Introduction
The lungfish (Class Dipnoi, Superclass Sarcopterygii) are air-breathing fishes whose extant crown group comprises six living species. These fall into two orders, the Ceratodontiformes (now represented by the Australian lungfish) and the Lepidosireniformes (the South American and the African lungfish). The following tree illustrates their phylogenetic context:
The stem lines of the Dipnoi and of the higher-order clade to which they belong, the Rhipidistia, are depicted as red and blue lines respectively in the above phylogenetic tree. The stem-Dipnoi are very well represented in the fossil record, but only one species, Styloichthys changae, has been suggested to belong to the stem-Rhipidistia. This species has also been interpreted as a stem-group coelacanth (e.g. Friedman, 2007 and Lu and Zhu, 2010), but here we will follow the majority of articles, which place it in the stem-Rhipidistia (see Zhu and Yu, 2002; Lu et al, 2016a; Gai et al, 2017; Lu et al, 2017). In any case, the late Lochkovian Styloichthys changae cannot be a direct ancestor of the crown group, because it is younger than the oldest known member of the crown-Rhidistia, which is of Early Lochkovian age (see below). Rather, it must be a descendant of older, currently unknown, stem rhipidistians that branched off the stem line before the crown group appeared and were more similar to the direct ancestors of the crown group. No image of Styloichthys changae is available in the public domain.
Given the lack of any stem-Rhipidistia fossils older than the crown-Rhipidistia, we will consider only the evolution of the stem and crown groups of the Dipnoi.
Given the lack of any stem-Rhipidistia fossils older than the crown-Rhipidistia, we will consider only the evolution of the stem and crown groups of the Dipnoi.
The stem group of the Dipnoi
Many fossil lungfishes have been assigned to the stem-Dipnoi, and several phylogenetic trees have been published (e.g. Ahlberg et al, 2006; Qiao and Zhu, 2009; Pardo et al, 2014; Kemp et al, 2017; Challands et al, 2019). A simplified version of that by Challands et al (2019) is shown below:
The earliest known representative of the stem-Dipnoi is Youngolepis sp., from the Early Devonian (Early Lochkovian) Xishancun Formation of Qujing, Yunnan, China (Zhu and Fan, 1995; Friedman and Brazeau, 2010). No public-domain image of this genus is available, but a few other members of the stem group are illustrated below (click on image for a larger view):
* after name indicates that the image represents a life restoration.
The above images are numbered in order from the most basal to those closest to the crown group, but no obvious trends can be seen in this limited set of images. In any case, the differences are seen most clearly in details of the skull structure, at least for Devonian taxa (Kemp et al, 2017).
The oldest known representative of the crown-Dipnoi is Gosfordia truncata, a member of the stem-Lepidosirenoformes from the Early Triassic (Olenekian) Terrigal Formation at Gosford Quarry, New South Wales, Australia (Woodward, 1890; Longrich, 2017). No image is available in the public domain.
The time frame of the evolution of the stem group is shown below (for a larger view, click on image):
The oldest known representative of the crown-Dipnoi is Gosfordia truncata, a member of the stem-Lepidosirenoformes from the Early Triassic (Olenekian) Terrigal Formation at Gosford Quarry, New South Wales, Australia (Woodward, 1890; Longrich, 2017). No image is available in the public domain.
The time frame of the evolution of the stem group is shown below (for a larger view, click on image):
The above plot indicates that the dipnoan stem group evolved from Early Devonian to Early Permian time, representing a stem-to-crown transition of at least 130 million years.
Evolution within the crown-Dipnoi
In this section we are concerned with the origin of the two clades which separated to form the lungfish crown group, the Ceratodontiformes and the Lepidosireniformes. No members of the stem-Ceratodontiformes have been recognized, but the stem-Lepidosireniformes do have representation in the fossil record. A simplified phylogenetic tree is shown below:
The oldest known member of the stem-Lepidosireniformes is Gosfordia truncata, described from the Early Triassic (Olenekian) Terrigal Formation at Gosford Quarry, New South Wales, Australia (Woodward, 1890; Longrich, 2017). No image is available in the public domain, and in fact that is also true for most of the species shown above. The two species for which images are available are shown below (click on image for a larger view):
* after name indicates that the image represents a life restoration.
The oldest known crown-group lepidosireniform is a species of the modern genus Protopterus described from early Oligocene deposits in the Fayum Depression of Egypt (Stromer, 1910; Longrich, 2017). No public-domain image is available.
The time frame of the evolution of the stem-Lepidosireniformes is shown below:
The time frame of the evolution of the stem-Lepidosireniformes is shown below:
The above plot illustrates the great length of the stem-to-crown transition for the Lepidosireniformes: a duration of around 218 million years.
The plot also shows the age of the oldest known member of the crown Ceratodontiformes, which is a fossil of the modern species Neoceratodus forsteri. The fossil was found in the Late Cretaceous (Cenomanian) Griman Creek Formation at Lightning Ridge, New South Wales, Australia (Kemp and Molnar, 1981). No image of the fossil exists in the public domain, but a living example of the species is illustrated above in the header to this page.
The plot also shows the age of the oldest known member of the crown Ceratodontiformes, which is a fossil of the modern species Neoceratodus forsteri. The fossil was found in the Late Cretaceous (Cenomanian) Griman Creek Formation at Lightning Ridge, New South Wales, Australia (Kemp and Molnar, 1981). No image of the fossil exists in the public domain, but a living example of the species is illustrated above in the header to this page.
References
Ahlberg, P. E., Smith, M. M., & Johanson, Z. (2006). Developmental plasticity and disparity in early dipnoan (lungfish) dentitions. Evolution & Development, 8(4), 331-349.
Challands, T. J., Smithson, T. R., Clack, J. A., Bennett, C. E., Marshall, J. E., Wallace-Johnson, S. M., & Hill, H. (2019). A lungfish survivor of the end-Devonian extinction and an Early Carboniferous dipnoan radiation. Journal of Systematic Palaeontology, 1-22.
Friedman, M. (2007). Styloichthys as the oldest coelacanth: implications for early osteichthyan interrelationships. Journal of Systematic Palaeontology, 5(3), 289-343.
Friedman, M., & Brazeau, M. D. (2010). A reappraisal of the origin and basal radiation of the Osteichthyes. Journal of Vertebrate Paleontology, 30(1), 36-56.
Gai, Z., Yu, X., & Zhu, M. (2017). The Evolution of the Zygomatic Bone From Agnatha to Tetrapoda. The Anatomical Record, 300(1), 16-29.
Kemp, A., & Molnar, R. E. (1981). Neoceratodus forsteri from the Lower Cretaceous of New South Wales, Australia. Journal of Paleontology, 211-217.
Kemp, A., Cavin, L., & Guinot, G. (2017). Evolutionary history of lungfishes with a new phylogeny of post-Devonian genera. Palaeogeography, Palaeoclimatology, Palaeoecology, 471, 209-219.
Longrich, N. R. (2017). A stem lepidosireniform lungfish (Sarcopterygia: Dipnoi) from the Upper Eocene of Libya, North Africa and implications for Cenozoic lungfish evolution. Gondwana Research, 42, 140-150.
Lu, J., & Zhu, M. (2010). An onychodont fish (Osteichthyes, Sarcopterygii) from the Early Devonian of China, and the evolution of the Onychodontiformes. Proceedings of the Royal Society B: Biological Sciences, 277(1679), 293-299.
Lu, J., Zhu, M., Ahlberg, P. E., Qiao, T., Zhu, Y. A., Zhao, W., & Jia, L. (2016a). A Devonian predatory fish provides insights into the early evolution of modern sarcopterygians. Science advances, 2(6), e1600154.
Lu, J., Giles, S., Friedman, M., & Zhu, M. (2017). A new stem sarcopterygian illuminates patterns of character evolution in early bony fishes. Nature communications, 8(1), 1932.
Pardo, J. D., Huttenlocker, A. K., & Small, B. J. (2014). An exceptionally preserved transitional lungfish from the Lower Permian of Nebraska, USA, and the origin of modern lungfishes. PloS One, 9(9), e108542.
Qiao, T., & Zhu, M. (2009). A new tooth‐plated lungfish from the Middle Devonian of Yunnan, China, and its phylogenetic relationships. Acta Zoologica, 90, 236-252.
Stromer, E. V. (1910). Ueber das Gebiss des Lepidosirenidae und die Verbreitung tertiärer und mesozoischer Lungenfische. Festschrift zum 60 Geburtstage der R Hertwigs, 2, 611-625.
Woodward, A. S. (1890). The fossil fishes of the Hawkesbury Series at Gosford. Memoirs of the Geological Survey of New South Wales. Palaeontology 4:1-57
Zhu, M., & Fan, J. (1995). Youngolepis from the Xishancun Formation (Early Lochkovian) of Qujing; China. Geobios, 28, 293-299.
Zhu, M., & Yu, X. (2002). A primitive fish close to the common ancestor of tetrapods and lungfish. Nature, 418(6899), 767-770.
Challands, T. J., Smithson, T. R., Clack, J. A., Bennett, C. E., Marshall, J. E., Wallace-Johnson, S. M., & Hill, H. (2019). A lungfish survivor of the end-Devonian extinction and an Early Carboniferous dipnoan radiation. Journal of Systematic Palaeontology, 1-22.
Friedman, M. (2007). Styloichthys as the oldest coelacanth: implications for early osteichthyan interrelationships. Journal of Systematic Palaeontology, 5(3), 289-343.
Friedman, M., & Brazeau, M. D. (2010). A reappraisal of the origin and basal radiation of the Osteichthyes. Journal of Vertebrate Paleontology, 30(1), 36-56.
Gai, Z., Yu, X., & Zhu, M. (2017). The Evolution of the Zygomatic Bone From Agnatha to Tetrapoda. The Anatomical Record, 300(1), 16-29.
Kemp, A., & Molnar, R. E. (1981). Neoceratodus forsteri from the Lower Cretaceous of New South Wales, Australia. Journal of Paleontology, 211-217.
Kemp, A., Cavin, L., & Guinot, G. (2017). Evolutionary history of lungfishes with a new phylogeny of post-Devonian genera. Palaeogeography, Palaeoclimatology, Palaeoecology, 471, 209-219.
Longrich, N. R. (2017). A stem lepidosireniform lungfish (Sarcopterygia: Dipnoi) from the Upper Eocene of Libya, North Africa and implications for Cenozoic lungfish evolution. Gondwana Research, 42, 140-150.
Lu, J., & Zhu, M. (2010). An onychodont fish (Osteichthyes, Sarcopterygii) from the Early Devonian of China, and the evolution of the Onychodontiformes. Proceedings of the Royal Society B: Biological Sciences, 277(1679), 293-299.
Lu, J., Zhu, M., Ahlberg, P. E., Qiao, T., Zhu, Y. A., Zhao, W., & Jia, L. (2016a). A Devonian predatory fish provides insights into the early evolution of modern sarcopterygians. Science advances, 2(6), e1600154.
Lu, J., Giles, S., Friedman, M., & Zhu, M. (2017). A new stem sarcopterygian illuminates patterns of character evolution in early bony fishes. Nature communications, 8(1), 1932.
Pardo, J. D., Huttenlocker, A. K., & Small, B. J. (2014). An exceptionally preserved transitional lungfish from the Lower Permian of Nebraska, USA, and the origin of modern lungfishes. PloS One, 9(9), e108542.
Qiao, T., & Zhu, M. (2009). A new tooth‐plated lungfish from the Middle Devonian of Yunnan, China, and its phylogenetic relationships. Acta Zoologica, 90, 236-252.
Stromer, E. V. (1910). Ueber das Gebiss des Lepidosirenidae und die Verbreitung tertiärer und mesozoischer Lungenfische. Festschrift zum 60 Geburtstage der R Hertwigs, 2, 611-625.
Woodward, A. S. (1890). The fossil fishes of the Hawkesbury Series at Gosford. Memoirs of the Geological Survey of New South Wales. Palaeontology 4:1-57
Zhu, M., & Fan, J. (1995). Youngolepis from the Xishancun Formation (Early Lochkovian) of Qujing; China. Geobios, 28, 293-299.
Zhu, M., & Yu, X. (2002). A primitive fish close to the common ancestor of tetrapods and lungfish. Nature, 418(6899), 767-770.
Image credits - Dipnoans
- Header (Neoceratodus forsteri (Australian lungfish) at the National Zoo & Aquarium in Canberra, Australia) By Mitch Ames, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Skull of Amadeodipterus kencampbelli By Clement, A.M., CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Chirodipterus australis By Ghedoghedo [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]
- Dipterus valenciennesi (3a) By Haplochromis [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]
- Dipterus valenciennesi (3b) By Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0)
- Skull of Asthenorhynchus meemannae By Clement, A.M., CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Skull of Griphognathus whitei By The Trustees of the Natural History Museum, London, http://creativecommons.org/licenses/by/4.0/
- Phaneropleuron andersoni By Lankester Edwin Ray [Public domain]
- Pentlandia macroptera By Ghedoghedo [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]
- Howidipterus donnae By Copyright Museums Victoria / CC BY (Licensed as Attribution 4.0 International)
- Posterior fins and axial skeleton of Barwickia downunda From Open Access article by Johanson et al, 2009, licensed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/)
- Conchopoma gadiforme By Ghedoghedo [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]
- Gnathorhiza sp. By DiBgd [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
- Arganodus sp. By File:Chinle fish.jpg, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Skull fragment and jawbones of Ptychoceratodus serratus By Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons