Rare Fossil Octopuses show Traits of Modern Cephalopods
Perhaps amongst all the animals to be found in the fossil record it is those members of the order Mollusca that assist palaeontologists the most when it comes to biostratigraphic dating. Biostratigraphic dating is the process by which rock strata can be dated in relation to other depositional layers by finding characteristic fossils within the sediment of a particular part of the strata. The rapidly evolving and numerous marine mollusc fossils such as the cephalopods ammonites and belemnites are particularly helpful. The Mollusca phylum is very diverse. It consists of shelled and unshelled forms, everything from bivalves such as cockles and mussels to the gastropods (slugs and snails) to the cephalopods squid, cuttlefish and the octopus. Scientists could argue that the Mollusca are perhaps numerically the most abundant large invertebrates in the fossil record. However, there is a problem with the Molluscan fossil record. Only very rarely are the soft bodied molluscs preserved; so the fossil record of this particular phylum is extremely biased towards the shelled forms. As a result, the evolution of this group is hotly debated, although most palaeontologists agree that the first shelled molluscs appeared in the Cambrian. Whether or not Mollusca is represented in the Cryptozoic (Precambrian) is controversial.
Recently, some light was shed on the evolution and development of soft bodied cephalopods with the discovery of some extremely well preserved fossil octopuses that date back to the Late Cretaceous (Cenemanian faunal stage). Such fossils are extremely rare, but this discovery indicates that Mesozoic octopuses were very similar to the extant relatives today, with ink sacs and suckers on their arms. The octopus lacks a hard external or internal skeleton, the body is composed almost entirely of muscle and skin. A dead octopus is either quickly eaten by scavengers or decays rapidly to leave no body fossil.
The result is that preservation of an octopus in the fossil record is an exceptionally rare event, so rare in fact that of the 300 or so species of octopi alive today, none have ever been found in the fossil record.
In the January edition of the scientific journal Palaeontology, Dirk Fuchs and his colleagues of the Freie University (Berlin) report on the discovery of three new species of prehistoric octopi in a study from five beautifully preserved specimens from Lebanon. The fossils have been dated to around 95 million years ago and show the animals in remarkable detail. Even traces of ink sacs and internal gills are present in some of the preserved specimens. The three new species have been named Styletoctopus annae, Keuppia hyperbolaris and Keuppia levante.
Pictures show a fossilised octopus classified as the new species Keuppia levante. The head is towards the left of the picture with traces of all eight tentacles pointing towards the right of the images. The strange purple and pink colours seen in the picture are not the actual colour of the fossil or the rock in which it is found, the picture has been taken when the fossil was under fluorescent light. Studying fossils of delicate creatures under ultraviolet and infrared light can show details that are hidden to the naked eye under natural or white light. Fine structures can be made out, this is also a technique used to check on the level of restoration found on a particular specimen. Materials used in restoration such as cement and putty, don’t bounce light back under fluorescent conditions, these parts of the fossil appear darker.
Commenting on these finds, Dirk Fuchs stated:
“The luck was that the corpse landed untouched on the sea floor. The sea floor was free of oxygen and therefore free of scavengers. Both the anoxy [absence of oxygen] and a rapid sedimentation rate prevented decay.”
Prior to these discoveries, only a single fossil species of octopus was known. The ancient octopi look remarkable similar to modern species and put back the evolution of extant forms of cephalopod by several million years. Similar animals to the octopuses that you see today in an aquarium would have lived in the sea alongside ichthyosaurs, marine crocodiles and plesiosaurs.
This provides important evolutionary information, revealing much earlier origins of modern octopuses and their characteristic eight-legged body-plan, according to the researchers.
“The more primitive relatives of octopuses had fleshy fins along their bodies. The new fossils are so well preserved that they show, like living octopus, that they didn’t have these structures,” Fuchs added.