Stem tetrapods: brain evolution from tetrapodomorph fishes + direct development without larval stage
44 views
Skip to first unread message
Ben Creisler
Jun 18, 2026, 3:11:45 PM (9 hours ago) Jun 18
to DinosaurMa...@googlegroups.com
Ben Creisler
Early tetrapod papers:
Alice M. Clement, Richard Cloutier, Oleg Lebedev, Tom J. Challands, Jing Lu, Joseph J. Bevitt, Laurent Houle, Shaun P. Collin & John A. Long (2026)
Ethmosphenoid endocasts elucidate evolutionary brain divergences and interrelationships of stem tetrapods (Sarcopterygii, Tetrapodomorpha)
Papers in Palaeontology 12(3): e70094
doi: https://doi.org/10.1002/spp2.70094
https://onlinelibrary.wiley.com/doi/10.1002/spp2.70094
Free pdf:
https://onlinelibrary.wiley.com/doi/epdf/10.1002/spp2.70094
Nearly half of all living vertebrate diversity can be traced back to a single lineage of lobe-finned fishes (piscine sarcopterygians) that radiated during the Palaeozoic Era. In recent years, the phylogenetic framework of tetrapodomorph fishes has largely stabilized, with the exception of the ‘Osteolepiformes’, the interrelationships of which are still under debate. To resolve these uncertainties, expanded taxonomic sampling and new morphological data are essential to refine our understanding of their evolutionary history. Emerging tomography imaging techniques are providing much of this new anatomical information, including that pertaining to cranial endocasts. Endocasts can serve as proxies for gross brain morphology, and thus have the added benefit of shedding light on palaeoneurological evolution in long-extinct lineages. Here, using a combination of synchrotron, neutron and micro-computed tomography, we generate high-resolution 3D virtual models of ethmosphenoids and their associated cranial endocast and sensory (lateral) line canal systems in 13 stem tetrapods. Using principal components analysis for incomplete data we identify distinct patterns of morphospace occupation among the different families. While the ‘Tristichopteridae’ usually occupy a wholly distinct region, the ‘Osteolepididae’ and Megalichthyidae exhibit partial overlap, but with ‘Osteolepididae’ always showing a broader range of variation. Our findings demonstrate that ethmosphenoids and their endocasts retain morphological features of shared phylogenetic affinity that can aid in resolving phylogenetic placement of fragmentary or enigmatic taxa. Furthermore, palaeoneurobiological evidence from these ‘Osteolepiformes’ suggests that these fishes retained a more conservative sensory umwelt prior to the rapid emergence of enhanced visual acuity in the earliest tetrapods.
=====
Jason D. Pardo & Arjan Mann (2026)
Direct development of stem tetrapods across the fin-to-limb transition.
Science 392(6804): 1292-1296
DOI:10.1126/science.aeb7635
https://www.science.org/doi/10.1126/science.aeb7635
Editor’s summary
The earliest tetrapod colonizers of land have been considered to have life histories somewhat similar to modern amphibians, including the presence of an aquatic larval stage, and it has been hypothesized that this transition may have facilitated the broader transition from water to land. Pardo et al. looked at many fossils of stem tetrapods from the Mazon Creek Lagerstatte and found no evidence of such larval morphological change. Instead, both before and after the fin-to-limb transition, hatchling to adult growth proceeded through a direct development model. —Sacha Vignieri
Abstract
Modern amphibians are characterized by an aquatic larval stage that ends abruptly with a period of widespread tissue remodeling (metamorphosis) upon transition to terrestrial adulthood. A transient larval stage ending in gradual metamorphosis is often assumed for the earliest digited tetrapods, but direct evidence of this larval stage is lacking. Exceptionally preserved stem tetrapod hatchlings show that a transient larval stage was absent in tetrapods both before and after the fin-to-limb transition; instead we identified soft- and hard-tissue evidence of direct development, falsifying hypotheses of an ancestral origin of metamorphosis or of a gradual larval-postlarval transition serving as a template for lissamphibian metamorphosis. We argue that a transient larval period culminating in metamorphosis originated near or within the tetrapod crown group as part of a broader suite of traits associated with terrestrialization.
===
Free pdf:
Alice M. Clement, Richard Cloutier, Oleg Lebedev, Tom J. Challands, Jing Lu, Joseph J. Bevitt, Laurent Houle, Shaun P. Collin & John A. Long (2026)
Ethmosphenoid endocasts elucidate evolutionary brain divergences and interrelationships of stem tetrapods (Sarcopterygii, Tetrapodomorpha)
Papers in Palaeontology 12(3): e70094
doi: https://doi.org/10.1002/spp2.70094
https://onlinelibrary.wiley.com/doi/10.1002/spp2.70094
Free pdf:
https://onlinelibrary.wiley.com/doi/epdf/10.1002/spp2.70094
Nearly half of all living vertebrate diversity can be traced back to a single lineage of lobe-finned fishes (piscine sarcopterygians) that radiated during the Palaeozoic Era. In recent years, the phylogenetic framework of tetrapodomorph fishes has largely stabilized, with the exception of the ‘Osteolepiformes’, the interrelationships of which are still under debate. To resolve these uncertainties, expanded taxonomic sampling and new morphological data are essential to refine our understanding of their evolutionary history. Emerging tomography imaging techniques are providing much of this new anatomical information, including that pertaining to cranial endocasts. Endocasts can serve as proxies for gross brain morphology, and thus have the added benefit of shedding light on palaeoneurological evolution in long-extinct lineages. Here, using a combination of synchrotron, neutron and micro-computed tomography, we generate high-resolution 3D virtual models of ethmosphenoids and their associated cranial endocast and sensory (lateral) line canal systems in 13 stem tetrapods. Using principal components analysis for incomplete data we identify distinct patterns of morphospace occupation among the different families. While the ‘Tristichopteridae’ usually occupy a wholly distinct region, the ‘Osteolepididae’ and Megalichthyidae exhibit partial overlap, but with ‘Osteolepididae’ always showing a broader range of variation. Our findings demonstrate that ethmosphenoids and their endocasts retain morphological features of shared phylogenetic affinity that can aid in resolving phylogenetic placement of fragmentary or enigmatic taxa. Furthermore, palaeoneurobiological evidence from these ‘Osteolepiformes’ suggests that these fishes retained a more conservative sensory umwelt prior to the rapid emergence of enhanced visual acuity in the earliest tetrapods.
=====
Jason D. Pardo & Arjan Mann (2026)
Direct development of stem tetrapods across the fin-to-limb transition.
Science 392(6804): 1292-1296
DOI:10.1126/science.aeb7635
https://www.science.org/doi/10.1126/science.aeb7635
Editor’s summary
The earliest tetrapod colonizers of land have been considered to have life histories somewhat similar to modern amphibians, including the presence of an aquatic larval stage, and it has been hypothesized that this transition may have facilitated the broader transition from water to land. Pardo et al. looked at many fossils of stem tetrapods from the Mazon Creek Lagerstatte and found no evidence of such larval morphological change. Instead, both before and after the fin-to-limb transition, hatchling to adult growth proceeded through a direct development model. —Sacha Vignieri
Abstract
Modern amphibians are characterized by an aquatic larval stage that ends abruptly with a period of widespread tissue remodeling (metamorphosis) upon transition to terrestrial adulthood. A transient larval stage ending in gradual metamorphosis is often assumed for the earliest digited tetrapods, but direct evidence of this larval stage is lacking. Exceptionally preserved stem tetrapod hatchlings show that a transient larval stage was absent in tetrapods both before and after the fin-to-limb transition; instead we identified soft- and hard-tissue evidence of direct development, falsifying hypotheses of an ancestral origin of metamorphosis or of a gradual larval-postlarval transition serving as a template for lissamphibian metamorphosis. We argue that a transient larval period culminating in metamorphosis originated near or within the tetrapod crown group as part of a broader suite of traits associated with terrestrialization.
===
Ben Creisler
Jun 18, 2026, 4:27:07 PM (8 hours ago) Jun 18
to DinosaurMa...@googlegroups.com
News:
Fossilized babies of ancient crocodile-like predators uproot scientists’ understanding of how animals adapted to the land
Reply all
Reply to author
Forward
0 new messages