This page covers the stem group of the cyclostomes (Clade Cyclostomata, subphylum Vertebrata), a group of extant primitive fishes that represents the jawless vertebrates. It contains two orders, the lampreys and the hagfishes.
As indicated in Figure 1 of the Vertebrates page, the Cyclostomata are monophyletic. This has long been the consistent result of molecular analysis (Janvier, 2015) although a recent paper (Theofanopoulou et al, 2021) suggests on the basis of molecular data that the cyclostomes might actually be paraphyletic. This is also the conclusion of some studies using morphological data (e.g. Larouche et al, 2017; Chevrinais et al, 2018; Clements et al, 2019) while other morphological analyses support monophyly (e.g. Keating and Donoghue, 2016; Hirasawa et al, 2016; Terrill et al, 2018; Miyashita et al, 2019). This issue remains unresolved, but we will follow, at least for now, the monophyletic interpretation given the strong molecular evidence for that view.
On the basis of phylogenetic analysis of morphological characteristics, several stem-group cyclostomes have been identified by Miyashita et al (2021), as illustrated in modified form in the following phylogenetic time tree:
As indicated in Figure 1 of the Vertebrates page, the Cyclostomata are monophyletic. This has long been the consistent result of molecular analysis (Janvier, 2015) although a recent paper (Theofanopoulou et al, 2021) suggests on the basis of molecular data that the cyclostomes might actually be paraphyletic. This is also the conclusion of some studies using morphological data (e.g. Larouche et al, 2017; Chevrinais et al, 2018; Clements et al, 2019) while other morphological analyses support monophyly (e.g. Keating and Donoghue, 2016; Hirasawa et al, 2016; Terrill et al, 2018; Miyashita et al, 2019). This issue remains unresolved, but we will follow, at least for now, the monophyletic interpretation given the strong molecular evidence for that view.
On the basis of phylogenetic analysis of morphological characteristics, several stem-group cyclostomes have been identified by Miyashita et al (2021), as illustrated in modified form in the following phylogenetic time tree:
Figure 1. Time tree of the stem-Cyclostomata
The above tree (Figure 1) has been modified from that presented by Miyashita et al (2021) because in that tree the Anaspida (a group of scaly jawless fish) are considered as part of the cyclostome stem group; this is inconsistent with many articles (e.g. Keating et al, 2018) that place the anaspids in the stem-Gnathostomata. Given this weight of opinion in the literature, we will for the time being consider the anaspids as stem gnathostomes. This means that only the Euconodonta can be considered as belonging to the stem-Cyclostomata. Euconodonts are an infraclass of condonts, which are a group of animals known mainly by scattered elements of their feeding apparatus (Aldridge et al, 1993); not all of the latter are known with certainty to represent vertebrates, but the euconodonts, or "true" conodonts, have been classified as vertebrates since they were found as fossils in which their soft-tissue anatomy could be seen (Donoghue and Keating, 2014).
The oldest known fossil representative of the stem-Cyclostomata is Cambropustula kinnekullensis, the oldest known Euconodont, described from the Late Cambrian Alum Shale at the Gum quarry in Västergötland, Sweden (Müller and Hinz, 1991; Müller and Hinz-Schallreuter, 1998). No image of this species is available in the public domain, but some other euconodonts are illustrated below (click on image for larger version):
The oldest known fossil representative of the stem-Cyclostomata is Cambropustula kinnekullensis, the oldest known Euconodont, described from the Late Cambrian Alum Shale at the Gum quarry in Västergötland, Sweden (Müller and Hinz, 1991; Müller and Hinz-Schallreuter, 1998). No image of this species is available in the public domain, but some other euconodonts are illustrated below (click on image for larger version):
Names in red indicate that the fossil is younger than the oldest known crown-group fossil.
Figure 2. Images of stem-group cyclostomes
The above images illustrate the eel-like body form, the large eyes and the nature of the feeding apparatus in the euconodonts, which represent the cyclostome stem group. The main difference between these fossils and those in the stem group of the Vertebrata (see vertebrate page) is that the euconodonts have a feeding apparatus with teeth, while the stem-Vertebrata are toothless. The development of such a feeding apparatus is thus an important evolutionary novelty that occurred on the vertebrate stem line sometime before the appearance of the earliest known stem-group cyclostome, Cambropustula kinnekullensis, in the Late Cambrian.
Some idea of the nature of the transition from the stem group to the crown group of the cyclostomes can be derived from a comparison of the above images with the examples of early crown cyclostomes shown below:
Some idea of the nature of the transition from the stem group to the crown group of the cyclostomes can be derived from a comparison of the above images with the examples of early crown cyclostomes shown below:
Figure 3. Examples of early crown-Cyclostomata
The transition from the stem-Vertebrata to the crown-Cyclostomata, represented by the fossils illustrated in Figures 2 and 3, took place over a period of between 125 and 140 million years, from the Late Cambrian to the Late Devonian (Figure 1).
References
Aldridge, R. J., Briggs, D. E. G., Smith, M. P., Clarkson, E. N. K., & Clark, N. D. L. (1993). The anatomy of conodonts. Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences, 340(1294), 405-421.
Chevrinais, M., Johanson, Z., Trinajstic, K., Long, J., Morel, C., Renaud, C. B., & Cloutier, R. (2018). Evolution of vertebrate postcranial complexity: axial skeleton regionalization and paired appendages in a Devonian jawless fish. Palaeontology, 61(6), 949-961.
Clements, T., Purnell, M., & Gabbott, S. (2019). The Mazon Creek Lagerstätte: a diverse late Paleozoic ecosystem entombed within siderite concretions. Journal of the Geological Society, 176(1), 1-11.
Donoghue, P. C., & Keating, J. N. (2014). Early vertebrate evolution. Palaeontology, 57(5), 879-893.
Hirasawa, T., Oisi, Y., & Kuratani, S. (2016). Palaeospondylus as a primitive hagfish. Zoological letters, 2(1), 1-9.
Janvier, P. (2015). Facts and fancies about early fossil chordates and vertebrates. Nature, 520(7548), 483-489.
Keating, J. N., & Donoghue, P. C. (2016). Histology and affinity of anaspids, and the early evolution of the vertebrate dermal skeleton. Proceedings of the Royal Society B: Biological Sciences, 283(1826), 20152917.
Keating, J. N., Marquart, C. L., Marone, F., & Donoghue, P. C. (2018). The nature of aspidin and the evolutionary origin of bone. Nature ecology & evolution, 2(9), 1501.
Larouche, O., Zelditch, M. L., & Cloutier, R. (2017). Fin modules: an evolutionary perspective on appendage disparity in basal vertebrates. BMC biology, 15(1), 1-26.
Miyashita, T., Coates, M. I., Farrar, R., Larson, P., Manning, P. L., Wogelius, R. A., ... & Currie, P. J. (2019). Hagfish from the Cretaceous Tethys Sea and a reconciliation of the morphological–molecular conflict in early vertebrate phylogeny. Proceedings of the National Academy of Sciences, 116(6), 2146-2151.
Miyashita, T., Gess, R. W., Tietjen, K., & Coates, M. I. (2021). Non-ammocoete larvae of Palaeozoic stem lampreys. Nature, 591(7850), 408-412.
Müller, K.J. & Hinz, I., 1991. Upper Cambrian Conodonts from Sweden. Fossils and Strata no. 28. 153 pp. Oslo: Universitetsforlaget
Müller, K. J., & Hinz-Schallreuter, I. (1998). Internal structure of Cambrian conodonts. Journal of Paleontology, 72(1), 91-112.
Murdock, D. J., & Smith, M. P. (2021). Panderodus from the Waukesha Lagerstätte of Wisconsin, USA: a primitive macrophagous vertebrate predator. Papers in Palaeontology, 7(4), 1977-1993.
Terrill, D. F., Henderson, C. M., & Anderson, J. S. (2018). New applications of spectroscopy techniques reveal phylogenetically significant soft tissue residue in Paleozoic conodonts. Journal of Analytical Atomic Spectrometry, 33(6), 992-1002.
Theofanopoulou, C., Gedman, G., Cahill, J. A., Boeckx, C., & Jarvis, E. D. (2021). Universal nomenclature for oxytocin–vasotocin ligand and receptor families. Nature, 592(7856), 747-755.
Chevrinais, M., Johanson, Z., Trinajstic, K., Long, J., Morel, C., Renaud, C. B., & Cloutier, R. (2018). Evolution of vertebrate postcranial complexity: axial skeleton regionalization and paired appendages in a Devonian jawless fish. Palaeontology, 61(6), 949-961.
Clements, T., Purnell, M., & Gabbott, S. (2019). The Mazon Creek Lagerstätte: a diverse late Paleozoic ecosystem entombed within siderite concretions. Journal of the Geological Society, 176(1), 1-11.
Donoghue, P. C., & Keating, J. N. (2014). Early vertebrate evolution. Palaeontology, 57(5), 879-893.
Hirasawa, T., Oisi, Y., & Kuratani, S. (2016). Palaeospondylus as a primitive hagfish. Zoological letters, 2(1), 1-9.
Janvier, P. (2015). Facts and fancies about early fossil chordates and vertebrates. Nature, 520(7548), 483-489.
Keating, J. N., & Donoghue, P. C. (2016). Histology and affinity of anaspids, and the early evolution of the vertebrate dermal skeleton. Proceedings of the Royal Society B: Biological Sciences, 283(1826), 20152917.
Keating, J. N., Marquart, C. L., Marone, F., & Donoghue, P. C. (2018). The nature of aspidin and the evolutionary origin of bone. Nature ecology & evolution, 2(9), 1501.
Larouche, O., Zelditch, M. L., & Cloutier, R. (2017). Fin modules: an evolutionary perspective on appendage disparity in basal vertebrates. BMC biology, 15(1), 1-26.
Miyashita, T., Coates, M. I., Farrar, R., Larson, P., Manning, P. L., Wogelius, R. A., ... & Currie, P. J. (2019). Hagfish from the Cretaceous Tethys Sea and a reconciliation of the morphological–molecular conflict in early vertebrate phylogeny. Proceedings of the National Academy of Sciences, 116(6), 2146-2151.
Miyashita, T., Gess, R. W., Tietjen, K., & Coates, M. I. (2021). Non-ammocoete larvae of Palaeozoic stem lampreys. Nature, 591(7850), 408-412.
Müller, K.J. & Hinz, I., 1991. Upper Cambrian Conodonts from Sweden. Fossils and Strata no. 28. 153 pp. Oslo: Universitetsforlaget
Müller, K. J., & Hinz-Schallreuter, I. (1998). Internal structure of Cambrian conodonts. Journal of Paleontology, 72(1), 91-112.
Murdock, D. J., & Smith, M. P. (2021). Panderodus from the Waukesha Lagerstätte of Wisconsin, USA: a primitive macrophagous vertebrate predator. Papers in Palaeontology, 7(4), 1977-1993.
Terrill, D. F., Henderson, C. M., & Anderson, J. S. (2018). New applications of spectroscopy techniques reveal phylogenetically significant soft tissue residue in Paleozoic conodonts. Journal of Analytical Atomic Spectrometry, 33(6), 992-1002.
Theofanopoulou, C., Gedman, G., Cahill, J. A., Boeckx, C., & Jarvis, E. D. (2021). Universal nomenclature for oxytocin–vasotocin ligand and receptor families. Nature, 592(7856), 747-755.
Image credits - Stem-Cyclostomes
- Figure 2 (Panderodus unicostatus): Open Access article Murdock, D. J., & Smith, M. P. (2021). Panderodus from the Waukesha Lagerstätte of Wisconsin, USA: a primitive macrophagous vertebrate predator. Papers in Palaeontology, 7(4), 1977-1993.
- Figure 2 (fossil, Promissum pulchrum): Open Access article Gabbott, S. E., Donoghue, P. C., Sansom, R. S., Vinther, J., Dolocan, A., & Purnell, M. A. (2016). Pigmented anatomy in Carboniferous cyclostomes and the evolution of the vertebrate eye. Proceedings of the Royal Society B: Biological Sciences, 283(1836), 20161151.
- Figure 2 (life restoration, Promissum pulchrum): Nobu Tamura under Creative Commons Attribution- ShareAlike (CC BY-SA) license
- Figure 2 (Clydagnathus windsorensis): Nobu Tamura under Creative Commons Attribution- ShareAlike (CC BY-SA) license
- Figure 3 (Gilpichthys greenei): Nobu Tamura under Creative Commons Attribution- ShareAlike (CC BY-SA) license
- Figure 3 (Myxinikela siroka): Nobu Tamura under Creative Commons Attribution- ShareAlike (CC BY-SA) license
- Figure 3 (Priscomyzon riniensis): Nobu Tamura under Creative Commons Attribution- ShareAlike (CC BY-SA) license
- Figure 3 (Mayomyzon pieckoensis): Nobu Tamura under Creative Commons Attribution- ShareAlike (CC BY-SA) license