Howler monkey dietary changes Fossil lower jaws recovered from the La Venta deposits in Colombia preserved the anatomical clues behind the early dietary change.<\/p>\n By analyzing the fossils, Dr. Siobhan B. Cooke at Johns Hopkins University<\/a> documented teeth built for grinding and slicing tough leaves.<\/p>\n The fossils place leaf eating in the howler monkey lineage more than 13 million years ago, far earlier than previously documented in South American primates.<\/p>\n The discovery anchors a critical turning point in primate evolution, but leaves open broader questions about how this adaptation reshaped life in the ancient Amazonian ecosystem<\/a>.<\/p>\n Teeth adapted for chewing leaves<\/p>\n Tall ridges on the molars mattered because they met like blades when the animal<\/a> chewed tougher plant tissue.<\/p>\n As the teeth closed, those cutting edges helped break down tough plant fibers, which are harder to handle than soft fruit.<\/p>\n Modern howler monkeys show much the same pattern, which made the fossil resemblance hard to dismiss as chance.<\/p>\n \u201cBefore the discovery of Stirtonia, we didn\u2019t have any evidence of leaf consumption in South American primates,\u201d said Dr. Cooke.<\/p>\n Leaves and howler monkey size<\/p>\n Body size estimates placed Stirtonia victoriae, an extinct ancestor of modern howler monkeys, at roughly 15 to 19 pounds \u2013 far above most older South American monkey fossils.<\/p>\n With leaves available across a forest, that broader food supply could support larger bodies even when ripe fruit ran low.<\/p>\n \u201cPrior to this, the South American monkeys we have in the fossil record are much smaller,\u201d noted Dr. Cooke.<\/p>\n That size makes Stirtonia victoriae the earliest known larger-bodied monkey in the South American fossil record.<\/p>\n La Venta is significant because many monkey species shared one landscape while northern South America was still reorganizing.<\/p>\n By adding leaves to fruit, these early howler relatives likely reduced direct competition with neighbors chasing softer foods.<\/p>\n Researchers counted 12 primate species at the site, making it the earliest known Amazon-like monkey community with striking dietary variety.<\/p>\n \u201cNow, we can begin to pinpoint when different modern lineages started to evolve,\u201d said Dr. Cooke.<\/p>\n Broader environmental change <\/p>\n Evidence<\/a> from La Venta points to a mostly forested mosaic shaped by shifting rivers, not one stable habitat.<\/p>\n As channels moved and feeding zones changed, monkeys faced a menu that rewarded flexibility more than strict dependence on fruit.<\/p>\n More than 100 vertebrate species came from the site, showing that these primates lived in a busy and varied animal world.<\/p>\n That backdrop made the new jaws more than an isolated fossil, because they captured adaptation during broader environmental change.<\/p>\n Howler monkey \u201chowls\u201d evolved<\/p>\n Deep lower jaws gave the fossils another kind of importance by hinting at when the howler call may have taken shape.<\/p>\n In living howlers<\/a>, an enlarged hyoid \u2013 a throat bone that can amplify sound \u2013 helps produce booming calls.<\/p>\n Matching jaw depth in Stirtonia victoriae suggested space for a similar structure, even though that bone was not preserved.<\/p>\n That clue stayed tentative, because fossils cannot record soft tissue, living behavior, or the sound itself.<\/p>\n The leaf diet shaped survival<\/p>\n Leaves are common, but they are tougher and less energy-rich than ripe fruit, so they reward specialized chewing and slow digestion.<\/p>\n Modern howlers manage that challenge with strong shearing teeth, long digestion, and a low-energy routine built around abundant food.<\/p>\n In that light, the fossil teeth suggest not a brief experiment but an early form of a long-lasting strategy.<\/p>\n That continuity gave the jaws more weight, because it linked an ancient diet to a living monkey way of life.<\/p>\n Early branch of the family tree<\/p>\n Timing strengthened the argument because newer family trees<\/a> place Stirtonia near the base of the howler branch.<\/p>\n By tying a recognizable feeding style to that early split, the jaws turned an abstract family tree into an ecological story.<\/p>\n Another point mattered just as much: Stirtonia victoriae closely resembled living howler monkeys in jaw shape, not just diet.<\/p>\n That overlap gives researchers a sharper marker for when South American monkey branches began to look and live differently.<\/p>\n Plant diet changed monkey evolution<\/p>\n These fossils answered one major question, but they left several others open, including how loudly this animal could actually call.<\/p>\n Lower jaws can reveal diet and possible voice anatomy, yet they cannot show soft tissue, gut biology, or daily behavior.<\/p>\n Body mass estimates also changed with the calculation method, leaving the specialization of some early howler relatives<\/a> less certain.<\/p>\n Additional skulls, throat bones, and limb fossils may reveal how quickly this monkey line acquired the full modern howler package.<\/p>\n Ultimately, the fossils show that leaf eating was already shaping howler monkey evolution 13 million years ago.<\/p>\n The study reveals how a single dietary shift helped redefine body size, competition, and life in South America\u2019s ancient forests.<\/p>\n The study is published in the journal PaleoAnthropology<\/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":"Ancient relatives of howler monkeys were eating leaves 13 million years ago, providing the earliest clear fossil evidence…\n","protected":false},"author":2,"featured_media":479588,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[26],"tags":[90,56,54,55,4407],"class_list":{"0":"post-479587","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-wildlife","8":"tag-science","9":"tag-uk","10":"tag-united-kingdom","11":"tag-unitedkingdom","12":"tag-wildlife"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/posts\/479587","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/comments?post=479587"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/posts\/479587\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/media\/479588"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/media?parent=479587"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/categories?post=479587"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/uk\/wp-json\/wp\/v2\/tags?post=479587"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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