​The camels and the llamas comprise the taxon known as tylopods (suborder Tylopoda, order Artiodactyla). This group contains one living family, Camelidae, which contains the camels and the lamoids (the llamas, alpacas, guanacos, and vicuñas) (Encyclopædia Britannica).

​More than 10 fossil species have been proposed as possible stem-Tylopoda, but only two for which there is consensus that they belong to the stem group: Poebrotherium sp. and Eotylopus reedi. Their phylogenetic relationships are illustrated in the following time tree:
Figure 2. Time tree of the stem-Tylopoda
​The oldest known member of the stem-Tylopoda is Eotylopus reedi, described from Middle Eocene (Late Bartonian) deposits at various sites in Presidio County, Texas (Paleobiology Database). It is illustrated below, together with the other generally accepted member of the stem-Tylopoda, Poebrotherium sp.. The life restoration of Poebrotherium sp. suggests that these species appeared more like llamas than camels.
Figure 3. Images of stem-Tylopoda
​The oldest known member of the crown-Tylopoda is Aepycamelus alexandrae, described from Early Miocene (Burdigalian) deposits at various sites in California (Paleobiology Database). No images of this species are available in the public domain, but another species of the same genus, Aepycamelus giraffinus, is illustrated below (click on image for a larger view):
Figure 4. Aepycamelus giraffinus, from the oldest known genus of the crown-Tylopoda
​The tylopod stem line includes a ghost lineage (shown as a blue bar in Figure 2), because the oldest known member of the crown-Artiofabula (the stem whale Pakicetus attocki, of Early Eocene age) is older than the stem group of the Tylopoda, which is of Middle Eocene and younger age. Given that the two stem groups must have appeared at the same time, the tylopod stem group transition must also have begun in the Early Eocene (Ypresian). Comparing this age with that of the known crown-Tylopoda, which are of Early Miocene and younger age, indicates that the tylopod stem-to-crown transition could have lasted as long as around 40 million years, from the Early Eocene to the Early Miocene (Figure 1).

References

Gatesy, J., Geisler, J. H., Chang, J., Buell, C., Berta, A., Meredith, R. W., ... & McGowen, M. R. (2013). A phylogenetic blueprint for a modern whale. Molecular phylogenetics and evolution, 66(2), 479-506.
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​Lynch, S., Sánchez-Villagra, M. R., & Balcarcel, A. (2020). Description of a fossil camelid from the Pleistocene of Argentina, and a cladistic analysis of the Camelinae. Swiss journal of palaeontology, 139(1), 1-17.
Image credits – stem-Tylopoda
  • Header (A pair of young alpacas (Lama pacos) at the pre-Inca burial site of Sillustani, Peru): Christophe Meneboeuf, CC BY-SA 2.5 <https://creativecommons.org/licenses/by-sa/2.5>, via Wikimedia Commons
  • Figure 1: Figures 4 and 7 in Open Access article Lynch, S., Sánchez-Villagra, M. R., & Balcarcel, A. (2020). Description of a fossil camelid from the Pleistocene of Argentina, and a cladistic analysis of the Camelinae. Swiss journal of palaeontology, 139(1), 1-17.
  • Figure 3 (Eotylopus reedi): James St. John, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons
  • Figure 3 (Poebrotherium sp., fossil): Smithsonian Institution, CC0, via Wikimedia Commons
  • Figure 3 (Poebrotherium sp., life restoration): Robert Bruce Horsfall, Public domain, via Wikimedia Commons
  • Figure 4 (Aepycamelus giraffinus, fossil): Ryan Somma, CC BY-SA 2.0 <https://creativecommons.org/licenses/by-sa/2.0>, via Wikimedia Commons
  • Figure 4 (Aepycamelus giraffinus, life restoration): Nobu Tamura, under Creative Commons Attribution- ShareAlike (CC BY-SA) license