How the ammonite is bent step by step

Ammonite is the general name of Ammonoidea, a subclass of ammonites of the phylum Cephalopoda, molluscs, which is a kind of extinct marine life. They rose from the early Devonian, experienced many mass extinction events, and finally withdrew from the natural stage with dinosaurs at the end of the Cretaceous. These creatures, which once dominated the Paleozoic and Mesozoic oceans for more than 300 million years, can only be seen from the remaining fossils.

Ammonite fossils. Picture: Takkk / wikimedia

Ammonites, coming from myths and legends

For ammonites, today's non-professionals do not necessarily know too many detailed concepts, after all, it has been extinct for 65 million years. For the ancient people with larger brains, it is impossible to give a reasonable explanation for all kinds of ammonite fossils that appear in the strata. Over time, the ammonite is covered with a magical color.

In Egypt there was a god called Ammon, and the Greeks called it Zeus Ammon. He had goat-like horns on his head. Europe is very rich in Mesozoic ammonite fossils. People found that the ammonites excavated are very similar to the horns on the head of Ammon. They thought that the ammonites here were probably made by the horns on the head of God Ammon, so they named these stones after God Ammon. This is the origin of the name Ammonoidea of ammonite subclass.

The god Ammon with sheep's horn. Picture: Dan Mihai Pitea / wikimedia

Walk into an ammonite

Putting aside the bonus of mythology, let's seriously go into the heart of ammonite and understand the life of this elder. Ammonites have a variety of shells, no matter what the shape, they will go through the process from small to large. The original shell of the small ammonite is called the original shell, and as the ammonite grows, the internal software continues to secrete new shell walls and horizontal walls to the back.

The life cycle of ammonites. Picture: De Baets.et al./Paleontology Online (2016)

The shell space next door is divided into many small rooms, and the ammonite software only lives in the outermost room, which is called the living room. And many small rooms inside are called air chambers. The air chamber can be filled with gas and water to control the ups and downs of ammonites. Scientists have calculated that if there is only gas in the chamber, the ammonite will float on the sea surface. If 20% volume of sea water is loaded in the air chamber, the ammonite can be suspended in the sea like a submarine.

You can see the air chambers one by one. Picture: John Alan Elson / wikipedia

The exquisite embellishment of sutures

When you think of ammonites, the impression in your mind may still be the appearance of their close relative Nautilus, and it is generally difficult to tell the specific difference between them and Nautilus. Indeed, some ammonites, like Nautilus, have conical (fossil), angular (fossil) or spiral shells, and separate chambers inside the shell. Just looking at the shape, it seems difficult to tell them apart.

Palau Nautilus Nautilus belauensis. Picture: Profberger / wikipedia

The key to distinguish between ammonite and Nautilus is the suture. As mentioned earlier, there are many air chambers in the shells of ammonites and Nautilus, which are separated by the next door. The thread that comes into contact with the inner surface of the shell next door is the suture, which is a feature of the interior of the shell, which can only be observed when the shell skin is peeled off. Compared with the sutures of Nautilus, the sutures of ammonites are generally more complex and gorgeous.

The section of Nautilus (left) and the section and outer surface of ammonite fossils (right). Photo: Chris 73 countries Ra "ike / wikimedia"

However, the sutures of ammonites are not so exquisite and complex from the very beginning. If we put the ammonites of different periods together, we may find the law of evolution-the early ammonites sutures are relatively simple, and the sutures become more complex as time goes by. In the long history of evolution, more complex sutures increase the strength of the ammonite shell, adding an important weight for the ammonite to survive in the sea.

Goniatite species of the order Gymnoliformes that appeared in the early Devonian. Picture: Ghedoghedo / wikimedia

Dentate ammonite Ceratitic from late Permian to Triassic. Picture: Drow_male / wikimedia

Cretaceous Cleon ammonite Cleoniceras. Picture: Drow_male / wikimedia

As a creature that has dominated the ocean for more than 300 million years and has preserved its strength in several mass extinction events, their trick is more than simply increasing the complexity of sutures. Along with the evolution is the shape of their shells.

According to the current research, the ammonite subclass evolved from the Nautilus subclass. In the process of continuous evolution, the shape of their shells is also changing. If you can go back to the time when Nautilus appeared and watch their evolution along the way, you should be able to see how their shells are "bent" step by step.

With the succession of ammonite shell shape, the shell is curled step by step. a. Lobobactrites, Bmerc, Cyrtobactrites Dmurf Anetoceras (Anetoceras), Gmurh Anetoceras (Erbenoceras). Picture: palaeos.com

Being "bent" can be exchanged for the benefit of moving speed. Research shows that with the increase of the degree of shell hovering, the swimming speed is also increasing.

The true face of ammonite

The fossils of ammonite shells are widely distributed, and a large number of ammonite fossils have been found all over the world, but their tissue samples are very few. As a result, scientists have to restore ammonites based on the structure of their shell fossils and with reference to the appearance of modern nautilus. The restored ammonites have the iconic wrists, horny beaks and funnels of cephalopods. The restored form is between Nautilus and modern octopus. As to whether this is really the case, I am afraid we have to ask the dinosaurs.

Tentative reconstruction of soft tissue of Jurassic ammonite fossils. Picture: Dzik, J / Acta Palaeontologica Polonica (1981)

A restoration of a kind of ammonite. Picture: Nobu Tamura / wikipedia

The widely distributed and considerable amount of ammonites is not only a treasure pursued by all kinds of paleontologists, but also a right-hand man for geologists.

By calculating the strength of the ammonite shell structure, geologists can calculate the depth of water where the fossils were found. In addition, because of its fast evolution rate and short individual life, ammonites exist in many marine sedimentary rocks, relatively common, easy to identify and worldwide distribution, so they can be used for accurate geological dating and can distinguish geological time intervals of less than 500000 years.

The largest ammonite Parapuzosia seppenradensis is expected to reach 2.55m in diameter. Picture: Gunnar Ries / wikimedia

Ammonites have been gone for 65 million years, but the fossils of these former marine creatures still show us the way they have traveled and tell stories of vicissitudes.

This is the 227 article in the fourth year of the species Calendar, from the author of the species Calendar @ Sundayhao.