User:KibbyCake/sandbox

The cephalopod family includes squid, octopi and cuttlefish but they also have a distant relative known as the Nautilus. Nautilus are living fossils and existed in the late Cambrian era, although there are still some species left to this day and the more common cephalopods we see today all descended from ancient shelled ancestors that weren’t too different from the nautilus.

Over half a billion years ago the cephalopod family tree branched away from ours. This happened before trees had evolved. Even though they developed independently they still, unlike their Mollusc cousins, evolved with intellectual feats similar to mammals, although they did it their own way. They even developed eyes independently and they have three brains and blue blood. Their limbs are highly modified mollusc feet and you can find a molluscum foot at the bottom of most molluscs. The word cephalopod means “head feet” in Greek and notions towards the fact that their limbs both surround their mouths/beaks and are attached to their heads. Many scientists believe that cephalopods are related to a group of molluscs that are not too different from the Limpet. The family is called Monoplacophora but the species is called Knightoconus. They are ancestors of squids and share features with the earliest confirmed cephalopod that we know of called Plectronoceras that existed 480 million years ago in the early Ordovician period. This would make cephalopods highly evolved limpet like animals. The only problem with this theory is that there is another stranger and much older animal known as Nectocaris that might have been the earliest known cephalopod. The nectocaris had two tentacles and no shell. If the nectocaris was the first cephalopod then the current ones may not have inherited their hard coverings from their shelled foreign ancestors and these shells would then have been a later innovation, although many scientists doubt that nectocaris was a cephalopod, and more fossils will need to be tested to know for sure.

Hidden inside the shell of the plectronoceras was one of the most useful pieces of equipment that the early cephalopods had at their disposal, known as a Siphuncle. A siphuncle is a little tube that pierces through all chambers found in a cephalopod shell. The creature can flood this tube with salty blood which then dehydrates the chambers leaving them filled with gas. This protective shell can therefore be used as a flotation device and can accurately control buoyancy in the water. Nautilus still uses its shell as a flotation device to this day.

During the Ordovician period, 440 - 480 million years ago, the population of cephalopods exploded and they were one of the most common animals around at that time period. Their shells gave them protection from predators and their ability to float would’ve allowed them to seek food more easily. They had very advanced features not seen before and were some of the first animals to develop circulatory systems but instead of red blood like vertebrates they have blood that is bright blue. The reason for this is that while most vertebrates rely on iron rich hemoglobin to transport oxygen through their body, cephalopods rely on a copper based substance called hemocyanin and because this substance is copper based it turns blue when it oxidizes. Despite their very different starting point their circulatory and respiratory system is unique among relatives like the horseshoe crab and mirrors the vertebrates. This also gave them an edge over their mollusc cousins and they were often seen at the top of the food chain. Ancient relatives of theirs called Cameroceras are thought to have been about the same length as a great white shark and were among some of the first larger animals.

Among new coned nautilus there were some nautilus that had started to evolve coiled shells and this gave them multiple advantages. This was not isolated to only cephalopods either as some molluscs also started to develop the coileds shells. This adaptation gave them many advantages as it took less resources since the chambers overlapped and shared walls, it was easier to withstand pressure as it was evenly distributed leaving no weak spots and they were also more stable in the water as their center of gravity was closer to the center of their body.

About 400 million years ago a new group of coiled cephalopods started to evolve and they are called Coleoides. Most current cephalopods are included in the coleoide family and it includes cuttlefish, squid and octopi but unlike their ancestors they don’t have shells. Cuttlefish have a chambered shell and a siphuncle hidden under their skin. Squid have a small hard part inside them that is a leftover from when they had a shell. This old shell is now vestigial and is no longer used to control buoyancy. Octopi are quite different from the other two as they have lost their shells entirely.

The earliest coleoides known were called Belemnoids and lived in the Devonian period 400 million years ago. These animals looked like squids but were more closely related to cuttlefish as they had a similar internal shell.

During the Devonian period there were some cephalopods that were forced into deeper waters to avoid competition from some fish. When they were that deep under water their shells were at risk of cracking or breaking which caused them to lose their shells so that they could colonize this new and deep habitat.