4/6/2023 0 Comments Are squids mammals![]() ![]() It has somewhat of a central brain as well, but the ganglia have a fair amount of autonomous control over each tentacle. Although complex and large like ours, most of the nervous tissue is clustered into bundles called ‘ganglia’ located in the tentacles rather than one large central unit like the vertebrate brain. ![]() The octopus’s nervous system, on the other hand, is quite unrecognisable from our own. Our common ancestor, the flatworm, may well have been equipped with a simple nervous system and primitive light sensors we might call ‘eyes’, but they weren’t anywhere near the complexity of either ours or the octopus. Octopuses have strong eyes for a sea creature, and the similarity between our eyeball anatomies are unlikely a result of our distant common ancestry, but rather an example of evolution independently creating the same eye design at least twice. The eyes of an octopus are surprisingly similar to our own, with the only significant difference being the location of the retina. The octopus liberated itself from the weight (and protection) of this shell but retained the tentacular limbs, the three hearts pumping blood rich in copper, and gained its own uniquely complex nervous system. The ammonite is a cephalopod from the Jurassic and Cretaceous periods, and its impressive protective shell structure is the reason it has been so well retained in the fossil record. ![]() The cephalopod branch of life, on the other hand, acquired an external shell rather than a backbone, which was eventually lost or internalised by the time octopuses and squids came into being. We humans exist out of the sea with lungs to breathe air, a spine down our back, and a central nervous system linked to a large brain. Since then, we have followed very different evolutionary paths. To illustrate just how early this was, this was 80 million years before any animal showed bilateral symmetry – the familiar body plan with a defined top and bottom, and right and left 350 million years before tetrapods – the first four legged creatures that gave rise to all birds, reptiles, mammals and amphibians – came into existence and 500 million years before the emergence of dinosaurs. This is the most recent creature that we both have a direct line of descent from – it represents the point at which we diverged down separate evolutionary pathways. ![]() The last common ancestor of us and octopuses is a flatworm that trawled the sea floor 750 million years ago. In terms of separation down the evolutionary timeline, the octopus is about as far away from humans as an animal can get. The name cephalopod indicates a species that has tentacles attached to a distinct head, Cephalo coming from the Greek for ‘head’ and pod from ‘foot’ The octopus belongs to a class of marine species called cephalopods within the Mollusca phylum, along with the likes of cuttlefish and squid. Why the film’s vision for this species is so obviously octopian is open to interpretation, but centuries of art and literature have certainly demonstrated that the octopus has always inspired our collective imaginations and it’s definitely not the first time it has been associated with alien life. A mollusc-looking seven limbed creature, with a long protruding body, and no external shell the heptapod is clearly modelled on a cephalopod. Had these species originated instead from Earth, I wouldn’t blame you for assuming them to be related to the similarly unearthly-looking octopus. In 2016, one of my favourite sci-fi films Arrival was released, and – mild spoiler alert – it presented us with an alien species named the heptapods, who challenged human perception of the universe and life. ![]()
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