For these dragons, having a tail that's too big is also a problem...

When it comes to the largest animal on land today, people must think of elephants. An adult African male elephant weighs 7-10 tons, is 8 meters long, and can be up to 4 meters tall. However, in the long history of the earth, elephants are not the largest animals that have appeared on land. Compared with sauropod dinosaurs, their size is dwarfed. Sauropod dinosaurs were the largest animals walking on land 66 million years ago. They could be up to 40 meters long and weigh up to 70 tons. Such a behemoth not only eclipses mammals on land, but can even compete with the giant beast in the ocean today - the blue whale (Figure 1).

Figure 1. Size comparison of elephants, sauropods (Diplodocus fragilis), blue whales, and humans

Image source: Reference 1

Sauropod dinosaurs are a huge family, which can be divided into two orders and multiple families according to taxonomy. They were once distributed all over the world. Their common characteristics are small heads, long necks, large nostrils, leaf-shaped teeth, femurs longer than tibias, quadrupedal walking, and they are all vegetarians. It is difficult to rank the members of their family by size. Because these huge dinosaurs have evolved their bones into porous, hollow or thin-walled states in order to reduce weight and make their movements lighter. Such bones are easily broken under long geological effects. Therefore, 95% of the sauropod dinosaurs discovered so far are broken and incomplete. Many times, people can only speculate the huge bodies of their owners through a few huge fossil bones (Figure 2). Today, this ranking list has been controversial and changing. Argentinosaurus, Diplodocus, Titanosaurus, etc. are all strong competitors for this ranking list.

Figure 2. Sauropod dinosaur skeleton fossils discovered by paleontologists Image source: Reference 2

Another important feature of these giant dinosaurs is their large and long tails, which can be more than 14 meters long. Their tails are also the largest tails on the planet. This giant tail can play many roles in the life of sauropod dinosaurs, such as keeping the body balanced during movement, helping the hind legs to support the body when the front legs are raised and the hind legs stand to forage for high plants, defending themselves when predators approach, and fighting when the same sex competes for mates. However, researchers have found that the "capable" giant tail also has a fragile side.

Recently, researchers discovered two Titanosaur tail vertebrae fossils in Argentina, which is not surprising (Figure 3). Because Argentina is located in South America, where there were once a large number of sauropod dinosaurs, so giant dinosaur fossils are often found here, such as the famous Argentinosaur. However, what is interesting is that researchers also found pathological characteristics on these two fossils.

Figure 3. Two Titanosaur tail vertebrae fossils discovered by researchers and the tail parts where they are located

Image source: Reference 3

Thanks to the application of modern medical diagnostic theories and technologies to paleontological research, people can "diagnose" prehistoric creatures and infer their living conditions, behavioral characteristics and surrounding environment by analyzing their health conditions. For the two tail vertebrae fossils, the researchers first conducted an external surface morphology analysis and found that the tail vertebra 1 belongs to the front part of the tail, and some areas have pits suspected to be caused by infection. The tail vertebra 2 belongs to the middle part of the tail, and there are also pits suspected to be caused by infection. The possibility of fractures of the two tail vertebrae was then ruled out through computer tomography (CT) scanning technology (Figure 4).

Combined with pathological analysis, the researchers determined that the owner of coccyx 1 had a suppurative infection, and the owner of coccyx 2 had spondyloarthritis, the latter being a chronic aseptic inflammation. We will call the owners of coccyx 1 and 2 Dragon No. 1 and Dragon No. 2, respectively. Based on the research materials, it can be inferred that Dragon No. 1 suffered a trauma in the middle of its tail during a fight with a predator or a companion, and the wound became infected and suppurated, affecting the iliocervical muscles. What's worse, this diseased tail restricted its movements, making it unable to escape or resist the attack of predators, and it may have died in the end.

Dragon No. 2 was much luckier. Although it had spinal arthritis in its tail, the disease affected only the longus femoris muscle of the caudal calvaria, which did not restrict its movement. It did not even feel pain until modern pathological analysis detected its "minor ailment".

Figure 4. Researchers performed CT scans on two tail vertebrae fossils Reference 3

The researchers also counted the reports of injuries or disease symptoms detected in the tail fossils of existing sauropod dinosaurs, and found that the largest number of cases were in Titanosaurs. It seems that for these giant dragons, the big tail also has troubles.

References:

1.2020 Giant Sauropod Dinosaur Ranking (Final Edition), Science Park, Author: Microraptor

2. 37-meter dinosaur fossil! The herbivorous Titanosaur is the same length as 4 double-decker buses, Baidu Encyclopedia, TA said, scientific exploration

3. Cruzado-Caballero P, Filippi LS, González-Dionis J, et al. How common are lesions on the tails of sauropods? Two new pathologies in titanosaurs from the late cretaceous of argentine patagonia[J]. Diversity, 2023, 15(3): 464.

4. Qian Maiping, Hu Baixiang, Zhan Gengshen, et al. Study on large sauropod dinosaurs[J]. Geological Journal, 2010, 34(04): 337-350.