Questioning hagfish affinities of the enigmatic Devonian vertebrate<i>Palaeospondylus</i>

Johanson, Zerina; Smith, Moya Meredith; Sanchez, Sophie; Senden, Tim J.; Trinajstic, Kate; Pfaff, Cathrin

doi:10.1098/rsos.170214

Cited by 8 publications

(5 citation statements)

References 41 publications

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“…Although the latter does not reveal any new anatomical details, it precisely localized an unexpected distribution of copper surrounding the vertebrae and, very specifically, located posterior to the paired rostral sensory structures (see Johanson et al . ). Such organized distribution is very likely to represent palaeobiological ( in vivo incorporation) or taphonomic (post mortem incorporation) tissue‐specific chemistry, possibly representing the ‘chemical ghosts’ of soft‐tissues that could provide new arguments for P. gunni taxonomic assignment.…”

Section: Yttrium Mappingmentioning

confidence: 97%

Show me your yttrium, and I will tell you who you are: implications for fossil imaging

2018

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The development of X‐ray tomography in the last decade has led to a revolution in palaeontology by providing a means of imaging 3D fossils. In turn, imaging of flat fossils has strongly benefitted from critical improvement of synchrotron X‐ray fluorescence (XRF). The latter, which allows the mapping of 2D distributions of major‐to‐trace elements over decimetre‐scale objects, usually targets metals with atomic number (Z) up to strontium (K‐shell emission lines); in the same energy domain, L‐shell emission lines of heavier elements (particularly lead) can also be analysed. A fluorescence signal from strontium can escape from a depth of a few 100 μm in fossils, thereby revealing, due to its substitution for calcium in calcium phosphates (apatite group minerals and bone), hidden fossil bone or phosphatized remains. Nonetheless, strontium similarly substitutes for calcium in calcium carbonates, resulting in the absence of contrast when fossils are preserved in limestone. Here, we show that this issue can easily be overcome by using X‐rays slightly higher in energy (17.2 keV and above) to excite and detect yttrium fluorescence. Together with lanthanides (collectively known as the rare earth elements), yttrium preferentially substitutes for calcium in calcium phosphates, offering anatomical contrasts for a wider range of fossils. This is demonstrated here for three fossils (vertebrate and invertebrate) from different ages and depositional environments. We then discuss the different chemical behaviours of strontium and yttrium in calcium phosphates and carbonates. Although yttrium is also found in other (rarer) minerals, its mapping using synchrotron XRF could be used as a proxy to pinpoint calcium phosphates in fossils and other geological materials.

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Section: Yttrium Mappingmentioning

confidence: 97%

Show me your yttrium, and I will tell you who you are: implications for fossil imaging

2018

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“…However, the interrelationships of hagfishes and the age of living hagfish diversity remain underexplored [ 37 , 38 , 40 , 43 , 69 ]. This problem is compounded by the poor fossil record of the two living jawless vertebrate clades [ 36 – 39 , 64 – 67 , 70 – 74 ]; only a handful of fossils with well-characterized anatomy are identifiable as early total clade lampreys and hagfishes, and many fossil taxa identified as putative stem-group hagfishes and lampreys [ 75 ] may not even be jawless vertebrates [ 76 – 78 ].…”

Section: Introductionmentioning

confidence: 99%

Colonization of the ocean floor by jawless vertebrates across three mass extinctions

Brownstein,

Near

2024

BMC Ecol Evo

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Background The deep (> 200 m) ocean floor is often considered to be a refugium of biodiversity; many benthic marine animals appear to share ancient common ancestry with nearshore and terrestrial relatives. Whether this pattern holds for vertebrates is obscured by a poor understanding of the evolutionary history of the oldest marine vertebrate clades. Hagfishes are jawless vertebrates that are either the living sister to all vertebrates or form a clade with lampreys, the only other surviving jawless fishes. Results We use the hagfish fossil record and molecular data for all recognized genera to construct a novel hypothesis for hagfish relationships and diversification. We find that crown hagfishes persisted through three mass extinctions after appearing in the Permian ~ 275 Ma, making them one of the oldest living vertebrate lineages. In contrast to most other deep marine vertebrates, we consistently infer a deep origin of continental slope occupation by hagfishes that dates to the Paleozoic. Yet, we show that hagfishes have experienced marked body size diversification over the last hundred million years, contrasting with a view of this clade as morphologically stagnant. Conclusion Our results establish hagfishes as ancient members of demersal continental slope faunas and suggest a prolonged accumulation of deep sea jawless vertebrate biodiversity.

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“…This position is most likely an artefact in the dis/similarity matrix resulting in a lack of the hagfish synapomorphies used to assign affinity within the fossil occurring in the character list of this study. Finally, the Johanson ‘version’ (chondrichthyan, Pa. Johanson [ 20 ]) unexpectedly occupies an unoccupied area furthest away from all other taxa.…”

Section: Resultsmentioning

confidence: 99%

“…Full details and references are available in the electronic supplementary material. ontogenetic stages (semaphoronts) decay stages (semataphonts) total hagfish adult decay states 1–6 (adult) 7 lamprey ammocoete, metamorphic stages 1–7, adult decay stages 1–6 (adult) 21 decay stages 1–6 (ammocoete) shark embryo, pre-hatchling decay stages 1–6 (embryo) 14 decay stages 1–6 (pre-hatchling) Branchiostoma adult decay stages 1–6 (adult) 7 Myxinikela fossil specimen 1 Tethymyxine fossil specimen 1 Mayomyzon fossil specimens of varying completeness 22 Priscomyzon fossil specimens of varying completeness 7 Mesomyzon two fossil specimens (adult, subadult) 2 ‘euphaneropoids’ six extinct genera: Lasanius, Jamoytius, Ciderius, Achanarella, Cornovichthys and Euphanerops (multiple specimens of varying completeness) 24 Palaeospondylus one extinct genus interpreted with different models of homology [ 17 , 18 , 20 , 66 ] 5 total 111 …”

Section: Data and Data Analysismentioning

confidence: 99%

“…In the Devonian acanthodian Triazeugacanthus affinis [14,15], the 'scaumenellization' decay series has been reinterpreted as an ontogenetic sequence of transformation [16]. Whereas with the notorious Palaeospondylus gunni, known from thousands of Devonian fossil specimens, it remains unclear whether the small number of traits preserved in the fossils is due to taphonomically induced loss, or ontogenetic change, resulting in a huge number of proposed conflicting affinities and ontogenetic interpretations [17][18][19][20]. Difficulties like these are not constrained to just soft-tissue fossils.…”

Section: Introductionmentioning

confidence: 99%

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Multivariate mapping of ontogeny, taphonomy and phylogeny to reconstruct problematic fossil taxa

Reeves

Sansom

2023

Proc. R. Soc. B.

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Exceptionally preserved fossils of soft-bodied organisms provide unique evidence of evolutionary history, but they are often contentious; different approaches frequently produce radically different reconstructions of taxa and their affinities. Conflict arises due to difficulties in disentangling the three non-independent factors that underlie all morphological variation within and between fossils: ontogeny, taphonomy and phylogeny. Comparative data from extant organisms can be extremely powerful in this context, but is often difficult to apply given the multi-dimensionality of anatomical variation. Here, we present a multivariate ordination method using discrete morphological character data from modern taxa at different ontogenetic and taphonomic stages (semaphoront and ‘semataphonts’). Analysing multiple axes of morphological variation simultaneously allows us to visualize character combinations that are likely to exist in fossil specimens at intersecting stages of growth and decay, and thus constrain interpretation of fossils. Application to early vertebrates finds variation in fossil specimens to be accounted for by all three axes: primarily decay in Mayomyzon , ontogeny in Priscomyzon and phylogeny in ‘euphaneropoids’ and Palaeospondylus . Our demonstration of empirical multi-factorial variation underscores the power of multivariate approaches to fossil interpretation, especially non-biomineralized taxa. As such, this conceptual approach provides a new method for resolving enigmatic taxa throughout the fossil record.

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Questioning hagfish affinities of the enigmatic Devonian vertebratePalaeospondylus

Cited by 8 publications

References 41 publications

Show me your yttrium, and I will tell you who you are: implications for fossil imaging

Show me your yttrium, and I will tell you who you are: implications for fossil imaging

Colonization of the ocean floor by jawless vertebrates across three mass extinctions

Multivariate mapping of ontogeny, taphonomy and phylogeny to reconstruct problematic fossil taxa

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