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Some treated it as a stray edge of the abdominal wall. Others said it was part of a thigh muscle.<\/p>\n
For more than a century, the tissue sat in the scientific literature, misidentified or ignored.<\/p>\n
Its role in one of the most recognizable walks in the animal kingdom was completely unknown.<\/p>\n
A century-old puzzle<\/p>\n
The strange tissue had been spotted since Victorian biologists first dissected penguins<\/a> brought back from Antarctic expeditions. <\/p>\n Some called it a slip of a belly muscle. Others tied it to a thigh muscle along the back of the leg.<\/p>\n Penguins are known for many oddities. They have dense bones, stiff flippers, and knees tucked deep inside the body cavity in a permanent squat. <\/p>\n The soft tissue behind that posture stayed murky for an animal that draws crowds in every major aquarium.<\/p>\n A new dissection-based study finally settles the question. That long-confused tissue is in fact a distinct muscle, found in no other living bird<\/a>. <\/p>\n And it does something specific for how penguins move.<\/p>\n Comparing the limb muscles <\/p>\n The answer came from a careful comparative dissection co-led by Dr. Justin A. Georgi and Dr. Margaret I. Hall, anatomists at Midwestern University<\/a> in Glendale, Arizona. <\/p>\n The team also included veterinary staff at SeaWorld San Diego and experts at a medical imaging firm.<\/p>\n Two macaroni penguins<\/a> formed the basis of the work. Both had been humanely euthanized at the marine park during end-of-life veterinary care and donated for research. <\/p>\n Macaronis are smaller than emperor penguins, named for the bright yellow plumes above each eye.<\/p>\n The team compared every limb muscle in the macaronis against equivalents in flying birds. Old dissection records \u2013 some over a century deep \u2013 went into the comparison too. <\/p>\n New work on both fronts pinned down what attaches where and what each piece actually does.<\/p>\n A muscle that\u2019s exclusive to penguins <\/p>\n The long-disputed tissue, the researchers concluded, is not a sliver of anything else. It stands on its own. <\/p>\n They propose naming it the adductor tibialis, after its main job of pulling the leg bones inward toward the center of the body.<\/p>\n The muscle starts at the breastbone, runs down on either side, and attaches near the top of each lower leg bone. <\/p>\n Both halves meet along a fibrous seam beneath the chest. When it fires, both knees draw inward together.<\/p>\n It does not appear in any other living bird the team examined. That makes it a penguin specialty \u2013 an anatomical novelty tied to a body that does two very different jobs in two very different environments<\/a>.<\/p>\n Penguins are built for water<\/p>\n Penguins do not fly through air<\/a>. They fly through water, which is roughly 800 times denser.<\/p>\n Moving a wing through that resistance takes power on both the upstroke and downstroke \u2013 not just the single push down flying birds rely on.<\/p>\n The chest muscle flying birds use to lift the wing, the supracoracoideus<\/a>, came back strikingly enlarged in the macaronis. <\/p>\n A different shoulder arrangement also gave the flipper a wider arc, with a strong backward sweep that propels the bird through water.<\/p>\n Underwater, drag becomes the real enemy. A penguin pursuing krill cannot afford splayed legs behind it. <\/p>\n The newly named muscle appears to hold the lower legs tucked close together during a dive, a posture that would smooth the body into a cleaner profile.<\/p>\n The muscle supports waddling <\/p>\n On land, the same muscle pulls double duty. Penguins stand on bent knees tucked deep into the body with their feet far apart at the base. <\/p>\n Without something holding the lower legs toward center, balance would fail step after step.<\/p>\n Earlier biomechanics work had already shown the rocking is not the energy drain people assumed. <\/p>\n A paper<\/a> from 2000 found the sway actually captures and releases energy between steps. Short legs, not the waddle itself, are what make penguin walking expensive.<\/p>\n What the new anatomy adds is the mechanism. The adductor tibialis appears to hold one leg steady while the bird leans, then helps power the other leg forward. <\/p>\n \u201cIt stabilizes the leg against the body when the penguin is leaning to one side,\u201d Georgi said.<\/p>\n What this changes<\/p>\n The new map will be useful to people working with penguins every day. <\/p>\n Zoo veterinarians, aquarium staff, and rehabilitation centers handling rescued birds have been working from anatomical references that were patchy and, in places, simply wrong.<\/p>\n \u201cThis muscle has been mentioned for over a century, but usually in a confused way,\u201d said Caro Acosta Hospitaleche, a paleontologist at the La Plata Museum in Argentina, calling the dissection a long-overdue clarification.<\/p>\n The mapped musculature also gives evolutionary biologists a cleaner picture of how flightless underwater birds rebuilt the basic bird body plan. <\/p>\n Earlier research<\/a> had shown the swap from flapping wing to swimming flipper involves real trade-offs in limb function.<\/p>\n Broader implications of the study <\/p>\n For the first time, a muscle that puzzled anatomists for more than a century finally has both a name and a clear purpose. <\/p>\n The newly identified adductor tibialis appears to help penguins stay streamlined underwater and stable during their signature waddle on land. <\/p>\n The discovery not only rewrites part of penguin anatomy, but could also improve veterinary care, rehabilitation, and future studies of how birds evolved to thrive in the sea.<\/p>\n The study is published in the journal The Anatomical Record<\/a>.<\/p>\n \u2014\u2013<\/p>\n Like what you read? Subscribe to our newsletter<\/a> for engaging articles, exclusive content, and the latest updates.<\/p>\n Check us out on EarthSnap<\/a>, a free app brought to you by Eric Ralls<\/a> and Earth.com.<\/p>\n \u2014\u2013<\/p>\n","protected":false},"excerpt":{"rendered":"Every penguin dissection going back to the 1880s turned up the same puzzling scrap of tissue \u2013 a…\n","protected":false},"author":2,"featured_media":700759,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[26],"tags":[64,63,128,338],"class_list":["post-700758","post","type-post","status-publish","format-standard","has-post-thumbnail","category-wildlife","tag-au","tag-australia","tag-science","tag-wildlife"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts\/700758","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/comments?post=700758"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts\/700758\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/media\/700759"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/media?parent=700758"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/categories?post=700758"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/tags?post=700758"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}