Megalochelys: gigantic tortoise from the Neogene of Myanmar
- Published
- Accepted
- Subject Areas
- Paleontology
- Keywords
- turtle, Testudinidae, Cryptodira, Testudines, upper Miocene to lower Pliocebe, Neogene, Cenozoic, systenatics, sexual dimorphism
- Copyright
- © 2015 Hirayama et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ PrePrints) and either DOI or URL of the article must be cited.
- Cite this article
- 2015. Megalochelys: gigantic tortoise from the Neogene of Myanmar. PeerJ PrePrints 3:e961v1 https://doi.org/10.7287/peerj.preprints.961v1
Abstract
Background. The genus Megalochelys is the largest known testudinid (family Testudnidae) found from the upper Miocene to lower Pleistocene of India to Indonesian Islands. The maximum length of the shell in this genus has been estimated as up to about 2 m long based on a specimen from the lower Pleistocene of Java Island, Indonesia. Recently, joint paleontological expeditions of Japan and Myanmar led by M. Takai have unearthed abundant fossils of this genus from the Neogene since 2003. These materials shed new light on this unique gigantic tortoise. Methods. All materials of Megalochelys were found from the Lower Irrawaddy Beds in poor preservation except for one nearly complete shell. The shell lengths from the fragmentary materials were estimated by using those of medium to large–sized testudinids. Results. Postcranial materials, including twenty-five epiplastra, one cervical vertebra, appendicular skeletons, and one nearly complete shell (about 180 cm long) have been discovered from the Lower Irrawaddy Beds in narrow area near Pauk Township. They are associated with terrestrial mammals such as Stegodon, suggesting that the age of the fossil bearing beds are attributed to the late Miocene to the early Pliocene. Of these, the epiplastra in two morphological states appear to be derived from sexual dimorphism of this genus as seen in several testudinids and noted previously by second author on the relevant materials. A huge distal portion of the humerus (ca. 31 cm long) suggests that its original length was about 75 cm. Discussion. A nearly complete shell is about 180 cm long, although this seems a rather young male individual of Megalochelys based on its rather slender epiplastral morphology, which is nearly as large as given estimation of the maximum shell length from Java material. On the other hand, the largest humerus, estimated as 75 cm in original length, suggests its shell was about 270 cm long. This estimation seems to be supported by other isolated materials such as the nuchal plate, largest epiplastron, and the pectoral girdle. Hitherto, Stupendemys geographica (from the Pliocene of Venezuela) and Archelon ischyros (from the Lower Cretaceous of North America) were regarded as largest known turtles with about 220 cm long shell. However, Megalochelys from Myanmar involves much larger specimens, suggesting this is a true largest known turtle.
Author Comment
This is an abstract which has been accepted for the 5th Turtle Evolution Symposium.