Previous work has shown increased morphological variance within the forelimbs of the Permian synapsid group known as Therapsida over that of their Carboniferous and early Permian forerunners (“pelycosaurs”). Considering that disparity trends have been known to point to underlying macroevolutionary transitions, here we analyzed morphological variance alongside several additional macroevolutionary metrics to better isolate possible evolutionary mechanisms. Shape data was collected on a sample of 119 humeri and 99 ulnae comprising three major synapsid radiations with a temporal
range from the Carboniferous into the Triassic. Taxonomic sample included all major groups of pelycosaur-grade synapsids, all five recognized non-cynodontian therapsid clades, and a sample of pre-prozostrodontian cynodonts. Procrustes variance - a multivariate quantification of morphospace occupation - was the chosen disparity metric for the study. Rate of phenotypic change, which considers the amount of shape change that would be necessary to achieve observed morphologies given the shape of the closely related taxa, was analyzed as the metric for evolutionary rate. Both metrics were considered through-time upon genera present in sequential 5 million year time bins.
Our results expand upon previous findings that disparity increases throughout the earliest stages of the Permian, coincident with the diversification of pelycosaurs and the emergence of Therapsida. This expanded dataset further shows that disparity approaches an asymptote around 270 million years ago and only increases marginally through the late Permian, remaining between 0.018–0.021 from 275-245
mya. In contrast, evolutionary rate does not appear to asymptote during this same interval, starting at a low of 6.17e-6 (300 mya) and increasing to a peak of 1.78e-5 right before the End Permian Mass Extinction Event (252 mya). The continuing increase of evolutionary rate shows that morphological change continues across taxa, but the plateauing of morphological disparity suggests that morphospace is not expanding concurrent with this. The incongruence between these two metrics suggests a critical
change in evolutionary mode, wherein morphological change continues rapidly but does not result in the evolution of novel morphologies. These results provide some of the strongest quantitative data yet of an evolutionary constraint acting upon the morphology of the synapsid forelimb through deep time.
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Modularity and heterochrony in the evolution of the ceratopsian dinosaur frill
The fossil record provides compelling examples of heterochrony at macroevolutionary scales such as the peramorphic giant antlers of the Irish elk. Heterochrony has also been invoked in the evolution of the distinctive cranial frill of ceratopsian dinosaurs such as
- Award ID(s):
- 1925884
- NSF-PAR ID:
- 10456181
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecology and Evolution
- Volume:
- 10
- Issue:
- 13
- ISSN:
- 2045-7758
- Page Range / eLocation ID:
- p. 6288-6309
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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ABSTRACT The article reports on the first detailed vertebral and rib morphology of anguine taxon
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null (Ed.)Synopsis Pygopodids are elongate, functionally limbless geckos found throughout Australia. The clade presents low taxonomic diversity (∼45 spp.), but a variety of cranial morphologies, habitat use, and locomotor abilities that vary between and within genera. In order to assess potential relationships between cranial morphology and ecology, computed tomography scans of 29 species were used for 3D geometric morphometric analysis. A combination of 24 static landmarks and 20 sliding semi-landmarks were subjected to Generalized Procrustes Alignment. Disparity in cranial shape was visualized through Principal Component Analysis, and a multivariate analysis of variance (MANOVA) was used to test for an association between shape, habitat, and diet. A subset of 27 species with well-resolved phylogenetic relationships was used to generate a phylomorphospace and conduct phylogeny-corrected MANOVA. Similar analyses were done solely on Aprasia taxa to explore species-level variation. Most of the variation across pygopodids was described by principal component (PC) 1(54%: cranial roof width, parabasisphenoid, and occipital length), PC2 (12%: snout elongation and braincase width), and PC3 (6%: elongation and shape of the palate and rostrum). Without phylogenetic correction, both habitat and diet were significant influencers of variation in cranial morphology. However, in the phylogeny-corrected MANOVA, habitat remained weakly significant, but not diet, which can be explained by generic-level differences in ecology rather than among species. Our results demonstrate that at higher levels, phylogeny has a strong effect on morphology, but that influence may be due to small sample size when comparing genera. However, because some closely related taxa occupy distant regions of morphospace, diverging diets, and use of fossorial habitats may contribute to variation seen in these geckos.more » « less
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ABSTRACT Morphology forms the most fundamental level of data in vertebrate palaeontology because it is through interpretations of morphology that taxa are identified, creating the basis for broad evolutionary and palaeobiological hypotheses. Assessing maturity is one of the most basic aspects of morphological interpretation and provides the means to study the evolution of ontogenetic changes, population structure and palaeoecology, life‐history strategies, and heterochrony along evolutionary lineages that would otherwise be lost to time. Saurian reptiles (the least‐inclusive clade containing Lepidosauria and Archosauria) have remained an incredibly diverse, numerous, and disparate clade through their ~260‐million‐year history. Because of the great disparity in this group, assessing maturity of saurian reptiles is difficult, fraught with methodological and terminological ambiguity. We compiled a novel database of literature, assembling >900 individual instances of saurian maturity assessment, to examine critically how saurian maturity has been diagnosed. We review the often inexact and inconsistent terminology used in saurian maturity assessment (e.g. ‘juvenile’, ‘mature’) and provide routes for better clarity and cross‐study coherence. We describe the various methods that have been used to assess maturity in every major saurian group, integrating data from both extant and extinct taxa to give a full account of the current state of the field and providing method‐specific pitfalls, best practices, and fruitful directions for future research. We recommend that a new standard subsection, ‘Ontogenetic Assessment’, be added to the Systematic Palaeontology portions of descriptive studies to provide explicit ontogenetic diagnoses with clear criteria. Because the utility of different ontogenetic criteria is highly subclade dependent among saurians, even for widely used methods (e.g. neurocentral suture fusion), we recommend that phylogenetic context, preferably in the form of a phylogenetic bracket, be used to justify the use of a maturity assessment method. Different methods should be used in conjunction as independent lines of evidence when assessing maturity, instead of an ontogenetic diagnosis resting entirely on a single criterion, which is common in the literature. Critically, there is a need for data from extant taxa with well‐represented growth series to be integrated with the fossil record to ground maturity assessments of extinct taxa in well‐constrained, empirically tested methods.
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Premise Although numerous phylogenetic studies have been conducted in Cactaceae, whole‐plastome datasets have not been employed. We used the chollas to develop a plastome dataset for phylogeny reconstruction to test species relationships, biogeography, clade age, and morphological evolution.
Methods We developed a plastome dataset for most known diploid members of the chollas (42 taxa) as well as for other members of Cylindropuntieae. Paired‐end, raw reads from genome skimming were reference‐mapped onto a de novo plastome assembly of one species of cholla,
Cylindropuntia bigelovii , and were used to build our plastome dataset, which was analyzed using various methods.Results Our plastome dataset resolved the phylogeny of the chollas, including most interspecific and intraspecific relationships. Tribe Cylindropuntieae arose ~18 mya, during the early Miocene in southern South America, and is supported as sister to the South American clade Tephrocacteae. The (
Micropuntia (Cylindropuntia +Grusonia )) clade most likely originated in the Chihuahuan Desert region around 16 mya and then migrated into other North American desert regions. Key morphological characters for recognizing traditional taxonomic series inCylindropuntia (e.g., spiny fruit) are mostly homoplasious.Conclusions This study provides the first comprehensive plastome phylogeny for any clade within Cactaceae. Although the chollas s.l. are widespread throughout western North American deserts, their most recent common ancestor likely arose in the Chihuahuan Desert region during the mid‐Miocene, with much of their species diversity arising in the early to mid‐Pliocene, a pattern strikingly similar to those found in other western North American desert groups.
