All life on Earth started out under water. However, around 400 million years ago some vertebrates, such as fish, started developing limbs and other characteristics that allowed them to explore life on land. One of the most pivotal features to evolve was the lungs, which gave vertebrates the ability to breathe above water.

Most land-living vertebrates, including humans, have two lungs which sit on either side of their chest. The lungs extract oxygen from the atmosphere and transfer it to the bloodstream in exchange for carbon dioxide which then gets exhaled out in to the atmosphere. How this important organ first evolved is a hotly debated topic. This is largely because lung tissue does not preserve well in fossils, making it difficult to trace how the lungs of vertebrates changed over the course of evolution.

To overcome this barrier, Cupello et al. compared the lungs of living species which are crucial to understand the early stages of the water-to-land transition. This included four species of lunged bony fish which breathe air at the water surface, and a four-legged salamander that lives on land.

Cupello et al. used a range of techniques to examine how the lungs of the bony fish and salamander changed shape during development. The results suggested that the lungs of vertebrates started out as a single organ, which became truly paired later in evolution once vertebrates started developing limbs. This anatomical shift increased the surface area available for exchanging oxygen and carbon dioxide so that vertebrates could breathe more easily on land.

These findings provide new insights in to how the lung evolved into the paired structure found in most vertebrates alive today. It likely that this transition allowed vertebrates to fully adapt to breathing above water, which may explain why this event only happened once over the course of evolution.

Lungs, the most important organ of the pulmonary complex, are rarely preserved in fossils, hindering direct evidence of how the earliest air-breathing vertebrates breathed air. Indeed, among fossil taxa, the presence of lungs has only been confirmed in coelacanths (Brito et al., 2010; Cupello et al., 2017b; Cupello et al., 2019), a salamander (Tissier et al., 2017), an ornithuromorph bird (Wang et al., 2018), and possibly a tadpole (Rossi et al., 2019). In addition, the presence of specialized skeletal structures, such as cranial ribs and enlarged spiracular openings, provided indirect evidence of air-breathing behaviour in a wider range of fossil sarcopterygians including lungfishes and early tetrapods, but also actinopterygians (Long, 1993; Long et al., 2006; Clement and Long, 2010; Clement et al., 2016; Cupello et al., 2019).

Altogether, the evolutionary origin of the vertebrate lung can therefore be narrowed down to osteichthyans (Goujet, 2011; Tatsumi et al., 2016). The interpretation of thoracic paired masses in the antiarch placoderm Bothriolepis canadensis as a lung (Denison, 1941; Arsenault et al., 2004) even suggested an origin among early jawed vertebrates, dating back to at least the Devonian period. Yet, lung affinities for such structures remain elusive (Janvier et al., 2007) and could not be confirmed by anatomical, phylogenetic, or biological data (Goujet, 2011; Béchard et al., 2014). Here, we follow Janvier et al., 2007, Goujet, 2011 and Béchard et al., 2014, and consider that observable evidences are elusive and do not support the interpretation of these paired masses as a lung.

Our knowledge about the morphological and genetic development of the lung is, however, highly biased towards amniotes, and consequently the original form of this evolutionary novelty among osteichthyans remains largely elusive. One hypothesis, formed and supported by studies on tetrapods (particularly mammals and birds), assumes that the lung evolved through a modification of the pharyngeal pouch (Kastschenko, 1887), as the lung bud develops at the pharyngo-oesophageal junction during embryonic development. Consequently, this view (Kastschenko, 1887; Kuratani and Tanaka, 1990) predicts that the primitive lungs appeared as bilaterally paired organs at the caudolateral part of the pharynx. Indeed, in embryology, lungs of living tetrapods have been mostly described as paired derivates of the respiratory tube, arisen from paired and small hollow swellings (Flint, 1906). Previous studies on amphibians have also proposed that the lung bud develop from paired rudiments of the ventral portions of the eighth pharyngeal pouches (Goodrich, 1931; Marcus, 1937; Perry et al., 2001). Additionally, the plesiomorphic state of lungs has been mostly described as paired organs (Funk et al., 2020). On the other hand, another hypothesis does not constrain the evolutionary origin of the lung to the serial homologue of the pharyngeal pouch (Greil, 1913; Neumayer, 1930; Wassnetzov, 1932). In this view, although the possibility that the primitive lung developed on the pharyngeal endoderm is not excluded, the primitive lung is considered to appear on the floor of the pharynx, or more generally, on the floor of the foregut. This scenario does not predict bilaterally paired forms of primitive lungs.

Curiously, some living vertebrates display an unpaired organ, leaving the ancestral condition equivocal. The sister group to all other extant actinopterygians, the obligate air-breathing polypterids (Icardo et al., 2017), breath air using lungs, which have previously been described as a paired organ (Icardo et al., 2017; Geoffrey Saint Hilaire, 1802; Graham, 1997). However, in adult specimens of Polypterus senegalus the glottis only opens to the right sac and the left sac is connected to the right sac by a separate opening (Graham, 1997), raising old questions about its true paired condition. Among sarcopterygians, the unpaired lung of coelacanths is unequivocal. The living coelacanth Latimeria chalumnae, that inhabits moderate deep-water and makes gas exchanges only through gills, have an unpaired lung with no outline of a second bud at different developmental stages (Cupello et al., 2015; Cupello et al., 2017a; Cupello et al., 2017b; Cupello et al., 2019). In the extant sister group of all tetrapods (Amemiya et al., 2013), namely lungfishes, the three extant genera have lungs capable to uptake oxygen from the air. However, in the facultative air-breather Neoceratodus forsteri, the lung is described as unpaired in adults (Greil, 1913; Graham, 1997; Grigg, 1965). In contrast with both South American and African lungfishes, the Lepidosirenoidea, that are obligated air-breathers and have a lung described as a ventral paired organ (Graham, 1997) like tetrapod lungs.

To follow lung evolutionary history in vertebrates, we analyzed the morphogenesis of lungs of key living osteichthyans (Figures 1 and 2, Figures 3 and 4, Figures 5 and 6). Embryos, larvae, juveniles and adults of P. senegalus, N. forsteri, Lepidosiren paradoxa were examined. To compare the lung anatomy of osteichthyan fishes with tetrapods, we studied also an extensive developmental series of the living salamandrid Salamandra salamandra, from early and late larvae to juveniles before and after metamorphosis (Figure 5). As salamanders are often considered to have retained plesiomorphic characteristics of tetrapod stance and locomotion (Pierce et al., 2020), we used them here also as a model for understanding lung evolution in tetrapods. Specimens of mentioned taxa were examined through x-ray microtomography, the unique effective non-invasive methodology to study their morphology and histology at a three-dimensional (sub) microscale. When possible, we proceeded also with dissections and the study of histological sections. We compare our results with the available information from the lung of fossil taxa, the coelacanths and salamanders (Cupello et al., 2019; Brito et al., 2010; Tissier et al., 2017).

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Traditionally, vertebrate lungs are defined as ventral paired organs derived from the ventral portion of the posterior pharynx or post-pharyngeal foregut (Perry et al., 2001; Funk et al., 2020; Lambertz et al., 2015; Graham, 1997; Kardong, 2015). However, we demonstrate here the presence of an unambiguous unpaired lung, that develops from the ventral foregut, but sometimes occupy the dorsal position later in the development of osteichthyan fishes (Figure 7). Based on extensive developmental series of different vertebrate taxa, we present a new interpretation of some lungs previously considered as paired, and therefore, a new definition of paired lungs. Based on our results, true paired lungs are stated when bilateral lung buds arise simultaneously and are both connected directly to the foregut, as observed in the salamander (Figures 5B, D, 7).

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The sister group to all other living actinopterygian (polypterids) and all living sarcopterygian fishes have a clearly unpaired lung in early developmental stages (Figure 1B) that can be developed in later stages either in a unilobed or a secondarily multilobed lung (Figures 1D–F ,–7), but not in a true paired lung. P. senegalus and the lungfish L. paradoxa possess secondary multilobed structure from the larval stage onward since the lung is derived from a unilateral connection to the foregut (Figure 4G, H, J and K). The presence of this secondary multilobed morphology likely represents an advantage for the obligatory air-breathing behavior of these taxa, raising the respiratory compliance. In the teleost Batrachomoeus trispinosus, the non-respiratory gas bladder is also described as paired (Rice and Bass, 2009), although it is most probably a secondary condition.

The most parsimonious scenario inferred from our data mapped on the phylogenetic framework (Figure 7) is that the vertebrate lung was unpaired at the evolutionary origin. Since soft tissues are rarely preserved in fossils, living lunged osteichthyans are key taxa for the understanding of how evolutionary constraints shaped breathing adaptations on land. Our study suggests that the ancestral condition of the lung is a median unpaired organ (Figure 7), thereby being inconsistent with the scenario that the lung evolved through a modification of the posteriormost pharyngeal pouch assumed to be present in primitive taxa (Kastschenko, 1887; Goodrich, 1931). Consequently, the evolutionary origin of the lung was likely independent of the pharyngeal pouch at the morphological level.

From this evolutionary point of view, our results lead to a new definition of the vertebrate lung: either an unpaired or paired respiratory organ developing ventrally from the foregut. Vestigial forms secondarily released from the respiratory function should be also designated as lungs (e.g. the lung of coelacanths). Some criteria previously used for discriminating lungs from gas bladders are no longer supported, including: paired/unpaired organization, position ventral to the alimentary tract (Marcus, 1937; Funk et al., 2020; Lambertz et al., 2015; Graham, 1997), as well as its function. The dorsal position of the majority of osteichthyans lungs described here may be related to its dual and secondary functionality of respiration and buoyancy control (Thomson, 1968). Actually, the only morphological characteristic that can be used to distinguish lungs and gas bladders is the ventral and dorsal origins from the foregut, respectively (Funk et al., 2020; Cass et al., 2013). This phenotypic differentiation into true paired lungs in tetrapods may be related to differential gene expressions (Funk et al., 2020; Bi et al., 2021). Nevertheless, at a level of developmental mechanism, the possibility of co-options of gene regulatory networks of the pharyngeal pouch morphogenesis cannot be excluded, as both the lung bud and pharyngeal pouch develop through the invagination of the foregut endoderm. Our results open the door for future molecular analyses to trace possible regulatory elements for the evolutionary transition from unpaired lungs to true paired lungs in tetrapods.

According to morphological evidence presented here, bifurcation morphogenesis into true paired lungs was not developed yet in osteichthyan fish ancestors. Based on the extant phylogenetic bracket, we infer that the bilaterally paired nature of the lung evolved only in the lineage towards fossil and extant tetrapods, as a synapomorphy of this clade (Figures 5 and 7). This morphological modification brought about improvement of the efficiency in oxygen-uptake from the air, as the paired lungs having parallel air flows exchange the air more quickly than the unpaired lung having only single air flow does. This innovation led to the elevation of metabolic rate that was required for the sustained body support against the gravity. Paired lungs may have been present also in early tetrapods and were probably essential to raise lung surface area and volume capacity during the evolution of vertebrate respiratory system and the air-breathing intensification at the water-to-land transition.

All data used in this work are publicly available via Dryad https://doi.org/10.5061/dryad.vdncjsxx1.

1. 1. Cupello C

   (2022) Dryad Digital Repository

   Data from: Lung evolution in vertebrates and the water-to-land transition.

   https://doi.org/10.5061/dryad.vdncjsxx1

1. 1. Amemiya CT
   2. Alföldi J
   3. Lee AP
   4. Fan S
   5. Philippe H
   6. Maccallum I
   7. Braasch I
   8. Manousaki T
   9. Schneider I
   10. Rohner N
   11. Organ C
   12. Chalopin D
   13. Smith JJ
   14. Robinson M
   15. Dorrington RA
   16. Gerdol M
   17. Aken B
   18. Biscotti MA
   19. Barucca M
   20. Baurain D
   21. Berlin AM
   22. Blatch GL
   23. Buonocore F
   24. Burmester T
   25. Campbell MS
   26. Canapa A
   27. Cannon JP
   28. Christoffels A
   29. De Moro G
   30. Edkins AL
   31. Fan L
   32. Fausto AM
   33. Feiner N
   34. Forconi M
   35. Gamieldien J
   36. Gnerre S
   37. Gnirke A
   38. Goldstone JV
   39. Haerty W
   40. Hahn ME
   41. Hesse U
   42. Hoffmann S
   43. Johnson J
   44. Karchner SI
   45. Kuraku S
   46. Lara M
   47. Levin JZ
   48. Litman GW
   49. Mauceli E
   50. Miyake T
   51. Mueller MG
   52. Nelson DR
   53. Nitsche A
   54. Olmo E
   55. Ota T
   56. Pallavicini A
   57. Panji S
   58. Picone B
   59. Ponting CP
   60. Prohaska SJ
   61. Przybylski D
   62. Saha NR
   63. Ravi V
   64. Ribeiro FJ
   65. Sauka-Spengler T
   66. Scapigliati G
   67. Searle SMJ
   68. Sharpe T
   69. Simakov O
   70. Stadler PF
   71. Stegeman JJ
   72. Sumiyama K
   73. Tabbaa D
   74. Tafer H
   75. Turner-Maier J
   76. van Heusden P
   77. White S
   78. Williams L
   79. Yandell M
   80. Brinkmann H
   81. Volff JN
   82. Tabin CJ
   83. Shubin N
   84. Schartl M
   85. Jaffe DB
   86. Postlethwait JH
   87. Venkatesh B
   88. Di Palma F
   89. Lander ES
   90. Meyer A
   91. Lindblad-Toh K

   (2013) The African coelacanth genome provides insights into tetrapod evolution

   Nature 496:311–316.

   https://doi.org/10.1038/nature12027

   • PubMed
   • Google Scholar
2. Book

   1. Arsenault M
   2. Desbiens S
   3. Janvier P
   4. Kerr J

   (2004)

   New data on the soft tissues and external morphology of the antiarch Bothriolepis canadensis (Whiteaves, 1880) from the Upper Devonian of Miguasha, Québec

   In: Arratia G, Wilson MVH, Cloutier R, editors. Recent Advances in the Origin and Early Radiation of Vertebrates. Munich, Germany: Verlag Dr. Friedrich Pfeil. pp. 439–454.

   • Google Scholar
3. 1. Bartsch P
   2. Gemballa S
   3. Piotrowski T

   (1997) The embryonic and larval development of Polypterus senegalus cuvier, 1829: its staging with reference to external and skeletal features, behaviour and locomotory habits

   Acta Zoologica 78:309–328.

   https://doi.org/10.1111/j.1463-6395.1997.tb01014.x

   • Google Scholar
4. 1. Béchard I
   2. Arsenault F
   3. Cloutier R
   4. Kerr J

   (2014) The Devonian placoderm fish Bothriolepis canadensis revisited with three-dimensional digital imagery

   Palaeontologia Electronica 17:1–19.

   https://doi.org/10.26879/417

   • Google Scholar
5. 1. Bi X
   2. Wang K
   3. Yang L
   4. Pan H
   5. Jiang H
   6. Wei Q
   7. Fang M
   8. Yu H
   9. Zhu C
   10. Cai Y
   11. He Y
   12. Gan X
   13. Zeng H
   14. Yu D
   15. Zhu Y
   16. Jiang H
   17. Qiu Q
   18. Yang H
   19. Zhang YE
   20. Wang W
   21. Zhu M
   22. He S
   23. Zhang G

   (2021) Tracing the genetic footprints of vertebrate landing in non-teleost ray-finned fishes

   Cell 184:1377–1391.

   https://doi.org/10.1016/j.cell.2021.01.046

   • PubMed
   • Google Scholar
6. 1. Brito PM
   2. Meunier FJ
   3. Clément G
   4. Geffard-kuriyama D

   (2010) The histological structure of the calcified lung of the fossil coelacanth Axelrodichthys araripensis (Actinistia: Mawsoniidae

   Palaeontology 53:1281–1290.

   https://doi.org/10.1111/j.1475-4983.2010.01015.x

   • Google Scholar
7. 1. Cass AN
   2. Servetnick MD
   3. McCune AR

   (2013) Expression of a lung developmental cassette in the adult and developing zebrafish swimbladder

   Evolution & Development 15:119–132.

   https://doi.org/10.1111/ede.12022

   • PubMed
   • Google Scholar
8. 1. Clement AM
   2. Long JA

   (2010) Air-breathing adaptation in a marine Devonian lungfish

   Biology Letters 6:509–512.

   https://doi.org/10.1098/rsbl.2009.1033

   • PubMed
   • Google Scholar
9. 1. Clement AM
   2. Long JA
   3. Tafforeau P
   4. Ahlberg PE

   (2016) The dipnoan buccal pump reconstructed in 3D and implications for air breathing in Devonian lungfishes

   Paleobiology 42:289–304.

   https://doi.org/10.1017/pab.2015.41

   • Google Scholar
10. 1. Cupello C
    2. Brito PM
    3. Herbin M
    4. Meunier FJ
    5. Janvier P
    6. Dutel H
    7. Clément G

    (2015) Allometric growth in the extant coelacanth lung during ontogenetic development

    Nature Communications 6:8222.

    https://doi.org/10.1038/ncomms9222

    • PubMed
    • Google Scholar
11. 1. Cupello C
    2. Meunier FJ
    3. Herbin M
    4. Clément G
    5. Brito PM

    (2017a) Lung anatomy and histology of the extant coelacanth shed light on the loss of air-breathing during deep-water adaptation in actinistians

    Royal Society Open Science 4:161030.

    https://doi.org/10.1098/rsos.161030

    • PubMed
    • Google Scholar
12. 1. Cupello C
    2. Meunier FJ
    3. Herbin M
    4. Janvier P
    5. Clément G
    6. Brito PM

    (2017b) The homology and function of the lung plates in extant and fossil coelacanths

    Scientific Reports 7:1–8.

    https://doi.org/10.1038/s41598-017-09327-6

    • PubMed
    • Google Scholar
13. Book

    1. Cupello C
    2. Clément G
    3. Brito PM

    (2019)

    Evolution of air breathing and lung distribution among fossil fishes

    In: Johanson Z, editors. Evolution and Development of Fishes. Cambridge University Press. pp. 252–262.

    • Google Scholar
14. 1. Denison RH

    (1941)

    The soft anatomy of Bothriolepis

    Journal of Paleontology 15:553–561.

    • Google Scholar
15. 1. Flint JM

    (1906) The development of the lungs

    American Journal of Anatomy 6:1–137.

    https://doi.org/10.1002/aja.1000060102

    • Google Scholar
16. 1. Funk E
    2. Lencer E
    3. McCune A

    (2020) Dorsoventral inversion of the air-filled organ (lungs, gas bladder) in vertebrates: RNAsequencing of laser capture microdissected embryonic tissue

    Journal of Experimental Zoology. Part B, Molecular and Developmental Evolution 334:325–338.

    https://doi.org/10.1002/jez.b.22998

    • PubMed
    • Google Scholar
17. 1. Geoffrey Saint Hilaire E

    (1802)

    Histoire naturelle et description anatomique d’un nouveau genre de poisson du Nil, nommé Polyptére

    Annales Du Muséum d’Histoire Naturelle 1:57–68.

    • Google Scholar
18. 1. Goniakowska-Witalińska L

    (1978) Ultrastructural and morphometric study of the lung of the European salamander, Salamandra salamandra L

    Cell and Tissue Research 191:343–356.

    https://doi.org/10.1007/BF00222429

    • PubMed
    • Google Scholar
19. 1. Goniakowska-Witalińska L

    (1982) Development of the larval lung of Salamandra salamandra L

    Anatomy and Embryology 164:113–137.

    https://doi.org/10.1007/BF00301884

    • PubMed
    • Google Scholar
20. 1. Goodrich ES

    (1931) Studies on the structure and development of vertebrates

    The Journal of Nervous and Mental Disease 74:678.

    https://doi.org/10.1097/00005053-193111000-00026

    • Google Scholar
21. 1. Goujet D

    (2011) “Lungs” in Placoderms, a persistent palaeobiological myth related to environmental preconceived interpretations

    Comptes Rendus Palevol 10:323–329.

    https://doi.org/10.1016/j.crpv.2011.03.008

    • Google Scholar
22. Book

    1. Graham JB

    (1997)

    Air Breathing Fishes: Evolution, Diversity and Adaptation

    Academic Press.

    • Google Scholar
23. 1. Greil A

    (1913)

    Entwickelungsgeschichte des kopfes und des blutgefäßsystems von ceratodus forsteri. ii. die epigenetischen erwerbungen während der stadien 39-48

    Denkschriften Der Medizinisch-Naturwissenschaftlichen Gesellschaft Zu Jena 4:935–1492.

    • Google Scholar
24. 1. Grigg GC

    (1965)

    Studies on the Queensland lungfish, Neoceratodus forsteri (Krefft). 1. Anatomy, histology, and functioning of the lung

    Australian Journal of Zoology 13:243–253.

    • Google Scholar
25. 1. Icardo JM
    2. Colvee E
    3. Kuciel M
    4. Lauriano ER
    5. Zaccone G

    (2017) The lungs of Polypterus senegalus and Erpetoichthys calabaricus: Insights into the structure and functional distribution of the pulmonary epithelial cells

    Journal of Morphology 278:1321–1332.

    https://doi.org/10.1002/jmor.20715

    • PubMed
    • Google Scholar
26. 1. Janvier P
    2. Desbiens S
    3. Willett JA

    (2007) New evidence for the controversial “lungs” of the late devonian antiarch Bothriolepis canadensis (Whiteaves, 1880) (Placodermi: Antiarcha)

    Journal of Vertebrate Paleontology 27:709–710.

    https://doi.org/10.1671/0272-4634(2007)27[709:NEFTCL]2.0.CO;2

    • Google Scholar
27. Book

    1. Kardong KV

    (2015)

    The Respiratory System, Vertebrates: Comparative Anatomy, Function, Evolution

    McGraw-Hill Europe.

    • Google Scholar
28. 1. Kastschenko N

    (1887)

    Das Schlundspaltengebiet des Hühnchens

    Arch. Anat. Phys. Anat. Abt pp. 258–300.

    • Google Scholar
29. 1. Kemp A

    (1982)

    The embryological development of the Queensland lungfish, Neoceratodus forsteri (Krefft)

    Mem. Qd. Mus 20:553–597.

    • Google Scholar
30. 1. Kemp A

    (1986) The biology of the australian lungfish, Neoceratodus forsteri (Krefft 1870)

    Journal of Morphology 190:181–198.

    https://doi.org/10.1002/jmor.1051900413

    • Google Scholar
31. 1. Kemp A

    (2011) Comparison of embryological development in the threatened Australian lungfish Neoceratodus forsteri from two sites in a Queensland river system

    Endangered Species Research 15:87–101.

    https://doi.org/10.3354/esr00358

    • Google Scholar
32. 1. Kerr SGV

    (1900) V. The the external features the development of lepidosiren paradoxa, Fitz

    Philosophical Transactions of the Royal Society of London 192:299–330.

    https://doi.org/10.1098/rstb.1900.0005

    • Google Scholar
33. 1. Kuratani S
    2. Tanaka S

    (1990) Peripheral development of the avian vagus nerve with special reference to the morphological innervation of heart and lung

    Anatomy and Embryology 182:435–445.

    https://doi.org/10.1007/BF00178908

    • PubMed
    • Google Scholar
34. 1. Lambertz M
    2. Grommes K
    3. Kohlsdorf T
    4. Perry SF

    (2015) Lungs of the first amniotes: why simple if they can be complex?

    Biology Letters 11:20140848.

    https://doi.org/10.1098/rsbl.2014.0848

    • PubMed
    • Google Scholar
35. 1. Liem KF

    (1988) Form and function of lungs: the evolution of air breathing mechanisms

    American Zoologist 28:739–759.

    https://doi.org/10.1093/icb/28.2.739

    • Google Scholar
36. 1. Long JA

    (1993)

    Cranial ribs in Devonian lungfishes and the origin of air-breathing

    Mem. Austral. Ass. Palaeontol 15:199–210.

    • Google Scholar
37. 1. Long JA
    2. Young GC
    3. Holland T
    4. Senden TJ
    5. Fitzgerald EMG

    (2006) An exceptional Devonian fish from Australia sheds light on tetrapod origins

    Nature 444:199–202.

    https://doi.org/10.1038/nature05243

    • PubMed
    • Google Scholar
38. Book

    1. Marcus H

    (1937)

    Handbuch Der Vergleichenden Anatomie Der Wirbeltiere

    Berlin: Urban and Schwarzenberg.

    • Google Scholar
39. 1. Mirone A
    2. Brun E
    3. Gouillart E
    4. Tafforeau P
    5. Kieffer J

    (2014) The PyHST2 hybrid distributed code for high speed tomographic reconstruction with iterative reconstruction and a priori knowledge capabilities

    Nuclear Instruments and Methods in Physics Research Section B 324:41–48.

    https://doi.org/10.1016/j.nimb.2013.09.030

    • Google Scholar
40. 1. Neumayer L

    (1904)

    Die entwicklung des darmkanales, von lunge, leber, milz und pankreas bei ceratodus

    Forsteri. Zool. Forsch. Reisen 1:379–422.

    • Google Scholar
41. 1. Neumayer L

    (1930) Die entwicklung des darms von acipenser

    Acta Zoologica 11:39–150.

    https://doi.org/10.1111/j.1463-6395.1930.tb00123.x

    • Google Scholar
42. 1. Paganin D
    2. Mayo SC
    3. Gureyev TE
    4. Miller PR
    5. Wilkins SW

    (2002) Simultaneous phase and amplitude extraction from a single defocused image of a homogeneous object

    Journal of Microscopy 206:33–40.

    https://doi.org/10.1046/j.1365-2818.2002.01010.x

    • PubMed
    • Google Scholar
43. 1. Perry SF
    2. Wilson RJA
    3. Straus C
    4. Harris MB
    5. Remmers JE

    (2001) Which came first, the lung or the breath?

    Comparative Biochemistry and Physiology. Part A, Molecular & Integrative Physiology 129:37–47.

    https://doi.org/10.1016/s1095-6433(01)00304-x

    • PubMed
    • Google Scholar
44. 1. Pierce SE
    2. Lamas LP
    3. Pelligand L
    4. Schilling N
    5. Hutchinson JR

    (2020) Patterns of limb and epaxial muscle activity during walking in the fire salamander, salamandra salamandra

    Integrative Organismal Biology 2:obaa015.

    https://doi.org/10.1093/iob/obaa015

    • PubMed
    • Google Scholar
45. 1. Rice AN
    2. Bass AH

    (2009) Novel vocal repertoire and paired swimbladders of the three-spined toadfish, Batrachomoeus trispinosus: insights into the diversity of the Batrachoididae

    The Journal of Experimental Biology 212:1377–1391.

    https://doi.org/10.1242/jeb.028506

    • PubMed
    • Google Scholar
46. 1. Rossi V
    2. McNamara ME
    3. Webb SM
    4. Ito S
    5. Wakamatsu K

    (2019) Tissue-specific geometry and chemistry of modern and fossilized melanosomes reveal internal anatomy of extinct vertebrates

    PNAS 116:17880–17889.

    https://doi.org/10.1073/pnas.1820285116

    • PubMed
    • Google Scholar
47. Book

    1. Spencer WB

    (1893)

    Contributions to Our Knowledge of Ceratodus: The Blood Vessels

    Linnean Soc of New South Wales.

    • Google Scholar
48. 1. Tatsumi N
    2. Kobayashi R
    3. Yano T
    4. Noda M
    5. Fujimura K
    6. Okada N
    7. Okabe M

    (2016) Molecular developmental mechanism in polypterid fish provides insight into the origin of vertebrate lungs

    Scientific Reports 6:30580.

    https://doi.org/10.1038/srep30580

    • PubMed
    • Google Scholar
49. 1. Thomson KS

    (1968)

    Lung ventilation in dipnoan fishes

    Pea. Mus. Nat. Hist 122:1–6.

    • Google Scholar
50. 1. Tissier J
    2. Rage JC
    3. Laurin M

    (2017) Exceptional soft tissues preservation in a mummified frog-eating Eocene salamander

    PeerJ 5:e3861.

    https://doi.org/10.7717/peerj.3861

    • PubMed
    • Google Scholar
51. 1. Wang X
    2. O’Connor JK
    3. Maina JN
    4. Pan Y
    5. Wang M
    6. Wang Y
    7. Zheng X
    8. Zhou Z

    (2018) Archaeorhynchus preserving significant soft tissue including probable fossilized lungs

    PNAS 115:11555–11560.

    https://doi.org/10.1073/pnas.1805803115

    • PubMed
    • Google Scholar
52. 1. Wassnetzov W

    (1932)

    Über die Morphologie der Schwimmblase

    Zool. Jahrb. Allg. Zool 56:1–36.

    • Google Scholar
53. 1. Ziermann JM
    2. Clement AM
    3. Ericsson R
    4. Olsson L

    (2018) Cephalic muscle development in the Australian lungfish, Neoceratodus forsteri

    Journal of Morphology 279:494–516.

    https://doi.org/10.1002/jmor.20784

    • PubMed
    • Google Scholar

Author details

1. Camila Cupello

   Departamento de Zoologia-IBRAG, Universidade do Estado do Rio de Janeiro, Rio de Janeiro RJ, Brazil

   Contribution

   Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review and editing

   For correspondence

   camila.dc@gmail.com

   Competing interests

   No competing interests declared

   "This ORCID iD identifies the author of this article:" 0000-0001-6030-8670

2. Tatsuya Hirasawa

   Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, Tokyo, Japan

   Contribution

   Data curation, Formal analysis, Investigation, Methodology, Software, Validation, Visualization, Writing – original draft, Writing – review and editing

   Competing interests

   No competing interests declared

   "This ORCID iD identifies the author of this article:" 0000-0001-6868-3379

3. Norifumi Tatsumi

   Department of Anatomy, The Jikei University School of Medicine, Tokyo, Japan

   Contribution

   Data curation, Formal analysis, Investigation, Methodology, Resources, Software, Validation, Visualization, Writing – original draft, Writing – review and editing

   Competing interests

   No competing interests declared

   "This ORCID iD identifies the author of this article:" 0000-0001-6640-150X

4. Yoshitaka Yabumoto

   Kitakyushu Museum of Natural History and Human History, 2-4-1 Higashida, Yahatahigashi-ku, Kitakyushu, Fukuoka, Japan

   Contribution

   Conceptualization, Data curation, Funding acquisition, Investigation, Methodology, Software, Validation, Visualization, Writing – original draft, Writing – review and editing

   Competing interests

   No competing interests declared

   "This ORCID iD identifies the author of this article:" 0000-0002-4736-8246

5. Pierre Gueriau

   1. Institute of Earth Sciences, University of Lausanne, Lausanne, Switzerland
   2. Université Paris-Saclay, CNRS, ministère de la Culture, UVSQ, MNHN, Institut photonique d’analyse non-destructive européen des matériaux anciens, Saint-Aubin, France

   Contribution

   Data curation, Investigation, Methodology, Software, Validation, Visualization, Writing – original draft, Writing – review and editing

   Competing interests

   No competing interests declared

   "This ORCID iD identifies the author of this article:" 0000-0002-7529-3456

6. Sumio Isogai

   Department of Anatomy, Iwate Medical University School of Medicine, Iwate, Japan

   Contribution

   Data curation, Methodology, Validation, Writing – review and editing

   Competing interests

   No competing interests declared

7. Ryoko Matsumoto

   Kanagawa Prefectural Museum of Natural History, Kanagawa, Japan

   Contribution

   Data curation, Methodology, Validation, Writing – review and editing

   Competing interests

   No competing interests declared

   "This ORCID iD identifies the author of this article:" 0000-0002-0334-7259

8. Toshiro Saruwatari

   1. Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, Japan
   2. Seikei Education and Research Center for Sustainable Development, Tokyo, Japan

   Contribution

   Data curation, Funding acquisition, Validation, Writing – review and editing

   Competing interests

   No competing interests declared

   "This ORCID iD identifies the author of this article:" 0000-0002-5761-8528

9. Andrew King

   Synchrotron SOLEIL, L’orme des Merisiers Saint-Aubin, Gif-sur-Yvette Cedex, France

   Contribution

   Methodology, Software, Validation, Writing – review and editing

   Competing interests

   No competing interests declared

   "This ORCID iD identifies the author of this article:" 0000-0001-8542-1354

10. Masato Hoshino

    Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), Hyogo, Japan

    Contribution

    Methodology, Software, Validation, Writing – review and editing

    Competing interests

    No competing interests declared

    "This ORCID iD identifies the author of this article:" 0000-0002-4167-2706

11. Kentaro Uesugi

    Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), Hyogo, Japan

    Contribution

    Methodology, Software, Validation, Writing – review and editing

    Competing interests

    No competing interests declared

    "This ORCID iD identifies the author of this article:" 0000-0003-2579-513X

12. Masataka Okabe

    Department of Anatomy, The Jikei University School of Medicine, Tokyo, Japan

    Contribution

    Data curation, Investigation, Methodology, Validation, Writing – original draft, Writing – review and editing

    Competing interests

    No competing interests declared

    "This ORCID iD identifies the author of this article:" 0000-0002-8618-6859

13. Paulo M Brito

    Departamento de Zoologia-IBRAG, Universidade do Estado do Rio de Janeiro, Rio de Janeiro RJ, Brazil

    Contribution

    Conceptualization, Data curation, Funding acquisition, Methodology, Validation, Writing – original draft, Writing – review and editing

    For correspondence

    pbritopaleo@yahoo.com.br

    Competing interests

    No competing interests declared

    "This ORCID iD identifies the author of this article:" 0000-0002-4853-8630

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