Few creatures have pushed anatomy to its limits as much as the sauropods. Those dinosaurs giants moved on column-like legs that supported their massive bodies, waving whiplike tails to ward off predators and using their long necks to devour foliage.
This entire group of dinosaurs is commonly known as the long-necked dinosaurs, but the Mamenchisauruswho lived in the current China at the end of the Jurassic period, it would have been the envy of other sauropods. In a study published on Wednesday (15) in the Journal of Systematic Paleontologyresearchers estimated that the neck of the Mamenchinsaurus could reach almost 15 meters in length. Longer than an ordinary school bus, it is the estimated longest neck of any sauropod species. It may be the longest neck ever seen on any animal.
In 1987, paleontologists discovered a partial skeleton of a sauropod in the red sandstone of the Shishogou Formation in northwest China, an area rich in dinosaurs. The remains were fragmentary, consisting mainly of a lower jaw, pieces of skull and two vertebrae, but they were evidence of a massive animal that roamed marshy plains 162 million years ago alongside early tyrannosaurs.
Researchers named the dinosaur Mamenchisaurus sinocanadorum and linked it to several other East Asian long-necked sauropods. But the true size of Mamenchisaurus it is still unknown. No other fossilized sauropod remains have been excavated, and scientists only have those two vertebrae to examine.
Andrew Moore, a paleontologist at Stony Brook University who studies sauropod anatomy, said that was the case for many of the largest dinosaurs. “What’s especially intriguing and frustrating is that in many cases the longest necks belong to the least known things in the fossil record, for the simple reason that it’s really hard to bury something that big,” said Moore, who led the new study.
So he resorted to fossils of several close relatives of the Mamenchisurusespecially the Xinjiang Titana slightly older sauropod discovered in northwest China in 2013. Notably, the researchers excavated the entire vertebral column of the Xinjiang Titan. At 13 meters long, it represents the longest complete neck in the fossil record.
“Using these more complete, albeit smaller, specimens, we can come up with a pretty competent estimate of what it must have looked like. Mamenchisaurus“, disse Moore.
After comparing the Mamenchisaurus and the Xinjiang Titan, Moore and his team concluded that the former had a neck nearly 15 meters long. This would represent roughly half of its estimated total body length. It is equivalent to just over eight giraffe necks positioned consecutively.
To determine how the Mamenchisaurus moved with a neck the length of a semi-trailer, Moore and his colleagues used a CT scanner to analyze the animal’s vertebrae. Rather than being filled with bone marrow and heavy tissue when the dinosaur was alive, sauropod vertebrae contained large air pockets similar to those found in modern birds like storks and swans. These empty pockets accounted for up to 77% of the volume of each bone, and this tremendously reduced the weight of the animal’s spine.
Cary Woodruff, a paleontologist at the Frost Science Museum in Miami who specializes in the study of sauropods, said reducing neck load was essential for all sauropods. “Such a long neck is a big weight that the animal had to position away from its body,” said Woodruff, who was not involved in the new study. “If you’re going to hold a hammer with your arm straight horizontally, your arm will get tired in no time.”
Although its vertebrae are hollow, the neck of the Mamenchisaurus it was far from fragile. During the initial excavation, paleontologists discovered a fossilized rod of bone tissue a few feet long. It may have been a rigid extension of the vertebrae, often known as the cervical ribs. These extensions would have run the length of the neck, supporting its light bones like a strut. This reduced the flexibility of the neck, but these ribs helped to keep the large structure stable.
“Although it had a lot of bones, it wasn’t a snake, which can coil itself up,” Woodruff said. “Basically, it was like a rod.”
With its reinforced spine, the Mamenchisaurus it probably kept its neck horizontal at a relatively shallow angle above the ground. But, due to the length of its neck, it still managed to pluck leaves from the tops of many trees. This may have helped the sauropod occupy a unique niche in an ecosystem that was likely full of other giant herbivores.
According to the researchers, several groups of sauropods appear to have evolved extremely long necks that may have rivaled the projections made from the Mamenchisaurus.
“We don’t really know what the limits are, because they continue to be stretched as we make more and more discoveries,” Moore said. “We always need to assume that there’s something bigger out there.”
Translated by Clara Allain
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