Meteor hammers, maces...how many other tricks can a dinosaur's tail have?

Dinosaurs are definitely the stars of ancient creatures. As early as 1933, in the first version of King Kong, a Stegosaurus fought King Kong for 300 rounds. Although the Stegosaurus is a vegetarian, its terrifying appearance with bony plates on its back and spikes on its tail is enough to leave a deep impression on the audience.

The several bony spines at the end of the Stegosaurus' tail were powerful weapons to defend against predators. Paleontologist Kenneth Carpenter once reported that a scar of about 4×4.1 cm was found on the vertebrae fossil of Allosaurus fragilis, which was presumably caused by the tail spine of the Stegosaurus. Allosaurus was a carnivorous dinosaur with a body length of 8 to 9 meters. It can be seen that even rabbits will bite when they are angry, and vegetarian dinosaurs should not be underestimated when they explode.

The skeletons of Allosaurus and Stegosaurus are displayed together at the Denver Museum of Natural Science, showing what it would look like if the "enemies" met. | mrwynd / Wikimedia Commons

A hammer on the tail

After the extinction of Stegosaurus, another group of warriors were active in North America during the Cretaceous. Unlike the sharp-edged Stegosaurus, the Ankylosaurinae, which also belonged to the Thyreophoroidea, were more restrained. They were more like iron pagodas holding bone flowers - the fangs and claws of the bone plates were replaced by low-key nodules and plates, and the occasional protruding spines seemed much safer than Stegosaurus.

However, this seemingly harmless herbivorous "big lizard" has a dense bone tail hammer at the end of its tail. The diameter of those large tail hammers can even exceed 40 cm. Driven by the powerful tail muscles, the hammer as big as a watermelon can easily injure bones and crush internal organs. It can be said that it is a "tough guy" that predators of the same period are very afraid of.

Ankylosaur's tail was like a sledgehammer. | Ryan Somma / Wikimedia Commons

The unique images of Stegosaurus and Ankylosaur create a fantasy ancient world for us. But when we observe other animal groups, we will find that the "weaponization" of the tail is extremely rare in the entire terrestrial vertebrate group. In terms of the number of species, there are not many creatures like Stegosaurus and Ankylosaur that have exaggerated tail weapons, but the evolutionary branch they belong to includes turtles, crocodiles, and mammals (such as glyptodonts) and other categories.

Doedicurus, a glyptodont, had a spiked tail, from A history of land mammals in the western hemisphere | Wikimedia Commons

This kind of "unconventional" and "all-embracing" evolution has puzzled paleontologists and evolutionary biologists - do these strange structures have a common origin? What is the reason that these animals have such tails? What advantages do these "weapons" provide to organisms?

Both have tail weapons, but they are not relatives

In 2017, a team from the University of North Carolina tried to use systematic evolution methods and trait association methods to analyze known organisms with "weaponized" tails. In their view, the emergence of tail weapons is inseparable from the behavior and individual morphology of these animals.

Animals with bony tail weapons have no obvious kinship in the evolutionary tree. And by comparing fossil structures, we can also identify the differences in the organization and morphological characteristics of "tail weapons". For example, the tail spines of stegosaurus are independent structures connected to the end of the tail vertebrae, while the tail clubs of ankylosaurs are accompanied by the healing of the end of the tail vertebrae. The specialized structures of Meiolania and glyptodonts are wrapped outside the vertebrae. The completely different structures show that they are unlikely to come from a common ancestor and are unlikely to be controlled by a certain type of gene. They are so different that it seems that apart from looking like they can be used as weapons, they have nothing to do with "tail weapons".

Tail structure of ankylosaur | Arbour et al. / Wikimedia Commons

In addition to these species with obvious signs of "weaponization", there are some species that deserve attention. Although they do not have specialized structures, they also use their tails as weapons, such as a colorful small lizard, the rainbow flying lizard (Agama agama). They will fight for the right to mate, and the specific way of fighting is to hold down the other's body and then whip the other with a slender tail. In previous studies, large sauropods are believed to have similar defense methods. Although there are constant controversies, many scholars still believe that these "whips" can deal heavy damage to carnivorous dinosaurs.

A brightly colored male rainbow flying lizard | Bernard DUPONT / Wikimedia Commons

Among living animals, crocodiles, pangolins, Komodo dragons and even porcupines will try to attack their enemies with their tails, but only the Cordylidae have specialized bone structures like dinosaurs. The possibility of studying the evolution of "weaponized tails" directly by analyzing morphological structures is extremely slim, but researchers still try to analyze what factors are related to "weaponized" tails through the supplement of morphology and behavior.

A big guy in armor, maybe with a meteor hammer

Through morphological analysis, the researchers divided weaponized tails into four types:

The first type has no specialized structures but can attack by swinging its tail, such as the rainbow flying lizard;

The second type has a bony tail spike, such as the stegosaurus;

The third type has a hardened tail end, such as the glyptodonts;

The fourth type has an extended tail, such as ankylosaurs.

Afterwards, the researchers measured the body length, weight, tail mobility, diet, and armor of other parts of the body of these species, and conducted correlation studies based on the tails that were previously divided into four categories. They found that whether the tail is used as a weapon is related to the body length of the species (the length from the tip of the mouth to the anus is greater than one meter), the armor of the body, the flexibility of the tail, and the diet. The "weaponized" bone structure is also related to the rigid chest cavity and the "armor" of bone deposits (called osteoderms) under the dermis.

Crocodiles have bone armor | Pixabay

If a creature is large, has bony armor covering much of its body, a rigid thorax, and is a plant-eater, then it is more likely to have a weird tail weapon and use it to defend against predators.

As for why these morphological structures are related to the "weaponized" tail, this requires considering the synergy between the structure and function of the organism.

First of all, a large enough body size indicates that this type of creature may live in a relatively open environment. Such a body size makes it difficult to hide quickly, so it has the necessity of active defense. The more common intradermal bone formation in the body provides the raw materials for evolution - it is because they light up this technology tree that more complex armor and even specialized tail structures become possible. The large and rigid thorax provides a fulcrum for the rapid swinging of the tail; and herbivory is the root of all this evolutionary process - they have always faced the survival pressure brought by predators.

Meiolania platyceps fossil model with spikes on its tail | Fanny Schertzer / Wikimedia Commons

These traits also seem to hint at why the "tail weapon" defense strategy is so rare: after all, to obtain a complete and effective tail defense system, various prerequisites need to be met. It needs to be filled with armor first, and then the attack power is improved. In the fierce natural selection process, this evolutionary process is undoubtedly costly.

There are more weapons...

Although the researchers have provided an evolutionary correlation model for the "tail weapon", they have not been able to answer the possible origin of this type of trait - it seems that they were completely independently produced and are just a coincidence of nature. However, existing systematic evolutionary analysis shows that Ankylosaurs and Stegosaurus are very close in kinship and have similar evolutionary strategies.

In 2021, a study in the journal Nature announced that a new type of armored dinosaur, Stegouros elengassen, was discovered in Chile. Its genus name means the covered tail, so it is temporarily translated as "covered tail dragon."

The tail of the dinosaur is not as iconic as other large ankylosaurs, but this does not mean that it is an ordinary "early species" - its tail is more shocking than a sledgehammer, it is an "obsidian saw sword" from 74 million years ago! Seven pairs of large intradermal bone plates are neatly attached to the end of the tail vertebrae; the bone plates are flat, extending to both sides and triangular.

The tail of the dinosaur was lined with bony plates | Sergio Soto Acuña et al. / Nature (2021)

Obsidian saw sword macuahuitl made of wood and obsidian flakes | Arjuno3 / Wikimedia Commons

This new "weapon" expands the "arsenal" of tail weapons. The bone spurs of Stegosaurus, the tail club of Ankylosaur, and the "obsidian saw sword" of Diplodocus suggest that armored dinosaurs are likely to have a unique evolutionary logic in the "weaponization" of their tails.

Earlier studies on Liaoningosaurus paradoxus suggested that the tail club of ankylosaurs may have originated from the handle-shaped tail vertebrae of the Early Cretaceous 120 million years ago. However, the current view of paleontology is that the Parasaurolophus (Parankylosauria), to which Parasaurolophus paradoxus belongs, parted ways with the Euankylosauria as early as 167 million years ago. This shows that Parasaurolophus is likely to have a more complex tail evolution relationship. As creatures living on the magical land of Gondwana, they may have evolved a more complex and diverse tail structure under special environmental conditions.

The evolutionary tree of ankylosaurs and stegosaurus and their distinctive tails | Sergio Soto Acuña et al. / Nature (2021)

Perhaps with the continuous discoveries of paleontologists, in the near future, more and more "weapons" will be added to the library, and we will have the opportunity to understand more comprehensively the evolutionary patterns of colorful tail weapons.

Author: Broken Sunny

Editor: pee pee shrimp

This article comes from the Species Calendar, welcome to forward

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