{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,8]],"date-time":"2026-09-08T03:26:14Z","timestamp":1788837974210,"version":"build-2803163510"},"reference-count":45,"publisher":"PeerJ","license":[{"start":{"date-parts":[[2023,6,20]],"date-time":"2023-06-20T00:00:00Z","timestamp":1687219200000},"content-version":"unspecified","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"JSPS KAKENHI","award":["JP 19H03290"],"award-info":[{"award-number":["JP 19H03290"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"abstract":"<jats:p>The mammalian lower jaw comprises a single bone, the dentary, which is a unique feature among vertebrates. The lower jaws of extinct non-mammalian synapsids were composed of the dentary and several postdentary bones. Synapsid fossils exhibit variation in the dentary size relative to the overall lower jaw. An evolutionary trend toward dentary enlargement and postdentary reduction in non-mammalian synapsids has long been documented but has not been established using modern phylogenetic comparative methods. In this study, we examine the evolutionary pattern of dentary size relative to the lower jaw through phylogenetic analyses of measurements in a broad range of non-mammalian synapsid taxa. Our analyses revealed an evolutionary trend toward dentary area enlargement relative to the overall lower jaw in the lateral view across all non-mammalian synapsids. This trend is likely due to vertical expansion of the dentary given that the same trend is not evident when looking at anterior to posterior measurements of the dentary relative to the lower jaw as a whole in lateral view. Ancestral character reconstructions revealed that the evolution of the measurements was not unidirectional in non-mammalian synapsids. Our results provide no evidence of an evolutionary trend toward the dentary enlargement at the expense of postdentary bones across non-mammalian synapsids. This implies that the evolutionary origin of the mammalian lower jaw is not adequately explained by the evolutionary trend of dentary enlargement throughout non-mammalian synapsids. Instead, selection that occurred during the transition from non-mammalian cynodonts to early mammals may have produced the mammalian lower jaw.<\/jats:p>","DOI":"10.7717\/peerj.15575","type":"journal-article","created":{"date-parts":[[2023,6,20]],"date-time":"2023-06-20T07:47:30Z","timestamp":1687247250000},"page":"e15575","source":"Crossref","is-referenced-by-count":1,"title":["Revisiting the evolutionary trend toward the mammalian lower jaw in non-mammalian synapsids in a phylogenetic context"],"prefix":"10.7717","volume":"11","author":[{"given":"Tomohiro","family":"Harano","sequence":"first","affiliation":[{"name":"Division of Liberal Arts and Sciences, Aichi Gakuin University, Nisshin, Aichi, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Masakazu","family":"Asahara","sequence":"additional","affiliation":[{"name":"Division of Liberal Arts and Sciences, Aichi Gakuin University, Nisshin, Aichi, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"4443","published-online":{"date-parts":[[2023,6,20]]},"reference":[{"key":"10.7717\/peerj.15575\/ref-1","doi-asserted-by":"publisher","first-page":"403","DOI":"10.1002\/jmor.1051470404","article-title":"Evolution of the mammalian middle ear","volume":"147","author":"Allin","year":"1975","journal-title":"Journal of Morphology"},{"key":"10.7717\/peerj.15575\/ref-2","doi-asserted-by":"crossref","first-page":"117","DOI":"10.1515\/9783110341553-005","article-title":"Non-mammalian synapsids: the deep roots of the mammalian family tree","volume-title":"Handbook of zoology: mammalia: mammalian evolution, diversity and systematics","author":"Angielczyk","year":"2018"},{"key":"10.7717\/peerj.15575\/ref-3","doi-asserted-by":"publisher","first-page":"20141642","DOI":"10.1098\/rspb.2014.1642","article-title":"Nocturnality in synapsids predates the origin of mammals by over 100 million years","volume":"281","author":"Angielczyk","year":"2014","journal-title":"Proceedings of the Royal Society B: Biological Sciences"},{"key":"10.7717\/peerj.15575\/ref-4","doi-asserted-by":"publisher","first-page":"573","DOI":"10.1126\/science.168.3931.573","article-title":"Dentary-squamosal joint and the origin of mammals","volume":"168","author":"Barghusen","year":"1970","journal-title":"Science"},{"key":"10.7717\/peerj.15575\/ref-5","doi-asserted-by":"publisher","first-page":"68","DOI":"10.1139\/facets-2016-0046","article-title":"Selection towards larger body size in both herbivorous and carnivorous synapsids during the Carboniferous","volume":"2","author":"Brocklehurst","year":"2017","journal-title":"Facets"},{"key":"10.7717\/peerj.15575\/ref-6","doi-asserted-by":"publisher","first-page":"490","DOI":"10.1111\/j.1469-7998.1904.tb08307.x","article-title":"On the structure of the theriodont mandible, and on its mode of articulation with the skull","volume":"74","author":"Broom","year":"1904","journal-title":"Proceedings of the Zoological Society of London"},{"key":"10.7717\/peerj.15575\/ref-7","volume-title":"Model selection and multimodel inference: a practical information-theoretic approach","author":"Burnham","year":"2002","edition":"2"},{"key":"10.7717\/peerj.15575\/ref-8","doi-asserted-by":"publisher","first-page":"104","DOI":"10.1038\/s41597-019-0049-y","article-title":"A dataset of egg size and shape from more than 6,700 insect species","volume":"6","author":"Church","year":"2019","journal-title":"Scientific Data"},{"key":"10.7717\/peerj.15575\/ref-9","doi-asserted-by":"publisher","first-page":"20190138","DOI":"10.1098\/rstb.2019.0138","article-title":"Were the synapsids primitively endotherms? 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