ecological analogs, resulting from parallel evolution in two distantly related dinosaurian lineages to fill a similar niche.
Brachytrachelopan mesai is known from the Cañadón Calcáreo Formation of Late Jurassic Argentina. It would have lived alongside other sauropods such as Tehuelchesaurus, which would have filled the niche of high browser instead, an indeterminate stegosaur, and crocodylomorphs like Almadasuchus. It could have been preyed on by the enigmatic theropod Pandoravenator, as well as an indeterminate abelisaurid.
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Small in size for a sauropod, Brachytrachelopan had an exceptionally short neck - 40% shorter than any other dicraeosaurid and the shortest of any known sauropod. Brachytrachelopan measured only 10–11 metres (33–36 ft) in length and weighed only 5 metric tons (5.5 short tons).
Dicraeosaurus is a short-necked sauropod from Tanzania! Though related to some of the dinosaurs with the longest necks like Diplodocus and Supersaurus, Dicraeosaurus had a short neck which let it feed on middle level plants. It also had a big head to help it get more food!
Time and Place: Between 129 and 125 million years ago, in the Barremian of the Early Cretaceous
Amargasaurus is known from the Puesto Antigual Member of the La Amarga Formation in Neuquén, Argentina
Physical Description: Amargasaurus is a Dicraeosaurid - a group of super weird, highly specialized sauropods with short necks and a general aura of epic weirdness. Amargasaurus is the weirdest of them all, characterized by its long neck spines. A small sauropod, it was about 10 meters long, and weighed about 2.6 tonnes. Height is more uncertain, but it couldn’t have been more than 2.7 meters tall. It had a short neck compared to other sauropods, an average length tail, and a medium length torso. Distinctively, Amargasaurus had long spines coming off of its neck, which appear to have been covered in thin layers of keratin (similar to the material on nails). These spines were split down the middle, forming two rows along the neck, and they pointed back to the body of the animal - away from the head. These spines were almost certainly sexual display structures, though they also would have probably made fun clackity-clack sounds if they hit each other when the animal moved its neck. Amargasaurus also had long spines shaped into a paddle over the hip and the start of the tail
Amargasaurus was weird in other ways, too - it had a very strong rib cage and short hips. It had shorter forelimbs than hindlimbs, as in other Diplodocoids. It had a broad snout, kind of like a horse, with very thin teeth like other related sauropods. It also had long bones connecting the braincase with the roof of its mouth, unique amongst sauropods. Thus it was a short, stocky sauropod, a weirdo on the floodplains of South America.
Diet: Amargasaurus would have been a low to medium level browser, not able to get very high up in the foliage line for food.
By José Carlos Cortés
Behavior: Amargasaurus, being a weird sauropod, wouldn’t have necessarily behaved by some of the more iconic types (diplodocids, titanosaurs, etc.) - it had a short neck and, honestly, was really just a sauropod trying to do the Hadrosaur Thing, just not to the same extent as, say, Brachytrachelopan. It didn’t have a very good sense of hearing, and so it probably would have relied on other senses more; it also would have had some trouble balancing itself, and it would have had to have its snout facing downward by quite a lot, and its neck held horizontally (though this has been debated extensively). Still, it couldn’t raise its head very high at all because of the spines, only able to get its neck 270 centimeters above the horizontal. This probably would have only been done while alert, given the amount of noise it would have created.
Amargasaurus, despite its short legs, was probably able to move fairly quickly - like the living white rhinoceros, which can gallop, it had very stocky legs. In fact, when compared to the rhinoceros, it had even stockier legs, so it probably could run when needed. The spines would have been used primarily for display, and probably were bright in color as a result - they might have been shown off by moving the neck back and forth, or bending it somewhat to make them splay out more along the neck. Still, any such behavior is largely speculative at this time, and their exact function is up to considerable debate - some even think they may have conducted neck wrestling with the spines.
Amargasaurus has not been found extensively, so it’s possible it wasn’t a herding animal - but this seems circumspect, given the fact that many other sauropods are herding animals. More fossils are needed to know more. In addition, it is uncertain how - or if - they took care of their young, but it seems likely due to their smaller size.
By Scott Reid
Ecosystem: Amargasaurus lived in the Puesto Antigual Member of the La Amarga Formation, which was a braided river system and very complex ecosystem. Though the plants of the ecosystem aren’t known, the rich soil of the environment indicates a lush ecology. There were many other dinosaurs there - the Rebbachisaurid Zapalasaurus, the Dicraeosaurid that’s probably just Amargasaurus Amargatitanis, the potential the stegosaur “Amargastegos”, and an Abelisaurid - Ligabueino - that was probably the main predator of Amargasaurus. There was also a crocodylomorph, Amargasuchus, an unnamed Pterosaur, and the mammal Vincelestes. Hopefully, more study of the site will uncover more animals that lived with Amargasaurus!
Other: Though it was once thought that Amargasaurus supported a sail on the neural spines, this seems unlikely, given the lack of any fossil evidence of such a structure. Amargasaurus is one of many weird relatives of more classic sauropods such as Diplocodus; recently, the sauropod Bajadasaurus was found, which is a lot like Amargasaurus - except its spines face the front!
~ By Meig Dickson
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Bajadasaurus...where extremes reach a tipping point!
Bajadasaurus…where extremes reach a tipping point!
Dinosaurs continue to be the source of amazement beyond all expectations. Now is the turn of sauropods, with the newly described South American dicraeosaurid Bajadasaurus. If you thought that the elongated cervical spines along the neck of Amargasaurus were a bit too much (and source of a lot of controversy)… think again while looking at Bajadasaurus: Same spines but twisted, facing permanently…
