{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,1]],"date-time":"2026-08-01T09:51:46Z","timestamp":1785577906892,"version":"3.56.0"},"reference-count":21,"publisher":"The Royal Society","issue":"1608","license":[{"start":{"date-parts":[[2006,10,31]],"date-time":"2006-10-31T00:00:00Z","timestamp":1162252800000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/royalsociety.org\/journals\/ethics-policies\/data-sharing-mining\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Proc. R. Soc. B."],"published-print":{"date-parts":[[2007,2,7]]},"abstract":"<jats:p>Elephants have the longest pregnancy of all mammals, with an average gestation of around 660 days, so their embryonic and foetal development have always been of special interest. Hitherto, it has only been possible to estimate foetal ages from theoretical calculations based on foetal mass. The recent development of sophisticated ultrasound procedures for elephants has now made it possible to monitor the growth and development of foetuses of known gestational age conceived in captivity from natural matings or artificial insemination. We have studied the early stages of pregnancy in 10 captive Asian and 9 African elephants by transrectal ultrasound. Measurements of foetal crown\u2013rump lengths have provided the first accurate growth curves, which differ significantly from the previous theoretical estimates based on the cube root of foetal mass. We have used these to age 22 African elephant foetuses collected during culling operations. Pregnancy can be first recognized ultrasonographically by day 50, the presumptive yolk sac by about day 75 and the zonary placenta by about day 85. The trunk is first recognizable by days 85\u201390 and is distinct by day 104, while the first heartbeats are evident from around day 80. By combining ultrasonography and morphology, we have been able to produce the first reliable criteria for estimating gestational age and ontological development of Asian and African elephant foetuses during the first third of gestation.<\/jats:p>","DOI":"10.1098\/rspb.2006.3738","type":"journal-article","created":{"date-parts":[[2006,11,3]],"date-time":"2006-11-03T16:15:32Z","timestamp":1162570532000},"page":"323-331","source":"Crossref","is-referenced-by-count":30,"title":["Foetal age determination and development in elephants"],"prefix":"10.1098","volume":"274","author":[{"given":"Thomas","family":"Hildebrandt","sequence":"first","affiliation":[{"name":"Institute for Zoo and Wildlife ResearchAlfred-Kowalke-Stra\u00dfe 17 10315 Berlin, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Barbara","family":"Drews","sequence":"additional","affiliation":[{"name":"Institute for Zoo and Wildlife ResearchAlfred-Kowalke-Stra\u00dfe 17 10315 Berlin, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ann P","family":"Gaeth","sequence":"additional","affiliation":[{"name":"Department of Zoology, University of MelbourneMelbourne, Victoria 3010, Australia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Frank","family":"Goeritz","sequence":"additional","affiliation":[{"name":"Institute for Zoo and Wildlife ResearchAlfred-Kowalke-Stra\u00dfe 17 10315 Berlin, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Robert","family":"Hermes","sequence":"additional","affiliation":[{"name":"Institute for Zoo and Wildlife ResearchAlfred-Kowalke-Stra\u00dfe 17 10315 Berlin, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Dennis","family":"Schmitt","sequence":"additional","affiliation":[{"name":"Department of Agriculture, Missouri State UniversitySpringfield, MO 65897, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Charlie","family":"Gray","sequence":"additional","affiliation":[{"name":"African Lion SafariCambridge, Ontario, Canada N1R 5S2"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Peter","family":"Rich","sequence":"additional","affiliation":[{"name":"African Lion SafariCambridge, Ontario, Canada N1R 5S2"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wolf Juergen","family":"Streich","sequence":"additional","affiliation":[{"name":"Institute for Zoo and Wildlife ResearchAlfred-Kowalke-Stra\u00dfe 17 10315 Berlin, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Roger V","family":"Short","sequence":"additional","affiliation":[{"name":"Department of Zoology, University of MelbourneMelbourne, Victoria 3010, Australia"},{"name":"Faculty of Medicine, University of MelbourneMelbourne, Victoria 3010 Australia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marilyn B","family":"Renfree","sequence":"additional","affiliation":[{"name":"Department of Zoology, University of MelbourneMelbourne, Victoria 3010, Australia"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"175","published-online":{"date-parts":[[2006,10,31]]},"reference":[{"key":"e_1_3_2_2_1","doi-asserted-by":"publisher","DOI":"10.1098\/rstb.2006.1831"},{"key":"e_1_3_2_3_1","doi-asserted-by":"publisher","DOI":"10.1016\/S0143-4004(03)00102-4"},{"key":"e_1_3_2_4_1","doi-asserted-by":"publisher","DOI":"10.1098\/rstb.1964.0007"},{"key":"e_1_3_2_5_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.ygcen.2004.01.013"},{"key":"e_1_3_2_6_1","first-page":"512","article-title":"Foetal mass and date of conception in African elephants: a revised formula","volume":"80","author":"Craig G.C","year":"1984","journal-title":"S. 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