- Study dates earliest sponges to 600-615 million years ago.
- Researchers analyzed 133 genes and fossil data.
- Findings suggest early sponges lacked mineralized skeletons.
- Results published in journal Science Advances.
The earliest sponges to live on the earth were soft and skeletonless pioneers - rewriting the story of the origin of animal life.
Over decades, an irritating gap had been at the centre of palaeontology. Genetic research and chemical biomarkers of ancient rocks indicated that the earliest animals on Earth, sponges, developed at least half a billion years ago.
However, the earliest definable sponge fossils, known as spicules, which are tiny glass like formations, do not occur until about 543 million years ago.That created a gap of over 100 million years: it was too big not to notice, too strong to believe.
The world has now been given an answer by a global research team of natural scientists assembled around a new team leader, Dr M. Eleonora Rossi of the University of Bristol School of Biological Sciences, in conjunction with the Natural History Museum, in London, and the Museum of Natural Sciences, in Madrid, with a oftentimes baffling resolution to the mystery. The primitive sponges had been there all along. They just lacked something to set back.
A Record of Fossils and the Missing Spicules
In the modern sponges, the skeletons consist of an infinite number of tiny, microscopic, glass-like points known as spicules. These fragile components are long lasting and thus fossilise easily and have been observed in rocks as early as 543 million years and towards the end of the Ediacaran Period. Nevertheless, spicules have not been discovered in the older rocks by scientists.
That lack has led to doubts as to whether the sponges actually began to develop in such an early way as has been argued by genetic finding. In order to deal with the mismatch, Dr Rossi and her team applied a two-part approach. Of course, these researchers first analyzed the information on 133 protein-coding genes and covered background data on fossils to create a new evolutionary chronology.
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Their findings put the date of the origin of the sponges at 600 -615 million years ago, making the difference between genetic expectations and fossil records smaller. Then they considered the issue of sponge skeletons advancing over time and found that spicules independently evolved in individual lineages of sponge.
Honorary Research Associate Dr Rossi said: "We found the earliest sponges made without mineralised skeletons and soft bodies. This is why we do not find sponge spicules in 600 million year old rocks there were none there to conserve.
"Six hundred million years ago, the ancestors of every animal alive today were little more than soft specks in a primordial sea. That they made it this far is, frankly, extraordinary."
Sponge Skeletons to independent evolution
The evolutionary theory that the sponge skeletons appeared twice or more is corroborated by structural and genetic distinctions in existing species as well. World-leading sponge evolution expert Dr Ana Riesgo of the Museum of Natural Sciences in Madrid said: "We already had some indications which point at skeletons of sponges having developed independently.
Modern sponge skeletons can resemble each other, however, these are constructed in a completely different manner. Others consist of chalk, or rather the mineral, calcite, others of silica which is air and we find that there are totally different genes being acted on when we look at their genomes.
In order to work out this evolutionary history, the researchers employed a statistical Markov process model, which is the same type of predictive system used in finance, artificial intelligence, search engines and weather forecasting, to simulate the process of skeletal type transition. The view that the earliest sponges contained mineralised skeletons was forcefully dismissed by all of the models.
Revisiting The emergence of the First Animals
These findings also pose new questions concerning what motivated the first steps in the evolution of sponges. Almost all sponges today contain the mineralised spicules and this may imply that skeletons were instrumental in their initial success. The new analysis however refutes that assumption.
Professor Phil Donoghue, Professor of Palaeobiology at the University of Bristol contributed: Since almost all extant sponges have skeletons formed of mineralised spicules it is quite natural to suppose that spicules played an important role in the early development of the sponge.
Our findings undermine this concept, and it has inflexibly been proposed that it is another factor that provoked the initial sponge evolution and that we merely do not know what it was.
Its ramifications go far and wide past sponges. Professor Davide Pisani, Professor of Phylogenomics at the University of Bristol came to the conclusion: This is not just about sponges. The earliest lineage of reef-building animals to evolve, possibly also the earliest lineage of animal, are sponges, which is disputed.
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The knowledge of how they have developed gives important information about the formation of the earliest reef systems. It is concerning the co-evolution of life and the Earth, how the development of primitive animals altered our world forever, and eventually gave rise to the animal forms of life that we currently know, humans included.
