Fossil Lineages Research Articles

East Asian origins of European holly oaks (Quercus section Ilex Loudon) via the Tibet‐Himalaya

AbstractAimMany subtropical organisms exhibit an East Asian‐Tethyan disjunction, a distribution split between East Asia and the Mediterranean. The underlying mechanisms and timing have remained unclear to date. The evolutionary history of Quercus section Ilex Loudon, a representative East Asian‐Tethyan disjunct lineage with a rich and widespread fossil record, was investigated to understand the key drivers of this disjunction.LocationEurasia.MethodsThe phylogeny of Quercus section Ilex was reconstructed using RAD‐seq. Divergence times were estimated based on three fossil calibrations. Ancestral range and niche were reconstructed on the calibrated tree to infer the timing of transitions in geographic distributions and niche. Convergence in ecological space was estimated by fitting alternative multiple‐regime Ornstein‐Uhlenbeck models. Leaf shape affinities among extant and fossil taxa of section Ilex were assessed using geometric morphometric approaches.ResultsSix clades were well resolved in section Ilex. Ancestral range reconstruction and divergence time dating suggest a wide distribution along the East Tethys seaway, with initial divergence at the mid‐Eocene, and all six clades originating before the Miocene. The section dispersed from East Asia to the Mediterranean at the Eocene‐Oligocene boundary. A shift toward higher elevations was detected in the Himalayan clade during the middle or late Miocene. European fossil lineages during the early Miocene differ in leaf morphology from later lineages, which we infer to be a consequence of adaptive differentiation or species turnover.Main conclusionsQuercus section Ilex was widespread along the East Tethys seaway from the middle Eocene onward. The European holly oaks originated from an East Asian ancestral lineage that dispersed to Europe via the Tibet‐Himalaya corridor in the Oligocene. Lowlands along the margins of the Himalayas and through an Oligocene Tibetan valley served as the dispersal route(s) for these species. Changing climates drove Miocene extinction and local adaptation of European lineages.

Into Africa via docked India: a fossil climbing perch from the Oligocene of Tibet helps solve the anabantid biogeographical puzzle

The northward drift of the Indian Plate and its collision with Eurasia have profoundly impacted the evolutionary history of the terrestrial organisms, especially the ones along the Indian Ocean rim. Climbing perches (Anabantidae) are primary freshwater fishes showing a disjunct south Asian-African distribution, but with an elusive paleobiogeographic history due to the lack of fossil evidence. Here, based on an updated time-calibrated anabantiform phylogeny integrating a number of relevant fossils, the divergence between Asian and African climbing perches is estimated to have occurred in the middle Eocene (ca. 40 Ma, Ma: million years ago), a time when India had already joined with Eurasia. The key fossil lineage is †Eoanabas, the oldest anabantid known so far, from the upper Oligocene of the Tibetan Plateau. Ancestral range reconstructions suggest a Southeast Asian origin in the early Eocene (ca. 48 Ma) and subsequent dispersals to Tibet and then India for this group. Thereby we propose their westbound dispersal to Africa via the biotic bridge between India and Africa. If so, climbing perch precursors had probably followed the paleobiogeographical route of snakehead fishes, which have a slightly older divergence between African and Asian taxa. As such, our study echoes some recent molecular analyses in rejecting the previously held “Gondwana continental drift vicariance” or late Mesozoic dispersal scenarios for the climbing perches, but provides a unique biogeographical model to highlight the role of the pre-uplift Tibet and the docked India in shaping the disjunct distribution of some air-breathing freshwater fishes around the Indian Ocean.

Longitudinal Changes in Facial and Basicranial Integration in the Mediolateral Axis

ObjectivesMany studies over the past decade have employed morphological integration as a framework for understanding the interaction of the facial and basicranial skeleton in humans, the great apes, and our fossil lineage. Fewer studies, however, have examined morphological integration in the facial and basicranial portions of the skull in a true longitudinal sample. Most of these longitudinal studies have focused primarily on lateral cephalograms. While useful, these datasets only examine shape and morphological integration from the lateral aspect, limiting the types of questions that can be explored, primarily in the mediolateral axis. To rectify this gap in the data, we set out to study aspects of both symmetric and asymmetric shape variation in a longitudinal postero‐anterior (PA) celphalometric dataset in order to ascertain how patterns of morphological integration change in the mediolateral plane as a function of growth.MethodsPA cephalograms from a total of 55 individuals from the longitudinal Iowa Facial Growth Study were digitized using 13 coordinate landmarks across the mandible, face, and cranial base to capture patterns of integration and modularity. This data was collected at three time points per patient: age 4, age 11, and in adulthood. Data were submitted to MorphoJ for a Two‐Block Partial Least Squares (2‐B PLS) analysis of both the symmetric and asymmetric shape components in order to examine morphological integration between the face and cranial base.Results2‐B PLS results for the symmetric shape component show that integration between the face and cranial base decrease (becoming more modularized) from age 4 (RV=0.41, p<0.001), to age 11 (RV=0.25, p<0.001) before increasing again at the adult time point (RV=0.35, p<0.001). For the asymmetric component, however, levels of integration between the face and basicranium decrease consistently from age 4 (RV=0.59, p<0.001) to adult (RV=0.47, p<0.001). These results indicate that while levels of cranial integration tend to decrease throughout growth, this decrease is only consistent in the asymmetric shape component, potentially indicating that modularity of the face and cranial base has a strong mediolateral (side‐to‐side) component.ConclusionThese results show that while overall trajectories of facial/cranial base integration show a similar trend toward modularity as individuals grow, this pattern of modularity is only a linear when examining the asymmetric shape component. This aspect of shape has been largely overlooked in the integration literature to date and warrants further study.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Model Adequacy and Microevolutionary Explanations for Stasis in the Fossil Record.

Long-term phenotypic stasis is frequently observed in the fossil record, but not readily predicted from microevolutionary theory. To test competing explanations for stasis on macroevolutionary timescales we need reliably estimated parameters from appropriate evolutionary models that adequately describe the evolutionary trait dynamics. Here, we develop tests to assess the adequacy of the most commonly used stasis model in evolutionary biology and apply them to time series of phenotypic traits from fossil lineages. Of the 572 fossil time series we analyzed from the literature, 263 time series showed a better fit to the stasis model relative to alternative models, but only 172 of those fitted the stasis model in both relative and absolute terms. The estimated trait variances from these 172 time series do not correlate with rough proxies of effective population size. Our preliminary investigation of the fixed-optimum hypothesis hence fails to give empirical support to the idea that genetic drift around a constant trait optimum is an explanation for stasis in the fossil record. We argue that optima following stationary processes on the adaptive landscape is a viable hypothesis for stasis that needs further investigation. We end by discussing how investigations of model adequacy can be a valuable approach for increasing our understanding of the dynamics of the adaptive landscape on macroevolutionary timescales.

Out of the Antilles: Fossil phylogenies support reverse colonization of bats to South America

AbstractAimPrevious phylogenies of extant short‐faced bats (Chiroptera: Stenodermatina) supported either two colonization events from the mainland to the Antilles, or reverse colonization, but lacked both fossil data and statistical modelling of biogeography. Recent multi‐locus phylogenies of noctilionoid bats and likelihood modelling of ancestral ranges support a continental origin for the clade. We include all known extinct and extant stenodermatina species and apply statistical modelling to test competing biogeographical hypotheses.LocationThe Neotropics, including the Antilles.MethodsWe combined mitochondrial and nuclear sequences with 302 new morphological characters to infer phylogenies. Bayesian tip‐dating analyses applied codon models to protein‐coding genes, with relaxed molecular clocks fitting a compound Poisson process. The combined maximum clade credibility tree was used in comparisons of alternative biogeographical models.ResultsThe new phylogenies support the fossil Cubanycteris silvai as sister to all extant species of short‐faced bats. Among Artibeus (the sister group to short‐faced bats), the Antillean fossil A. anthonyi has distinctive characters and is nested within the subgenus Artibeus. The common ancestor of all short‐faced bats is inferred to be Antillean, as a mainland origin is unlikely. Founder‐event speciation is the most probable process explaining the distribution of these highly divergent fossil lineages.Main conclusionsDated, character‐based phylogenies of fossil species are indispensable for biogeographical inference: without fossils, biogeographical analyses find a mainland origin for short‐faced bats. The rate of founder speciation in this clade is twice as high as the estimate from noctilionoids in general, highlighting the role of founder events in the diversification of island taxa. Although rare, reverse colonization contributes key species to continental communities. Short‐faced bats, including Cubanycteris, share biomechanical adaptations for a strong bite conferring access to harder figs. We hypothesize these adaptations and characters related to roosting ecology enabled ancestral lineages to successfully establish and diversify on the mainland.

On the Cretaceous origin of the Order Syracosphaerales and the genusSyracosphaera

New scanning electron microscope observations of unadulterated calcareous nannofossil assemblages on lamina surfaces of Cretaceous Tanzania Drilling Project sediments reveal high diversity in the lagerstatte , but also our discovery of several new Cretaceous taxa provides evidence for greatly extended fossil lineages of extant orders, with implications for both deep-time biodiversity divergence and survival through the end-Cretaceous mass extinction. Our findings include: new species that are the first-recorded Mesozoic representatives of the extant Syracosphaeraceae and Papposphaeraceae; potentially previously unrecorded diversity in the Mesozoic Calciosoleniaceae, another extant order, represented by extant species that have been described already; and new species and unusually high abundances of the Mesozoic Stephanolithiaceae. We also highlight the extended range of an incertae sedis Cenozoic genus, Ellipsolithus , into at least the Turonian. Here, we describe seven new miniscule to very small Cretaceous species: Syracosphaera antiqua , S. repagula , Pocillithus macleodii , P. crucifer , Stradnerlithus wendleri , S .? haynesiae and Tortolithus foramen .

Evolutionarily distinct “living fossils” require both lower speciation and lower extinction rates

AbstractAs a label for a distinct category of life, “living fossil” is controversial. The term has multiple definitions, and it is unclear whether the label can be genuinely used to delimit biodiversity. Even taking a purely phylogenetic perspective in which a proxy for the living fossil is evolutionary distinctness (ED), an inconsistency arises: Does it refer to “dead-end” lineages doomed to extinction or “panchronic” lineages that survive through multiple epochs? Recent tree-growth model studies indicate that speciation rates must have been unequally distributed among species in the past to produce the shape of the tree of life. Although an uneven distribution of speciation rates may create the possibility for a distinct group of living fossil lineages, such a grouping could only be considered genuine if extinction rates also show a consistent pattern, be it indicative of dead-end or panchronic lineages. To determine whether extinction rates also show an unequal distribution, we developed a tree-growth model in which the probability of speciation and extinction is a function of a tip’s ED. We simulated thousands of trees in which the ED function for a tip is randomly and independently determined for speciation and extinction rates. We find that simulations in which the most evolutionarily distinct tips have lower rates of speciation and extinction produce phylogenetic trees closest in shape to empirical trees. This implies that a distinct set of lineages with reduced rates of diversification, indicative of a panchronic definition, is required to create the shape of the tree of life.

Novel Approaches for Phylogenetic Inference from Morphological Data and Total-Evidence Dating in Squamate Reptiles (Lizards, Snakes, and Amphisbaenians).

Here, I combine previously underutilized models and priors to perform more biologically realistic phylogenetic inference from morphological data, with an example from squamate reptiles. When coding morphological characters, it is often possible to denote ordered states with explicit reference to observed or hypothetical ancestral conditions. Using this logic, we can integrate across character-state labels and estimate meaningful rates of forward and backward transitions from plesiomorphy to apomorphy. I refer to this approach as MkA, for “asymmetric.” The MkA model incorporates the biological reality of limited reversal for many phylogenetically informative characters, and significantly increases likelihoods in the empirical data sets. Despite this, the phylogeny of Squamata remains contentious. Total-evidence analyses using combined morphological and molecular data and the MkA approach tend toward recent consensus estimates supporting a nested Iguania. However, support for this topology is not unambiguous across data sets or analyses, and no mechanism has been proposed to explain the widespread incongruence between partitions, or the hidden support for various topologies in those partitions. Furthermore, different morphological data sets produced by different authors contain both different characters and different states for the same or similar characters, resulting in drastically different placements for many important fossil lineages. Effort is needed to standardize ontology for morphology, resolve incongruence, and estimate a robust phylogeny. The MkA approach provides a preliminary avenue for investigating morphological evolution while accounting for temporal evidence and asymmetry in character-state changes.

Measuring Stratigraphic Congruence Across Trees, Higher Taxa, and Time.

The congruence between the order of cladistic branching and the first appearance dates of fossil lineages can be quantified using a variety of indices. Good matching is a prerequisite for the accurate time calibration of trees, while the distribution of congruence indices across large samples of cladograms has underpinned claims about temporal and taxonomic patterns of completeness in the fossil record. The most widely used stratigraphic congruence indices are the stratigraphic consistency index (SCI), the modified Manhattan stratigraphic measure (MSM*), and the gap excess ratio (GER) (plus its derivatives; the topological GER and the modified GER). Many factors are believed to variously bias these indices, with several empirical and simulation studies addressing some subset of the putative interactions. This study combines both approaches to quantify the effects (on all five indices) of eight variables reasoned to constrain the distribution of possible values (the number of taxa, tree balance, tree resolution, range of first occurrence (FO) dates, center of gravity of FO dates, the variability of FO dates, percentage of extant taxa, and percentage of taxa with no fossil record). Our empirical data set comprised 647 published animal and plant cladograms spanning the entire Phanerozoic, and for these data we also modeled the effects of mean age of FOs (as a proxy for clade age), the taxonomic rank of the clade, and the higher taxonomic group to which it belonged. The center of gravity of FO dates had not been investigated hitherto, and this was found to correlate most strongly with some measures of stratigraphic congruence in our empirical study (top-heavy clades had better congruence). The modified GER was the index least susceptible to bias. We found significant differences across higher taxa for all indices; arthropods had lower congruence and tetrapods higher congruence. Stratigraphic congruence—however measured—also varied throughout the Phanerozoic, reflecting the taxonomic composition of our sample. Notably, periods containing a high proportion of arthropods had poorer congruence overall than those with higher proportions of tetrapods. [Fossil calibration; gap excess ratio; manhattan stratigraphic metric; molecular clocks; stratigraphic congruence.]

New species of fossil oribatid mites (Acariformes, Oribatida), from the Lower Cretaceous amber of Spain

Mites are relatively common and diverse in fossiliferous ambers, but remain essentially unstudied. Here, we report on five new oribatid fossil species from Lower Cretaceous Spanish amber, including representatives of three superfamilies, and five families of the Oribatida. Hypovertex hispanicus sp. nov. and Tenuelamellarea estefaniae sp. nov. are described from amber pieces discovered in the San Just outcrop (Teruel Province). This is the first time fossil oribatid mites have been discovered in the El Soplao outcrop (Cantabria Province) and, here, we describe the following new species: Afronothrus ornosae sp. nov., Nothrus vazquezae sp. nov., and Platyliodes sellnicki sp. nov. The taxa are discussed in relation to other fossil lineages of Oribatida as well as in relation to their modern counterparts. Some of the inclusions were imaged using confocal laser scanning microscopy, demonstrating the potential of this technique for studying fossil mites in amber. A table, including all the known Mesozoic oribatid mites preserved in amber, is included.

A palaeontological case study for species delimitation in diverging fossil lineages

A general lineage concept is widely adopted in studies of species delimitation for extant taxa with DNA sequence data. In the general lineage concept, species are separately evolving metapopulations that acquire sets of properties during the process of speciation. Murine rodents from the Miocene Siwalik Group of Pakistan have an excellent fossil record showing temporal trends of morphological change, and are therefore ideal to observe the process of lineage divergence as fossil evidence. Here, we review the evolution of Siwalik murine rodents in the sense of the general lineage concept and draw lines of evidence for lineage separation. For currently available datasets, we applied the initial split criterion as well as three operational criteria (phenetic, diagnosable and ecological properties). In early Siwalik murine rodents, the acquisition of distinct phenetic properties emerges subsequent to the event of the evolutionary split. The phenetic evidence occurs closer in time to ‘true’ divergence, while distinct diagnosable and ecological properties fully arise later. Within a sequence of time-controlled samples, these observations explicitly show that phenetic properties (here, shape data and a combination of linear measurements) more precisely delimit the divergence of fossil species than does the fixation of diagnostic properties.

Specialised emission pattern of leaf trace in a late Permian (253 million-years old) conifer.

Leaf traces are important structures in higher plants that connect leaves and the stem vascular system. The anatomy and emission pattern of leaf traces are well studied in extant vascular plants, but remain poorly understood in fossil lineages. We quantitatively analysed the leaf traces in the late Permian conifer Ningxiaites specialis from Northwest China based on serial sections through pith, primary and secondary xylems. A complete leaf traces emission pattern of a conifer is presented for the first time from the late Palaeozoic. Three to five monarch leaf traces are grouped in clusters, arranged in a helical phyllotaxis. The leaf traces in each cluster can be divided into upper, middle and lower portions, and initiate at the pith periphery and cross the wood horizontally. The upper leaf trace increases its diameter during the first growth increment and then diminishes completely, which indicates leaf abscission at the end of the first year. The middle trace immediately bifurcates once or twice to form two or three vascular bundles. The lower trace persists as a single bundle during its entire length. The intricate leaf trace dynamics indicates this fossil plant had a novel evolutionary habit by promoting photosynthetic capability for the matured plant.

Phylogenetic analysis of molecular and morphological data highlights uncertainty in the relationships of fossil and living species of Elopomorpha (Actinopterygii: Teleostei)

Elopomorpha is one of the three main clades of living teleost fishes and includes a range of disparate lineages including eels, tarpons, bonefishes, and halosaurs. Elopomorphs were among the first groups of fishes investigated using Hennigian phylogenetic methods and continue to be the object of intense phylogenetic scrutiny due to their economic significance, diversity, and crucial evolutionary status as the sister group of all other teleosts. While portions of the phylogenetic backbone for Elopomorpha are consistent between studies, the relationships among Albula, Pterothrissus, Notacanthiformes, and Anguilliformes remain contentious and difficult to evaluate. This lack of phylogenetic resolution is problematic as fossil lineages are often described and placed taxonomically based on an assumed sister group relationship between Albula and Pterothrissus. In addition, phylogenetic studies using morphological data that sample elopomorph fossil lineages often do not include notacanthiform or anguilliform lineages, potentially introducing a bias toward interpreting fossils as members of the common stem of Pterothrissus and Albula. Here we provide a phylogenetic analysis of DNA sequences sampled from multiple nuclear genes that include representative taxa from Albula, Pterothrissus, Notacanthiformes and Anguilliformes. We integrate our molecular dataset with a morphological character matrix that spans both living and fossil elopomorph lineages. Our results reveal substantial uncertainty in the placement of Pterothrissus as well as all sampled fossil lineages, questioning the stability of the taxonomy of fossil Elopomorpha. However, despite topological uncertainty, our integration of fossil lineages into a Bayesian time calibrated framework provides divergence time estimates for the clade that are consistent with previously published age estimates based on the elopomorph fossil record and molecular estimates resulting from traditional node-dating methods.

The impact of shifts in marine biodiversity hotspots on patterns of range evolution: Evidence from the Holocentridae (squirrelfishes and soldierfishes).

One of the most striking biodiversity patterns is the uneven distribution of marine species richness, with species diversity in the Indo-Australian Archipelago (IAA) exceeding all other areas. However, the IAA formed fairly recently, and marine biodiversity hotspots have shifted across nearly half the globe since the Paleogene. Understanding how lineages have responded to shifting biodiversity hotspots represents a necessary historic perspective on the formation and maintenance of global marine biodiversity. Such evolutionary inferences are often challenged by a lack of fossil evidence that provide insights into historic patterns of abundance and diversity. The greatest diversity of squirrelfishes and soldierfishes (Holocentridae) is in the IAA, yet these fishes also represent some of the most numerous fossil taxa in deposits of the former West Tethyan biodiversity hotspot. We reconstruct the pattern of holocentrid range evolution using time-calibrated phylogenies that include most living species and several fossil lineages, demonstrating the importance of including fossil species as terminal taxa in ancestral area reconstructions. Holocentrids exhibit increased range fragmentation following the West Tethyan hotspot collapse. However, rather than originating within the emerging IAA hotspot, the IAA has acted as a reservoir for holocentrid diversity that originated in adjacent regions over deep evolutionary time scales.

Revision of the fossil rodent Acaremys Ameghino, 1887 (Hystricognathi, Octodontoidea, Acaremyidae) from the Miocene of Patagonia (Argentina) and the description of a new acaremyid

Within South American rodents, the Acaremyidae is an independent fossil lineage of octodontoids represented in the late Oligocene–middle Miocene of Patagonia. Acaremys is represented by six species recorded in the early Miocene, which have not been re-studied since their original description. Morphological and phylogenetic analyses suggest that Acaremys is paraphyletic. Three species are valid, Acaremysmurinus, Acaremysmajor, and Acaremysmessor. Acaremyskaraikensis is a junior synonym of Acaremysmurinus. ‘Acaremys’ tricarinatus is excluded from the genus being closely related to Sciamys. The new species, Pseudoacaremys kramarzi, is closely related to ‘Acaremys’ tricarinatus and Sciamys. ‘Acaremys’ preminutus is excluded from the family being closely related to the early Miocene Protacaremys prior, or living octodontoids. The phylogenetic analysis demonstrated that Acaremyidae includes Platypittamys, Galileomys, Acaremys, Pseudoacaremys and Sciamys. The new acaremyid increases the diversity of extinct octodontoids and added a new evolutionary lineage within Acaremyidae. The evolutionary history of the superfamily suggests that the hypsodonty and the consequently occlusal simplification evolved twice within Octodontoidea: in Acaremyidae and in Octodontidae. In addition, the cladistic analysis confirmed that most character ambiguities are due to missing data, and hence, it is essential to find better remains to elucidate the relationships among acaremyids.

Current status of the systematics and evolutionary biology of Grylloblattidae (Grylloblattodea)

Current status of the systematics and evolutionary biology of <scp>G</scp>rylloblattidae (<scp>G</scp>rylloblattodea)

Evolutionary Modes within Fossil Lineages: An Expanded Survey

Evolutionary Modes within Fossil Lineages: An Expanded Survey

Inclusion of a near‐complete fossil record reveals speciation‐related molecular evolution

Summary The rate of genetic evolution is often too variable among lineages to be explained by a strict molecular clock, prompting alternative ecological and evolutionary hypotheses to explain this rate heterogeneity. One controversial hypothesis is that speciation provokes a burst of rapid genetic change, giving molecular evolution a punctuational component. The amount of root‐to‐tip genetic change therefore tends to increase with the number of identified speciation events (nodes) along the root‐to‐tip path in molecular phylogenies. The controversy arises because nodes on molecular phylogenies can typically only be counted if both descendants are extant. Here, using stratigraphic, phylogenetic and ecological data from the exceptional fossil record of Cenozoic macroperforate planktonic foraminifera, we test whether among‐lineage rate heterogeneity is explained by ecological factors (abundance, life history and environment) and by the numbers of speciation events according to fossil lineage, fossil morphospecies and molecular species concepts. The number of nodes between root and tips on the fossil lineage phylogeny was a statistically significant correlate of the rate of molecular evolution over the same root‐to‐tip path. The speciation counts from other species concepts and hypothesized ecological drivers had considerably less support. Our results showcase how the fossil record contains signals of biological processes that drive genetic evolution, justifying calls to further marry fossil and molecular data when studying macroevolution over geological time‐scales.

Ecomorphology of Mammalian Fossil Lineages: Identifying Morphotypes in a Case Study of Endemic South American Ungulates

The notoungulates are one major clade of extinct native South American ungulate mammals. Several notoungulate morphotypes have been proposed by comparison with mammals from other large land masses, representing instances of convergent evolution in continental isolation. As with other entirely fossil lineages, the reconstruction of their functional biology is challenging, one major obstacle being the fragmentary and distorted nature of the fossil remains for which application of conventional quantitative data analysis techniques is compromised. Here we explored the patterns in morphospace of representatives of all notoungulate families on the basis of the qualitative scoring of 31 cranial characters that provided a basic description of shape and an approximation to sensory and mechanical functions of the skull. We calculated pairwise distances between all taxa with an index that proportionally corrected overall similarity by both character number and dissimilarities. The distances were used to generate a morphospace with a multivariate technique, Principal Coordinates Analysis. We recovered a tight group of basal Paleocene-Eocene notoungulates and a scattered group of Oligocene and Neogene forms. Lines drawn in that space connecting successive sister terminals clearly showed a departure from basal genera toward four diverging, previously proposed morphotypes, namely rabbit-, large-rodent-, small-horse-, and rhino-like forms. An extensive analysis identified the character basis of these morphotypes. Mapping additional information such as body size and degree of hypsodonty effectively aided in the interpretation of notoungulate morphofunctional evolution. We briefly discuss the utility of the qualitative morphospace as a tool for exploring the ecomorphology of fossil lineages and the evolutionary implications of this reconstruction.

A simple method for estimating informative node age priors for the fossil calibration of molecular divergence time analyses.

Molecular divergence time analyses often rely on the age of fossil lineages to calibrate node age estimates. Most divergence time analyses are now performed in a Bayesian framework, where fossil calibrations are incorporated as parametric prior probabilities on node ages. It is widely accepted that an ideal parameterization of such node age prior probabilities should be based on a comprehensive analysis of the fossil record of the clade of interest, but there is currently no generally applicable approach for calculating such informative priors. We provide here a simple and easily implemented method that employs fossil data to estimate the likely amount of missing history prior to the oldest fossil occurrence of a clade, which can be used to fit an informative parametric prior probability distribution on a node age. Specifically, our method uses the extant diversity and the stratigraphic distribution of fossil lineages confidently assigned to a clade to fit a branching model of lineage diversification. Conditioning this on a simple model of fossil preservation, we estimate the likely amount of missing history prior to the oldest fossil occurrence of a clade. The likelihood surface of missing history can then be translated into a parametric prior probability distribution on the age of the clade of interest. We show that the method performs well with simulated fossil distribution data, but that the likelihood surface of missing history can at times be too complex for the distribution-fitting algorithm employed by our software tool. An empirical example of the application of our method is performed to estimate echinoid node ages. A simulation-based sensitivity analysis using the echinoid data set shows that node age prior distributions estimated under poor preservation rates are significantly less informative than those estimated under high preservation rates.