Fossil Mammals from the Late Miocene of Vietnam

Fossil mammals are able to tell us much about the ancient world but little is known about the evolutionary history of mammals in Southeast Asia. The vast amount of knowledge comes from Burma and Thailand but research in Vietnam has given us much insight.

Scholars travelled to Hangmon, a location in the northwest region of Vietnam in Son La Province, west of Moc Chau and southeast of Son La. At the site of a deserted coalmine, coal-bearing sediments were shown to preserve fossil plants indicative of a humid, subtropical climate. The researchers were able to be collected with surface prospecting and also by screen washing.

“A fragmentary left maxilla preserving M1-2 and an isolated left P4, that was found close to the maxilla, represent a tragulid. The specimens are similar in morphology to those of Dorcatherium minus from the Chinji of Pakistan but are slightly smaller: Ml is 9.2 mm in its anteroposterior length and M2 is 8.8 mm. The first and second upper molars resemble those of other tragulids in: (1) being bunose lenodont teeth; (2) having a mesostyle that is pyramid shaped and larger than the parastyle; (3) having an anterior lingual lobe (protocone) that is rounded and projects strongly anteriorly; and (4) having a protocone crescent that is L-shaped - that is the posterior arm of the crescent is perpendicular to the anterior arm. These upper molars resemble Dorcatherium specimens from the middle Miocene of Sihong, China, described by Zhanxiang and Yumin in having a weakly developed cingulum that is stronger on the posterior lingual lobe (hypocone) than on the anterior lingual lobe. The partial maxilla does, however, differ from previously described Dorcatherium specimens described by Gentry and Zhanxiang and Yumin in having a first molar that is larger than the second molar”.

Scientists were able to learn much from the fossils that were found. A lower left molar, a lower right third molar and an upper left fourth premolar were among the fossils found. Some of these represent the presence of a rhinocerotid and the fully bilophodont morphology characteristic of the rhinocerotid subfamilies Aceratheriinae and Rhinocerotinae.

Looking at the fossils and the data scientists collected, scholars suggested that they belonged to the late Miocene, based on the presence of invertebrate genera such as Acuticosta, Cu neopsis, Oxynaia, and Unio.

This site is extremely important as it gives scholars the chance to learn more about the evolution of mammals in this area, a region that has only just begun to be fully explored.

Bibliography:

Covert, H. Herbert & Hamrick, Mark W. & Dzanh, Trinh & McKinney, C. Kevin (2001) Fossil Mammals from the Late Miocene of Vietnam, Journal of Vertebrate Paleontology, The Society of Vertebrate Paleontology.