1 Scientific RepoRts | 7: 1964 | DOI:10.1038/s41598-017-01899-7 www.nature.com/scientificreports What the skull and scapular morphology of the dugong (Dugong dugon) can tell us: sex, habitat and body length? Korakot Nganvongpanit 1,2 , Kittisak Buddhachat 1,2,3 , patcharaporn Kaewmong 4 , phaothep Cherdsukjai 4 & Kongkiat Kittiwatanawong 4 the dugong (Dugong dugon, Müller) is an endangered marine mammal species. We examined the relationship between sex, habitat and body length based on the skull and scapular morphology and morphometrics of 81 dugong samples in Thailand. A total of 58 parameters from the skull and scapula (25 from the cranium, 23 from the mandible and 10 from the scapula) as well as tusks were used in this study. Data were analyzed by univariate analysis, followed by discriminant analysis and multivariate linear regression. Here we show, 100% and 98.5% accuracy rates for sexing using large tusks and the skull, respectively. scapular morphology using the caudal border tubercle and coracoid process showed 91.30% and 96.15% accuracy rates for identifying males and females. Skull morphometrics could categorize dugong habitat, i.e. living in the Andaman Sea or Gulf of Thailand, with 100% accuracy. Moreover, our model could be used to estimate body length with coefcient of determination (R 2 ) of 0.985. The results of our study showed that skull morphology and morphometric measurements could be used as a tool for sex identifcation, location identifcation and estimation of body length. But scapular morphology is the best tool for sex identifcation in dugongs. Te dugong (Dugong dugon, Müller) is one of four herbivorous marine mammal species surviving in the family Dugongidae, order Sirenia 1 . Presently, the dugong is an endangered species and has been placed in Appendix I of the Convention on International Trade in Endangered Species (CITES). Te highest population of dugongs is found in Australia 2 . In the South to Southeast Asia region, Tailand is the country with the highest population of dugongs 3–6 . Nevertheless, dugongs are rare and are restricted only to some areas along both coastlines of Tailand: the Andaman Sea (i.e. Ranong, Phang Nga, Phuket, Krabi, Trang and Satun) and the Gulf of Tailand (i.e. Rayong, Chanthaburi, Trat and Surat Tani provinces) 4 . Te population of dugongs in Tailand was observed in 2000– 2001 and reported in 2005. About 200 dugongs were estimated to be living in the Andaman Sea and about 50 in the Gulf of Tailand 3 . Te best minimum estimate of population abundance is 123 animals (CV = 60.8%) in Trang province. Due to the limited numbers of this animal, scientists around the world have been trying to study all aspects of dugong biology (i.e. morphology, physiology, ecology and theriology). However, it is very difcult to design a standard study on this animal for many reasons, e.g. the number of animal specimens available at each institute is very low, and because dugongs live in the ocean they cannot be maintained in tanks or aquariums. For these reasons, all studies that are conducted on this animal are very important, even a small study. Moreover, for better understanding of dugong biology, scientists must combine those small studies together. Animal bone morphology – in particular, skull (cranium plus mandible) morphology – has been studied in many aspects: for example, the diversity of skull morphology within canine species 7 ; for species classifcation in canids and felids 8–10 , and for classifying animals living in diferent locations, such as captive and wild African lions 11 ; for estimating age in African elephants 12 ; and for sexing in dogs 13 , cats 14 and humans 15 . Bones of the dugong have been studied for over 100 years. Based on a literature review by James 16 , skeletal features of the 1 Excellence Center in Veterinary Bioscience, Chiang Mai University, Chiang Mai, 50100, Thailand. 2 Animal Bone and Joint Research Laboratory, Department of Veterinary Biosciences and Public Health, Faculty of Veterinary Medicine, Chiang Mai University, Chiang Mai, 50100, Thailand. 3 Department of Biology, Faculty of Science, Naresuan University, Phitsanulok, 65000, Thailand. 4 Phuket Marine Biological Center, Phuket, 83000, Thailand. Correspondence and requests for materials should be addressed to K.N. (email: korakot.n@cmu.ac.th) Received: 19 December 2016 Accepted: 6 April 2017 Published: xx xx xxxx opeN