{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,1]],"date-time":"2026-09-01T03:33:55Z","timestamp":1788233635630,"version":"build-2803163510"},"reference-count":57,"publisher":"PeerJ","license":[{"start":{"date-parts":[[2021,6,17]],"date-time":"2021-06-17T00:00:00Z","timestamp":1623888000000},"content-version":"unspecified","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"University of Wroc\u0142aw through the donation by Ministry of Science and Higher Education","award":["0420\/2316\/17"],"award-info":[{"award-number":["0420\/2316\/17"]}]},{"name":"University of Wroc\u0142aw through the donation by Ministry of Science and Higher Education","award":["0420\/2566\/18"],"award-info":[{"award-number":["0420\/2566\/18"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"abstract":"<jats:p>\n                    Despite the long history of embryological studies of squamates, many groups of this huge clade have received only limited attention. One such understudied group is the anguimorphs, a clade comprising morphologically and ecologically very diverse lizards. We describe several stages of embryonic development of\n                    <jats:italic>Anguis fragilis<\/jats:italic>\n                    , a limbless, viviparous anguimorph. Interestingly, in several clutches we observe high morphological variation in characters traditionally important in classifying embryos into developmental stages. The causes of this variation remain unknown but environmental factors do not seem to be very important. Additionally, we describe the state of ossification in several perinatal specimens of\n                    <jats:italic>A. fragilis<\/jats:italic>\n                    . The cranial skeleton is relatively poorly ossified around the time of birth, with all of the bones constituting the braincase unfused. On the other hand, the vertebral column is well ossified, with the neurocentral sutures closed and the neural arches fused in all postatlantal vertebrae. Such an advanced state of ossification may be related to the greater importance of the vertebral column in locomotion in limbless species than in ones with fully-developed limbs. Numerous factors seem to affect the state of ossification at the time of hatching or birth in squamates, including phylogenetic position, mode of reproduction and, potentially, limblessness. However, data from a greater number of species are needed to reach firmer conclusions about the relative importance of these variables in certain clades.\n                  <\/jats:p>","DOI":"10.7717\/peerj.11621","type":"journal-article","created":{"date-parts":[[2021,6,17]],"date-time":"2021-06-17T04:33:23Z","timestamp":1623904403000},"page":"e11621","source":"Crossref","is-referenced-by-count":15,"title":["Embryonic development and perinatal skeleton in a limbless, viviparous lizard,\n                    <i>Anguis fragilis<\/i>\n                    (Squamata: Anguimorpha)"],"prefix":"10.7717","volume":"9","author":[{"given":"Tomasz","family":"Skawi\u0144ski","sequence":"first","affiliation":[{"name":"Department of Evolutionary Biology and Conservation of Vertebrates, University of Wroclaw, Wroc\u0142aw, Poland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Grzegorz","family":"Sk\u00f3rzewski","sequence":"additional","affiliation":[{"name":"Museum of Natural History, University of Wroclaw, Wroc\u0142aw, Poland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Bartosz","family":"Borczyk","sequence":"additional","affiliation":[{"name":"Department of Evolutionary Biology and Conservation of Vertebrates, University of Wroclaw, Wroc\u0142aw, Poland"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"4443","published-online":{"date-parts":[[2021,6,17]]},"reference":[{"key":"10.7717\/peerj.11621\/ref-1","doi-asserted-by":"publisher","first-page":"326","DOI":"10.1111\/ede.12042","article-title":"Developmental sequences of squamate reptiles are taxon specific","volume":"15","author":"Andrews","year":"2013","journal-title":"Evolution & Development"},{"key":"10.7717\/peerj.11621\/ref-2","doi-asserted-by":"publisher","first-page":"451","DOI":"10.1670\/10-312.1","article-title":"Character variation in embryonic development of the lizard Uta stansburiana","volume":"45","author":"Andrews","year":"2011","journal-title":"Journal of Herpetology"},{"key":"10.7717\/peerj.11621\/ref-3","doi-asserted-by":"publisher","first-page":"396","DOI":"10.1670\/16-124","article-title":"Oviposition to hatching: development of Varanus rosenbergi","volume":"51","author":"Andrews","year":"2017","journal-title":"Journal of Herpetology"},{"key":"10.7717\/peerj.11621\/ref-4","first-page":"707","article-title":"Die Gastrulation bei der Blindschleiche (Anguis fragilis L.)","volume":"83","author":"Ballowitz","year":"1905","journal-title":"Zeitschrift f\u00fcr wissenschaftliche Zoologie"},{"key":"10.7717\/peerj.11621\/ref-5","doi-asserted-by":"publisher","first-page":"482","DOI":"10.1111\/j.1096-3642.1940.tb02418.x","article-title":"The anterior brain-case and interorbital septum in Sauropsida, with a consideration on the origin of snakes, with a consideration on the origin of snakes","volume":"41","author":"Bellairs","year":"1949","journal-title":"Journal of the Linnean Society of London, Zoology"},{"key":"10.7717\/peerj.11621\/ref-6","doi-asserted-by":"publisher","first-page":"439","DOI":"10.1016\/S0940-9602(00)80050-3","article-title":"Correlative changes during early morphogenesis of the sacroiliac complex in squamate reptiles","volume":"182","author":"Borkhvardt","year":"2000","journal-title":"Annals of Anatomy"},{"key":"10.7717\/peerj.11621\/ref-7","doi-asserted-by":"publisher","first-page":"230","DOI":"10.1111\/j.1096-0031.2010.00330.x","article-title":"A combined evidence phylogenetic analysis of Anguimorpha (Reptilia: Squamata)","volume":"27","author":"Conrad","year":"2011","journal-title":"Cladistics"},{"key":"10.7717\/peerj.11621\/ref-8","doi-asserted-by":"publisher","first-page":"376","DOI":"10.1038\/s41467-017-02788-3","article-title":"The ecological origins of snakes as revealed by skull evolution","volume":"9","author":"Da\u00a0Silva","year":"2018","journal-title":"Nature Communications"},{"key":"10.7717\/peerj.11621\/ref-9","first-page":"707","article-title":"The early development of the chondrocranium of the lizard","volume":"s2-73","author":"De Beer","year":"1930","journal-title":"Quarterly Journal of Microscopical Science"},{"key":"10.7717\/peerj.11621\/ref-10","doi-asserted-by":"publisher","first-page":"229","DOI":"10.3109\/10520297709116780","article-title":"Enzyme clearing of Alcian blue stained whole small vertebrates for demonstration of cartilage","volume":"52","author":"Dingerkus","year":"1977","journal-title":"Stain Technology"},{"key":"10.7717\/peerj.11621\/ref-11","first-page":"1","article-title":"The skull of lizards and tuatara","volume-title":"Biology of the Reptilia. 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