Introduction
The holostean fishes (Class Holostei) comprise the bowfin and the gars, which belong to the clades Halecomorphi and Ginglymodi, respectively. Only 8 species of Holostei are known at the present day.
The following figure is a summarized phylogenetic tree for the Holostei, showing that the stem line of the taxon is documented by transitional fossils. However, the entire stem group known to date is younger than the crown group, and thus represents descendants of undiscovered ancestors that would have separated from the stem line before the crown group appeared.
The following figure is a summarized phylogenetic tree for the Holostei, showing that the stem line of the taxon is documented by transitional fossils. However, the entire stem group known to date is younger than the crown group, and thus represents descendants of undiscovered ancestors that would have separated from the stem line before the crown group appeared.
The crown group of the Holostei, represented above by the black dot, comprises all living holostean fishes, together with all extinct species descended from the last common ancestor of all living Holostei.
We will now consider the evolution of the Holostei in the following two stages:
We will now consider the evolution of the Holostei in the following two stages:
- The stem-Holostei
- Within the crown-Holostei
The stem group of the Holostei
The stem-Holostei are well represented in the fossil record. An interpretation of their phylogenetic relationships is shown in the tree below:
The oldest known member of the stem-Holostei is Sargodon tomicus, described from multiple sites within the late Triassic (Middle Norian) Zorzino Limestone in the Southern Alps of Italy (Tintori, 1983; Latimer and Giles, 2018). This species is illustrated below, together with other members of the stem group for which public-domain images are available (for a larger view, click on image):
Names in red indicate that the fossil is younger than the oldest known crown-group fossil.
* after name indicates that the image represents a life restoration
* after name indicates that the image represents a life restoration
The images shown above are numbered in order from most basal towards the crown group, but no obvious trends can be seen apart from the fact that the most basal species, Hulletia americana, does not have the deep-bodied form of all the other stem-Holostei illustrated above.
The oldest known crown-group holostean is Watsonulus eugnathoides, a member of the stem-Halecomorphi, found in the Early Trassic (Induan) Middle Sakamena Formation, Sakamena Group, Ambilombe Bay, Madagascar (Benton et al, 2015). No public-domain image is available.
The time-frame of appearance of the known stem-Holostei is illustrated below:
The oldest known crown-group holostean is Watsonulus eugnathoides, a member of the stem-Halecomorphi, found in the Early Trassic (Induan) Middle Sakamena Formation, Sakamena Group, Ambilombe Bay, Madagascar (Benton et al, 2015). No public-domain image is available.
The time-frame of appearance of the known stem-Holostei is illustrated below:
Given that the entire stem group is younger than the oldest known member of the crown group, we have no information about the duration of the stem-to-crown transition for the Holostei, although we know it must have begun no earlier than the age of the oldest known stem-group fossil of the ancestor clade (Neopterygii), Discoserra pectinodon. This implies a maximum possible duration of around 75 million years.
Evolution within the crown-Holostei
In this section we are concerned with the origin of the two clades which separated to form the Holostean crown group. These are the Halecomorphi and Ginglymodi, which are represented at the present day by the orders Amiiformes and Lepisosteiformes, respectively. Two living examples are illustrated below (click on image for larger view):
The Ammiformes (bowfin) contain the crown-Halecomorphi, while the Lepisosteiformes (the gars) contain the crown-Ginglymodi, as illustrated in the following phylogenetic tree of fossils interpreted to belong to the respective stem groups:
The oldest known member of the stem-Halecomorphi is Watsonulus eugnathoides, described from the Early Trassic (Induan) Middle Sakamena Formation, Sakamena Group, Ambilombe Bay, Madagascar (Benton et al, 2015). No public-domain image of this species is available, but other stem-Halecomorphi are illustrated below (for a larger view, click on image):
* after name indicates that the image represents a life restoration.
The images shown above are numbered in order from most basal towards the crown group. The only obvious trend is that the more crownward species have the long dorsal fin that is characteristic of the modern bowfin (compare Sinamia zdanskyi and Cyclurus kehreri with the modern Amia calva shown above near the beginning of this section).
As illustrated in the plot below, the stem group of the Halecomorphi developed from the Early Triassic until at least the Eocene (no crown-group fossils have been described):
As illustrated in the plot below, the stem group of the Halecomorphi developed from the Early Triassic until at least the Eocene (no crown-group fossils have been described):
Thus the stem-to-crown transition for the Halecomorphi lasted at least 200 million years.
Turning now to the Ginglymodi, the oldest known member of the stem group is Sangiorgioichthys sui, described from the Middle Triassic (Middle Anisian) Vertebrate Level of the Upper Member of the Guanling Formation near the village of Dawazi, Luoping County, Yunnan Province, South China (López-Arbarello et al, 2011; López-Arbarello and Sferco, 2018). No public-domain image is available for this species and it is not included in the phylogenetic tree above, but other stem-Ginglymodi from the tree are illustrated below (click on image for a larger view):
Turning now to the Ginglymodi, the oldest known member of the stem group is Sangiorgioichthys sui, described from the Middle Triassic (Middle Anisian) Vertebrate Level of the Upper Member of the Guanling Formation near the village of Dawazi, Luoping County, Yunnan Province, South China (López-Arbarello et al, 2011; López-Arbarello and Sferco, 2018). No public-domain image is available for this species and it is not included in the phylogenetic tree above, but other stem-Ginglymodi from the tree are illustrated below (click on image for a larger view):
* after name indicates that the image represents a life restoration.
Again, the images shown are numbered in order from most basal towards the crown group and a trend can be seen from deep-bodied to more slender forms. The most crownward species (e.g. Araripelepidotes temnurus and Obaichthys decorates) show a fair resemblance to modern gars (compare with Lepisosteus oculatus shown above near the beginning of this section).
The oldest known member of the crown-Ginglymodi is Atractosteus falipoui (previously known as Oniichthys falipoui), described from the Late Cretaceous (Early Cenomanian) “Unit 1”, Kem Kem beds, Aoufous Formation at an unspecified location in southern Morocco (Cavin and Brito, 2001; Benton et al, 2015). No image is available in the public domain.
The time-frame of development of the stem-Ginglymodi is shown below:
The oldest known member of the crown-Ginglymodi is Atractosteus falipoui (previously known as Oniichthys falipoui), described from the Late Cretaceous (Early Cenomanian) “Unit 1”, Kem Kem beds, Aoufous Formation at an unspecified location in southern Morocco (Cavin and Brito, 2001; Benton et al, 2015). No image is available in the public domain.
The time-frame of development of the stem-Ginglymodi is shown below:
Allowing for the ghost lineage of the Ginglymodi, representing the difference in age between the oldest known stem-Halecomorphi (Watsonulus eugnathoides) and the oldest known stem-Ginglymodi, the stem-to-crown transition for the Ginglymodi lasted from Early Triassic to Late Cretaceous time, an interval of around 153 million years.
References
Benton, M. J., Donoghue, P. C., Asher, R. J., Friedman, M., Near, T. J., & Vinther, J. (2015). Constraints on the timescale of animal evolutionary history. Palaeontologia Electronica, 18(1), 1-106.
Cavin, L., & Brito, P. M. (2001). A new Lepisosteidae (Actinopterygii, Ginglymodi) from the Cretaceous of the Kem Kem beds, Southern Morocco. Bulletin de la Société géologique de France, 172(5), 661-670.
Latimer, A. E., & Giles, S. (2018). A giant dapediid from the Late Triassic of Switzerland and insights into neopterygian phylogeny. Royal Society open science, 5(8), 180497.
López-Arbarello, A., & Sferco, E. (2018). Neopterygian phylogeny: the merger assay. Royal Society open science, 5(3), 172337.
López-Arbarello, A., Sun, Z. Y., Sferco, E., Tintori, A., Xu, G. H., Sun, Y. L., ... & Jiang, D. Y. (2011). New species of Sangiorgioichthys Tintori and Lombardo, 2007 (Neopterygii, Semionotiformes) from the Anisian of Luoping (Yunnan Province, South China). Zootaxa, 2749(1), 25-39.
Tintori, A. (1983). Hypsisomatic Semionotidae (Pisces, Actinopterygii) from the Upper Triassic of Lombardy (N. Italy). Rivista Italiana di Paleontologia e Stratigrafia 88(3):417-442.
Xu, G. H. (2019). Osteology and phylogeny of Robustichthys luopingensis, the largest holostean fish in the Middle Triassic. PeerJ, 7, e7184.
Cavin, L., & Brito, P. M. (2001). A new Lepisosteidae (Actinopterygii, Ginglymodi) from the Cretaceous of the Kem Kem beds, Southern Morocco. Bulletin de la Société géologique de France, 172(5), 661-670.
Latimer, A. E., & Giles, S. (2018). A giant dapediid from the Late Triassic of Switzerland and insights into neopterygian phylogeny. Royal Society open science, 5(8), 180497.
López-Arbarello, A., & Sferco, E. (2018). Neopterygian phylogeny: the merger assay. Royal Society open science, 5(3), 172337.
López-Arbarello, A., Sun, Z. Y., Sferco, E., Tintori, A., Xu, G. H., Sun, Y. L., ... & Jiang, D. Y. (2011). New species of Sangiorgioichthys Tintori and Lombardo, 2007 (Neopterygii, Semionotiformes) from the Anisian of Luoping (Yunnan Province, South China). Zootaxa, 2749(1), 25-39.
Tintori, A. (1983). Hypsisomatic Semionotidae (Pisces, Actinopterygii) from the Upper Triassic of Lombardy (N. Italy). Rivista Italiana di Paleontologia e Stratigrafia 88(3):417-442.
Xu, G. H. (2019). Osteology and phylogeny of Robustichthys luopingensis, the largest holostean fish in the Middle Triassic. PeerJ, 7, e7184.
Image credits - Holostei
- Header: Florida gar (Lepisosteus platyrhincus) By Raimond Spekking / CC BY-SA 4.0 (via Wikimedia Commons)
- Hulettia americana By Isaac T Valtez [Public domain]
- Tetragonolepis semicincta By Ghedoghedo [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]
- Hemicalypterus weiri (3a) By Gibson SZ (2016) [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
- Hemicalypterus weiri (3b) By Gibson SZ (2016) [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
- Dandya ovalis By Ghedoghedo [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]
- Sargodon tomicus By Ghedoghedo [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]
- Dapedium noricum By Ghedoghedo [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]
- Dapedium caelatum By Daderot [Public domain]
- Dapedium punctatum By Ghedoghedo [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
- Dapedium stollorum By Daderot [Public domain]
- Dapedium pholidotum By Daderot [Public domain]
- Bowfin (Amia calva) By Stan Shebs, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons
- Gar (Lepisosteus oculatus) By Tino Strauss, CC BY-SA 2.5 <https://creativecommons.org/licenses/by-sa/2.5>, via Wikimedia Commons
- Asialepidotus shingyiensis By Morosaurus millenii, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Robustichthys luopingensis From Open Access article by Xu (2019); Guang-Hui Xu, Creative Commons Attribution 4.0 International (CC BY 4.0)
- Ophiopsis muensteri By Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Heterolepidotus latus Copyright The Trustees of the Natural History Museum, London. Creative Commons Attribution 4.0 International
- Ophiopsis procera By Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
- Macrepistius arenatus By Geological Survey (U.S.), No restrictions, via Wikimedia Commons
- Teoichthys kallistos From Open Access article by Cantalice et al (2019); CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
- Oshunia brevis By Marcos Santos/USP Imagens, Creative Commons Atribuição-NãoComercial 3.0 Brasil (CC BY-NC 3.0 BR)
- Ionoscopus cyprinoides By Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Quetzalichthys perrilliatae From Open Access article by Cantalice et al (2019); CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
- Caturus furcatus (21a) By Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Caturus furcatus (21b) By Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0)
- Amiopsis lepidota By Haplochromis, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
- Solnhofenamia elongata By Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
- Calamopleurus cylindricus By Muséum de Toulouse, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Sinamia zdanskyi By Laikayiu, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons
- Cyclurus kehreri By H. Zell, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
- Ticinolepis longaeva By López-Arbarello A, Bürgin T, Furrer H, Stockar R. 2016., CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Kyphosichthys grandei (28a) By Xu GuangHui & Wu FeiXiang, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
- Kyphosichthys grandei (28b) By Apokryltaros, licensed under the Creative Commons Attribution-Share Alike 4.0 International license.
- Macrosemimimus fegerti By Ebert M, Kölbl-Ebert M, Lane JA, CC BY-SA 2.5 <https://creativecommons.org/licenses/by-sa/2.5>, via Wikimedia Commons
- Eosemionotus diskosomus From Open Access article by López-Arbarello et al (2019) Creativecommons.org/licenses/by/4.0/
- Macrosemius rostratus By Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Propterus elongatus By Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Notagogus denticulatus By Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Lepidotes semiserratus By Emőke Dénes, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- Araripelepidotes temnurus By Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
- Obaichthys decoratus By Ghedoghedo, Public domain, via Wikimedia Commons