Decay of vertebrate characters in hagfish and lamprey (Cyclostomata) and the implications for the vertebrate fossil record

Sansom, Robert S.; Gabbott, Sarah E.; Purnell, Mark A.

doi:10.1098/rspb.2010.1641

Cited by 80 publications

(161 citation statements)

References 51 publications

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“…If only taphonomic alterations occurred in Triazeugacanthus, the smallest specimens would represent the most rotten specimens; accordingly some of these observed structures are among the last elements to decay or to be lost during decomposition of a vertebrate in an aquatic environment [18,19]. These elements are also among the first anatomical structures to form in early ontogeny that have a great potential to be fossilized.…”

Section: Discussionmentioning

confidence: 99%

The revival of a so-called rotten fish: the ontogeny of the Devonian acanthodian Triazeugacanthus

2015

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Since its original description as a chordate, the Late Devonian Scaumenella mesacanthi has been interpreted alternately as a prochordate, a larval ostracoderm and an immature acanthodian. For the past 30 years, these minute specimens were generally considered as decayed acanthodians, most of them belonging to Triazeugacanthus affinis. Among the abundant material of 'Scaumenella', we identified a size series of 188 specimens of Triazeugacanthus based on otolith characteristics. Despite taphonomic alteration, we describe proportional growth and progressive appearance of skeletal elements through size increase. Three ontogenetic stages are identified based on squamation extent, ossification completion and allometric growth. We demonstrate that what has been interpreted previously as various degrees of decomposition corresponds to ontogenetic changes.

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Section: Discussionmentioning

confidence: 99%

The revival of a so-called rotten fish: the ontogeny of the Devonian acanthodian Triazeugacanthus

2015

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“…[51,55] Decay in seawater has now been monitored in a range of taxa in laboratory experiments (see Table S1, Supporting Information): anthozoans, [56] annelids, [48] chaetognaths, [57] priapulids, [18] onychophorans, [17] pterobranchs, [58] enteropneusts, [59] nonvertebrate chordates, [20] and cyclostomes. [60] Thus the sequence of character loss has been determined for taxa representing most clades of eumetazoans. Despite the diversity of body plans analyzed in these experiments, collectively they show that different tissues decay at different rates, with some common patterns of susceptibility to decay across different organisms, and that different character systems are lost at different stages in the decay process.…”

Section: Boxmentioning

confidence: 99%

“…Experiments on cyclostomes and invertebrate chordates [20,60] showed that the notochord persists until the latest stages of decay ( Figure 4). Nonetheless, the notochord is apparently absent in several taxa from Mazon Creek [63] even though other characters indicate that they belong to the vertebrate crown group, and therefore, possessed a notochord.…”

Section: Some Decay Resistant Features Do Not Preserve In Exceptionalmentioning

confidence: 99%

“…The notochord is also absent in Haikouichthys, a total group vertebrate from the early Cambrian ( Figure 4B), despite the preservation of characters such as eyes, gill pouches, and a dorsal fin, which disappear more rapidly in decay experiments, but clearly indicate a phylogenetic position consistent with the presence of a notochord. [20,60,110] Haikouichthys preserves a chimaeric assemblage of decay-prone and decayresistant characters rather than corresponding to a particular decay stage (Figure 4). Likewise, the notochord is poorly preserved or equivocal in Pikaia and Haikouichthys, whereas other decay-prone characters including the eyes and nasal capsules are preserved in both taxa as well as the liver and heart in Metaspriggina, a vertebrate from the Burgess Shale.…”

Section: Some Decay Resistant Features Do Not Preserve In Exceptionalmentioning

confidence: 99%

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Soft‐Bodied Fossils Are Not Simply Rotten Carcasses – Toward a Holistic Understanding of Exceptional Fossil Preservation

et al. 2017

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Exceptionally preserved fossils are the product of complex interplays of biological and geological processes including burial, autolysis and microbial decay, authigenic mineralization, diagenesis, metamorphism, and finally weathering and exhumation. Determining which tissues are preserved and how biases affect their preservation pathways is important for interpreting fossils in phylogenetic, ecological, and evolutionary frameworks. Although laboratory decay experiments reveal important aspects of fossilization, applying the results directly to the interpretation of exceptionally preserved fossils may overlook the impact of other key processes that remove or preserve morphological information. Investigations of fossils preserving nonbiomineralized tissues suggest that certain structures that are decay resistant (e.g., the notochord) are rarely preserved (even where carbonaceous components survive), and decay-prone structures (e.g., nervous systems) can fossilize, albeit rarely. As we review here, decay resistance is an imperfect indicator of fossilization potential, and a suite of biological and geological processes account for the features preserved in exceptional fossils.

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“…5). Eyes in basal vertebrates are relatively decay resistant 18,19 and pigment is one of the most decay resistant features in lampreys 18,19 . In Tullimonstrum, the dark structures are paired, bilaterally disposed and comprise thick, multi-layered masses of melanosomes.…”

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The eyes of Tullimonstrum reveal a vertebrate affinity

Clements

Dolocan

Martin

et al. 2016

Nature

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*Corresponding authorswith Tullimonstrum being a notable anomaly in this respect. Tullimonstrum, a monotypic taxon known from several hundred specimens, is preserved as stains with some relief within Mazon Creek siderite nodules. Despite the uncertainty about its position in the tree of life, there is a surprisingly high level of agreement regarding the arrangement and shape of anatomical features ( Fig.1 and Table. 1). The anatomical complexity, evident cardinal axes and the bilateral symmetry demonstrates that Tullimonstrum is a bilaterian 1-3,5 but beyond this, it has defied systematic placement. Given the consensus regarding the shape and anatomical disposition of body parts this might seem perplexing but the issue is in fact quite simple: there is little agreement about its affinities because no study has identified unequivocal homologies/synapomorphies upon which to base a solid comparative anatomical interpretation. This is a classic example of how, without the criterion of topological relations between body parts as a potential falsifier of character hypotheses, testing of alternative hypotheses becomes problematic 9,10 . Different choices of extant anatomical comparator result in radically different hypotheses of homology and affinity for Tullimonstrum ( Table. 1) but evidence to test which hypothesis is correct remains elusive.Where topological data in fossils are equivocal, other homology criteria, normally subordinate to topology assume greater importance 9-11 . Here we apply the criterion of the intrinsic properties of body parts (also referred to as 'special qualities'' 10 or 'correspondence of composition' 11 ) allowing us to resolve the phylogenetic placement of Tullimonstrum.One of the defining characters of Tullimonstrum is the transverse bar. Associated with this in many specimens is a pair of dark structures which, regardless of the orientation of the fossil, occur at the distal ends of the bar (Figs 1-2; Extended Data Fig. 1). The transverse bar is relatively straight, although it bends forwards or backwards in some specimens 3 ; it is preserved in relief, suggesting a relatively recalcitrant structure, but there is no evidence that it was biomineralised 3 . Scanning electron microscopy and EDS reveal that the dark structures comprise thick, multi-layered masses of tightly-packed, micron-sized bodies composed of carbonaceous material (Fig. 2). They exhibit two distinct morphologies: The composition, anatomical localisation and fabrics indicate that the cylindrical and oblate bodies are layers of melanosomes; the range of shape and size compares closely with extant and fossilised melanosomes 6 . To further test this hypothesis we employed TOF-SIMS and principal component analyses (PCA) to compare the relative intensity distribution of the melanin-specific peaks originating from fresh, artificially matured, fossil melanin and non-melanin samples (Extended Data Fig. 3). Spectra from Tullimonstrum and pure melanin samples 12 shows a similar spectral composition (Fig. 3, Extended Data Fig.3). PCA...

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Decay of vertebrate characters in hagfish and lamprey (Cyclostomata) and the implications for the vertebrate fossil record

Cited by 80 publications

References 51 publications

The revival of a so-called rotten fish: the ontogeny of the Devonian acanthodian Triazeugacanthus

The revival of a so-called rotten fish: the ontogeny of the Devonian acanthodian Triazeugacanthus

Soft‐Bodied Fossils Are Not Simply Rotten Carcasses – Toward a Holistic Understanding of Exceptional Fossil Preservation

The eyes of Tullimonstrum reveal a vertebrate affinity

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