Sauropods. They are the giants of the dinosaur world, which has no shortage of large animals. Many sauropods are among the largest animals that ever lived. Some could grow well over 100 feet long and weigh over 150,000 pounds!
“Sauropod” means “lizard feet”, but in actuality their thick, padded feet are nothing like those of lizards. This group of dinos developed in the Late Triassic Period, around 210 million years ago, and lived right on up to the extinction event at the end of the Late Cretaceous, a little over 65 million years ago. Sauropods evolved from a line of dinosaurs commonly called “prosauropods”. They shared the long necks and basic body shape of sauropods, but were smaller, and unlike sauropods they could walk on both two legs and four legs.
Sauropods are immediately recognizable with their long necks, small heads, tree trunk-like legs, long tails, and plump bodies. They were herbivores, with specialized teeth that helped them snip off plants to chomp. The purpose of their long necks has been the subject of much study, with no proven conclusion, but lots of theories. Originally, it was believed that their necks allowed these dinosaurs to graze on plants that were out of reach of smaller, shorter animals, like a giraffe. However, a bit more recently, it was proposed that sauropod necks hung much lower, and that they were swung about left and right to be able to better reach nearby plants closer to ground level. Still another theory suggests that the necks of sauropods had little to do with feeding and were meant to impress mates. The longer the neck, the more appealing that sauropod looked to potential partners.
Despite mostly sharing the same basic body shape, there are many variations within the different types and species of sauropods. Their skulls are not well known, since they don’t preserve well, but those that have been discovered can be either long and narrow, like Diplodocus and Apatosaurus, or blunt and short like Brachiosaurus or Malawisaurus. Some had very specialized skulls, like Nigersaurus, which had broad flat jaws that helped it graze on plants very close to the ground like a lawnmower.
Some sauropod types had very unique features, such as Shunosaurus, which had a tail club similar to that of the unrelated dinosaur Ankylosaurus. Amargasaurus was another strange sauropod, with a double row of giant spines sprouting from its neck. The purpose of both the club and the spines were thought to be similar – to defend the animals from predators. Both Shunosaurus and Amargasaurus grew to around 33 feet, which may sound big, but is actually quite small for a sauropod. Larger sauropods tend to lack these obvious defensive features, possibly because their sheer size prevented most predators from wanting to risk an attack. It has also been theorized by scientists that the long, tapering tails of large sauropods could be used as a whip against predators, and they might have even been able to swing them fast enough to break the sound barrier!
These days, our largest land animal is the African Elephant, and while it’s quite large, it’s nowhere near as big as the biggest sauropods. They only living species that come close are the great whales in the sea, like the Blue Whale. How did sauropods grow so big, and why does nothing so large exist on land today? Many theories have been proposed, including some claiming that there was less gravity hundreds of millions of years ago, or that more oxygen in the air could have allowed for such large land animals. Neither of these is likely true.
To get an idea for how sauropods could achieve such gigantic sizes, you have to understand that for all the space they took up, these dinosaurs were relatively light. Which is not to say you could go pick one up with one hand, but the reality is for as big as they were, you would expect them to weigh a lot more. The reason for this lightness is that their necks were full of air sacs. Similar structures are found in birds today, to help keep them light and ensure that their blood got enough oxygen. They served the same purpose in sauropods, helping them support their long necks by keeping them lightweight. Another way sauropods got around size restrictions: small heads. Today, most large land mammals require strong jaws and large teeth to help them chew, which means their heads need to be quite large. Sauropods didn’t chew, relying on other mechanisms to break down their food, which allowed their heads to be small, meaning their necks could be larger and longer without worrying about supporting a massive noggin.
(largest living land animal)
(tallest living land animal)
(largest living animal on Earth)
Probably the most important factor in sauropod size, however, was the way they reproduced. Today, many of the largest land animals are mammals, like the Giraffe or the Elephant. These animals tend to produce only one or two large babies at a time, and care for their young long after their birth. Such an investment requires a lot of time and energy, which means there’s less energy available to grow, and to support a sauropod-sized body. Sauropods, meanwhile, laid a large number of relatively tiny eggs, and once they hatched, the babies were on their own. Without having to devote so many resources to carrying and raising their young, sauropods were less restricted in how large they could grow.
While this all may help explain how these dinosaurs got so big, it doesn’t answer the question of WHY. And this, like many other questions about the lives of dinosaurs, may never truly be answered. Though paleontologists are discovering new and exciting things about these prehistoric reptiles every day, there are some things that may always remain a mystery.
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