Teleostean stem group

This page deals with the stem group of the teleostean fishes (class Teleostei, Superclass Actinopterygii), which comprise a clade that contains most of the ray-finned fishes alive in the world today, with nearly 30,000 species (Ravi and Venkatesh, 2018). They consist of two major divisions ("megacohorts"), the Elopocephalai and the Osteoglossocephalai, as shown in the following phylogenetic tree:

Figure 1. Phylogenetic tree of living Teleostei

The synapomorphies of the stem-Teleostei are as follows (López-Arbarello and Sferco, 2018):

Orbitosphenoid (a bone between the eyes) confined to the dorsal portion of the orbit
Quadratojugal (small bone on each side of the skull) fused to quadrate (bone to which the lower jaw is articulated)
Presence of median basibranchial tooth plates (plates at the base of the tongue overlying the basibranchial bones between the gill arches)

As is the case with the neopterygians, these characteristics, which are evolutionary novelties along the teleostean stem line, will not be obvious without very detailed inspection of fossil skeletons.

The stem-Teleostei are very well represented in the fossil record. Their phylogeny is shown below in a combined time tree taken from two recent publications:

Figure 2. Time tree of the stem-Teleostei

The oldest known member of the stem-Teleostei is the genus Parapholidophorus, which has been described from the Middle Triassic (Ladinian) of Catalonia, Spain (Beltan, 1972, cited in Fossilworks; Arratia, 2017). No image is available of that fossil, which was not assigned to a species, but a Late Triassic species of genus Parapholidophorus (P. nybelini), together with other members of the stem group, are shown below (click on image for larger version):

Names in red indicate that the fossil is younger than the oldest known crown-group fossil.

Figure 3. Images of stem-group Teleostei

The images shown above are numbered in order from most basal towards the crown group, but no obvious trends can be seen.

The earliest known member of the teleostean crown group is Anaethalion zapporum, a member of the total-group Elopomorpha (synonymous with the Elopocephalai) found in the Late Jurassic (Late Kimmeridgian) Rögling Formation at the village of Schamhaupten, near Eichstätt, Bavaria, Germany (Benton et al, 2015). No image of this species is available in the public domain, but another species of the same genus is shown below:

Figure 4. Image of oldest known member of the crown-Teleostei

Making allowance for the ghost lineage on the teleostean stem line (Figure 2), the time between the origin of the teleostean stem group and the initiation of the crown group was at least 97 million years, from Early Triassic to Late Jurassic time. However, as indicated in the histogram below, the rate of appearance of new stem-group genera increased rapidly during the Late Jurassic:

Figure 5. Time of appearance of stem-Teleostei (predating the crown group and including only the genera shown in Figure 2)

References

Arratia, G. (2017). New Triassic teleosts (Actinopterygii, Teleosteomorpha) from northern Italy and their phylogenetic relationships among the most basal teleosts. Journal of Vertebrate Paleontology, 37(2), e1312690.

Beltan, L.L. (1972). La faune Ichthyologique du Muschelkalk de la Catalogne. Memorias de la Real Academia de Ciencias y Artes XLI:281-325.

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.

López-Arbarello, A., & Sferco, E. (2018). Neopterygian phylogeny: the merger assay. Royal Society Open Science, 5(3), 172337.

Ravi, V., & Venkatesh, B. (2018). The Divergent Genomes of Teleosts. Annual Review of Animal Biosciences, 6:1, 47-68.

Image credits - Stem-Teleostei

Header (Banded Archerfish, Toxotes jaculatrix, Schönbrunn Zoo, Vienna): Norbert Potensky, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
Figure 3 (Pachycormus bollensis): Jeff Kubina from the milky way galaxy, CC BY-SA 2.0 <https://creativecommons.org/licenses/by-sa/2.0>, via Wikimedia Commons
Figure 3 (Orthocormus cornutus, fossil): Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
Figure 3 (Orthocormus cornutus, life restoration): DiBgd, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Figure 3 (Hypsocormus insignis, fossil): Leo Fyllnet, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Figure 3 (Hypsocormus insignis, life restoration): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
Figure 3 (Vinctifer comptoni): Hectonichus, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
Figure 3 (Belonostomus tenuirostris): Oilshale, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Figure 3 (Aspidorhynchus sanzenbacheri): Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Figure 3 (Aspidorhynchus acutirostris): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
Figure 3 (Prohalecites sp.): Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Figure 3 (Eurycormus speciosus): Gloria Arratia & Hans-Peter Schultze, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Figure 3 (Parapholidophorus nybelini): Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
Figure 3 (Siemensichthys macrocephalus): Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
Figure 3 (Ankylophorus similis): Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Figure 3 (Ichthyokentema purbeckensis): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
Figure 3 (Dorsetichthys bechei): Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Figure 3 (Leptolepis coryphaenoides): Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Figure 3 (Tharsis elleri): Open Access article Arratia, G., Schultze, H. P., & Tischlinger, H. (2019). On a remarkable new species of Tharsis, a Late Jurassic teleostean fish from southern Germany: its morphology and phylogenetic relationships. Fossil Record, 22(1).
Figure 3 (Tharsis dubius): Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
Figure 3 (Ebertichthys ettlingensis): Open Access article Arratia, G. (2016). New remarkable Late Jurassic teleosts from southern Germany: Ascalaboidae n. fam., its content, morphology, and phylogenetic relationships. Fossil Record, 19(1), 31-59.
Figure 3 (Ascalabos voithii, fossil): Open Access article Arratia, G. (2016). New remarkable Late Jurassic teleosts from southern Germany: Ascalaboidae n. fam., its content, morphology, and phylogenetic relationships. Fossil Record, 19(1), 31-59.
Figure 3 (Ascalabos voithii, life restoration): Open Access article Arratia, G. (2016). New remarkable Late Jurassic teleosts from southern Germany: Ascalaboidae n. fam., its content, morphology, and phylogenetic relationships. Fossil Record, 19(1), 31-59.
Figure 3 (Varasichthys ariasi, fossil): Sergio Soto-Acuña; Rodrigo A. Otero; David Rubilar-Rogers; Alexander O. Vargas, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Figure 3 (Varasichthys ariasi, life restoration): Art by Gloria Arratia. Published by Sergio Soto-Acuña; Rodrigo A. Otero; David Rubilar-Rogers; Alexander O. Vargas, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Figure 3 ( Luisichthys vinalesensis): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
Figure 4: Daderot, CC0, via Wikimedia Commons