Gondwana fossil bird tracks ichnodisparity + alligator tail tail swipes + squamate rapid vertebral evolution + angiosperms Late Jurassic origin + end-Permian plant extinctions
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Ben Creisler
Jun 12, 2026, 2:29:19 PM (6 days ago) Jun 12
to DinosaurMa...@googlegroups.com
Ben Creisler
Martin E. Farina, M. Gabriela Mángano, Luis A. Buatois, Claudia A. Marsicano & Verónica Krapovickas (2026)
Macroevolutionary trends of avian ichnodisparity in Gondwana
Scientific Reports (advance online publication)
doi: https://doi.org/10.1038/s41598-026-56695-z
https://link.springer.com/article/10.1038/s41598-026-56695-z
The concept of ichnodisparity is herein introduced for the study of fossil vertebrates, using Gondwanan avian footprints. We define ichnodisparity for trackways as the qualitative variation in morphological patterns of autopodial impressions, most likely reflecting functional or ecological thresholds. Foot architectural designs are defined based on anatomical features, including digit number and orientation and interdigital webbing, and size. Ichnodisparity in fossil bird tracks is proposed here as a useful proxy for analyzing evolutionary radiations and characterizing macroevolutionary patterns. Twenty-three geological formations from Gondwana were analyzed, spanning from the Early Cretaceous to the Late Pleistocene. The earliest morphotypes were predominantly large-sized, while small morphotypes became dominant over time. No zygodactyl footprints are recorded from Gondwana. Prior to the K/Pg boundary, ichnodisparity was high, consistent with a Cretaceous avian radiation. During the Eocene, morphological variety remained comparable to that of the Late Cretaceous — except for the large tridactyl design — suggesting ecological turnover rather than functional expansion; elevated ichnodisparity may be associated with the Early Eocene Climatic Optimum. The decline recorded in the Oligocene is likely attributable to sampling bias. The Miocene concentrates the highest ichnodisparity in the fossil record, with the reappearance of large pedal architectures linked to cursorial birds, supporting an expansion into open spaces. In the Pleistocene, small tridactyl forms disappeared and the large palmate architecture emerged for the first time, indicating a new episode of ecological turnover.
Nearly all modern animal phyla emerged ‘suddenly’ during the early Cambrian Period about 518 million years ago (Ma) in an event known as the Cambrian explosion. Following this evolutionary milestone, the marine invertebrate fossil record is punctuated by five major mass extinction events, collectively called the ‘Big Five’. These events include the end-Ordovician, Late Devonian, end-Permian, end-Triassic, and end-Cretaceous mass extinctions (Figure 1). Among them, the end-Permian extinction was the most catastrophic event, resulting in the loss of approximately 81% of marine species within a short geological interval. In this primer, I will discuss the potential reasons why the End-Permian extinction event had such a profound effect on terrestrial plant life. I will draw examples from the best preserved ecosystem from this time period — the Cathaysian Flora.
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Recent non-dino papers:
Free pdf:
Martin E. Farina, M. Gabriela Mángano, Luis A. Buatois, Claudia A. Marsicano & Verónica Krapovickas (2026)
Macroevolutionary trends of avian ichnodisparity in Gondwana
Scientific Reports (advance online publication)
doi: https://doi.org/10.1038/s41598-026-56695-z
https://link.springer.com/article/10.1038/s41598-026-56695-z
The concept of ichnodisparity is herein introduced for the study of fossil vertebrates, using Gondwanan avian footprints. We define ichnodisparity for trackways as the qualitative variation in morphological patterns of autopodial impressions, most likely reflecting functional or ecological thresholds. Foot architectural designs are defined based on anatomical features, including digit number and orientation and interdigital webbing, and size. Ichnodisparity in fossil bird tracks is proposed here as a useful proxy for analyzing evolutionary radiations and characterizing macroevolutionary patterns. Twenty-three geological formations from Gondwana were analyzed, spanning from the Early Cretaceous to the Late Pleistocene. The earliest morphotypes were predominantly large-sized, while small morphotypes became dominant over time. No zygodactyl footprints are recorded from Gondwana. Prior to the K/Pg boundary, ichnodisparity was high, consistent with a Cretaceous avian radiation. During the Eocene, morphological variety remained comparable to that of the Late Cretaceous — except for the large tridactyl design — suggesting ecological turnover rather than functional expansion; elevated ichnodisparity may be associated with the Early Eocene Climatic Optimum. The decline recorded in the Oligocene is likely attributable to sampling bias. The Miocene concentrates the highest ichnodisparity in the fossil record, with the reappearance of large pedal architectures linked to cursorial birds, supporting an expansion into open spaces. In the Pleistocene, small tridactyl forms disappeared and the large palmate architecture emerged for the first time, indicating a new episode of ecological turnover.
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Free pdf:
Marshall Brace, Michael Cramberg, Lauren Gray, Kaitlyn Pyatt, Luanne Xiao & Bruce Young (2026)
The crook in the caudals: Kinematics of defensive tail swipes in the American alligator (Alligator mississippiensis).
Vertebrate Anatomy Morphology Palaeontology 14.
https://doi.org/10.18435/vamp29414
https://journals.library.ualberta.ca/vamp/index.php/VAMP/article/view/29414
The American alligator responds to physical threats with a defensive tail swipe, a lateral and vertical sweep of the tail. Despite the large size of the alligator tail, it accounts for roughly half the length and a quarter of the mass of the entire animal, the tail swipe had a mean duration of only 0.2 s, about the duration of a human eye blink. During this interval the distal tip of the tail may be displaced over a meter, resulting in high terminal velocity values (mean = 10.1 m/s) and, not surprising given the large size of the tail, high impact force values (mean = 1.2 kN). Kinematically, the defensive tail swipe was found to consist of two phases; an initial phase during which the base of the tail was elevated vertically, the terminal phase during which the distal (laterally compressed) portion of the tail was accelerated. Both phases were found to be variable, both in terms of longitudinal positioning along the tail and magnitude of displacement. The initial elevation phase may be a counter-torque strategy for head strikes; a functional role in aiming or ground clearance of the distal tip is also possible. A better understanding of the kinematics of the alligator tail may provide insight into the interpretation of tail structures in other archosaurs.
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The crook in the caudals: Kinematics of defensive tail swipes in the American alligator (Alligator mississippiensis).
Vertebrate Anatomy Morphology Palaeontology 14.
https://doi.org/10.18435/vamp29414
https://journals.library.ualberta.ca/vamp/index.php/VAMP/article/view/29414
The American alligator responds to physical threats with a defensive tail swipe, a lateral and vertical sweep of the tail. Despite the large size of the alligator tail, it accounts for roughly half the length and a quarter of the mass of the entire animal, the tail swipe had a mean duration of only 0.2 s, about the duration of a human eye blink. During this interval the distal tip of the tail may be displaced over a meter, resulting in high terminal velocity values (mean = 10.1 m/s) and, not surprising given the large size of the tail, high impact force values (mean = 1.2 kN). Kinematically, the defensive tail swipe was found to consist of two phases; an initial phase during which the base of the tail was elevated vertically, the terminal phase during which the distal (laterally compressed) portion of the tail was accelerated. Both phases were found to be variable, both in terms of longitudinal positioning along the tail and magnitude of displacement. The initial elevation phase may be a counter-torque strategy for head strikes; a functional role in aiming or ground clearance of the distal tip is also possible. A better understanding of the kinematics of the alligator tail may provide insight into the interpretation of tail structures in other archosaurs.
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Natasha Stepanova, Hayley L Crowell, Daniel L Rabosky & Alison R Davis Rabosky (2026)
Clade-specific drivers of rapid vertebral evolution in squamate reptiles
Evolution, qpag104
doi: https://doi.org/10.1093/evolut/qpag104
https://academic.oup.com/evolut/advance-article-abstract/doi/10.1093/evolut/qpag104/8702389
In vertebrates, larger body length can evolve through two mechanisms: the addition of vertebrae (pleomerism) versus the enlargement of vertebrae (proportional change). These two processes have significant but distinct functional consequences for locomotion and stem from different developmental mechanisms. Squamate reptiles (lizards and snakes) show tremendous variation in precloacal vertebral number, ranging from 14 to nearly 400 vertebrae. By compiling vertebral counts for 2,357 squamate species from radiographs of museum specimens and supplementing with data from primary literature records, we tested how body size and habitat may influence variation in vertebral number across clades. We found that much of the variation in vertebral number reflects phylogenetic relatedness, likely due to other conserved causal variables or “macroevolutionary drift”. Size and habitat also explained a small proportion of variance in elongate clades. Vertebral number in amphisbaenians and blind snakes differed significantly from patterns observed in other elongate clades, showing little influence of body size or phylogenetic history. Their extreme fossoriality may explain the decoupling between vertebrae and body size in these groups. Taken together, our results indicate a surprising complexity to vertebral evolution and we find little evidence that any single factor affects vertebral variation consistently across all squamates.
Clade-specific drivers of rapid vertebral evolution in squamate reptiles
Evolution, qpag104
doi: https://doi.org/10.1093/evolut/qpag104
https://academic.oup.com/evolut/advance-article-abstract/doi/10.1093/evolut/qpag104/8702389
In vertebrates, larger body length can evolve through two mechanisms: the addition of vertebrae (pleomerism) versus the enlargement of vertebrae (proportional change). These two processes have significant but distinct functional consequences for locomotion and stem from different developmental mechanisms. Squamate reptiles (lizards and snakes) show tremendous variation in precloacal vertebral number, ranging from 14 to nearly 400 vertebrae. By compiling vertebral counts for 2,357 squamate species from radiographs of museum specimens and supplementing with data from primary literature records, we tested how body size and habitat may influence variation in vertebral number across clades. We found that much of the variation in vertebral number reflects phylogenetic relatedness, likely due to other conserved causal variables or “macroevolutionary drift”. Size and habitat also explained a small proportion of variance in elongate clades. Vertebral number in amphisbaenians and blind snakes differed significantly from patterns observed in other elongate clades, showing little influence of body size or phylogenetic history. Their extreme fossoriality may explain the decoupling between vertebrae and body size in these groups. Taken together, our results indicate a surprising complexity to vertebral evolution and we find little evidence that any single factor affects vertebral variation consistently across all squamates.
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Free pdf:
Ruolin Wu, Sandra Álvarez-Carretero, Yue Tong, Shan Wan, Harald Schneider, James Clark, Davide Pisani, Daniele Silvestro & Philip C. J. Donoghue (2026)
Integrated analysis of fossils and molecular divergence time estimates a latest Jurassic origin of angiosperms
Nature Plants (advance online publication)
doi: https://doi.org/10.1038/s41477-026-02311-x
https://www.nature.com/articles/s41477-026-02311-x
Molecular timescales are based on the calibration of molecular evolution to geological time using fossil constraints, but conventional calibration strategies use limited and often subjectively interpreted fossil data. Here we used the Bayesian Brownian Bridge model to derive data-driven calibration densities on the basis of extensive fossil occurrence data. This approach integrates the uncertainty on extant and historical diversity to estimate clade age. We transformed the estimated ages based on >25,000 fossil occurrences into calibration densities, which we used to constrain 110 node ages in a 644-species angiosperm phylogenetic tree inferred from a molecular alignment of 83 genes. The results are incompatible with a post-Jurassic origin of angiosperms, instead inferring a short, Late Jurassic history. Our study demonstrates the utility of a mechanistic approach to establish node-age constraints in molecular-clock-dating analyses, resulting in a more objective method to integrate molecular and palaeontological data when inferring evolutionary timescales.
Integrated analysis of fossils and molecular divergence time estimates a latest Jurassic origin of angiosperms
Nature Plants (advance online publication)
doi: https://doi.org/10.1038/s41477-026-02311-x
https://www.nature.com/articles/s41477-026-02311-x
Molecular timescales are based on the calibration of molecular evolution to geological time using fossil constraints, but conventional calibration strategies use limited and often subjectively interpreted fossil data. Here we used the Bayesian Brownian Bridge model to derive data-driven calibration densities on the basis of extensive fossil occurrence data. This approach integrates the uncertainty on extant and historical diversity to estimate clade age. We transformed the estimated ages based on >25,000 fossil occurrences into calibration densities, which we used to constrain 110 node ages in a 644-species angiosperm phylogenetic tree inferred from a molecular alignment of 83 genes. The results are incompatible with a post-Jurassic origin of angiosperms, instead inferring a short, Late Jurassic history. Our study demonstrates the utility of a mechanistic approach to establish node-age constraints in molecular-clock-dating analyses, resulting in a more objective method to integrate molecular and palaeontological data when inferring evolutionary timescales.
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Free pdf:
Zhuo Feng (2026)
Mass extinctions and land plant evolution
Current Biology 36(11): R511-R516
doi: https://doi.org/10.1016/j.cub.2026.01.037
https://www.sciencedirect.com/science/article/pii/S096098222600076X
Mass extinctions and land plant evolution
Current Biology 36(11): R511-R516
doi: https://doi.org/10.1016/j.cub.2026.01.037
https://www.sciencedirect.com/science/article/pii/S096098222600076X
Nearly all modern animal phyla emerged ‘suddenly’ during the early Cambrian Period about 518 million years ago (Ma) in an event known as the Cambrian explosion. Following this evolutionary milestone, the marine invertebrate fossil record is punctuated by five major mass extinction events, collectively called the ‘Big Five’. These events include the end-Ordovician, Late Devonian, end-Permian, end-Triassic, and end-Cretaceous mass extinctions (Figure 1). Among them, the end-Permian extinction was the most catastrophic event, resulting in the loss of approximately 81% of marine species within a short geological interval. In this primer, I will discuss the potential reasons why the End-Permian extinction event had such a profound effect on terrestrial plant life. I will draw examples from the best preserved ecosystem from this time period — the Cathaysian Flora.
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