XLI.—<i>On the limits and classification of the Ganoids</i>

Newly discovered fossils from the Silurian and Devonian periods are beginning to challenge embedded perceptions about the origin and early diversification of jawed vertebrates (gnathostomes). Nevertheless, an explicit cladistic framework for the relationships of these fossils relative to the principal crown lineages of the jawed vertebrates (osteichthyans: bony fishes and tetrapods; chondrichthyans: sharks, batoids, and chimaeras) remains elusive. We critically review the systematics and character distributions of early gnathostomes and provide a clearly stated hierarchy of synapomorphies covering the jaw-bearing stem gnathostomes and osteichthyan and chondrichthyan stem groups. We show that character lists, designed to support the monophyly of putative groups, tend to overstate their strength and lack cladistic corroboration. By contrast, synapomorphic hierarchies are more open to refutation and must explicitly confront conflicting evidence. Our proposed synapomorphy scheme is used to evaluate the status of the problematic fossil groups Acanthodii and Placodermi, and suggest profitable avenues for future research. We interpret placoderms as a paraphyletic array of stem-group gnathostomes, and suggest what we regard as two equally plausible placements of acanthodians: exclusively on the chondrichthyan stem, or distributed on both the chondrichthyan and osteichthyan stems.

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“…In other words, Huxley admits that he is lost: the 'essentials' of ganoids are only accessible in Recent fishes, and there is no way of distinguishing fossil ganoids from fossil teleosts. Lutken (1868Lutken ( , 1871Lutken ( , 1873 reviewed all earlier work, in neontology and paleontology, on the limits of the ganoids. From this review he concluded (Dallas's translation, 1871:330) 'no one has ever been able to give an exact definition of what is a Ganoid • • • • We must therefore, provisionally at least, limit the name of Ganoids to the indubitable existing types (that is to s~, the Lepidostei and Polypteri), and to the fossil types which will naturally group themselves around these.…”

Section: S81mentioning

confidence: 99%

Major Patterns in Vertebrate Evolution

Blair¹,

Hecht²,

Goody³

et al. 1977

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“…Others simply ignored placoderms in their classifications (e.g. Gill, 1872) or declared the assemblage incertae sedis (Lutken, 1871).…”

Section: Introductionmentioning

confidence: 99%

The characters of Palaeozoic jawed vertebrates

2014

Zoological Journal of the Linnean Society

1

0

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Newly discovered fossils from the Silurian and Devonian periods are beginning to challenge embedded perceptions about the origin and early diversification of jawed vertebrates (gnathostomes). Nevertheless, an explicit cladistic framework for the relationships of these fossils relative to the principal crown lineages of the jawed vertebrates (osteichthyans: bony fishes and tetrapods; chondrichthyans: sharks, batoids, and chimaeras) remains elusive. We critically review the systematics and character distributions of early gnathostomes and provide a clearly stated hierarchy of synapomorphies covering the jaw-bearing stem gnathostomes and osteichthyan and chondrichthyan stem groups. We show that character lists, designed to support the monophyly of putative groups, tend to overstate their strength and lack cladistic corroboration. By contrast, synapomorphic hierarchies are more open to refutation and must explicitly confront conflicting evidence. Our proposed synapomorphy scheme is used to evaluate the status of the problematic fossil groups Acanthodii and Placodermi, and suggest profitable avenues for future research. We interpret placoderms as a paraphyletic array of stem-group gnathostomes, and suggest what we regard as two equally plausible placements of acanthodians: exclusively on the chondrichthyan stem, or distributed on both the chondrichthyan and osteichthyan stems.

show abstract

XLI.—On the limits and classification of the Ganoids

Cited by 3 publications

References 0 publications

The characters of Palaeozoic jawed vertebrates

The characters of Palaeozoic jawed vertebrates

Major Patterns in Vertebrate Evolution

The characters of Palaeozoic jawed vertebrates

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