No bones about it: An enigmatic Devonian fossil reveals a new skeletal framework—A potential role of loss of gene regulation

Johanson, Zerina; Kearsley, A. T.; Blaauwen, Jan den; Newman, Michael J.; Smith, Moya Meredith

doi:10.1016/j.semcdb.2009.10.011

Cited by 25 publications

(34 citation statements)

References 45 publications

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“…3C, box), associated with the increase in phosphorus and calcium. In the large specimens examined (Johanson et al, 2010), hypertrophied cells dominate all parts of the skeleton (Fig. 4A).…”

Section: Comparisons Between Small and Large Specimens Of Palaeospondmentioning

confidence: 97%

“…In the large specimens of Palaeospondylus, hypertrophied lacunae dominate the entire skeleton and mineralization of the surrounding matrix occurs throughout ( Fig. 4; Johanson et al, 2010; elemental carbon is maximized in cell lacunae).…”

Section: Comparisons Between Small and Large Specimens Of Palaeospondmentioning

confidence: 99%

“…The skeletal histology of the larger Palaeospondylus specimens was described as mineralized cartilage, but differed from all other known early vertebrate mineralized cartilages (Johanson et al, 2010). Instead, the histology was said to most closely resemble an early stage of endochondral bone development.…”

mentioning

confidence: 99%

“…We recently reviewed the histology of the Palaeospondylus skeleton (Johanson et al, 2010) and found that the tissue was composed throughout of calcified cartilage, but lacked any bone. Because the Achanarras Quarry is known for exceptional preservation of soft-bodied organisms such as the jawless vertebrate Achanarella trewini (Newman, 2003; Fig.…”

mentioning

confidence: 99%

“…Skeletal histology in Palaeospondylus was distinct from other vertebrate mineralized cartilages, such as the globular calcified cartilage (GCC) seen in a variety of early vertebrates, and the prismatic cartilage in chondrichthyans (Wang et al, 2005;Dean and Summers, 2006). Once hypertrophy and mineralization with calcium hydroxyapatite had occurred during development in Palaeospondylus, it restricted future expansive internal growth of the cartilages (Johanson et al, 2010). This restriction of growth prevented an increase in size from within; growth could only occur by accretion at the periphery of each cartilage module.…”

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confidence: 99%

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Ontogenetic development of an exceptionally preserved Devonian cartilaginous skeleton

et al. 2011

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Cartilaginous vertebrate skeletons leave few records as fossils, unless mineralized. Here, we report outstanding preservation of early stages of cartilage differentiation, present in the Devonian vertebrate Palaeospondylus gunni. In large specimens of Palaeospondylus, enlarged, hypertrophic cell spaces (lacunae) are dominant in the cartilage matrix, each defined by thin mineralized matrix, where phosphorus and calcium co-occur. This is comparable to living endochondral cartilage, where cell hypertrophy and matrix mineralization mark the end of an ontogenetic process of cell growth and division before bone formation. New information from small individuals of Palaeospondylus demonstrates that the skeleton comprises mostly unmineralized organic matrix with fewer hypertrophic cell spaces, these occurring only in the central regions of each element. Only here has the surrounding matrix begun to mineralize, differing from the larger specimens in that phosphorus is dominant with little associated calcium at these earlier stages. This reflects cellular control of mineralization in living tissues through phosphate accumulation around hypertrophic cells, with later increase in calcium in the cartilaginous matrix. These features are always associated with endochondral bone development, but in the Palaeospondylus skeleton, this bone never develops. This skeletal state is thus far unique among vertebrates, with two alternative explanations: either later stages of endochondral bone development have been lost in Palaeospondylus, or, in a stepwise acquisition of the mineralized skeleton, these late stages have not yet evolved.

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“…3C, box), associated with the increase in phosphorus and calcium. In the large specimens examined (Johanson et al, 2010), hypertrophied cells dominate all parts of the skeleton (Fig. 4A).…”

Section: Comparisons Between Small and Large Specimens Of Palaeospondmentioning

confidence: 97%

Section: Comparisons Between Small and Large Specimens Of Palaeospondmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Ontogenetic development of an exceptionally preserved Devonian cartilaginous skeleton

et al. 2011

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Potential genetic bases of morphological evolution in the triassic fish Saurichthys

Schmid

Sánchez‐Villagra

2010

J Exp Zool Pt B

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Originating from an ancestor covered entirely by uniform rhomboid scales with numerous, highly segmented fin rays, the Triassic basal actinopterygian fish Saurichthys radiated into species diagnosed by different degrees of loss in scales, rays, and dermal bones. Such changes are analogous to those reported in mutants of different extant species, such as sticklebacks, zebrafish, and medaka. With this background, we infer a loss of function or a regulatory change of a signaling pathway as a key mechanism behind the morphological diversity of Saurichthys. Either the fibroblast growth factor pathway was affected, assuming that gene duplication had occurred, as for example in the closely related acipenserids or in teleosts, or the ectodysplasin pathway was involved, assuming that its pleiotropic effects led to viable morphological diversification. In contrast to a gradualistic model of evolution, a change in a major developmental gene serves as a viable explanation for the essential differences among the species of Saurichthys in the paleoecological context in which they originated.

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In the Beginning

Shapiro,

Landis

2023

Mechanisms of Mineralization of Vertebrate Skeletal and Dental Tissues

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No bones about it: An enigmatic Devonian fossil reveals a new skeletal framework—A potential role of loss of gene regulation

Cited by 25 publications

References 45 publications

Ontogenetic development of an exceptionally preserved Devonian cartilaginous skeleton

Ontogenetic development of an exceptionally preserved Devonian cartilaginous skeleton

Potential genetic bases of morphological evolution in the triassic fish Saurichthys

In the Beginning

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