A new petalichthyid placoderm from the Early Devonian of Yunnan, China

Pan, Zhaohui; Zhu, Maoyan; Yuanlin, Zhu; Jia, Liantao

doi:10.1016/j.crpv.2014.10.006

Cited by 6 publications

(9 citation statements)

References 27 publications

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“…However, a rhinocapsular division has been inferred in ‘quasipetalichthyids’, although it has not been directly observed (Zhu ; Pan et al . ). Furthermore, we observe a ridge inside the orbit of Shearsbyaspis , corresponding with the external signature of the partially closed fissure in Brindabellaspis (Young , ).…”

Section: Discussionmentioning

confidence: 97%

“…Indeed, the earliest known petalichthyids (quasipetalichthyids) (Zhu ; Pan et al . ) bear a strong external resemblance to early arthrodires, such as Bryantolepis (Elliott & Carr ) and Wuttagoonaspis (Ritchie ). This would be consistent with convergent similarities between osteostracan and macropetalichthyid neurocranial morphology.…”

Section: Discussionmentioning

confidence: 99%

“…; Pan et al . ). Due to the incompleteness of the specimen, only the supraorbital sensory canals (soc) and part of the infraorbital sensory canals (ioc) are preserved in NHMUK P33580 (Fig.…”

Section: Descriptionmentioning

confidence: 97%

“…Along with these are forms like Diandongpetalichthys (P'an & Wang ), often recovered as sister to all other petalichthyids (Zhu ; Pan et al . ). Phylogenetic analyses suggest that quasipetalichthyids could either be sister group to the other petalichthyids (Zhu & Wang ; Pan et al .…”

mentioning

confidence: 97%

“…Phylogenetic analyses suggest that quasipetalichthyids could either be sister group to the other petalichthyids (Zhu & Wang ; Pan et al . ) or fall in a more distant phylogenetic position from macropetalichthyids, closer to phyllolepid arthrodires (Giles et al . ).…”

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confidence: 99%

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Neurocranial anatomy of the petalichthyid placodermShearsbyaspis oepikiYoung revealed by X‐ray computed microtomography

Castiello

Brazeau

2018

Palaeontology

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Stem‐group gnathostomes reveal the sequence of character acquisition in the origin of modern jawed vertebrates. The petalichthyids are placoderm‐grade stem‐group gnathostomes known from both isolated skeletal material and rarer articulated specimens of one genus. They are of particular interest because of anatomical resemblances with osteostracans, the jawless sister group of jawed vertebrates. Because of this, they have become central to debates on the relationships of placoderms and the primitive cranial architecture of gnathostomes. However, among petalichthyids, only the braincase of Macropetalichthys has been studied in detail, and the diversity of neurocranial morphology in this group remains poorly documented. Using X‐ray computed microtomography, we investigated the endocranial morphology of Shearsbyaspis oepiki Young, a three‐dimensionally preserved petalichthyid from the Early Devonian of Taemas‐Wee Jasper, Australia. We generated virtual reconstructions of the external endocranial surfaces, orbital walls and cranial endocavity, including canals for major nerves and blood vessels. The neurocranium of Shearsbyaspis resembles that of Macropetalichthys, particularly in the morphology of the brain cavity, nerves and blood vessels. Many characters, including the morphology of the pituitary vein canal and the course of the trigeminal nerve, recall the morphology of osteostracans. Additionally, the presence of a parasphenoid in Shearsbyaspis (previously not known with confidence outside of arthrodires and osteichthyans) raises some questions about current proposals of placoderm paraphyly. Our detailed description of this specimen adds to the known morphological diversity of petalichthyids, and invites critical reappraisal of the phylogenetic relationships of placoderms.

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Section: Descriptionmentioning

confidence: 97%

mentioning

confidence: 97%

mentioning

confidence: 99%

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Neurocranial anatomy of the petalichthyid placodermShearsbyaspis oepikiYoung revealed by X‐ray computed microtomography

Castiello

Brazeau

2018

Palaeontology

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A new antiarch placoderm from the Emsian (Early Devonian) of Wuding, Yunnan, China

Pan¹,

Zhu²,

Yuanlin³

et al. 2017

Alcheringa: An Australasian Journal of Palaeontology

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Bayesian Morphological Clock Methods Resurrect Placoderm Monophyly and Reveal Rapid Early Evolution in Jawed Vertebrates

et al. 2016

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The phylogeny of early gnathostomes provides an important framework for understanding one of the most significant evolutionary events, the origin and diversification of jawed vertebrates. A series of recent cladistic analyses have suggested that the placoderms, an extinct group of armoured fish, form a paraphyletic group basal to all other jawed vertebrates. We revised and expanded this morphological data set, most notably by sampling autapomorphies in a similar way to parsimony-informative traits, thus ensuring this data (unlike most existing morphological data sets) satisfied an important assumption of Bayesian tip-dated morphological clock approaches. We also found problems with characters supporting placoderm paraphyly, including character correlation and incorrect codings. Analysis of this data set reveals that paraphyly and monophyly of core placoderms (excluding maxillate forms) are essentially equally parsimonious. The two alternative topologies have different root positions for the jawed vertebrates but are otherwise similar. However, analysis using tip-dated clock methods reveals strong support for placoderm monophyly, due to this analysis favoring trees with more balanced rates of evolution. Furthermore, enforcing placoderm paraphyly results in higher levels and unusual patterns of rate heterogeneity among branches, similar to that generated from simulated trees reconstructed with incorrect root positions. These simulations also show that Bayesian tip-dated clock methods outperform parsimony when the outgroup is largely uninformative (e.g., due to inapplicable characters), as might be the case here. The analysis also reveals that gnathostomes underwent a rapid burst of evolution during the Silurian period which declined during the Early Devonian. This rapid evolution during a period with few articulated fossils might partly explain the difficulty in ascertaining the root position of jawed vertebrates.

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A new petalichthyid placoderm from the Early Devonian of Yunnan, China

Cited by 6 publications

References 27 publications

Neurocranial anatomy of the petalichthyid placodermShearsbyaspis oepikiYoung revealed by X‐ray computed microtomography

Neurocranial anatomy of the petalichthyid placodermShearsbyaspis oepikiYoung revealed by X‐ray computed microtomography

A new antiarch placoderm from the Emsian (Early Devonian) of Wuding, Yunnan, China

Bayesian Morphological Clock Methods Resurrect Placoderm Monophyly and Reveal Rapid Early Evolution in Jawed Vertebrates

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