Reconstruction of Jiangchuan biota
Credit: Xiaodong Wang.
A paper just published in Science by a team of palaeontologists from Oxford and Yunnan universities should, if creationists were honest enough and sufficiently knowledgeable to understand it, finally lay to rest two favourite canards they use to attack Darwinian evolution: the so-called Cambrian Explosion and their misrepresentation of Stephen Jay Gould’s idea of punctuated equilibrium.
The Cambrian Explosion is a favourite target for creationists, who exploit the word “explosion” to misrepresent it as the sudden appearance of multicellular life with multiple body plans, supposedly without ancestry, and therefore as a single act of supernatural creation. The fact that it happened some 535 million years ago is usually dismissed with the standard creationist repertoire: claims that scientists are inventing the dates, relying on “flawed” dating techniques, or, more bizarrely still, failing to take account of some unspecified change in radioactive decay rates that just happens to make 6,000–10,000 years look like 535 million.
But that fallacy was based on very limited data, especially the fossils from the Burgess Shale, which provided only a narrow snapshot of living organisms at one time and place. From evidence such as this, Stephen Jay Gould and Niles Eldredge developed the idea of punctuated equilibrium, in which long periods of relative stasis in the fossil record are interrupted by comparatively short episodes of more rapid evolutionary change. Creationists eagerly seized on this, dishonestly presenting it as though Gould had somehow replaced Darwinism and proved Darwin wrong. In reality, it did no such thing. It was not a rejection of evolution, nor of common descent, nor of natural selection, but a discussion within evolutionary biology about the pattern and tempo with which evolutionary change appears in the fossil record.
Darwin, of course, never claimed that evolution must proceed at a constant, steady rate. On the contrary, his theory makes it clear that changing environments drive evolutionary change, so more rapid evolution during periods of environmental upheaval is entirely consistent with Darwinian evolution and, indeed, a vindication of it. The appearance of long stasis followed by apparently abrupt change can also be exaggerated by the incompleteness of the geological record, in which spans of thousands of years may appear almost instantaneous when compressed into a thin layer of rock.
However, the notion that the Cambrian Explosion was a sudden event without ancestry has been steadily dismantled by discoveries pushing the origins of Cambrian-type biota back towards the Ediacaran, together with evidence that some Ediacaran organisms were already capable of movement. What emerges is not a miraculous burst of creation, but a clear evolutionary progression from the Ediacaran into the Cambrian.
Now this new paper strengthens that case by showing that complex body plans existed much earlier than previously thought, and by presenting evidence of gradual Darwinian evolution from the Ediacaran into the Cambrian.
The evidence comes from a treasure trove of fossils, the Jiangchuan Biota in Yunnan Province, southwest China, where more than 700 fossil specimens were recovered from rocks dated to between 554 and 539 million years old. Among the more surprising finds is a deuterostome — part of the broad group that includes vertebrates such as fish and humans.
The Jiangchuan Biota, Yunnan Province — background information.The discovery of these fossils by a team led by Dr Gaorong Li, formerly of Yunnan University and now based at the Oxford University Museum of Natural History, together with Dr Frankie Dunn of the Oxford University Museum of Natural History, is explained in an Oxford University news release:
- The Jiangchuan Biota is a fossil assemblage from Yunnan Province, south-west China, dating to the late Ediacaran, just before the start of the Cambrian. Current work places the key fossil-bearing interval at about 554–539 million years old. [1]
- Geologically, the biota comes from the Jiucheng Member of the Dengying Formation. Earlier studies had already shown it to be an important late Ediacaran site, especially for its abundant macroalgal fossils and other problematic forms. [2]
- Before the new Science paper, Jiangchuan was already recognised as unusual because it preserved a eukaryote-dominated late Neoproterozoic ecosystem, but it was known mainly for algae rather than clearly identified animals. That is why the newer discoveries are so important: they greatly expand the biological significance of the site. [3]
- The new work reports more than 700 fossil specimens, showing that Jiangchuan preserves a diverse late Ediacaran community including previously undescribed forms as well as animals once thought to be known only from Cambrian rocks. [1]
- One reason the site is so valuable is its style of preservation. Unlike many Ediacaran fossil localities, where organisms are preserved mainly as surface impressions in sandstone, the Jiangchuan fossils are preserved as carbonaceous films. This is a rarer mode of preservation for rocks of this age and can preserve much finer anatomical detail. [1]
- Because of that exceptional preservation, some Jiangchuan fossils show structures such as feeding organs, digestive tracts, attachment structures, and possible locomotory features. That makes the site especially important for working out what some of these early animals actually were. [1]
- Among the most important finds are fossils interpreted as early bilaterians and possible early deuterostomes, including forms related to ambulacrarians — the broader group that includes modern starfish, sea urchins and acorn worms. If these identifications are correct, they push parts of those lineages back into the Ediacaran. [1]
- The Jiangchuan Biota is therefore important not simply because it is old, but because it appears to document a transitional fauna between the classic Ediacaran world and the better-known Cambrian faunas. In other words, it helps fill part of the gap between the strange soft-bodied organisms of the Ediacaran and the more recognisably modern animal groups of the Cambrian. [1]
- More broadly, the site strengthens the case that the apparent “suddenness” of the Cambrian Explosion has been exaggerated by the incompleteness of the fossil record. Jiangchuan suggests that several animal lineages and body plans were already present before the Cambrian began, but have often gone unrecognised because fossils of the right age and preservation are so rare. [1]
- Earlier papers on the Jiangchuan Biota had already shown that it was compositionally distinct from other Chinese Ediacaran fossil assemblages, underlining that late Ediacaran ecosystems were more varied than once thought. [2]
Spectacular fossil treasure trove pushes back origins of complex animals
A newly discovered fossil site in southwest China has transformed our understanding of how complex animal life emerged on Earth, revealing that many key animal groups had already evolved before the start of the Cambrian Period. The study, led by researchers at Oxford University’s Museum of Natural History and Department of Earth Sciences as well as Yunnan University in China, has been published in Science.
Fossil of a sausage shaped animal with an end-positioned mouth. A newly-discovered fossil from the Jiangchuan Biota. Credit: Gaorong Li. One of the most transformative events in Earth’s history was the rapid diversification of animal life, resulting in a dramatic increase in complexity and diversity from simpler life forms. Up to now, this was thought to have occurred at the start of the Cambrian Period, in an event known as the Cambrian explosion, starting around 535 million years ago. The new study, however, shifts this timeframe back by at least 4 million years, to the end of the Ediacaran period.
Our discovery closes a major gap in the earliest phases of animal diversification. For the first time, we demonstrate that many complex animals, normally only found in the Cambrian, were present in the Ediacaran period, meaning that they evolved much earlier than previously demonstrated by fossil evidence.
Dr Gaorong Li, lead author
State Key Laboratory of Vegetation Structure, Function and Construction
Institute of Palaeontology
Yunnan University
Kunming, China.
The discovery comes from the Jiangchuan Biota in Yunnan Province, southwest China, where more than 700 fossil specimens were recovered, aged between 554 and 539 million years old. The fossil site revealed a diverse community of Ediacaran organisms - both new, undescribed animal forms and groups known from the Cambrian period. Most strikingly, the international team identified fossils thought to be the oldest known relatives of deuterostomes – the broader group that today includes vertebrates such as humans and fish. The new fossils push the fossil record of deuterostomes back into the Ediacaran Period for the first time.
Among these fossil specimens were ancestors of modern starfish and their closest relatives, the acorn worms (the Ambulacraria*). These fossils have a U-shaped body and were attached to the seafloor with a stalk, with a pair of tentacles on their head used to catch food.
The presence of these ambulacrarians in the Ediacaran period is really exciting. We have already found fossils which are distant relatives of starfish and sea cucumbers and are looking for more. The discovery of ambulacrarian fossils in the Jiangchuan biota also means that the chordates – animals with a backbone – must also have existed at this time.
Dr Francis S. Dunn, corresponding author.
Oxford University Museum of Natural History
University of Oxford
Oxford, UK.
Other ancestral groups among the fossils included worm-like bilaterian animals (having bilateral symmetry), some with complex feeding adaptations, alongside rare fossils interpreted as early comb jellies.
Many specimens showed novel combinations of anatomical features (such as tentacles, stalks, attachment discs, and feeding structures that can be turned inside out) that do not match any known Ediacaran or Cambrian species.
For instance, one specimen looks a lot like the sand worm from Dune!
Dr Francis S. Dunn.
This discovery is extremely exciting because it reveals a transitional community: the weird world of the Ediacaran giving way to the Cambrian, the following time period where the animals are much easier to place in groups that are alive today. When we first saw these specimens, it was clear that this was something totally unique and unexpected.
Associate Professor Luke Parry, co-corresponding author
Department of Earth Sciences
University of Oxford
Oxford, UK.
The new findings help to resolve a long-standing puzzle in evolutionary biology. While molecular studies and trace fossils suggested that animal lineages diversified well before the Cambrian explosion, up to now fossils of many of these groups of complex animals have been missing from the Ediacaran period.
Left: Haootia-like fossil (an early cnidarian – the phylum that includes jellyfish, sea anemones and corals) from the Jiangchuan Biota (scale bar: 2 mm) and artist’s reconstruction. Right: A deuterostome cambroernid fossil from the Jiangchuan Biota (scale bar: 2mm) and artist’s reconstruction.Credits: Gaorong Li (fossil photographs) and Xiaodong Wang (artistic reconstruction).
Unlike most Ediacaran fossil sites, which preserve organisms mainly as impressions on sandstone surfaces, the Jiangchuan Biota fossils are preserved as carbonaceous films, a mode of preservation more typical of famous Cambrian sites such as the Burgess Shale in Canada. This exceptional preservation reveals anatomical details such as feeding structures, guts and locomotory organs.
Our results indicate that the apparent absence of these complex animal groups from other Ediacaran sites may reflect differences in preservation rather than true biological absence. Carbonaceous compressions like those at Jiangchuan are rare in rocks of this age, meaning that similar communities may simply not have been preserved elsewhere.
Associate Professor Ross Anderson, co-author
Oxford University Museum of Natural History
University of Oxford
Oxford, UK.
A deuterostome cambroernid fossil from the Jiangchuan Biota.Credit: Gaorong Li.
The new fossils were discovered by a research group in Yunnan University, China, led by Professor Peiyun Cong and Associate Professor Fan Wei, who have spent nearly ten years looking for diverse Ediacaran animal fossils. The rocks from Eastern Yunnan were already known to contain fossils but previously had yielded only remains of algae and not animals.
After years of fieldwork, we finally found several sites with the right conditions where animal fossils are preserved together with the abundant algae.
Associate Professor Fan Wei, co-corresponding author
State Key Laboratory of Vegetation Structure, Function and Construction
Institute of Palaeontology
Yunnan University
Kunming, China.
The new fossils provide the most compelling evidence for the presence of diverse bilaterian animals at the end of the Ediacaran, evidence people have searched for across decades.
Professor Feng Tang, not an author of the current paper
Chinese Academy of Geological Science
Beijing, China.
* Ambulacraria, from the Latin ambulacrum, meaning ‘a walk planted with trees.’
Publication:
What the Jiangchuan Biota shows is not a sudden, unexplained burst of life appearing from nowhere, but exactly what evolutionary theory has long predicted: a deeper ancestry for Cambrian animals, transitional forms linking earlier and later biotas, and a fossil record that becomes clearer as more evidence is found. The so-called “Cambrian Explosion” turns out, yet again, not to have been an instantaneous act of magical creation, but a geologically extended phase in a much longer evolutionary story whose roots stretch back well into the Ediacaran.
It also exposes the dishonesty with which creationists have tried to exploit both the Cambrian fossil record and Gould’s punctuated equilibrium. Neither supports their childish parody of evolution as something that must proceed at a perfectly steady rate or collapse if the fossil record is incomplete. On the contrary, the Jiangchuan fossils show precisely why science works and dogma fails: each new discovery adds detail, fills gaps, and strengthens the evolutionary account, while creationism is left doing what it always does — denying, distorting, and improvising excuses to avoid the obvious conclusion.
So, far from refuting Darwinian evolution, the Jiangchuan Biota is another striking vindication of it. Complex animal body plans did not appear without ancestry, nor did the Cambrian fauna emerge in isolation from what came before. What we see instead is descent with modification unfolding through deep time, preserved imperfectly but increasingly clearly in the rocks. As always, the evidence fits evolution comfortably, while creationism survives only by misrepresentation and wilful ignorance.
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