Do extraordinarily high growth rates in Permo-Triassic dicynodonts (Therapsida, Anomodontia) explain their success before and after the end-Permian extinction?
Abstract:Dicynodonts were the most diverse and abundant herbivorous therapsids of the Permo-Triassic. They include Lystrosaurus, one of the few taxa known to survive the end-Permian extinction and the most abundant tetrapod during the Early Triassic postextinction recovery. Explanations for the success of Lystrosaurus and other dicynodonts remain controversial. This study presents an assessment of dicynodont growth patterns using bone histology, with special focus on taxa associated with the end-Permian extinction even… Show more
“…Interestingly, these therapsids have values ranging from 0.0 ± 1.6‰ to +1.8 ± 1.6‰ higher than the coexisting terrestrial archosauriform Erythrosuchus (Botha-Brink and Smith, 2011), a range suggesting that they shared a similar thermophysiology (Figure 2B). Therefore δ 18 O p values imply that, as in the case of the therapsids, Erythrosuchus was also endothermic which is consistent with the elevated growth rates implied by its palaeohistology (de Ricqlès et al, 2008; Botha-Brink and Angielczyk, 2010). 10.7554/eLife.28589.004Figure 2.δ 18 O p differences between Early to Middle Triassic therapsids and other tetrapods.Differences in δ 18 O p values between therapsids and stereospondyls (white symbols) and between therapsids and archosauriforms (black symbols) from the same localities are plotted against their corresponding palaeolatitude.…”
The only true living endothermic vertebrates are birds and mammals, which produce and regulate their internal temperature quite independently from their surroundings. For mammal ancestors, anatomical clues suggest that endothermy originated during the Permian or Triassic. Here we investigate the origin of mammalian thermoregulation by analysing apatite stable oxygen isotope compositions (δ18Op) of some of their Permo-Triassic therapsid relatives. Comparing of the δ18Op values of therapsid bone and tooth apatites to those of co-existing non-therapsid tetrapods, demonstrates different body temperatures and thermoregulatory strategies. It is proposed that cynodonts and dicynodonts independently acquired constant elevated thermometabolism, respectively within the Eucynodontia and Lystrosauridae + Kannemeyeriiformes clades. We conclude that mammalian endothermy originated in the Epicynodontia during the middle-late Permian. Major global climatic and environmental fluctuations were the most likely selective pressures on the success of such elevated thermometabolism.DOI:
http://dx.doi.org/10.7554/eLife.28589.001
“…Interestingly, these therapsids have values ranging from 0.0 ± 1.6‰ to +1.8 ± 1.6‰ higher than the coexisting terrestrial archosauriform Erythrosuchus (Botha-Brink and Smith, 2011), a range suggesting that they shared a similar thermophysiology (Figure 2B). Therefore δ 18 O p values imply that, as in the case of the therapsids, Erythrosuchus was also endothermic which is consistent with the elevated growth rates implied by its palaeohistology (de Ricqlès et al, 2008; Botha-Brink and Angielczyk, 2010). 10.7554/eLife.28589.004Figure 2.δ 18 O p differences between Early to Middle Triassic therapsids and other tetrapods.Differences in δ 18 O p values between therapsids and stereospondyls (white symbols) and between therapsids and archosauriforms (black symbols) from the same localities are plotted against their corresponding palaeolatitude.…”
The only true living endothermic vertebrates are birds and mammals, which produce and regulate their internal temperature quite independently from their surroundings. For mammal ancestors, anatomical clues suggest that endothermy originated during the Permian or Triassic. Here we investigate the origin of mammalian thermoregulation by analysing apatite stable oxygen isotope compositions (δ18Op) of some of their Permo-Triassic therapsid relatives. Comparing of the δ18Op values of therapsid bone and tooth apatites to those of co-existing non-therapsid tetrapods, demonstrates different body temperatures and thermoregulatory strategies. It is proposed that cynodonts and dicynodonts independently acquired constant elevated thermometabolism, respectively within the Eucynodontia and Lystrosauridae + Kannemeyeriiformes clades. We conclude that mammalian endothermy originated in the Epicynodontia during the middle-late Permian. Major global climatic and environmental fluctuations were the most likely selective pressures on the success of such elevated thermometabolism.DOI:
http://dx.doi.org/10.7554/eLife.28589.001
“…At least one large-bodied eutheriodont, Moschorhinus , exhibited within-lineage size reductions across the extinction boundary, implying that the extinction also had the potential to act upon microevolutionary processes in a constructive manner [68]. Similar body size reduction characterizes the Permian and Triassic species of the dicynodont Lystrosaurus
[65], [71].…”
The extent to which mass extinctions influence body size evolution in major tetrapod clades is inadequately understood. For example, the ‘Lilliput effect,’ a common feature of mass extinctions, describes a temporary decrease in body sizes of survivor taxa in post-extinction faunas. However, its signature on existing patterns of body size evolution in tetrapods and the persistence of its impacts during post-extinction recoveries are virtually unknown, and rarely compared in both geologic and phylogenetic contexts. Here, I evaluate temporal and phylogenetic distributions of body size in Permo-Triassic therocephalian and cynodont therapsids (eutheriodonts) using a museum collections-based approach and time series model fitting on a regional stratigraphic sequence from the Karoo Basin, South Africa. I further employed rank order correlation tests on global age and clade rank data from an expanded phylogenetic dataset, and performed evolutionary model testing using Brownian (passive diffusion) models. Results support significant size reductions in the immediate aftermath of the end-Permian mass extinction (ca. 252.3 Ma) consistent with some definitions of Lilliput effects. However, this temporal succession reflects a pattern that was underscored largely by Brownian processes and constructive selectivity. Results also support two recent contentions about body size evolution and mass extinctions: 1) active, directional evolution in size traits is rare over macroevolutionary time scales and 2) geologically brief size reductions may be accomplished by the ecological removal of large-bodied species without rapid originations of new small-bodied clades or shifts from long-term evolutionary patterns.
“…Osteohistological evidence suggests that the growth rate of both therapsids (Botha-Brink & Angielczyk, 2010;Huttenlocker & Botha-Brink, 2014) and archosaurs (Botha-Brink & Smith, 2011) increased during the Early Triassic. Faster growth rates allowed the attainment of earlier ages of reproduction which would have been highly adaptive in the unpredictable environments following the Permo-Triassic mass extinction.…”
Recent palaeontological data and novel physiological hypotheses now allow a timescaled reconstruction of the evolution of endothermy in birds and mammals. A three-phase iterative model describing how endothermy evolved from Permian ectothermic ancestors is presented. In Phase One I propose that the elevation of endothermy - increased metabolism and body temperature (T ) - complemented large-body-size homeothermy during the Permian and Triassic in response to the fitness benefits of enhanced embryo development (parental care) and the activity demands of conquering dry land. I propose that Phase Two commenced in the Late Triassic and Jurassic and was marked by extreme body-size miniaturization, the evolution of enhanced body insulation (fur and feathers), increased brain size, thermoregulatory control, and increased ecomorphological diversity. I suggest that Phase Three occurred during the Cretaceous and Cenozoic and involved endothermic pulses associated with the evolution of muscle-powered flapping flight in birds, terrestrial cursoriality in mammals, and climate adaptation in response to Late Cenozoic cooling in both birds and mammals. Although the triphasic model argues for an iterative evolution of endothermy in pulses throughout the Mesozoic and Cenozoic, it is also argued that endothermy was potentially abandoned at any time that a bird or mammal did not rely upon its thermal benefits for parental care or breeding success. The abandonment would have taken the form of either hibernation or daily torpor as observed in extant endotherms. Thus torpor and hibernation are argued to be as ancient as the origins of endothermy itself, a plesiomorphic characteristic observed today in many small birds and mammals.
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