This page deals with the stem group of the tapirs (superfamily Tapiroidea, suborder Ceratomorpha). The family Tapiridae comprises 5 extant species found in tropical forests of Malaysia and the Americas (Encyclopaedia Britannica).

Several recent publications (e.g. Bai et al, 2020; Dumbá, 2023) have presented phylogenetic analyses of the tapir stem group. The following time tree is a combination of trees presented by Bai et al and Dumbá:
Figure 1. Time tree of the stem-Tapiroidea
​The oldest known representatives of the tapir stem group are several species of the genus Heptodon, found in both North America and China. The oldest examples are of Early Eocene (Early Ypresian) age. Examples of the genus are shown below, together with other members of the stem group for which public-domain images are available (click on image for a larger view):
Figure 2. Images of stem-Tapiroidea
The above images are placed in left-to-right order from most basal towards the crown group, but no obvious trends can be seen. However, it is noteworthy that even the most basal stem tapir (Heptodon) appears very similar to modern tapirs, apart from the lack of an elongated snout. Furthermore, the two most crownward stem species belong to the modern genus Tapirus. It thus appears that the stem-to-crown transition involved relatively subtle evolutionary novelties.

The oldest known member of the tapir crown group is Tapirus polkensis, described from Late Miocene to Early Pliocene (Messinian to Zanclean) sediments at the Gray Fossil Site in northeastern Tennessee, USA (McConnell and Zavada, 2013). A skeleton and a life restoration of this species are illustrated below:
Figure 3. The oldest known member of the crown-Tapiroidea
​The above time tree (Figure 1) indicates that the tapir stem group developed from Early Eocene to Late Miocene time, representing a stem-to-crown transition of between 45 and 52 million years.

References

Bai, B., Meng, J., Zhang, C., Gong, Y. X., & Wang, Y. Q. (2020). The origin of Rhinocerotoidea and phylogeny of Ceratomorpha (Mammalia, Perissodactyla). Nature Communications Biology, 3(1), 509.

Dumbá, L. C. C. S.,  (2023). Dental ecomorphology, phylogeny and biogeography of Tapiridae (MAMMALIA, PERISSODACTYLA). Ph.D. thesis, Universidade Federal de Minas Gerais, Brazil.

McConnell, S. M., & Zavada, M. S. (2013). The occurrence of an abdominal fauna in an articulated tapir (Tapirus polkensis) from the Late Miocene Gray Fossil Site, northeastern Tennessee. Integrative Zoology, 8(1), 74-83.
Image credits – stem-Tapiridae
  • Header (Malayan tapir (Tapirus indicus), Hellabrunn Zoo, Munich, Germany): Diego Delso, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Figure 2 (Heptodon calciculus): Bin Bai, Yuanqing Wang, Jin Meng, Qian Li, Xun Jin, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Figure 2 (Heptodon posticus): Smokeybjb, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Figure 2 (Helaletes nanus): Smithsonian Museum, Creative Commons, no rights reserved
  • Figure 2 (Protapirus simplex): Robert Bruce Horsfall, Public domain, via Wikimedia Commons
  • Figure 2 (Paratapirus helvetia): Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Figure 2 (Plesiotapirus yagii): Captmondo, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons
  • Figure 2 (Tapirus webbi): Lokolauti9, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Figure 3 (Tapirus polkensis, skeleton): Zilantophis, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Figure 3 (Tapirus polkensis, life restoration): Jfstudiospaleoart, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons