Newton Axel H, Spoutil Frantisek, Prochazka Jan, Black Jay R, Medlock Kathryn, Paddle Robert N, Knitlova Marketa, Hipsley Christy A, Pask Andrew J
School of BioSciences, University of Melbourne, Melbourne, Victoria, Australia.
Melbourne Museum, Museums Victoria, Melbourne, Victoria, Australia.
R Soc Open Sci. 2018 Feb 21;5(2):171914. doi: 10.1098/rsos.171914. eCollection 2018 Feb.
The Tasmanian tiger or thylacine () was an iconic Australian marsupial predator that was hunted to extinction in the early 1900s. Despite sharing striking similarities with canids, they failed to evolve many of the specialized anatomical features that characterize carnivorous placental mammals. These evolutionary limitations are thought to arise from functional constraints associated with the marsupial mode of reproduction, in which otherwise highly altricial young use their well-developed forelimbs to climb to the pouch and mouth to suckle. Here we present the first three-dimensional digital developmental series of the thylacine throughout its pouch life using X-ray computed tomography on all known ethanol-preserved specimens. Based on detailed skeletal measurements, we refine the species growth curve to improve age estimates for the individuals. Comparison of allometric growth trends in the appendicular skeleton (fore- and hindlimbs) with that of other placental and marsupial mammals revealed that despite their unique adult morphologies, thylacines retained a generalized early marsupial ontogeny. Our approach also revealed mislabelled specimens that possessed large epipubic bones (vestigial in thylacine) and differing vertebral numbers. All of our generated CT models are publicly available, preserving their developmental morphology and providing a novel digital resource for future studies of this unique marsupial.
袋狼是澳大利亚标志性的有袋类食肉动物，于20世纪初被猎杀至灭绝。尽管它们与犬科动物有显著相似之处，但未能进化出许多肉食性胎盘哺乳动物特有的专门解剖特征。这些进化限制被认为源于与有袋类繁殖方式相关的功能限制，在这种繁殖方式中，原本极度早产的幼崽会用发育良好的前肢爬到育儿袋和母亲嘴边吸食乳汁。在此，我们利用X射线计算机断层扫描技术，对所有已知的用乙醇保存的标本进行扫描，展示了袋狼育儿袋期完整的首个三维数字发育序列。基于详细的骨骼测量，我们完善了该物种的生长曲线，以改进对个体的年龄估计。通过比较有袋类动物附肢骨骼（前肢和后肢）与其他胎盘哺乳动物和有袋类动物的异速生长趋势，我们发现，尽管袋狼成年后的形态独特，但它们在早期发育阶段仍保留了有袋类动物的一般发育模式。我们的方法还发现了标签错误的标本，这些标本有较大的耻骨（袋狼中已退化）和不同的脊椎数量。我们生成的所有CT模型均已公开，保留了它们的发育形态，为今后对这种独特有袋类动物的研究提供了新颖的数字资源。
