Latest news with #RegSprigg
Forbes
14-04-2025
- Science
- Forbes
In 2018, Dickinsonia Was Classified As The Oldest Known Animal — A Biologist Explains
Here's why Dickinsonia challenges our previously held beliefs and changes how we view evolutionary ... More history. For the longest time, it was believed all complex animal life could be traced to the Cambrian explosion that occurred over 500 million years ago. However, the discovery of Dickinsonia, a now-iconic member of the Ediacaran biota and possibly the oldest macroscopic animal fossil recorded to date, challenges these notions and our understanding of evolution on Earth. Living approximately 558 million years ago — well before the rapid diversification of animal body plans in the Cambrian — Dickinsonia raised fundamental questions about growth, movement and the evolution of early developmental strategies. Its fossilized imprints challenged conventional narratives on the origin of complex life and provided direct clues about early animal physiology and ecology. Furthermore, the 2018 discovery of distinctive molecular signatures in fossils, particularly cholesterol derivatives, has transformed our view of these soft-bodied organisms and provided strong evidence for their classification as some of the earliest animals in evolutionary history. Dickinsonia was first discovered in the late 1940s in South Australia's Flinders Ranges. Paleontologist Reg Sprigg initially identified its distinctive quilted pattern and named it in honor of Ben Dickinson, a government official with the South Australian Mines Department. The Flinders Ranges are renowned for preserving some of the world's oldest known complex life forms. Over the ensuing decades, fossils of Dickinsonia were reported from several continents, including sites in Russia and Ukraine, suggesting a cosmopolitan distribution during the Ediacaran period. These organisms were preserved only as impressions or casts in quartz sandstones — typical of soft-bodied organisms that left little by way of hard skeletal parts. The unique traits of Dickinsonia include its bilaterally symmetric, oval shape with a pronounced anterior–posterior axis. Repeating modules or isomeres run along its length, arranged in an alternating fashion that some researchers interpret as a form of glide reflection symmetry rather than strict bilateral segmentation. Studies on Dickinsonia have thus steadily shifted its classification due to how difficult it has been for scientists to peg it to a particular species. Once hypothesized as a jellyfish, fungus or even a giant protist, science now favors an animal interpretation. For decades, Dickinsonia's placement in the Tree of Life was hotly debated. Early interpretations ranged from it being a member of the Cnidaria, a group including jellyfish and sea anemones, to suggestions that it was a fungus or even a giant single-celled protist. Morphological features alone proved insufficient to resolve its systematic position since Dickinsonia exhibits few structures similar to modern animals. However, with the emergence of innovative geochemical techniques, researchers began to look at the molecules trapped within the fossil tissues, moving beyond mere morphology. The discovery of animal-specific cholesterol derivatives in Dickinsonia fundamentally altered its classification and strongly argued against non-metazoan alternatives. This is because cholesterol and its degradation product cholestane are found exclusively in animal cell membranes, thus providing molecular evidence of an animal affinity. Researchers suspect it likely lived on shallow marine substrates where it 'crawled' slowly, feeding on microbial mats by external digestion — a behavior somewhat analogous to modern placozoans, the phylum of free-living, non-parasitic marine invertebrates. The current consensus, therefore, leans toward classifying Dickinsonia as an animal. More specifically, it may have been an early relative of simple animals like placozoans or part of a completely new branch of early animals that later gave rise to creatures with bilateral symmetry. Studies of its growth patterns have shown consistent evidence for a regulated developmental program, a signature trait of animal life. These findings have not only provided the positive evidence needed to affirm Dickinsonia's animal status but have also reshaped our understanding of the Precambrian evolutionary landscape. The discovery and classification of Dickinsonia have had profound implications for our understanding of the Cambrian explosion. This rapid burst of evolutionary innovation, beginning around 500 million years ago, gave rise to nearly all the modern animal phyla. Dickinsonia and other Ediacaran organisms were once viewed as evolutionary dead ends — enigmatic forms with no descendants. However, the mounting evidence that Dickinsonia was an animal forces us to reframe these early organisms not as isolated experiments but as integral steps in the progression toward more complex body plans. Recent research has demonstrated that Dickinsonia's biological features — their regulated modular growth, evidence of animal-specific biomolecules and locomotive trace fossils — establish them as a credible evolutionary bridge between simple, soft-bodied organisms and the complex hard-bodied animals that dominate the Cambrian fossil record. In this light, the Ediacaran biota, far from representing failed experiments, appears to have set the stage for the diversification of animal life as we know it today. Does reading about how all life on Earth possibly traces back half a billion years fill you with appreciation for nature's guiding hand? Take the Connectedness To Nature Scale and find out how deep your connection is with the natural world.
The Independent
24-02-2025
- Science
- The Independent
Why a 380-million-year-old fossil ‘fish' from Scotland was discovered on the other side of the world
Queensland is renowned for its fossils of Australia's largest back-boned animals – dinosaurs, of course, like the Jurassic Rhoetosaurus, the Cretaceous Wintonotitan, and other large sauropods. However, our new paper published in the journal National Science Review documents the smallest vertebrate fossil animal described so far from the state. It's a highly enigmatic tiny 'fish' from a remote location close to the Northern Territory border. It lived in the shallow margins of a marine environment about 400 million years ago. A scattering of its skeletal elements was preserved in a small limestone outcrop at the southern end of the Toomba Range, on the edge of the Simpson Desert. Palaeospondylus, a fossil enigma Our paper describes a new species of the genus Palaeospondylus, only the second known. Remarkably, for the last 135 years, Palaeospondylus has been represented by a single species that lived in northern Scotland, on the other side of the world from our discovery. Unlike nearly all fossil fish of that age, Palaeospondylus was 'naked', lacking external dermal bones and scales. But it did have a mineralised internal skeleton. It is the oldest example from the fossil record to show a segmented vertebral column (a sort of backbone), hence its name – Greek for 'ancient vertebra'. The type species Palaeospondylus gunni is known from thousands of fairly complete specimens, almost all from a single flagstone quarry. When first described in 1890, it attracted a flurry of competing interpretations in Europe and North America. Which group of animals did it belong to? Since its discovery, it has been assigned to almost all major jawless and jawed vertebrate groups. All specimens were compressed, making the skeletal elements 'melt' together. Imagination has always played a great role in trying to identify its parts. Even after the advent of 3D scanning, three recent studies reached different conclusions. According to those, Palaeospondylus was related either to chondrichthyans (sharks), or tetrapods (the land vertebrates). Or maybe it was a stem jawed vertebrate – branching separately from the base of the evolutionary tree for all vertebrates with jaws. The Queensland Palaeospondylus The story of discovery of our new Queensland species, Palaeospondylus australis, began in 1977. In the 1960s, geologist Reg Sprigg had predicted oil and gas beneath the northern Simpson Desert. The Bureau of Mineral Resources was conducting seismic surveys and microfossil sampling across the Georgina Basin, immediately to the north. Microfossils are tiny fossils that can only be studied with a microscope, but are crucial to determining the age of the rock. Numerous sedimentary rock samples are collected, preferably limestones, because these can be dissolved in acid. The insoluble microfossils can then be identified and studied in the acid residues. In 1977, I collected bits of limestone from an obscure gully in the Cravens Peak Beds, the sandstone forming the main ridge of the Toomba Range. Surprisingly, these produced a rich collection of Devonian fish microfossils. This was the first evidence that an arm of the sea had extended into central Australia during the Early Devonian (about 400 million years ago). In the 2000s, palaeontologist Carole Burrow at the Queensland Museum was investigating the internal structure of Devonian fish microfossils to assist in dating the rocks. In the Cravens Peak samples, she noticed some distinctively shaped, tiny elements composed of an unusual honeycomb-like tissue. Carole hypothesised this could be a new species of Palaeospondylus, the only record from outside Scotland. So, in 2006, we organised another field trip to this remote location. Returning to the Queensland Museum after our field trip, Carole's colleague from the Netherlands, palaeontologist Jan den Blaauwen, sent her new images showing similar honeycomb-like structure in the Scottish Palaeospondylus gunni. Carole was acid-etching the newly collected samples so she could extract any microfossils. Luckily, she noticed a slightly larger specimen appearing on the rock surface (although still tiny, only about 3.6 millimetres long). It was highly interesting because it seemed bilaterally symmetrical. Could this be a braincase (the bony capsule inside the skull that encloses the brain)? She immediately stopped acid etching before it disintegrated into crumbs. The first uncrushed braincase At the Australian National University, our sample was carefully trimmed before CT scanning, revealing the first uncrushed braincase of Palaeospondylus known to science. It's now the holotype – defining type specimen – for our new species. And we have about 400 other elements with the same honeycomb structure which belong to it, too. The unique uncrushed preservation of this braincase, revealed by CT scanning and 3D printing techniques, provides the first details of brain structure in this tiny animal from 400 million years ago. These include the shape of the cranial cavity and inner ear canals, the position of the pituitary gland and optic nerve openings, and details of the carotid arteries and jugular veins for blood supply to the brain. More questions remain It is noteworthy that our curiosity-driven research into ancient brain morphology can be traced back to economically driven geological surveys of nearly 50 years ago, conducted to support exploration for oil and gas across central Australia. As with any research result, there are now new questions to be investigated. The honeycomb tissue seems unique to Palaeospondylus, but could be a precursor to calcified cartilage of some other groups, including modern sharks. Alternatively, it could be an early evolutionary stage for the spongy tissue (endochondral bone) filling the inside of most bones in modern land vertebrates, including humans. The unique holotype of our new species clearly shows that previous interpretations of the crushed Scottish material included many structures that were not part of the braincase. We've also now demonstrated that a recent study in the leading science journal Nature, which proposed that Palaeospondylus was closely related to our tetrapod ancestors, relied on many erroneous interpretations of braincase structure. Of one thing we can be sure – Palaeospondylus was not a stem tetrapod.
