The Age of Ammonites: Curse of the Golden Flower | Paleontological Rhapsody

Author: Wang Guanqun, Pan Haochen, Fang Xiang, Liu Yun, Tan Chao (Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences)

The article comes from the Science Academy official account (ID: kexuedayuan)

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In the last issue, we talked about the glory of the heavy cavalry Nautiloids in the Ordovician period (click here if you missed it!), which gave cephalopods their first golden age. However, just as the armored cavalry was eventually eliminated due to its clumsiness and high cost, the "iron pagoda" Nautiloids also gradually declined in the face of the mass extinction in the late Ordovician period and the vertebrates that evolved jaws in the Silurian period. However, cephalopods did not give up. They continued to improve themselves, just like the Mongolian cavalry, the final form of cavalry in history, and created the last glory of armored warriors before the advent of the firearms era.

Named after the chrysanthemum, ammonites, which were born in the Devonian period, a paradise for fish, would launch a desperate challenge to the newly emerged dominant vertebrates in the following 300 million years. The ocean world at that time would surely be "full of armor of gold".

In war, armor is the best

Ammonites were born in the Devonian period. This new star of cephalopods improved the armor of the ancestors of the Nautilus, which was no longer mainly straight pagoda-shaped, but curled and spiraled, which maximized their flexibility during swimming. At the same time, the septa began to curl and deform, which gave the ammonites extremely complex and beautiful sutures. In the late period, the complexity of the sutures even required the use of a magnifying glass to see clearly (Figure 1). The sutures of ammonites are also divided into goniatitic, ceratitic and ammonitic types according to their shapes (Figure 2). This is a major fossil feature that classifies ammonites and distinguishes them from other cephalopods.

Figure 1 Beautiful ammonite suture

(Photo source: Tianmu Geoscience, Shan Huachun)

Figure 2 Changes in the ammonite suture line

(Photo source: Hui Shifan Museum, University of Hong Kong)

This complex and unusual wall structure makes the armor of ammonites more resistant to pressure. In addition to being able to resist threats from natural enemies, it can also withstand greater water pressure. At the same time, the complex folds of the wall allow the soft part of the ammonite to be more closely combined with the hard part of the wall, thereby improving its own stability. These targeted changes have improved the flexibility and pressure resistance of ammonites. Like the Mongolian cavalry in history, the flexibility of the cavalry was maximized, and the iron can knights of Europe at the same time were pressed to the ground and rubbed continuously, and the Jin Dynasty, which once had the Iron Pagoda, was completely helpless.

Restoration of the ammonite (Photo credit: Nobu Tamura)

In addition to the changes in shape, ammonites also further thicken the surface of their shells. Some species thicken and coarsen the growth lines to form growth ribs, which look like blooming chrysanthemums (Figure 3), hence the name ammonites. Some species grow thorns and tumors on their shells (Figure 4), which makes them look even more powerful and weird. There are even beautiful and colorful amphibole shells (Figure 5). Due to the structural color of aragonite on the surface of its shell, amphibole ammonites are recognized as gemstones by the International Jewelry Federation.

Figure 3: Ammonites that resemble chrysanthemums

(Photo source: Tianmu Geoscience, Shan Huachun)

Figure 4: The thorny ammonite Crioceratites nolani

(Image source: Wikimedia: Author Teresa Martin)

Figure 5: The guard of honor in the ammonite

(Photo source: taken by the author)

The changes in the shells of ammonites are a bit like the leather armor craftsmanship in Chinese history. A thick layer of lacquer was applied on the finished leather armor, which not only enhanced the defense capability, but also prevented corrosion and made it beautiful. Therefore, the scenes of ancient armies fighting were mostly black and red seas of people. (Although the lacquer was milky white at first, it would darken to chestnut color after oxidation, and it would not be obvious after adding other pigments, so red and black were the mainstream colors of lacquerware and leather armor, Figure 6). If we go back to the oceans of the Mesozoic Era, we might see the most gorgeous colorful guard of honor of the ammonite army patrolling the sea with shining lights.

Figure 6 Top: Leather armor unearthed from Zenghouyi’s tomb (Source: see watermark)

Below: Colored Terracotta Warriors and Horses of Emperor Qin Shi Huang (Source: Official website of the Qin Shi Huang Mausoleum Museum)

Stand up where you fell

After vertebrates acquired jaws, they began to suppress the heavily armored forces of mollusks and arthropods. Under heavy pressure, many groups could only turn to open up a second battlefield. For example, arthropods, which once dominated the Cambrian period, successfully followed the plants to land and were even the first to rule the sky. The good brothers of cephalopods, gastropods (the closest relatives to cephalopods among mollusks) also landed and established their own army. Although vertebrates later chased after them and killed many people on land and in the air, that is another story.

However, this escapist spirit of lying down wherever you fall does not seem to affect our cephalopods at all. They are determined to fight vertebrates to the end in the ocean. This idea of ​​​​deepening naval warfare has created the cephalopods' indomitable demonic spirit.

With new armor, ammonites gradually replaced their ancestors, the nautilus, and joined the ocean war. With more flexible skills and changeable armor, ammonites were no longer heavy cavalry iron lumps waiting to die, but light cavalry that came and went like the wind and had certain defensive power. Just like the Mongolian cavalry's Great Leap Forward conquest war, ammonites soon began to occupy a large area of ​​ocean space and experienced the first golden age in the late Paleozoic (Devonian to Permian). They are huge in number and evolve very quickly, so they are often used to compare strata.

The rise of ammonites soon attracted the attention of vertebrates. Some vertebrates specialized their jaws and developed super "can openers" such as Helicoprion (Figure 7). However, this did not make ammonites retreat. Instead, they became more and more courageous. Until the end of the Permian period, the largest extinction in the entire geological era occurred, with a loss of more than 95% of marine species. The biological world was ruthlessly cleansed by Mother Earth, and ammonites were no exception. The first golden age of ammonites ended, and with the decline of ammonites, those specialized can openers also went extinct.

Figure 7 Top: The can opener of the ocean, Helicoprion

(Photo source: prehistoric-wildlife.com)

Below: Helicoprion pulled out the ammonite meat by opening and closing its teeth

(Image source: Ramsay et al., 2014)

Heroes emerge in troubled times, while fools are more common in prosperous times

Do you think the story ends here? No, ammonites let us know what "a centipede is still alive even after death" means. In the early Triassic period after the Great Cleansing, when nature had not yet fully recovered, ammonites began to appear in the strata of the Early Triassic, becoming one of the earliest marine organisms to recover along with bivalves.

In the following Mesozoic Era, although everyone is familiar with vertebrates, dinosaurs and pterosaurs were thriving on land and in the sky, and monsters were rampant in the ocean. Ichthyosaurs, plesiosaurs, and mosasaurs were rampant in the sea. However, ammonites continued to flourish in the ocean since their resurgence, and they were not at a disadvantage in the face of huge vertebrates throughout the Mesozoic Era.

Ammonites, with their beautiful armor, truly achieved the goal of "covering the whole city with golden armor". Their prosperity also gave the Mesozoic Era the nickname "Ammonite Age" in addition to the "Dinosaur Age" (Figure 8). However, the comfortable and prosperous era made ammonites a little arrogant, and some non-mainstream ammonites began to let themselves go in appearance, growing wildly and even forming a shape of fang (which is a bit weird, Figure 9).

Figure 8 Sea of ​​Ammonites (Source: cluelessconscience.com copyright: Robbie Sidhu)

Figure 9 Heteromorph ammonite, which is twisted into a flying shape, is preserved in the Houston Museum of Natural Science

(Image source: Wikipedia-Daderot)

Everything was still so familiar. The proud ammonite encountered another great cleansing of nature. This time, it was not so lucky and sank completely into the dark seabed. The ammonite dynasty and the dinosaur dynasty were ruthlessly buried by the irresistible force of nature.

However, in the desolate ocean after being tortured by meteorite impacts and volcanic eruptions, the last pride of the Cephalopod Empire, the octopithecus, are looking at the recovering world with their bright eyes. The armor-free era is coming. See you next time when the dragon takes off its armor!

References:

[1] Jason B. Ramsay, Cheryl D. Wilga, Leif Tapanila, et al., 2014. Eating with a Saw for a Jaw: Functional Morphology of the Jaws and Tooth-Whorl in Helicoprion davisii. JOURNAL OF MORPHOLOGY 00, 1–18.

[2] Shu-zhong Shen, Samuel A. Bowring, The end-Permian mass extinction: a still unexplained catastrophe, National Science Review, Volume 1, Issue 4, December 2014, Pages 492-495, https://doi.org/10.1093/nsr/nwu047

[3] Xu Hankui. Biological evolution from the rise and fall of cephalopods, 2015. Biological Evolution. (4): 33-40.