Creationism in Crisis - How the Arthropod Brain Evolved 525 million Years Ago

525-million-year-old fossil defies textbook explanation for brain evolution | University of Arizona News

Artist's impression if Cardiodictyon catenulum

Credit: Nicholas Strausfeld

A paper published a couple of days ago in Science closes yet another of those gaps so beloved of Creationists who fool their dupes with the false dichotomy fallacy that, if science hasn't explained something, the only alternative on offer is that their version of a creator god did it. This save them the bother of producing any evidence for their pet superstition and keeps their dupes believing that they have better answers than science does and so are much more clever than those elitist scientists with their big words. If there is one thing Creationists can't stand it's uncertainty, with the dreadful prospect that they might have to change their minds if the evidence changes.

The paper was written by a group of scientists led by Nicholas Strausfeld, a Regents Professor in the University of Arizona Department of Neuroscience, and Frank Hirth, a reader of evolutionary neuroscience at King's College London. It describes a fossil of Cardiodictyon catenulum, a 1.5 cm long, worm-like arthropod, found in China's southern Yunnan province. Close detailed analysis has revealed delicately preserved nervous system, including a brain. This is believed to be the oldest fossilised brain so far discovered.

The University of Arizona News describes the research and its significance:

Cardiodictyon belonged to an extinct group of animals known as armored lobopodians, which were abundant early in a period known as the Cambrian, when virtually all major animal lineages appeared over an extremely short time between 540 million and 500 million years ago. Lobopodians likely moved about the sea floor using multiple pairs of soft, stubby legs that lacked the joints of their descendants, the euarthropods – Greek for "real jointed foot." Today's closest living relatives of lobopodians are velvet worms that live mainly in Australia, New Zealand and South America.

A debate going back to the 1800s

Fossils of Cardiodictyon reveal an animal with a segmented trunk in which there are repeating arrangements of neural structures known as ganglia. This contrasts starkly with its head and brain, both of which lack any evidence of segmentation.

This anatomy was completely unexpected because the heads and brains of modern arthropods, and some of their fossilized ancestors, have for over a hundred years been considered as segmented

But Cardiodictyon shows that the early head wasn't segmented, nor was its brain, which suggests the brain and the trunk nervous system likely evolved separately.

Professor Nicholas J. Strausfeld, lead author
Department of Neuroscience
University of Arizona, Tucson, AZ, USA.

From the 1880s, biologists noted the clearly segmented appearance of the trunk typical for arthropods, and basically extrapolated that to the head. That is how the field arrived at supposing the head is an anterior extension of a segmented trunk.

Frank Hirth, corresponding author
Department of Basic and Clinical Neuroscience
Institute of Psychiatry, Psychology and Neuroscience
King’s College London, London, UK.

According to the authors, the finding resolves a long and heated debate about the origin and composition of the head in arthropods, the world's most species-rich group in the animal kingdom. Arthropods include insects, crustaceans, spiders and other arachnids, plus some other lineages such as millipedes and centipedes.

The fossilized Cardiodictyon catenulum was discovered in 1984 among a diverse assemblage of extinct creatures known as the Chengjian fauna in Yunnan, China. In this photo, the animal's head is to the right.

Credit: Nicholas Strausfeld

Brains do fossilize

Cardiodictyon was part of the Chengjiang fauna, a famous deposit of fossils in the Yunnan Province discovered by paleontologist Xianguang Hou. The soft, delicate bodies of lobopodians have preserved well in the fossil record, but other than Cardiodictyon, none have been scrutinized for their head and brain, possibly because lobopodians are generally small. The most prominent parts of Cardiodictyon were a series of triangular, saddle-shaped structures that defined each segment and served as attachment points for pairs of legs. Those had been found in even older rocks dating back to the start of the Cambrian.

That tells us that armored lobopodians might have been the earliest arthropods [predating even trilobites, an iconic and diverse group of marine arthropods that went extinct around 250 million years ago].

Professor Nicholas J. Strausfeld

Until very recently, the common understanding was 'brains don't fossilize,' so you would not expect to find a fossil with a preserved brain in the first place. And, second, this animal is so small you would not even dare to look at it in hopes of finding a brain.

Frank Hirth

However, work over the last 10 years, much of it done by Strausfeld, has identified several cases of preserved brains in a variety of fossilized arthropods.

Fossilized head of Cardiodictyon catenulum (anterior is to the right). The magenta-colored deposits mark fossilized brain structures.

Credit: Nicholas Strausfeld

A common genetic ground plan for making a brain

In their new study, the authors not only identified the brain of Cardiodictyon but also compared it with those of known fossils and of living arthropods, including spiders and centipedes. Combining detailed anatomical studies of the lobopodian fossils with analyses of gene expression patterns in their living descendants, the researchers concluded that a shared blueprint of brain organization has been maintained from the Cambrian until today.

By comparing known gene expression patterns in living species, we identified a common signature of all brains and how they are formed. We realized that each brain domain and its corresponding features are specified by the same combination of genes, irrespective of the species we looked at. This suggested a common genetic ground plan for making a brain.

Frank Hirth

In Cardiodictyon, three brain domains are each associated with a characteristic pair of head appendages and with one of the three parts of the anterior digestive system.

Strausfeld said their findings also offer a message of continuity at a time when the planet is changing dramatically under the influence of climatic shifts.

Fossilized body and head of Cardiodictyon catenulum. The magenta colored deposits denote fossilized neural tissue. Lower reconstruction shows the frontmost part of the animal.

Credit: Nicholas Strausfeld

At a time when major geological and climatic events were reshaping the planet, simple marine animals such as Cardiodictyon gave rise to the world's most diverse group of organisms – the euarthropods – that eventually spread to every emergent habitat on Earth, but which are now being threatened by our own ephemeral species.

Professor Nicholas J. Strausfeld

Lessons for vertebrate brain evolution

Hirth and Strausfeld say the principles described in their study probably apply to other creatures outside of arthropods and their immediate relatives. This has important implications when comparing the nervous system of arthropods with those of vertebrates, which show a similar distinct architecture in which the forebrain and midbrain are genetically and developmentally distinct from the spinal cord, they said.

In the abstract to their published paper in Science the authors say:

Abstract

For more than a century, the origin and evolution of the arthropod head and brain have eluded a unifying rationale reconciling divergent morphologies and phylogenetic relationships. Here, clarification is provided by the fossilized nervous system of the lower Cambrian lobopodian Cardiodictyon catenulum, which reveals an unsegmented head and brain comprising three cephalic domains, distinct from the metameric ventral nervous system serving its appendicular trunk. Each domain aligns with one of three components of the foregut and with a pair of head appendages. Morphological correspondences with stem group arthropods and alignments of homologous gene expression patterns with those of extant panarthropods demonstrate that cephalic domains of C. catenulum predate the evolution of the euarthropod head yet correspond to neuromeres defining brains of living chelicerates and mandibulates.

Strausfeld, Nicholas J.; Hou, Xianguang; Sayre, Marcel E. & Hirth, Frank (2022)
The lower Cambrian lobopodian Cardiodictyon resolves the origin of euarthropod brains
Science; 378(6622), 905-909. DOI; 10.1126/science.abn6264

Copyright © 2022 The Authors.
Published by American Association for the Advancement of Science
Reprinted by kind permission under license #5436640797487

Of special mote here is the fact that the authors concluded that because C. catenulum has the same basic 'design' for its brain as other, later arthropods, this is evidence of evolution and common ancestry, not of design. Where is that supposed rejection of the TOE in favour of a Bronze Age superstition with its unproven supernatural planner/designer, whose MO has never been demonstrated or witnessed? It isn't there of course, because mainstream biologists and palaeontologists are, in contrast to Creationist lies, utterly convinced of the truth and explanatory powers of the Theory of Evolution.

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