Carboniferous Crinoids Provide Evidence of Oldest Biomolecules Directly Isolated from Fossil Material
Study into 350 Million Year Old Echinoderms Reveals Presence of Biomolecules
America some 350 million years ago looked very different than it does today. For starters, much of the land mass which we now know as the United States formed part of a super-continent called Laurentia, but a considerable portion of the USA was covered by a warm, shallow tropical sea. Scientists from Ohio State University have been studying an unusual phenomena associated with Crinoid fossils from strata deposited in an ancient marine environment in the American Midwest and their research reveals that complex organic molecules may have been preserved. It had been thought that organic molecules could not survive the fossilisation process and remain present in fossil material after immense periods of time, but a number of recent studies using the most sophisticated analysis techniques ever to be employed in palaeontology are challenging this assumption.
Crinoid fossils preserved in rocks from the American Midwest (specifically Indiana, Ohio and Iowa), the remains of animals that lived during the Mississippian Epoch (Carboniferous), can be preserved in different colours depending on the species. Different species of Crinoid, preserved in the same matrix, the same fossil slab, can be blueish grey, creamy white or even dark grey when observed under natural light. Scientists had commented on this bizarre phenomenon over a hundred years ago, the fact that the Crinoid fossils found in some parts of the Midwest seemed to be colour coded, but it took a team of geologists and scientists from the Ohio State University to get to the bottom of this mystery.
An Example of the Different Coloured Crinoid Fossils Used in this Study
Picture Credit: Professor William Ausich, courtesy of Ohio State University.
Crinoids are members of the ancient Phylum known as Echinodermata (Echinoderms) – starfish, brittle stars, sea urchins and crinoids (sea-lilies). Their fossil record dates back to the Cambrian. Crinoids are often referred to as sea-lilies, as they superficially look like plants. The fossil record for Crinoids dates back to the Early Ordovician and there are a number of genera living today, including forms with stems that live attached to the sea-bed filling an ecological niche once filled by the Carboniferous Crinoids.
Most prehistoric Crinoids were attached to the sea-bed by a stem or a stalk, with a root-like holdfast at the bottom. The mouth and the digestive tract was located in an enclosed cup at the top of the stem. A series of feathery appendages which were covered in tiny, thin plates (pinnules) acted as a food gathering mechanism. The sea current brought particles of food which were caught by the pinnules on the arm-like appendages and these food items were than wafted into the mouth. The hard parts of the animal were formed of calcium carbonate (calcite), extracted from the surrounding sea water. This calcite was porous and a thin skin of living tissue covered these hard parts. Calcite is often very well preserved in the fossil record and the calcite plates that make up the flexible stem of these sea creatures are common fossils in Palaeozoic and Mesozoic aged marine, sedimentary deposits.
A series of dramatic storms seem to have devastated the sea-bed where vast colonies of these sea-lilies thrived. The sea-floor became choked in finely grained mud. Once these Crinoids were buried they were no longer able to feed and vast numbers of them were wiped out. Being rapidly buried, quickly isolated from scavengers and oxygen to speed up the degradation process the calcite skeletons were preserved in beautiful detail, many of which remain articulated. The porous calcium carbonate elements of the animal gradually became filled with minerals and preserved as fossils, however it seems that some of the pores that once contained living tissue were sealed so completely that traces of the molecules that made up the living tissue of the organism may have been preserved.
A Palaeozoic Marine Environment (Wemlock/Silurian)
Picture Credit: Open University
The University based research team were able to extract organic molecules from the individual sea-lily fossils. They discovered that different species contained different organic molecules. Some of these ancient sea creatures, that had died during these storm events, although they lay next to other species of Crinoid and had become preserved in the same slab of sedimentary rock: the different species were preserved in different colours – the greys, creams and blue-greys.
The organic molecules, referred to as biomarkers were extracted using a gas chromatograph mass spectrometer. Tiny samples were taken from the individual fossils, these were then dissolved into a solution. This liquid and its contents was analysed by the gas chromatograph mass spectrometer and individual molecules were identified based on their mass and their electric charge. A computer programme was used to sort the data and to find a match in living Crinoid species for the organic molecules recovered. The software identified these biomarkers as being similar to quinones found in Echinodermata. These quinones are aromatic, organic compounds that are found in a number of organisms, they are associated with pigmentation (the colour of an animal) or in the production of toxins and other unpalatable substances that deter predators from attacking.
Professor William Ausich, of the School of Earth Sciences (Ohio State University) and a co-author of the academic paper that has just been published in the scientific journal “Geology” stated:
“There are lots of fragmented biological molecules—we call them biomarkers—scattered in the rock everywhere. They’re the remains of ancient plant and animal life, all broken up and mixed together. But this is the oldest example where anyone has found biomarkers inside a particular complete fossil. We can say with confidence that these organic molecules came from the individual animals whose remains we tested.”
Christina O’Malley in conjunction with the Ohio State geochemist Yu-Ping Chin, confirmed that the quinone-like molecules occur in fossil Crinoids as well as in their extant descendants. Although different coloured fossils do contain different quinones, the research team stressed that there was no definitive evidence to suggest that the preserved molecules were directly associated with the extinct creatures colouration.
The researchers hope to be able to extract more organic material from the fossils in a bid to find out as much as they can about each individual species.
Explaining that these molecules did not represent genetic material such as DNA, Professor Ausich commented:
“We suspect that there’s some kind of biological signal there, we just need to figure out how specific it is before we can use it as a means to track different species.”
It is truly astonishing that these gregarious, benthic (living on the sea-floor), animals from the Palaeozoic can reveal traces of organic compounds when their fossilised remains are analysed.