Morphometric analysis of lungfish endocasts elucidates early dipnoan palaeoneurological evolution

Clement, Alice M.; Challands, Thomas J.; Cloutier, Richard; Houle, Laurent; Ahlberg, Per; Collin, Shaun P.; Long, John A.

doi:10.7554/elife.73461

Cited by 4 publications

(1 citation statement)

References 67 publications

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“…Based on these traits and other morphological, molecular and palaeontological evidence across the three genera of lobe‐finned fishes, N. forsteri , the sole extant species representing the family Ceratodontidae within the order Dipnoi, is considered to be the earliest branching lungfish having changed little over the last 100 million years (Kemp & Molnar, 1981; Tokita et al, 2005). Based on the importance of this critical stage in vertebrate evolution, studies on the morphology of the Australian lungfish remain a critical approach in tracing adaptations associated with the fish–tetrapod transition (Clement et al, 2022).…”

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confidence: 99%

Morphology of the cornea and iris in the Australian lungfish Neoceratodus forsteri (Krefft 1870) (Dipnoi): Functional and evolutionary perspectives of transitioning from an aquatic to a terrestrial environment

Barry Collin,

Ratcliffe,

Collin

2023

Journal of Morphology

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The Australian lungfish, Neoceratodus forsteri (Krefft 1870), is the sole extant member of the Ceratodontidae within the Dipnoi, a small order of sarcopterygian (lobe‐finned) fishes, that is thought to be the earliest branching species of extant lungfishes, having changed little over the last 100 million years. To extend studies on anatomical adaptations associated with the fish–tetrapod transition, the ultrastructure of the cornea and iris is investigated using light and electron (transmission and scanning) microscopy to investigate structure–function relationships and compare these to other vertebrate corneas (other fishes and tetrapods). In contrast to previous studies, the cornea is found to have only three main components, comprising an epithelium with its basement membrane, a stroma with a Bowman's layer and an endothelium, and is not split into a dermal (secondary) spectacle and a scleral cornea. The epithelial cells are large, relatively low in density and similar to many species of non‐aquatic tetrapods and uniquely possess numerous surface canals that contain and release mucous granules onto the corneal surface to avoid desiccation. A Bowman's layer is present and, in association with extensive branching and anastomosing of the collagen fibrils, may be an adaptation for the inhibition of swelling and/or splitting of the stroma during its amphibious lifestyle. The dorsal region of the stroma possesses aggregations of pigment granules that act as a yellow, short wavelength‐absorbing filter during bright light conditions. Desçemet's membrane is absent and replaced by an incomplete basement membrane overlying a monocellular endothelium. The iris is pigmented, well‐developed, vascularised and contractile containing reflective crystals anteriorly. Based upon its ultrastructure and functional adaptations, the cornea of N. forsteri is more similar to amphibians than to other bony fishes and is well‐adapted for an amphibious lifestyle.

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Section: Introductionmentioning

confidence: 99%

Morphology of the cornea and iris in the Australian lungfish Neoceratodus forsteri (Krefft 1870) (Dipnoi): Functional and evolutionary perspectives of transitioning from an aquatic to a terrestrial environment

Barry Collin,

Ratcliffe,

Collin

2023

Journal of Morphology

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A detailed 3D MRI brain atlas of the African lungfish Protopterus annectens

Lozano,

López,

Chinarro

et al. 2024

Sci Rep

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The study of the brain by magnetic resonance imaging (MRI) in evolutionary analyses is still in its incipient stage, however, it is particularly useful as it allows us to analyze detailed anatomical images and compare brains of rare or otherwise inaccessible species, evolutionarily contextualizing possible differences, while at the same time being non-invasive. A good example is the lungfishes, sarcopterygians that are the closest living relatives of tetrapods and thus have an interesting phylogenetic position in the evolutionary conquest of the terrestrial environment. In the present study, we have developed a three-dimensional representation of the brain of the lungfish Protopterus annectens together with a rostrocaudal anatomical atlas. This methodological approach provides a clear delineation of the major brain subdivisions of this model and allows to measure both brain and ventricular volumes. Our results confirm that lungfish show neuroanatomical patterns reminiscent of those of extant basal sarcopterygians, with an evaginated telencephalon, and distinctive characters like a small optic tectum. These and additional characters uncover lungfish as a remarkable model to understand the origins of tetrapod diversity, indicating that their brain may contain significant clues to the characters of the brain of ancestral tetrapods.

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Avian telencephalon and cerebellum volumes can be accurately estimated from digital brain endocasts

Keirnan,

Cunha,

Citron

et al. 2024

Preprint

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For studies of the evolution of vertebrate brain anatomy and potentially associated behaviours, reconstructions of digital brain endocasts from computed tomography scans have revolutionised our capacity to collect neuroanatomical data. However, measurements from digital endocasts must be validated as reflecting actual brain anatomy, which is difficult because the collection of soft tissue information through histology is laborious and time consuming. In birds, the reliability of digital endocast measurements as volume proxies for the two largest brain regions (the telencephalon and cerebellum) remains to be validated despite their use as proxies e.g. of cognitive performance or flight ability. We here use the largest dataset of histology and digital endocasts to date, including 136 species from 25 avian orders, to compare digital endocast surface area measurements with actual brain volumes of the telencephalon, cerebellum, and whole-brain endocast. Using linear and phylogenetically informed regression analyses, we demonstrate that endocast surfaces are strongly correlated with their brain volume counterparts for both absolute and relative size. This provides empirical support for using endocast-derived cerebellar and telencephalic surface areas in existing and future studies of living and extinct birds, with potential to expand to the dinosaur-bird transition in the future.

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Morphometric analysis of lungfish endocasts elucidates early dipnoan palaeoneurological evolution

Cited by 4 publications

References 67 publications

Morphology of the cornea and iris in the Australian lungfish Neoceratodus forsteri (Krefft 1870) (Dipnoi): Functional and evolutionary perspectives of transitioning from an aquatic to a terrestrial environment

Morphology of the cornea and iris in the Australian lungfish Neoceratodus forsteri (Krefft 1870) (Dipnoi): Functional and evolutionary perspectives of transitioning from an aquatic to a terrestrial environment

A detailed 3D MRI brain atlas of the African lungfish Protopterus annectens

Avian telencephalon and cerebellum volumes can be accurately estimated from digital brain endocasts

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