Number and arrangement of extraocular muscles in primitive gnathostomes: evidence from extinct placoderm fishes

Young, Grant M.

doi:10.1098/rsbl.2007.0545

Cited by 32 publications

(41 citation statements)

References 13 publications

(20 reference statements)

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“…In spite of this impressively long list of compatible similarities in placoderm taxa (Young, 2008(Young, , 2010, we cannot agree that they provide any a priori evidence of placoderm monophyly either collectively or individually. The status of all of these characters depends on their distribution in a cladogram that must be corroborated by other characters -a necessary background that has not been supplied.…”

Section: P a R E X U S A C A N T H O D E S I S C H N A C A N T H U Smentioning

confidence: 87%

The characters of Palaeozoic jawed vertebrates

2014

Zoological Journal of the Linnean Society

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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.

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Section: P a R E X U S A C A N T H O D E S I S C H N A C A N T H U Smentioning

confidence: 87%

The characters of Palaeozoic jawed vertebrates

2014

Zoological Journal of the Linnean Society

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“…Some modern vertebrates retain this configuration, such as dogs that have a 7th extraocular muscle, the retractor bulbi, not found in humans, although there is a report of an incidence of the retractor bulbi occurring in a human, a likely recitavistic trait (Young 2008).…”

Section: The Extraocular Musclesmentioning

confidence: 99%

Suboptimal Optics: Vision Problems as Scars of Evolutionary History

Novella

2008

Evo Edu Outreach

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“…Palaeontological evidence from the Silurian and Devonian Periods shows that the lateral eyes of the ancestral vertebrates were well-developed image-forming eyes, which were rotated within their orbits by seven extraocular eye muscles (Novitskaya 1993;Young 2008). These heavily armoured ostracoderms were benthic, presumably feeding by extracting food from the substrate.…”

Section: Early Vertebrates Viewed Their World In Colormentioning

confidence: 99%

Early evolution of vertebrate photoreception: lessons from lampreys and lungfishes

Collin¹

2009

Integrative Zoology

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Lampreys (Agnatha) and lungfish (Dipnoi) are representatives of the earliest and the intermediate stages in vertebrate evolution, respectively, and survived in the Cambrian (approximately 540 mA, lampreys) and Devonian (approximately 400 mA, lungfishes) Periods. The unique phylogenetic position of these two groups presents us with an exciting opportunity to understand life in ancient times and to begin to trace the evolution of vision and photoreception in vertebrates. Using a multidisciplinary approach employing anatomical and molecular techniques, the evolution of photoreception is explored in these extant, living fossils to predict the environmental lighting conditions to which our vertebrate ancestors were exposed. Contrary to expectations, the retinae of the southern hemisphere lamprey (Geotria australis Gray, 1851) and the Australian lungfish (Neoceratodus forsteri Krefft, 1870) are far from "primitive," each possessing five types of photoreceptors, many with spectral filters for tuning the light. Detailed ultrastructural analysis reveals that all five receptor types in G. australis are cone-like, whereas N. forsteri possesses four cone types and a single type of rod. Each receptor type also contains a different visual pigment (opsin gene); that is, LWS, SWS1, SWS2, RhA and RhB in G. australis and LWS, SWS1, SWS2, Rh1 and Rh2 in N. forsteri, all of which are expressed within the retina and are sensitive to different parts of the electromagnetic spectrum, providing the potential for pentachromatic and tetrachromatic color vision, respectively.

show abstract

Number and arrangement of extraocular muscles in primitive gnathostomes: evidence from extinct placoderm fishes

Cited by 32 publications

References 13 publications

The characters of Palaeozoic jawed vertebrates

The characters of Palaeozoic jawed vertebrates

Suboptimal Optics: Vision Problems as Scars of Evolutionary History

Early evolution of vertebrate photoreception: lessons from lampreys and lungfishes

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