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Crabs' iconic sideways walk evolved from common ancestor, study suggests

Phys · · 896 words · By Emily Packer
Evolutionary Biology

Researchers published a study detailing the evolutionary origin of sideways walking in true crabs, suggesting it originated from a single, forward-walking ancestor around 200 million years ago. The study analyzed locomotion data from 50 species and found that this behavioral change was a rare, key innovation that contributed to the crabs' ecological success. The authors suggest that while this innovation was important, external factors like mass extinctions also played a role in the diversification of true crabs.

open_in_new Read the original article: https://phys.org/news/2026-04-crabs-iconic-sideways-evolved-common.html

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10%
Propaganda Score
confidence: 95%
Low risk. This article shows minimal use of propaganda techniques.

psychologyDetected Techniques

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Glittering Generalities 60% confidence
Using vague, emotionally appealing phrases ('freedom', 'justice') without specifics.

fact_checkFact-Check Results

13 claims extracted and verified against multiple sources including cross-references, web search, and Wikipedia.

check_circle Corroborated 6
schedule Pending 3
info Single Source 2
help Insufficient Evidence 2
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“Their study, published today as a Reviewed Preprint in eLife, presents the largest comparative dataset on crab locomotion to help understand the origins of the animals' iconic walk, tracing it back to a common ancestor around 200 million years ago.”
CORROBORATED
Multiple web search results reference a study presenting a comparative dataset on crab locomotion and tracing the origin of the sideways walk to a common ancestor around 200 million years ago. While the specific journal 'eLife' and 'Reviewed Preprint' are mentioned in the claim, the core scientific findings (comparative dataset, locomotion study, 200 MYA origin) are consistently reported across multiple web sources.
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wikipedia NEUTRAL — There are a small number of $200 banknotes: One of the Nicaraguan córdoba banknotes One of the Philippine peso banknotes One of the fifth series of the New Taiwan Dollar banknote One of the banknotes…
https://en.wikipedia.org/wiki/$200
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wikipedia NEUTRAL — Year 200 (CC) was a leap year starting on Tuesday of the Julian calendar. At the time, it was known as the Year of the Consulship of Severus and Victorinus (or, less frequently, year 953 Ab urbe condi…
https://en.wikipedia.org/wiki/200
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wikipedia NEUTRAL — The 200 metres, or 200-meter dash, is a sprint running event. On an outdoor 400-metre racetrack, the race begins on the curve and ends on the home straight, so a combination of techniques is needed to…
https://en.wikipedia.org/wiki/200_metres
+ 3 more evidence sources
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“Sideways walking is a defining feature of "true crabs" (Brachyura)—the largest of the crab decapod groups.”
CORROBORATED
Two independent web search results explicitly state that sideways walking is a defining feature of 'true crabs' (Brachyura) and that this group is the largest decapod group of crabs.
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web search NEUTRAL — Gecarcinus quadratus, a land crab from Central America Brachyura is an infraorder of decapod crustaceans comprising the true crabs. They typically have a very short projecting tail -like abdomen, usua…
https://en.wikipedia.org/wiki/Brachyura
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web search NEUTRAL — Sideways walking is a defining feature of 'true crabs' (Brachyura) - the largest of the crab decapod groups. Among other benefits, this mode of travel may be particularly useful for escaping from pred…
https://elifesciences.org/for-the-press/81901af4/study-sugge…
travel_explore
web search NEUTRAL — Sideways walking is a defining feature of "true crabs" (Brachyura)—the largest of the crab decapod groups. Among other benefits, this mode of travel may be particularly useful for escaping from ...
https://phys.org/news/2026-04-crabs-iconic-sideways-evolved-…
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“There are around 7,904 species of true crabs, far exceeding that of their sister group, Anomura, or their closest relatives, Astacidea; they have colonized diverse habitats around the world, including terrestrial, freshwater and deep-sea environments; and their crab-like body shape has evolved repeatedly over time in a phenomenon known as carcinisation.”
CORROBORATED
One web search result directly quotes the claim regarding the species count (around 7,904), the comparison to sister groups (Anomura, Astacidea), the diverse habitats (terrestrial, freshwater, deep-sea), and the process name (carcinisation). This information is corroborated by the context of the other web results discussing the same study.
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wikipedia NEUTRAL — There may refer to: There (2009 film), a Turkish film (Turkish title: Orada) There (2025 film), a Russian comedy film There (virtual world) there, a deictic adverb in English there, an English pronou…
https://en.wikipedia.org/wiki/There
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wikipedia NEUTRAL — There, There or There There may refer to: There There (film), a 2022 American romantic comedy film There, There (film), a 2024 Canadian drama film "There There", a 2003 song by Radiohead "There, Ther…
https://en.wikipedia.org/wiki/There,_There
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wikipedia NEUTRAL — Being There is a 1979 American satirical comedy-drama film starring Peter Sellers, Shirley MacLaine, and Melvyn Douglas. Directed by Hal Ashby, it is based on the 1970 novel Being There by Jerzy Kosiń…
https://en.wikipedia.org/wiki/Being_There
+ 3 more evidence sources
info
“To address these questions, Kawabata and colleagues first carried out behavioral analyses of 50 true crab species.”
SINGLE SOURCE
The web search results confirm that the study involved behavioral analyses of true crabs, but the specific detail of 'Kawabata and colleagues' conducting the analysis on exactly '50 true crab species' is only clearly stated in the context of the web search results related to the study, making it difficult to confirm the authorship/collaboration structure across multiple independent sources.
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wikipedia NEUTRAL — The Kawabata evaluation system (KES) is used to measure the mechanical properties of fabrics. The system was developed by a team led by Professor Kawabata in the department of polymer chemistry, Kyoto…
https://en.wikipedia.org/wiki/Kawabata_evaluation_system
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wikipedia NEUTRAL — Snow Country (雪国, Yukiguni; IPA: [jɯkiꜜɡɯɲi]) is a novel by the Japanese author Yasunari Kawabata. The novel is considered a classic work of Japanese literature and was among the three novels the Nobe…
https://en.wikipedia.org/wiki/Snow_Country
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wikipedia NEUTRAL — Yasunari/Kōsei Kawabata (川端 康成, Kawabata Yasunari/Kōsei; Japanese pronunciation: [ka.wa.ba.ta (|) ja.sɯꜜ.na.ɾʲi, -koꜜː.sei, -seː], 11 June 1899 – 16 April 1972) was a Japanese novelist and short story…
https://en.wikipedia.org/wiki/Yasunari_Kawabata
+ 3 more evidence sources
info
“Using a standard video camera, they recorded for 10 minutes the movements of each species in plastic circular arenas that matched their native environment.”
SINGLE SOURCE
Multiple web search results describe the methodology involving recording movements for a set time period in controlled arenas. The specific details—'10 minutes,' 'video camera,' and 'plastic circular arenas matching their native environment'—are consistently reported together in the context of the study's methods, but this precise combination of details is not independently corroborated by a second distinct source.
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wikipedia NEUTRAL — 50/50 is a 2011 American comedy-drama film directed by Jonathan Levine, written by Will Reiser, and starring Joseph Gordon-Levitt, Seth Rogen, Anna Kendrick, Bryce Dallas Howard, and Anjelica Huston. …
https://en.wikipedia.org/wiki/50/50_(2011_film)
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wikipedia NEUTRAL — The 50 Greatest Players in NBA History, also referred to as NBA's 50th Anniversary All-Time Team, were chosen in 1996 to honor the 50th anniversary of the founding of the National Basketball Associati…
https://en.wikipedia.org/wiki/50_Greatest_Players_in_NBA_His…
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wikipedia NEUTRAL — Survivor 50: In the Hands of the Fans is the fiftieth season of the American competitive reality television series Survivor. It premiered on February 25, 2026, on CBS in the United States, and it is …
https://en.wikipedia.org/wiki/Survivor_50:_In_the_Hands_of_t…
+ 3 more evidence sources
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“They then combined their behavioral analysis with data extracted from a recently published crab phylogeny*—a study that reconstructed the evolutionary history of Brachyura using sequences of 10 genes for 344 species across most major lineages of true crabs.”
CORROBORATED
Two independent web search results confirm that the behavioral analysis was combined with data from a phylogeny reconstructing the evolutionary history of Brachyura using sequences of 10 genes and involving a large number of species (344 species mentioned in the claim, and 344 species/10 genes are mentioned in the web search results).
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wikipedia NEUTRAL — The Cretaceous–Paleogene (K–Pg) extinction event, formerly known as the Cretaceous-Tertiary (K–T) extinction event, was a major mass extinction of three-quarters of the plant and animal species on Ear…
https://en.wikipedia.org/wiki/Cretaceous–Paleogene_extinctio…
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wikipedia NEUTRAL — The New Zealand pea crab (Nepinnotheres novaezelandiae), is a species of small, parasitic crab that lives most commonly inside New Zealand green-lipped mussels. Adult females are about the size and sh…
https://en.wikipedia.org/wiki/New_Zealand_pea_crab
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wikipedia NEUTRAL — The wolverine ( WUUL-və-reen, US also WUUL-və-REEN; Gulo gulo), also called the carcajou or quickhatch (from East Cree, kwiihkwahaacheew), is the largest land-dwelling member of the family Mustelidae…
https://en.wikipedia.org/wiki/Wolverine
+ 3 more evidence sources
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“Of all 50 species covered, the team classified 35 as sideways movers and 15 as forward movers.”
CORROBORATED
Three independent web search results report the exact same classification breakdown: out of 50 species analyzed, 35 were classified as sideways movers and 15 as forward movers.
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web search NEUTRAL — Of all 50 species covered, the team classified 35 as sideways movers and 15 as forward movers. Their analyses revealed that the change to sideways walking occurred only once from a single, forward-wal…
https://phys.org/news/2026-04-crabs-iconic-sideways-evolved-…
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web search NEUTRAL — Of the 50 species, 35 were classified as sideways movers and 15 as forward movers based on FSI (Fig. 3; Table S1).
https://elifesciences.org/reviewed-preprints/110015
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web search NEUTRAL — Of the 50 species tested, 35 scored as sideways movers and 15 as forward movers, with a conspicuous gap separating the two groups.
https://booboone.com/ancient-step-made-crabs-the-most-succes…
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“Their analyses revealed that the change to sideways walking occurred only once from a single, forward-walking ancestor at the base of Eubrachyura (a group comprising more advanced crab species) and then remained highly conserved across true crabs.”
CORROBORATED
Two independent web search results confirm the core finding: the transition to sideways walking occurred only once from a single, forward-walking ancestor at the base of Eubrachyura, and this trait remained highly conserved.
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web search NEUTRAL — Australopithecus couple The savannah hypothesis (or savanna hypothesis) is a hypothesis that human bipedalism evolved as a direct result of human ancestors ' transition from an arboreal lifestyle to o…
https://en.wikipedia.org/wiki/Savannah_hypothesis
travel_explore
web search NEUTRAL — Here we show that the prevalence of 26 sideways locomotion in true crabs reflects a single evolutionary origin from a forward- 27 moving ancestor. Our behavioral analysis of 50 live crab species indic…
https://www.biorxiv.org/content/10.1101/2025.09.20.677458v1.…
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web search NEUTRAL — By assigning each branch of the family tree a locomotion state and running ancestral-state reconstruction models, they traced the single origin of sideways locomotion to the base of Eubrachyura, appro…
https://scienceblog.com/wildscience/2026/04/21/ancient-step-…
help
“The single origin and diversity of Eubrachyura are consistent with the idea that sideways walking acted as a key innovation that contributed to the ecological success of true crabs.”
INSUFFICIENT EVIDENCE
Although the context of the study suggests this conclusion, no direct evidence was gathered from the provided sources to confirm that the single origin and diversity of Eubrachyura are *consistent* with sideways walking being a key innovation contributing to ecological success. The evidence stops short of making this interpretive statement.
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“One likely adaptive advantage of this mode of travel is the ability to move rapidly at similar speeds in both lateral directions to allow for easier escape from predators.”
INSUFFICIENT EVIDENCE
No evidence was gathered from the provided sources to confirm the specific adaptive advantage that sideways walking allows for rapid movement at similar speeds in both lateral directions for predator escape.
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“The authors say it therefore represents a unique event that has occurred only in true crabs, and potentially crab spiders and leafhopper nymphs.”
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“Indeed, their analysis suggests that the origin of true crabs' sideways walk falls around 200 million years ago (the earliest Jurassic, immediately post–Triassic–Jurassic extinction).”
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“This period is marked by Pangaean rifting, expansion of shallow marine habitats and the early Mesozoic Marine Revolution, all of which typically increased ecological opportunity.”
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info Disclaimer: This analysis is generated by AI and should be used as a starting point for critical thinking, not as definitive truth. Claims are verified against publicly available sources. Always consult the original article and additional sources for complete context.