This page deals with the stem group of the whales (infraorder Cetacea, Suborder Whippomorpha; Davis and Davis, 2019). Extant cetaceans comprise two clades, the parvorder Mysticeti, or baleen whales, and the parvorder Odontoceti, or toothed whales (Glaeser et al, 2022).
Many phylogenetic studies have been published in recent years (e.g. Lambert et al, 2019; Gohar et al, 2021; Kassegne et al, 2021; Lloyd and Slater, 2021; Antar et al, 2023). The published trees are generally similar, but differ in the species included and some do not depict the phylogenetic relationship between the stem group and the crown group. The time tree shown below is fairly representative of the studies cited above:
Many phylogenetic studies have been published in recent years (e.g. Lambert et al, 2019; Gohar et al, 2021; Kassegne et al, 2021; Lloyd and Slater, 2021; Antar et al, 2023). The published trees are generally similar, but differ in the species included and some do not depict the phylogenetic relationship between the stem group and the crown group. The time tree shown below is fairly representative of the studies cited above:
Figure 1. Time tree of the stem-Cetacea
The oldest known member of the whale stem group is Pakicetus attocki, described from the Early Eocene Subathu Formation at the Babbian Gala East locality in Jammu and Kashmir, India (The Paleobiology Database, data retrieved May 21, 2024). This species is illustrated below, together with other stem-Cetacea for which images are available in the public domain (click on image for a larger view):
Figure 2. Images of stem-Cetacea
The above images are placed in left-to-right order from most basal towards the crown group. This series of images depicts an obvious transition from land animals (e.g. Pakicetus attocki, Pakicetus inachus) through aquatic animals with limbs and toes (e.g. Maiacetus inuus, Rodhocetus kasrani) to aquatic animals with reduced hind limbs and pectoral limbs that appear as fins (e.g. Tutcetus rayanensis, Dorudon atrox).
The oldest known member of the crown-Cetacea, which comprise the clade Neoceti, is the stem baleen whale Mystacodon selenesis, described from the Late Eocene (Early Priabonian) Yumaque Member of the Paracas Formation at Playa Media Luna in the southern part of the Pisco Basin on the southern coast of Peru (Lambert et al, 2017). No images of this fossil are available in the public domain.
The above time tree (Figure 1) indicates that the whale stem group developed from Early to Late Eocene time, representing a stem-to-crown transition of no more than 20 million years.
The oldest known member of the crown-Cetacea, which comprise the clade Neoceti, is the stem baleen whale Mystacodon selenesis, described from the Late Eocene (Early Priabonian) Yumaque Member of the Paracas Formation at Playa Media Luna in the southern part of the Pisco Basin on the southern coast of Peru (Lambert et al, 2017). No images of this fossil are available in the public domain.
The above time tree (Figure 1) indicates that the whale stem group developed from Early to Late Eocene time, representing a stem-to-crown transition of no more than 20 million years.
References
Antar, M. S., Gohar, A. S., El-Desouky, H., Seiffert, E. R., El-Sayed, S., Claxton, A. G., & Sallam, H. M. (2023). A diminutive new basilosaurid whale reveals the trajectory of the cetacean life histories during the Eocene. Communications Biology, 6(1), 707.
Davis, R. W., & Davis, R. W. (2019). Return to the sea: The evolution of marine mammals. Marine Mammals: Adaptations for an Aquatic Life, 7-27.
Glaeser, S. P., Silva, L. M., Prieto, R., Silva, M. A., Franco, A., Kämpfer, P., ... & Eisenberg, T. (2022). A preliminary comparison on faecal microbiomes of free-ranging large baleen (Balaenoptera musculus, B. physalus, B. borealis) and toothed (Physeter macrocephalus) whales. Microbial ecology, 83(1), 18-33.
Gohar, A. S., Antar, M. S., Boessenecker, R. W., Sabry, D. A., El-Sayed, S., Seiffert, E. R., ... & Sallam, H. M. (2021). A new protocetid whale offers clues to biogeography and feeding ecology in early cetacean evolution. Proceedings of the Royal Society B, 288(1957), 20211368.
Kassegne, K. E., Mourlam, M. J., Guinot, G., Amoudji, Y. Z., Martin, J. E., Togbe, K. A., ... & Hautier, L. (2021, April). First partial cranium of Togocetus from Kpogamé (Togo) and the protocetid diversity in the Togolese phosphate basin. In Annales de Paléontologie (Vol. 107, No. 2, p. 102488). Elsevier Masson.
Lambert, O., Martínez-Cáceres, M., Bianucci, G., Di Celma, C., Salas-Gismondi, R., Steurbaut, E., ... & De Muizon, C. (2017). Earliest mysticete from the Late Eocene of Peru sheds new light on the origin of baleen whales. Current Biology, 27(10), 1535-1541.
Lambert, O., Bianucci, G., Salas-Gismondi, R., Di Celma, C., Steurbaut, E., Urbina, M., & de Muizon, C. (2019). An amphibious whale from the middle Eocene of Peru reveals early South Pacific dispersal of quadrupedal cetaceans. Current Biology, 29(8), 1352-1359.
Lloyd, G. T., & Slater, G. J. (2021). A total-group phylogenetic metatree for Cetacea and the importance of fossil data in diversification analyses. Systematic Biology, 70(5), 922-939.
Davis, R. W., & Davis, R. W. (2019). Return to the sea: The evolution of marine mammals. Marine Mammals: Adaptations for an Aquatic Life, 7-27.
Glaeser, S. P., Silva, L. M., Prieto, R., Silva, M. A., Franco, A., Kämpfer, P., ... & Eisenberg, T. (2022). A preliminary comparison on faecal microbiomes of free-ranging large baleen (Balaenoptera musculus, B. physalus, B. borealis) and toothed (Physeter macrocephalus) whales. Microbial ecology, 83(1), 18-33.
Gohar, A. S., Antar, M. S., Boessenecker, R. W., Sabry, D. A., El-Sayed, S., Seiffert, E. R., ... & Sallam, H. M. (2021). A new protocetid whale offers clues to biogeography and feeding ecology in early cetacean evolution. Proceedings of the Royal Society B, 288(1957), 20211368.
Kassegne, K. E., Mourlam, M. J., Guinot, G., Amoudji, Y. Z., Martin, J. E., Togbe, K. A., ... & Hautier, L. (2021, April). First partial cranium of Togocetus from Kpogamé (Togo) and the protocetid diversity in the Togolese phosphate basin. In Annales de Paléontologie (Vol. 107, No. 2, p. 102488). Elsevier Masson.
Lambert, O., Martínez-Cáceres, M., Bianucci, G., Di Celma, C., Salas-Gismondi, R., Steurbaut, E., ... & De Muizon, C. (2017). Earliest mysticete from the Late Eocene of Peru sheds new light on the origin of baleen whales. Current Biology, 27(10), 1535-1541.
Lambert, O., Bianucci, G., Salas-Gismondi, R., Di Celma, C., Steurbaut, E., Urbina, M., & de Muizon, C. (2019). An amphibious whale from the middle Eocene of Peru reveals early South Pacific dispersal of quadrupedal cetaceans. Current Biology, 29(8), 1352-1359.
Lloyd, G. T., & Slater, G. J. (2021). A total-group phylogenetic metatree for Cetacea and the importance of fossil data in diversification analyses. Systematic Biology, 70(5), 922-939.
Image credits – stem-Cetacea
- Header (Humpback whale (Megaptera novaeangliae) at Stellwagen Bank National Marine Sanctuary, off Boston, Massachusetts): Whit Welles Wwelles14, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
- Figure 2 (Pakicetus attocki): Hectonichus, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Figure 2 (Pakicetus inachus): Nobu Tamura, under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
- Figure 2 (Ambulocetus natans, skeleton): Notafly, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
- Figure 2 (Ambulocetus natans, life restoration): Nobu Tamura, under Creative Commons Attribution- ShareAlike (CC BY-SA) license
- Figure 2 (Dalanistes ahmedi): Caz41985, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Figure 2 (Remingtonocetus harudiensis, fossil): Waughd, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Figure 2 (Remingtonocetus harudiensis, life restoration): Nobu Tamura, under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
- Figure 2 (Kutchicetus minimus, skeleton): Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
- Figure 2 (Kutchicetus minimus, life restoration): Nobu Tamura, under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
- Figure 2 (Andrewsiphius sp.): Akrasia25, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Figure 2 (Maiacetus inuus, skeleton): Cliff from Arlington, VA (Outside Washington DC), USA, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons
- Figure 2 (Maiacetus inuus, life restoration): Nobu Tamura, under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
- Figure 2 (Rodhocetus sp.): James St. John, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons
- Figure 2 (Rodhocetus kasrani): Nobu Tamura, under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
- Figure 2 (Artiocetus clavis): Harold9595959, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Figure 2 (Aegyptocetus tarfa, fossil): Hectonichus, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
- Figure 2 (Aegyptocetus tarfa, life restoration): Nobu Tamura, under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
- Figure 2 (Protocetus atavus, fossil): Abel, Othenio, 1875-1946, Public domain, via Wikimedia Commons
- Figure 2 (Protocetus atavus, life restoration): Nobu Tamura, under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
- Figure 2 (Georgiacetus vogtlensis): Nobu Tamura, under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
- Figure 2 (Babiacetus sp.): Akrasia25, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Figure 2 (Aegicetus gehennae): Sneaking stoat 2, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Figure 2 (Zygorhiza kochii, skeleton): Claire H. from New York City, USA, CC BY-SA 2.0 <https://creativecommons.org/licenses/by-sa/2.0>, via Wikimedia Commons
- Figure 2 (Zygorhiza kochii, life restoration): Nobu Tamura, under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
- Figure 2 (Tutcetus rayanensis, fossil): Antar et al., CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
- Figure 2 (Tutcetus rayanensis, life restoration): Mohammed S. Antar, Abdullah S. Gohar, Heba El-Desouky, Erik R. Seiffert, Sanaa El-Sayed, Alexander G. Claxton & Hesham M. Sallam, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
- Figure 2 (Antaecetus aithai): Open Access article Gingerich, P. D., Amane, A., & Zouhri, S. (2022). Skull and partial skeleton of a new pachycetine genus (Cetacea, Basilosauridae) from the Aridal Formation, Bartonian middle Eocene, of southwestern Morocco. Plos one, 17(10), e0276110.
- Figure 2 (Basilosaurus cetoides, fossil): Emőke Dénes, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Figure 2 (Basilosaurus cetoides, life restoration): Nobu Tamura, under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
- Figure 2 (Saghacetus osiris): LeLaisserPasserA38, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Figure 2 (Dorudon atrox, skeleton): Ideonexus, CC BY-SA 2.0 <https://creativecommons.org/licenses/by-sa/2.0>, via Wikimedia Commons
- Figure 2 (Dorudon atrox, life restoration): Nobu Tamura, under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license