Most mammals had an umbilical cord and eventually umbilicus, but sea shellfish, the whole animal, looks like an umbilicus.
- 2.Oldest live-birth fossil found; fish had umbilical cord. National Geographic News. 28 May 2008.Google Scholar
- 3.Flannery TF. Kangaroos: 15 million years of Australian bounders. In: Archer M, Clayton G, editors. Vertebrate zoogeography and evolution in Australasia. Carlisle: Hesperian Press; 1984. p. 817–35.Google Scholar
- 4.Frith HJ, Coleby JH. Kangaroos. Melbourne: F.W. Cheshire Publishing Pty Ltd; 1969. p. 110–9.Google Scholar
© Springer International Publishing AG 2018