There are too many evolutionary branches of the mollusk phylum.
The teeth are the most snails of all animals; a sea cucumber with a rectum; an octopus with a super high IQ and loves to beat fish; a graceful sea slug; an Antarctic middle-clawed squid that can reach an overall length of up to 13 meters... Whatever, mollusks want to get a kick. (Antarctic mid-clawed squid I have written before, interested friends can flip forward)
Today's conventional routes, we will not talk about, let's talk about the extinct ammonite subclass.
Ammonite survived from the Middle Ordovician to the Late Cretaceous, a large meteorite that shut down and restarted the Earth. Before this accident, the Ammonite family had been thriving, and the number of races and the abundance of species were enormous. In the Paleozoic, ammonites occupied an intermediate ecological niche, and the number of fossils was much higher than that of the radiated fin fish of the same period by more than 30 times.
Now in a treasure search for fossils, ammonite and trilobite fossils are still outrageous, as if they will not be sold out before the next mass extinction of the earth.
Such a huge population and abundant number naturally breed many strange things. Although it is not as confusing as the "Tully Monster", the members of the ammonite family are also casual enough about their appearance.
(Noster ammonaceae.) Image source: DeviantArt)
Just in November 2020, CNET reported on a new study of an ammonite species by Professor Linda Ivany and researcher Emily Artruc of Syracuse University in New York, which is diplomoceras maximum.
(There is no mistake with this paper clip in the picture above)
The largest double ammonite is up to 1.5 m long, and like the extant cephalopods, it has a lot of soft tentacles, and the front end is not much different from the squid, but it has a calcareous hard shell shaped like a paper clip on its back. To interject here, ammonites and hornstones and nautilus, although they look similar and belong to cephalopods, belong to different suborders, and the relationship is not as close as imagined.
The growth and development process of ammonite can be divided into four stages, and normal ammonite is such a superposition of one spin and one spin.
The largest double ammonites also follow this law, but their shape is really unique. At first, it was all spiraled, but when the ordinary ammonite began to superimpose and spiral, its shell began to elongate in a daze, and it was not until more than 10 years later that the second rotation began. Until it becomes a complete body, the largest double ammonite has to go through about 200 years! It should be known that the surviving cephalopods are all shelled nautilus with a lifespan of about 20 years; squid and octopus, their average lifespan is only 5 years.
The inference of its lifetime is well founded. When the researchers examined the snail shell, they found that there were layers of lines on the surface of the snail shell, and after detecting the carbon and oxygen isotopes, they found that there were repeated patterns in the isotope signal, indicating that the formation conditions of these lines are regular!
The largest ammonite is living in the Antarctic, when they prey on the deep sea cold spring methane microorganisms as food, will absorb the methane into carbon preservation in the shell, and these carbon is metabolic, about a year can form a layer of grain, so you can relatively accurately know the life of the largest double ammonite, and the time of spiral rotation.
So why did the largest double ammonite develop such a unique shell? It is not known, but the number of ammonites with a specific shell is not small, and if you find common ground between them, it may be the key to solving this problem.
Because there are many unknowns, every new discovery in the paleobiome inspires the scientific community. While thanking the paleontologists, I also want to pray for their hair volume, hoping that the spell of "less hair, the greater the knowledge" can be broken.
References:
1-Gate Fengqi Zhao Xianglin. Introduction to Paleontology (2nd Edition): Geological Publishing House, 1993
2-Hauschke N , Sch? Llmann L , Keupp H . Oriented attachment of a stalked cirripede on an orthoconic heteromorph ammonite – implications for the swimming position of the latter[J]. Neues Jahrbuch Für Geologie Und Palontologie Abhandlungen, 2011, 262(2):199-212.
3-Masukawa, G., & Ando, H. (2018). Late Campanian–early Maastrichtian heteromorph-dominated ammonoid assemblages of the Nakaminato Group, central Honshu, Japan: biostratigraphic and paleontological implications. Cretaceous Research, 91, 362–381. doi:10.1016/j.cretres.2018.06.018
4-Remin Z, Machalski M, Jagt J W M. The stratigraphically earliest record of Diplomoceras cylindraceum (heteromorph ammonite)–implications for Campanian/Maastrichtian boundary definition[J]. Geological Quarterly, 2015, 59(4): 843-848, doi: 10.7306/gq. 1253.
5-Genya M , Hisao A . Late Campanian–early Maastrichtian heteromorph-dominated ammonoid assemblages of the Nakaminato Group, central Honshu, Japan: biostratigraphic and paleontological implications[J]. Cretaceous Research, 2018, 91:362-381.