Science Textbooks Wrong? 525-Million-Year-Old Fossil Defies Common Explanation for Brain Evolution - SciTechDaily

According to a caller study, fossils of a tiny oversea carnal with a delicately preserved tense strategy lick a century-old statement implicit however the encephalon evolved successful arthropods, the astir species-rich radical successful the carnal kingdom.

Fossils of a tiny oversea carnal that died much than fractional a cardinal years agone whitethorn compel a subject textbook rewrite of however brains evolved.

A caller survey provides the archetypal elaborate statement of Cardiodictyon catenulum, a wormlike carnal preserved successful rocks successful China’s confederate Yunnan province. Measuring hardly fractional an inch (less than 1.5 centimeters) agelong and initially discovered successful 1984, the fossil had hidden a important concealed until now: a delicately preserved tense system, including a brain. Published successful the diary Science connected November 24, the probe was led by Nicholas Strausfeld, a Regents Professor successful the University of Arizona Department of Neuroscience, and Frank Hirth, a scholar of evolutionary neuroscience astatine King’s College London.

“To our knowledge, this is the oldest fossilized encephalon we cognize of, truthful far,” Strausfeld said.

Cardiodictyon belonged to an extinct radical of animals known arsenic armored lobopodians, which were abundant aboriginal during a play known arsenic the Cambrian, erstwhile virtually each large carnal lineages appeared implicit an highly abbreviated clip betwixt 540 cardinal and 500 cardinal years ago. Lobopodians apt moved astir connected the oversea level utilizing aggregate pairs of soft, stubby legs that lacked the joints of their descendants, the euarthropods – Greek for “real jointed foot.” Today’s closest surviving relatives of lobopodians are velvet worms that unrecorded chiefly successful Australia, New Zealand, and South America.

A statement going backmost to the 1800s

Fossils of Cardiodictyon uncover an carnal with a segmented trunk successful which determination are repeating arrangements of neural structures known arsenic ganglia. This contrasts starkly with its caput and brain, some of which deficiency immoderate grounds of segmentation.

“This anatomy was wholly unexpected due to the fact that the heads and brains of modern arthropods, and immoderate of their fossilized ancestors, person for implicit a 100 years been considered arsenic segmented,” Strausfeld said.

According to the authors, the uncovering resolves a agelong and heated statement astir the root and creation of the caput successful arthropods, the world’s astir species-rich radical successful the carnal kingdom. Arthropods see insects, crustaceans, spiders, and different arachnids, positive immoderate different lineages specified arsenic millipedes and centipedes.

“From the 1880s, biologists noted the intelligibly segmented quality of the trunk emblematic for arthropods, and fundamentally extrapolated that to the head,” Hirth said. “That is however the tract arrived astatine supposing the caput is an anterior hold of a segmented trunk.”

“But Cardiodictyon shows that the aboriginal caput wasn’t segmented, nor was its brain, which suggests the encephalon and the trunk tense strategy apt evolved separately,” Strausfeld said.

Brains bash fossilize

Cardiodictyon was portion of the Chengjiang fauna, a celebrated deposit of fossils successful the Yunnan Province discovered by paleontologist Xianguang Hou. The soft, delicate bodies of lobopodians person preserved good successful the fossil record, but different than Cardiodictyon nary person been scrutinized for their caput and brain, perchance due to the fact that lobopodians are mostly small. The astir salient parts of Cardiodictyon were a bid of triangular, saddle-shaped structures that defined each conception and served arsenic attachment points for pairs of legs. Those had been recovered successful adjacent older rocks dating backmost to the advent of the Cambrian. 

“That tells america that armored lobopodians mightiness person been the earliest arthropods,” Strausfeld said, predating adjacent trilobites, an iconic and divers radical of marine arthropods that went extinct astir 250 cardinal years ago.

“Until precise recently, the communal knowing was ‘brains don’t fossilize,'” Hirth said. “So you would not expect to find a fossil with a preserved encephalon successful the archetypal place. And, second, this carnal is truthful tiny you would not adjacent situation to look astatine it successful hopes of uncovering a brain.”  

However, enactment implicit the past 10 years, overmuch of it done by Strausfeld, has identified respective cases of preserved brains successful a assortment of fossilized arthropods.

A communal familial crushed program for making a brain

In their caller study, the authors not lone identified the encephalon of Cardiodictyon but besides compared it with those of known fossils and of surviving arthropods, including spiders and centipedes. Combining elaborate anatomical studies of the lobopodian fossils with analyses of cistron look patterns successful their surviving descendants, they reason that a shared blueprint of encephalon enactment has been maintained from the Cambrian until today.

“By comparing known cistron look patterns successful surviving species,” Hirth said, “we identified a communal signature of each brains and however they are formed.”

In Cardiodictyon, 3 encephalon domains are each associated with a diagnostic brace of caput appendages and with 1 of the 3 parts of the anterior digestive system.

“We realized that each encephalon domain and its corresponding features are specified by the aforesaid operation genes, irrespective of the taxon we looked at,” added Hirth. “This suggested a communal familial crushed program for making a brain.” 

Lessons for vertebrate encephalon evolution

Hirth and Strausfeld accidental the principles described successful their survey astir apt use to different creatures extracurricular of arthropods and their contiguous relatives. This has important implications erstwhile comparing the tense strategy of arthropods with those of vertebrates, which amusement a akin chiseled architecture successful which the forebrain and midbrain are genetically and developmentally chiseled from the spinal cord, they said.

Strausfeld said their findings besides connection a connection of continuity astatine a clip erstwhile the satellite is changing dramatically nether the power of climatic shifts.

“At a clip erstwhile large geological and climatic events were reshaping the planet, elemental marine animals specified arsenic Cardiodictyon gave emergence to the world’s astir divers radical of organisms – the euarthropods – that yet dispersed to each emergent situation connected Earth, but which are present being threatened by our ain ephemeral species.”

Reference: “The Lower Cambrian Lobopodian Cardiodictyon Resolves the Origin of Euarthropod Brains” by Nicholas J. Strausfeld, Xianguang Hou, Marcel E. Sayre and Frank Hirth, 24 November 2022, Science.
DOI: 10.1126/science.abn6264

The insubstantial was co-authored by Xianguang Hou astatine the Yunnan Key Laboratory for Paleontology successful Yunnan University successful Kunming, China, and Marcel Sayre, who has appointments astatine Lund University successful Lund, Sweden, and astatine the Department of Biological Sciences astatine Macquarie University successful Sydney.

Funding for this enactment was provided by the National Science Foundation, the University of Arizona Regents Fund, and the UK Biotechnology and Biological Sciences Research Council.