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17 results for “early tetrapod”
Fig. 7 in The fossil record of early tetrapods: Worker effort and the end-Permian mass extinction
Fig. 7. Species discovery curves for several groups of fossil organisms show substantial differences in form. All discovery curves are shown as percentages, even though final totals, in 2003, are very different: trilobites (n = 4126), early tetrapods (n = 515), dinosaurs (n = 694), fossil birds (n = 221), and fossil mammals of North America (n = 3340). The horizontal line marks the "half life" of the discovery curve, the date by which half the currently valid taxa had accumulated. Data from these sources: trilobites (Tarver et al. 2007), dinosaurs (Benton 2008), fossil birds (Fountaine et al. 2008), fossil mammals (Alroy 2002).
Fig. 2 in The fossil record of early tetrapods: Worker effort and the end-Permian mass extinction
Fig. 2. Perceptions of early tetrapod diversity at three points in research time, 1900, 1950, and 2000. Total numbers of valid species are indicated per series; the 1900 data distribution differs significantly from those for 1950 and 2000, but the 1950 and 2000 distributions do not differ significantly (see text).
Fig. 1 in The fossil record of early tetrapods: Worker effort and the end-Permian mass extinction
Fig. 1. Discovery curve of valid early tetrapod species (i.e., tetrapods, excluding Lissamphibia and Amniota), plotted against publication year. Species determined as synonymous or dubious in recent revisions are excluded. The curves show proportions through time, rising to 100% of current knowledge, for all early tetrapods (n = 528) and two major sub−divisions, temnospondyls (n = 368), and lepospondyls (n = 85).
Fig. 6 in The fossil record of early tetrapods: Worker effort and the end-Permian mass extinction
Fig. 6. Cumulative discovery curve of species of early tetrapods showing the relative completeness for each of the eight stratigraphic series, divided into two panels, from Upper Devonian to Middle Permian (A), and Upper Permian to Upper Triassic (B), plotted against decades in research time. The horizontal line marks the "half life" of the discovery curve, the date by which half the currently valid taxa had accumulated. Numbers of taxa per series are: Upper Devonian (17), Lower Carboniferous (25), Upper Carboniferous (108), Lower Permian (125), Middle Permian (36), Upper Permian (20), Lower Triassic (100), Middle Triassic (46), Upper Triassic (5), Jurassic (5), Cretaceous (1).
Fig. 4 in The fossil record of early tetrapods: Worker effort and the end-Permian mass extinction
Fig. 4. Cumulative discovery curves of species of early tetrapods showing the relative completeness for each of the nine major geographic regions: North America, Europe, and Africa (A), South America, Greenland, and Australia (B), Asia, India, and Russia (C), plotted against decades in research time. The horizontal line marks the "half life" of the discovery curve, the date by which half the currently valid taxa had accumulated. Total numbers of taxa are given for each continent.
Fig. 3 in The fossil record of early tetrapods: Worker effort and the end-Permian mass extinction
Fig. 3. Histogram of the total number of valid early tetrapod species from each major geographic region. Totals are: Europe (171), North America (156), Russia (77), Africa (51), Australia (30), India (14), Asia excluding India (12), South America (11), and Greenland (9).
Data from: Bony lesions in early tetrapods and the evolution of mineralized tissue repair
Bone healing is an important survival mechanism, allowing vertebrates to recover from injury and disease. Here we describe newly recognized paleopathologies in the hindlimbs of the early tetrapods Crassigyrinus scoticus and Eoherpeton watsoni from the Early Carboniferous of Cowdenbeath, Scotland. These pathologies are among the oldest known instances of bone healing in tetrapod limb bones in the fossil record (about 325 Myr old). X-ray microtomographic imaging of the internal bone structure of these lesions shows that they are characterized by a mass of trabecular bone separated from the shaft's trabeculae by a layer of cortical bone. We frame these paleopathologies in an evolutionary context, including additional data on bone healing and its pathways across extinct and extant sarcopterygians. These data allowed us to synthesize information on cell-mediated repair of bone and other mineralized tissues in all vertebrates, to reconstruct the evolutionary history of skeletal tissue repair mechanisms. We conclude that bone healing is ancestral for sarcopterygians. Furthermore, other mineralized tissues (aspidin and dentine) were also capable of healing and remodeling early in vertebrate evolution, suggesting that these repair mechanisms are synapomorphies of vertebrate mineralized tissues. The evidence for remodeling and healing in all of these tissues appears concurrently, so in addition to healing these early vertebrates had the capacity to restore structure and strength by remodeling their skeleton. Healing appears to be an inherent property of these mineralized tissues, and its linkage to their remodeling capacity has previously been under-appreciated.
Data from: Bony lesions in early tetrapods and the evolution of mineralized tissue repair
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Data from: Fish and tetrapod communities across a marine to brackish salinity gradient in the Pennsylvanian (early Moscovian) Minto Formation of New Brunswick, Canada, and their palaeoecological and palaeogeographical implications
Euryhaline adaptations in Pennsylvanian vertebrates allowed them to inhabit the marine to freshwater spectrum. This is illustrated by new assemblages of fish and tetrapods from the early Moscovian Minto Formation of New Brunswick, Canada. Fish include chondrichthyans (xenacanthids and the enigmatic Ageleodus), acanthodians (gyracanthids and acanthodiforms), sarcopterygians (rhizodontids, megalichthyids and dipnoans), and actinopterygians (eurynotiforms). Tetrapods include small- to medium-sized, and largely aquatic, stem tetrapods (colosteids) and anthracosaurs (embolomeres). A key finding is that the parautochthonous fossil assemblages are preserved across a salinity gradient, with diversity (measured by the Simpson Index) declining from open marine environments, through brackish embayments, and reaching a nadir in tidal estuaries. Chondrichthyans dominate the entire salinity spectrum (65% of fossils), a distribution that demonstrates a euryhaline mode of life, and one large predatory chondrichthyan, Orthacanthus, may have practised filial cannibalism in coastal nurseries because its heteropolar coprolites contain juvenile xenacanthid teeth. In contrast, other fish communities were more common in open marine settings while tetrapods were more common in coastal brackish waters. While all these faunas were also likely to have been euryhaline, their osmoregulation was, perhaps, less versatile. The demonstration of widespread euryhalinity among fish and aquatic tetrapods explains why Pennsylvanian faunas generally show a cosmopolitan biogeography because taxa were able to disperse via seaways. It also resolves the paradox of enriched strontium isotopic signatures observed in these faunas because organisms would have been, at times, exposed to continental water bodies as well. Therefore, our new findings contribute to the long-running debate about the ecology of Pennsylvanian fishes and tetrapods.
Micro-computed tomography of the holotype of the early tetrapod Ichthyerpeton bradleyae (Huxley in Wright and Huxley, 1866) from the Pennsylvanian of Ireland
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Data from: Fish and tetrapod communities across a marine to brackish salinity gradient in the Pennsylvanian (early Moscovian) Minto Formation of New Brunswick, Canada, and their palaeoecological and palaeogeographical implications
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Data from: Linked morphological changes during palate evolution in early tetrapods
We examined the shapes and sizes of dermal bones of the palate of selected Palaeozoic tetrapods in order to identify the ancestral states of palatal bone morphologies in the earliest tetrapods, to learn how the composition of the palate varies within and among early tetrapod radiations, and recognize evolutionary correlations among the size and shapes of skeletal elements in this important group of animals. We find that whereas the palatal bones themselves and their arrangements are usually conserved, considerable correlated evolutionary change occurs in the shapes and sizes of the bones. Some of the changes in the bones are allometrically linked to overall palate size, which varies more than 100-fold among the taxa in our sample. Often, these allometries were only hinted at in traditional independent contrasts-based regressions of log transformed data, particularly because many allometries are subtle, their slopes may vary among subclades, and the scatter around some trendlines is high. Rather, the allometries showed up in analyses of size-standardized palatal bone dimensions investigated using independent contrasts, bivariate phylomorphospace plots, and mirrored character reconstructions on the phylogenetic tree. We find negative allometry for parasphenoid lengths and widths essentially across the entire tree of Palaeozoic tetrapods, but with different trajectories characterizing the two largest clades, the temnospondyls and the lepospondyls. The lengths of several other elements may show positive allometries, either across the entire tree or in just a subclade. One possible positive allometry exists for the ectopterygoid, which appears to allometrically shorten in temnospondyls that evolve small body and palate size, and, as in Doleserpeton can be lost altogether. Both shortening and loss could be by the same developmental change, paedomorphosis, a form of heterochrony. Paedomorphosis might also account for evolution of relatively large parasphenoids in both lepospondyls and diminutive temnospondyls, but does not seem to explain evolution of ectopterygoid loss in lepospondyls. A regularity observed across nearly all taxa in our study set is an inverse correlation between the lengths of the vomer and pterygoid, bones that lie adjacent to one another along the long palatal axis. Further work is needed to learn whether such correlated evolution might be due to adaptation and/or to developmental bias, and particularly, to learn how correlations and allometries themselves evolve.
Data from: Phylogenetic stability, tree shape, and character compatibility: a case study using early tetrapods
Phylogenetic tree shape varies as the evolutionary processes affecting a clade change over time. In this study, we examined an empirical phylogeny of fossil tetrapods during several time intervals, and studied how temporal constraints manifested in patterns of tree imbalance and character change. The results indicate that the impact of temporal constraints on tree shape is minimal and highlights the stability through time of the reference tetrapod phylogeny. Unexpected values of imbalance for Mississippian and Pennsylvanian time slices strongly support the hypothesis that the Carboniferous was a period of explosive tetrapod radiation. Several significant diversification shifts take place in the Mississippian and underpin increased terrestrialization among the earliest limbed vertebrates. Character incompatibility is relatively high at the beginning of tetrapod history, but quickly decreases to a relatively stable lower level, relative to a null distribution based on constant rates of character change. This implies that basal tetrapods had high, but declining, rates of homoplasy early in their evolutionary history, although the origin of Lissamphibia is an exception to this trend. The time slice approach is a powerful method of phylogenetic analysis and a useful tool for assessing the impact of combining extinct and extant taxa in phylogenetic analyses of large and speciose clades.
Data from: Linked morphological changes during palate evolution in early tetrapods
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Data from: Phylogenetic stability, tree shape, and character compatibility: a case study using early tetrapods
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Data from: Ontogenetic sequence reconstruction and sequence polymorphism in extinct taxa: an example using early tetrapods (Tetrapoda: Lepospondyli)
Ontogenetic sequence reconstruction is challenging particularly for extinct taxa because of when, where, and how fossils preserve. Different methods of reconstruction exist, but the effects of preservational bias, the applicability of size-independent methods, and the prevalence of sequence polymorphism (intraspecific variation) remain unexplored for paleontological data. Here I compare five different methods of ontogenetic sequence reconstruction and their effects on the detection of sequence polymorphism, using a large collection of the extinct vertebrates Microbrachis pelikani and Hyloplesion longicostatum. The postcranial ossification sequences presented here for those taxa are the first examples known for extinct lepospondyls. Sequences were reconstructed according to skull length, trunk length, increasing number of ontogenetic events, majority-rule consensus, and Ontogenetic Sequence Analysis (OSA). Results generally were in agreement, demonstrating that paleontological data may be used to robustly reconstruct developmental patterns. When reconstructing sequences based on fossils, size-based methods and OSA are more objective and less dependent on preservational bias than other techniques. Apart from the other methods, OSA also allows for statistical analysis of observed and predicted polymorphism. However, OSA requires a large sample size to yield meaningful results, and size-based methods are justified in paleontological studies when sample size is limited by poor preservation. Different methods of reconstruction detected different patterns of sequence polymorphism, although across all methods the magnitude of sequence variation for M. pelikani and H. longicostatum (1.3−3.4%) was within the lower range of values reported for extant vertebrates. Compared with other extinct and extant tetrapods, all sequence reconstruction methods consistently showed that M. pelikani and H. longicostatum exhibit advanced ossification of the pubis and delayed ossification of the scapula. However, the postcranial ossification sequences of these two taxa largely are congruent with those of other tetrapods, suggesting an underlying conservative ancestral pattern that evolved early in tetrapod history.
Data from: Ontogenetic sequence reconstruction and sequence polymorphism in extinct taxa: an example using early tetrapods (Tetrapoda: Lepospondyli)
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