Identifying heterogeneity in rates of morphological evolution:Discrete character change in the evolution of lungfish (Sarcopterygii; Dipnoi)

Quantifying rates of morphological evolution is important in many macroevolutionary studies, and critical when assessing possible adaptive radiations and episodes of punctuated equilibrium in the fossil record. However, studies of morphological rates of change have lagged behind those on taxonomic diversification, and most authors have focused on continuous characters and quantifying patterns of morphological rates over time. Here, we provide a phylogenetic approach, using discrete characters and three statistical tests to determine points on a cladogram (branches or entire clades) that are characterized by significantly high or low rates of change. These methods include a randomization approach that identifies branches with significantly high rates and likelihood ratio tests that pinpoint either branches or clades that have significantly higher or lower rates than the pooled rate of the remainder of the tree. As a test case for these methods, we analyze a discrete character dataset of lungfish, which have long been regarded as living fossils due to an apparent slowdown in rates since the Devonian. We find that morphological rates are highly heterogeneous across the phylogeny and recover a general pattern of decreasing rates along the phylogenetic backbone toward living taxa, from the Devonian until the present. Compared with previous work, we are able to report a more nuanced picture of lungfish evolution using these new methods

Macroevolutionary Patterns In The Evolutionary Radiation Of Archosaurs (Tetrapoda: Diapsida)

The rise of archosaurs during the Triassic and Early Jurassic has been treated as a classic example of an evolutionary radiation in the fossil record. This paper reviews published studies and provides new data on archosaur lineage origination, diversity and lineage evolution, morphological disparity, rates of morphological character change, and faunal abundance during the Triassic–Early Jurassic. The fundamental archosaur lineages originated early in the Triassic, in concert with the highest rates of character change. Disparity and diversity peaked later, during the Norian, but the most significant increase in disparity occurred before maximum diversity. Archosaurs were rare components of Early–Middle Triassic faunas, but were more abundant in the Late Triassic and pre-eminent globally by the Early Jurassic. The archosaur radiation was a drawn-out event and major components such as diversity and abundance were discordant from each other. Crurotarsans (crocodile-line archosaurs) were more disparate, diverse, and abundant than avemetatarsalians (bird-line archosaurs, including dinosaurs) during the Late Triassic, but these roles were reversed in the Early Jurassic. There is no strong evidence that dinosaurs outcompeted or gradually eclipsed crurotarsans during the Late Triassic. Instead, crurotarsan diversity decreased precipitously by the end-Triassic extinction, which helped usher in the age of dinosaurian dominance

Petrosal anatomy of the Paleocene eutherian mammal Deltatherium fundaminis (Cope, 1881)

We describe the tympanic anatomy of the petrosal of Deltatherium fundaminis, an enigmatic Paleocene mammal based on cranial specimens recovered from New Mexico, U.S.A. Although the ear region of Deltatherium has previously been described, there has not been a comprehensive, well-illustrated contribution using current anatomical terminology. The dental and cranial anatomy of Deltatherium is a chimera, with morphological similarities to both ‘condylarth’ and ‘cimolestan’ taxa. As such, the phylogenetic relationships of this taxon have remained elusive since its discovery, and it has variably been associated with Arctocyonidae, Pantodonta and Tillodontia. The petrosal of Deltatherium is anteriorly bordered by an open space comprising a contiguous carotid opening and pyriform fenestra. The promontorium features both a small rostral tympanic process and small epitympanic wing but lacks well-marked sulci. A large ventral facing external aperture of the canaliculus cochleae is present and bordered posteriorly by a well-developed caudal tympanic process. The hiatus Fallopii opens on the ventral surface of the petrosal. The tegmen tympani is mediolaterally broad and anteriorly expanded, and its anterior margin is perforated by a foramen for the ramus superior of the stapedial artery. The tympanohyal is small but approximates the caudal tympanic process to nearly enclose the stylomastoid notch. The mastoid is widely exposed on the basicranium and bears an enlarged mastoid process, separate from the paraoccipital process. These new observations provide novel anatomical data corroborating previous hypotheses regarding the plesiomorphic eutherian condition but also reveal subtle differences among Paleocene eutherians that have the potential to help inform the phylogeny of Deltatherium. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10914-021-09568-3

A revision of the ‘coelophysoid-grade’ theropod specimen from the Lower Jurassic of the Isle of Skye (Scotland)

The broadest diversification of early predatory dinosaurs is represented by the ‘coelophysoid-grade’ neotheropods, but their Hettangian–Sinemurian (c. 191–201 Ma) record is scarce worldwide. More information is needed to shed light on the evolution of this dinosaur group after the end-Triassic mass extinction (c. 201 Ma). Here we revisit the anatomy and phylogeny of one of these earliest Jurassic neotheropod specimens, an isolated partial tibia from the lower Sinemurian of the Isle of Skye (Scotland) that was previously identified as probably closely related to Liliensternus liliensterni and coelophysids. However, we found that the Skye specimen is positioned in the branch leading to Averostra (Ceratosauria + Tetanurae), in a polytomy with Sarcosaurus woodi from the late Hettangian–lower Sinemurian of central England and a clade composed of Tachiraptor admirabilis and Averostra. The morphology of the Skye specimen is congruent with that of referred specimens of Sarcosaurus woodi, but because it probably represents a skeletally immature specimen, we assign it to cf. Sarcosaurus woodi. The Skye specimen increases the number of averostran-line neotheropod specimens recorded in the Lower Jurassic of Europe and current evidence indicates that these forms, and not coelophysoids, were relatively common in this part of the world at that time

First and most northern occurrence of a thalattosuchian crocodylomorph from the Jurassic of the Isle of Skye, Scotland

The Jurassic was a key interval for the evolution of dinosaurs, crocodylomorphs and many other vertebrate groups. In recent years, new vertebrate fossils have emerged from the Early–Middle Jurassic of the Isle of Skye, Scotland; however, much more is known about Skye's dinosaur fauna than its crocodylomorphs. Here we report new crocodylomorph material collected from Jurassic marine deposits at Prince Charlie's Cave on the NE coast of Skye. The specimen is a small cobble containing postcranial elements from an individual that is considerably larger in size than previous crocodylomorphs described from Skye. Based on features of the vertebrae and osteoderms, the specimen is assigned to Thalattosuchia, an extinct clade of semi-aquatic/pelagic crocodylomorphs. Specifically, the sub-circular and bean-shaped pit ornamentation on the dorsal surface of the osteoderms in alternating rows suggests affinities with the semi-aquatic lineage Teleosauroidea. Although the ornamentation pattern on the osteoderms is most similar to Macrospondylus (‘Steneosaurus’) bollensis, we conservatively assign the specimen to Teleosauroidea indeterminate. Regardless of its precise affinities and fragmentary nature, the specimen is the first thalattosuchian discovered in Scotland and is the most northerly reported Jurassic thalattosuchian globally, adding to our understanding of the palaeobiogeography and evolution of this group

Palaeontology meets metacommunity ecology: The Maastrichtian dinosaur fossil record of North America as a case study.

Documenting the patterns and potential associated processes of ancient biotas has always been a central challenge in palaeontology. Over the last decades, intense debate has focused on the organisation of dinosaur–dominated communities, yet no general consensus has been reached on how these communities were organised in a spatial context and if primarily affected by abiotic or biotic agents. Here, we used analytical routines typically applied in metacommunity ecology to provide novel insights into dinosaurian distributions across the latest Cretaceous of North America. To do this, we combined fossil occurrences with functional, phylogenetic and palaeoenvironmental modelling, and adopted the perspective that more reasonable conclusions on palaeoecological reconstructions can be gained from studies that consider the organisation of biotas along ecological gradients at multiple spatial scales. Our results showed that dinosaurs were restricted in range to different parts of the Hell Creek Formation, prompting the recognition of discrete and compartmentalised faunal areas during the Maastrichtian at fine-grained scales, whereas taxa ranges formed quasi–nested groups when combining data from various geological formations across the Western Interior of North America. Although groups of dinosaurs had coincident range boundaries, their communities responded to multiple ecologically–important gradients when compensating for differences in sampling effort. Metacommunity structures of both ornithischians and theropods were correlated with climatic barriers and potential trophic relationships between herbivores and carnivores, thereby suggesting that dinosaurian faunas were shaped by physiological constraints and a combination of bottom-up and top-down forces across multiple spatial grains and extents.Additional Supporting files include the following Appendices: Appendix S1. Body mass distributions based on product partition models with Markov sampling computations. Appendix S2. Functional and phylogenetic features for each spatial scale and study clade. Appendix S3. R packages and statistical routines. Appendix S4. Elements of metacommunity structure for the conservative fixed–fixed null model. Appendix S5. Results for the forward selection of explanatory variables. Appendix S6. Results for ordinary least squares (OLS) regression models. Appendix S7. Results for commonality analysis (CA) for each spatial scale and study clade. Appendix S8. Measuring the spatial autocorrelation of OLS model residuals. The Excel file includes occurrence data, palaeoenvironmental reconstructions, and functional features: Sheets 1 and 2 contain raw information on each study site for the Hell Creek and other North American geological formations, respectively. Sheet 1 includes palaeoenvironmental information for the Hell Creek Formation (i.e. lithofacies -C, channel; FP, floodplain- and palaeotopography -m.a.s.l. after log-transformation). Raw PalaeoDEM data (Scotese and Wright, 2018) are also available here: https://www.earthbyte.org/paleodem-resource-scotese-and-wright-2018/ Sheet 2 contains raw information on the log-transformed palaeoenvironmental reconstructions for the Maastrichtian of North America (Palaeotopography -m.a.s.l., TempMean and TempSDann in K; Prec and PrecSDann in kgm-2). Raw palaeoclimate GCMs (Valdés et al., 2017) can also be obtained here: https://www.paleo.bristol.ac.uk/ummodel/scripts/papers/ Sheet 3 includes a taxon-specific classification into several functional guilds (see the main text for details): These files may be opened and edited in Excel. For details or further queries, please contact Jorge García-Girón ([email protected]). Funding provided by: University of León*Crossref Funder Registry ID: Award Number: 2017Funding provided by: Spanish Ministry of Economy and Industry*Crossref Funder Registry ID: Award Number: CGL2017–84176RFunding provided by: Junta de Castilla y LeónCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100014180Award Number: LE004G18Funding provided by: Academy of FinlandCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100002341Award Number: 331957Funding provided by: Academy of FinlandCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100002341Award Number: 322652Funding provided by: European Research Council Starting Grant*Crossref Funder Registry ID: Award Number: ERC StG 2017, 756226, PalMFunding provided by: University of LeónCrossref Funder Registry ID: Award Number: 2017Funding provided by: Spanish Ministry of Economy and IndustryCrossref Funder Registry ID: Award Number: CGL2017–84176RFunding provided by: European Research Council Starting GrantCrossref Funder Registry ID: Award Number: ERC StG 2017, 756226, PalMDinosaur occurrences for the Maastrichtian of North America were retrieved from the Palaeobiology Database on May 2020, using the taxon name 'Dinosauria' and a time span of 72.1 – 66.0 Ma. Critically, although studies on modern community associations are limited to relatively brief periods of sampling time, fossil assemblages are windows on the faunas of ancient worlds occurring within particular chronostratigraphic units (Benson et al. 2018). Although this coarse temporal resolution will undoubtedly confound the data (which is addressed in detail below), it would be problematic to subdivide the time bins further, not least because only a handful of fossil assemblages are sufficiently informative to provide confident community-level estimates so far (Vavrek & Larsson 2010). Additionally, due to an insufficient amount of comparative data within high–resolution time bins (Dean et al. 2020) and the inherent errors in radiometric dating (Gates et al. 2010), the creation of a more tightly constrained correlative window is presently impractical. Here, we only retained occurrences belonging to Ornithischia and Theropoda since these two clades were the most diverse and abundant non–avian dinosaur groups in the latest Cretaceous of North America (Brusatte et al. 2015). Generic–level identifications were used in our study, and all avian taxa were excluded when delineating community types to keep our data more comparable to previous works (e.g. Vavrek & Larsson 2010; Dean et al. 2020). While birds are phylogenetically part of the dinosaurian clade, the different habits and habitats of latest Cretaceous Avialae (either diving or volant taxa) separates these faunas enough from ground-dwelling dinosaurs to justify their functional distinction in the context of the communities modelled here (see Heino et al. 2015b for an example on present-day biotas). Although the value of generic taxonomic ranks in community analyses has been debated, palaeontologists have used generic–level clades to investigate distributional patterns and variation in community composition of fossil taxa (e.g. Vavrek & Larsson 2010; Chiarenza et al. 2019; Dean et al. 2020). Indeed, generic–level identifications are preferred over species taxonomic ranks in dinosaur palaeobiology studies as most dinosaur genera (c. 87%) are easily diagnosed and monospecific (Weishampel et al. 2004; Mannion et al. 2012). Moreover, genus-level and species–level diversity patterns generally appear to track each other for Mesozoic tetrapods (Barrett et al. 2009), and genera are more taxonomically stable than species for many groups (Robeck et al. 2000). Here, however, taxa with unclear genus identification were discarded (i.e. we did not incorporate 'cryptic' diversity represented by taxonomically undiagnostic fossil remains that potentially represent distinct taxa, nor we did infer ghost lineages based on phylogenetic diversity estimates; Barrett et al. 2009; Mannion et al. 2011), and so were collections lacking formational assignment. If questionable ages appeared (e.g. ages notably deviating from ages of other collections from the same formation), they were either revised or excluded. These data are an up–to–date record of North American dinosaur faunas and therefore incorporate new Late Cretaceous fossils discovered over the past few years. Overall, our pruned dataset comprised 43 dinosaur genera, and consisted of 11 formations across the WIB of North America and 17 well–sampled locations across the Hell Creek landscape. Palaeoclimatic general circulation model. In this study, we used palaeoclimatic model outputs (here, near-surface [1.5 m] mean annual temperature (TempMean), near-surface [1.5 m] annual temperature standard deviation (TempSDann), annual average precipitation (PrecMean) and annual precipitation standard deviation (PrecSDann)) from the fully coupled atmosphere-ocean GCM HadCM3L v. 4.5 Atmospheric–Ocean General Circulation Model (Valdes et al. 2017). More specifically, we followed the nomenclature of Valdes et al. (2017) and applied the HadCM3BL–M2.1aE version of the model. The conditions of the model simulations for the Maastrichtian consist of an atmospheric CO2 concentration of 1120 ppmv, which is within the range of uncertainty provided by the recent proxy pCO2 reconstructions of Foster et al. (2017). The model simulations were run for a total of 1422 years, and the climate variables used in our analyses were an annual average of the last 30 years of these simulations. HadCM3L has contributed to the Coupled Mode Intercomparison Project experiments demonstrating skill when it comes to reproducing present-day climates (Collins et al. 2001; Valdes et al. 2017) and has also been used for an array of different palaeoclimate evaluations during the Eocene (Lunt et al. 2012), the Oligocene (Li et al. 2018) and the Miocene (Bradshaw et al. 2012). Detailed information on this palaeoclimatic model, including large–scale circulation (and associated energy and momentum fluxes) and temporal fluctuations, as well as the impacts of fine-scale orographic features on climate signals, are available elsewhere (e.g. Lunt et al. 2016; Chiarenza et al. 2019). Palaeogeographical digital elevation models (DEMs). The Maastrichtian palaeogeography for this study is that of Scotese & Wright (2018), which has been compiled as a palaeo-digital elevation model to facilitate grid-based analyses. In brief, these maps were created from publicly available stratigraphic literature, supplemented by fieldwork, including lithology, palaeoenvironmental information and broad-scale facies identification. For large–scale analyses, these palaeogeographies were upscaled to the palaeoclimatic model resolution (3.75° x 2.5°). This means that topographic and bathymetric information was broadly conserved, as it was resolved at a lower resolution (see Chiarenza et al. 2019 for a similar approach). Functional features. Each dinosaur taxon was classified into several functional guilds based on body mass (very small, small, medium, large and very large), locomotor mode (bipeds, facultative bipeds –capable of both quadrupedal and bipedal motion– and quadrupeds) and trophic habits (carnivores, omnivores and herbivores, and for the latter, low and high browsers). Body mass is perhaps the single most important and meaningful functional trait for animals, as it ultimately affects many aspects of their biology including metabolic rates, mechanical constraints, ecological performance and lifestyle strategies related to feeding, locomotion and reproduction (Loeuille & Loreau 2006; Iossa et al. 2008). Here, we used body mass estimates (very small ≤ 10 kg; 10 kg 10000 kg; Noto & Grossman 2010) based on adult representatives from the comprehensive dataset of Benson et al. (2014), which provides a wide list of dinosaur taxa using the scaling relationship of limb bone robustness (stylopodial circumference; Campione & Evans 2012). To obtain a more comprehensive understanding of body mass distributions in our data, we further applied an inflection point criterion based on the Barry & Hartigan (1993) product partition model with Markov chain Monte Carlo (MCMC). More specifically, this algorithm used the posterior probability of changes over 10000 MCMC iterations, excluding the first 1000 as burn in, to distinguish among different body mass categories in the latest Cretaceous dinosaurs of North America. Interestingly, this Bayesian analysis roughly identified most of the original body mass categories used in our study, with each category broadly representing an order of magnitude (García–Girón et al. 2020b, appendix S1, fig. S1). Trophic habits refer to the food processing strategies and diet of an animal, and it generally includes three primary categories, i.e. carnivores, herbivores and omnivores. Further subdivisions depend on the biological knowledge of the morphology (e.g. teeth morphology and skull) and behaviour of the study organismal group. Here, we assigned herbivores to categories of browse height rather than plant type due to the virtually unknown nature of plant preferences in dinosaurs. More specifically, we roughly assigned a simple maximum browsing limit (low ≤ 2 m; high > 2 m) based on characters such as limb length and neck posture using Noto & Grossman (2010) and Mallon et al. (2013). We further divided locomotor mode into two major categories: quadrupeds and bipeds. For those taxa with intermediate axial and limb morphologies in proportions between those of bipeds and obligate quadrupeds (e.g. Hadrosauridae), we included an additional locomotor division, i.e. facultative bipeds (see Noto & Grossman, 2010 for a similar approach). For the following analyses, we applied the mixed–variables coefficient of distance (i.e. a generalisation of Gower's distance; Pavoine et al. 2009) to extract a functional distance matrix, which described the functional differences between all taxon pairs based on body mass, trophic habits and locomotor mode (e.g. Heino & Tolonen 2017). Thereafter, the pairwise output values for the functional distance matrix were synthesised into separate axes using principal coordinate analysis (PCO) and following Duarte et al. (2012). See the main text for References