Molecular distance and divergence time in carnivores and primates

Numerous studies have used indices of genetic distance between species to reconstruct evolutionary relationships and to estimate divergence time. However, the empirical relationship between molecular-based indices of genetic divergence and divergence time based on the fossil record is poorly known. To date, the results of empirical studies conflict and are difficult to compare because they differ widely in their choice of taxa, genetic techniques, or methods for calibrating rates of molecular evolution. We use a single methodology to analyze the relationship of molecular distance and divergence time in 86 taxa (72 carnivores and 14 primates). These taxa have divergence times of 0.01-55 Myr and provide a graded series of phylogenetic divergences such that the shape of the curve relating genetic distance and divergence time is often well defined. The techniques used to obtain genetic distance estimates include one- and two-dimensional protein electrophoresis, DNA hybridization, and microcomplement fixation. Our results suggest that estimates of molecular distance and divergence time are highly correlated. However, rates of molecular evolution are not constant; rather, in general they decline with increasing divergence time in a linear fashion. The rate of decline may differ according to technique and taxa. Moreover, in some cases the variability in evolutionary rates changes with increasing divergence time such that the accuracy of nodes in a phylogenetic tree varies predictably with time.     

Phylogenetic relationships and divergence time estimate of African anguilliform catfish (Siluriformes: Clariidae) inferred from ribosomal gene and spacer sequences

The catfish family Clariidae comprises species in which the body shape ranges from fusiform to anguilliform. Recent studies have shown that this body elongation is the result of convergent evolution. This paper aims to study the evolution towards anguilliformity in a phylogenetic framework. Sequences of 29 taxa were analyzed using the neighbor-joining, maximum-likelihood, maximum-parsimony, and Bayesian inference algorithms and the parsimony algorithm in POY. The study yields phylogenetic hypotheses showing well-supported clades. Anguilliformity appears to have arisen at least four times, each time having a sister group relation with a fusiform Clarias-like ancestor. Divergence time estimation indicates that the African Clariidae started radiating between 123 and 56 My ago.     

Correlates of body mass evolution in primates

Body mass is undoubtedly central to the overall adaptive profile of any organism. Despite this, very little is known of what forces drive evolutionary changes in body mass and, consequently, shape patterns of body mass distribution exhibited by animal radiations. The search for factors that may influence evolutionary processes in general frequently focuses on environmental parameters such as climate change or interspecific competition. With respect to body mass, there is also the suggestion that evolutionary lineages may follow an inherent trend toward increased body mass, known as Cope's rule. The present paper investigates whether overall directional trends of body mass change, or correlations between patterns of body mass evolution and environmental factors have influenced the evolution of body mass in plesiadapiforms and primates. Analyses of the global fossil record of plesiadapiforms and primates suggest that the former did indeed follow an overall trend toward increased body mass compatible with the predictions of Cope's rule. In contrast, neither primates as a whole, nor a number of individual primate radiations (Adapiformes, Omomyiformes, and Anthropoidea), show any indication of overall directional patterns of body mass change. No correlations of primate body mass change with either the latitudinal distribution of fossil species, or with estimates of global temperature trends, were found. There is evidence, however, that direct competition between omomyiforms and adapiforms (the two main primate radiations known from the Paleogene) influenced processes of body mass evolution in omomyiforms.     

Exceptional avian herbivores: multiple transitions toward herbivory in the bird order Anseriformes and its correlation with body mass

Herbivory is rare among birds and is usually thought to have evolved predominately among large, flightless birds due to energetic constraints or an association with increased body mass. Nearly all members of the bird order Anseriformes, which includes ducks, geese, and swans, are flighted and many are predominately herbivorous. However, it is unknown whether herbivory represents a derived state for the order and how many times a predominately herbivorous diet may have evolved. Compiling data from over 200 published diet studies to create a continuous character for herbivory, models of trait evolution support at least five independent transitions toward a predominately herbivorous diet in Anseriformes. Although a nonphylogenetic correlation test recovers a significant positive correlation between herbivory and body mass, this correlation is not significant when accounting for phylogeny. These results indicate a lack of support for the hypothesis that a larger body mass confers an advantage in the digestion of low‐quality diets but does not exclude the possibility that shifts to a more abundant food source have driven shifts toward herbivory in other bird lineages. The exceptional number of transitions toward a more herbivorous diet in Anseriformes and lack of correlation with body mass prompts a reinterpretation of the relatively infrequent origination of herbivory among flighted birds.     

The tempo of genetic evolution in birds: body mass and climate effects

Aim Negative relationships between body mass and substitution rates have previously been reported. However, most of these studies have involved contrasted taxa that, due to their highly divergent phylogenetic histories, also differ in many additional characteristics other than mass. In particular, there has been little examination of the potentially confounding effects of climate or population size. Here we test for differences in rates of microevolution among bird species that, although differing in mass, are nonetheless very closely related phylogenetic pairs. We additionally tested for latitudinal/elevational and population size effects across these contrasts. Location Global. Methods The tempo of microevolution within the cytochrome b gene of mitochondrial DNA was compared between closely related bird species that differed in body mass, using 130 phylogenetically independent species pairs. In order to minimize climate effects, pairs not having overlapping latitudinal ranges were discarded. In addition, a subset of pairs was identified and analysed that involved comparisons between species that have different latitudinal or elevational midpoints. Results Species with smaller mass had substitution rates marginally faster than those with larger mass (small : large median ratio = 1.05). However, this result was only statistically significant when data were pruned to eliminate comparisons in which population or range size also varied substantially between contrasted species. Latitude and elevation had a much stronger association with substitution rates than body mass within the subset of pairs (n = 30) that also differed in their spatial distributions: lower elevation or latitude species had substantially more substitutions than those at higher latitudes or elevations (low : high ratio = 1.35). Furthermore, when the dataset was pruned of pairs in which body mass was confounded by latitude or elevation, the body mass effect was eliminated. Main conclusions Body mass is known to correlate with latitude, so that the latitudinal/elevational association with microevolution we found might either be additive to, or causal of, the body mass effect. These results are consistent with the evolutionary speed hypothesis, which suggests that latitudinal diversity gradients derive from variation in the rate of microevolution. Our findings also serve to raise concerns about biogeographical studies that use genetic distances between taxa to estimate time since divergence.     

A longirostrine tyrannosauroid from the Early Cretaceous of China

The fossil record of tyrannosauroid theropods is marked by a substantial temporal and morphological gap between small-bodied, Barremian taxa, and extremely large-bodied taxa from the latest Cretaceous. Here we describe a new tyrannosauroid, Xiongguanlong baimoensis n. gen. et sp., from the Aptian–Albian Xinminpu Group of western China that represents a phylogenetic, morphological, and temporal link between these disjunct portions of tyrannosauroid evolutionary history. Xiongguanlong is recovered in our phylogenetic analysis as the sister taxon to Tyrannosauridae plus Appalachiosaurus, and marks the appearance of several tyrannosaurid hallmark features, including a sharp parietal sagittal crest, a boxy basicranium, a quadratojugal with a flaring dorsal process and a flexed caudal edge, premaxillary teeth bearing a median lingual ridge, and an expanded axial neural spine surmounted by distinct processes at its corners. Xiongguanlong is characterized by a narrow and elongate muzzle resembling that of Alioramus. The slender, unornamented nasals of Xiongguanlong are inconsistent with recent hypotheses of correlated progression in tyrannosauroid feeding mechanics, and suggest more complex patterns of character evolution in the integration of feeding adaptations in tyrannosaurids. Body mass estimates for the full-grown holotype specimen of Xiongguanlong fall between those of Late Cretaceous tyrannosaurids and Barremian tyrannosauroids, suggesting that the trend of increasing body size observed in North American Late Cretaceous Tyrannosauridae may extend through the Cretaceous history of Tyrannosauroidea though further phylogenetic work is required to corroborate this.     

Colonization and diversification of Galápagos terrestrial fauna: a phylogenetic and biogeographical synthesis

Remote oceanic islands have long been recognized as natural models for the study of evolutionary processes involved in diversification. Their remoteness provides opportunities for isolation and divergence of populations, which make islands remarkable settings for the study of diversification. Groups of islands may share a relatively similar geological history and comparable climate, but their inhabitants experience subtly different environments and have distinct evolutionary histories, offering the potential for comparative studies. A range of organisms have colonized the Galápagos Islands, and various lineages have radiated throughout the archipelago to form unique assemblages. This review pays particular attention to molecular phylogenetic studies of Galápagos terrestrial fauna. We find that most of the Galápagos terrestrial fauna have diversified in parallel to the geological formation of the islands. Lineages have occasionally diversified within islands, and the clearest cases occur in taxa with very low vagility and on large islands with diverse habitats. Ecology and habitat specialization appear to be critical in speciation both within and between islands. Although the number of phylogenetic studies is continuously increasing, studies of natural history, ecology, evolution and behaviour are essential to completely reveal how diversification proceeded on these islands.     

Mitochondrial genomic investigation of flatfish monophyly

We present the first study to use whole mitochondrial genome sequences to examine phylogenetic affinities of the flatfishes (Pleuronectiformes). Flatfishes have attracted attention in evolutionary biology since the early history of the field because understanding the evolutionary history and patterns of diversification of the group will shed light on the evolution of novel body plans. Because recent molecular studies based primarily on DNA sequences from nuclear loci have yielded conflicting results, it is important to examine phylogenetic signal in different genomes and genome regions. We aligned and analyzed mitochondrial genome sequences from thirty-nine pleuronectiforms including nine that are newly reported here, and sixty-six non-pleuronectiforms (twenty additional clade L taxa [Carangimorpha or Carangimorpharia] and forty-six secondary outgroup taxa). The analyses yield strong support for clade L and weak support for the monophyly of Pleuronectiformes. The suborder Pleuronectoidei receives moderate support, and as with other molecular studies the putatively basal lineage of Pleuronectiformes, the Psettodoidei is frequently not most closely related to other pleuronectiforms. Within the Pleuronectoidei, the basal lineages in the group are poorly resolved, however several flatfish subclades receive consistent support. The affinities of Lepidoblepharon and Citharoides among pleuronectoids are particularly uncertain with these data.     

Directional evolution of stockiness coevolves with ecology and locomotion in lizards

Although studied in many taxa, directional macroevolution remains difficult to detect and quantify. We present an approach for detecting directional evolution in subclades of species when relatively few species are sampled, and apply it to studying the evolution of stockiness in Phrynosomatine lizards. Our approach is more sensitive to detecting the tempo of directional evolution than other available approaches. We use ancestral reconstruction and phylogenetic mapping of morphology to characterize the direction and magnitude of trait evolution. We demonstrate a directional trend toward stockiness in horned lizards, but not their sister groups, finding that stockier species tend to have relatively short and wide bodies, and relatively short heads, tails, and limbs. Ornstein–Uhlenbeck models show that the directional trend in horned lizards is due to a shift in selective regime and stabilizing selection as opposed to directional selection. Bayesian evolutionary correlation analyses indicate that stockier species run more slowly and eat a larger proportion of ants. Furthermore, species with larger horns tend to be slower and more ant-specialized. Directional evolution toward a stocky body shape has evolved in conjunction with changes in a suite of traits, representing a complex example of directional macroevolution.     

THE EVOLUTIONARY HISTORY OF CETACEAN BRAIN AND BODY SIZE

Cetaceans rival primates in brain size relative to body size and include species with the largest brains and biggest bodies to have ever evolved. Cetaceans are remarkably diverse, varying in both phenotypes by several orders of magnitude, with notable differences between the two extant suborders, Mysticeti and Odontoceti. We analyzed the evolutionary history of brain and body mass, and relative brain size measured by the encephalization quotient (EQ), using a data set of extinct and extant taxa to capture temporal variation in the mode and direction of evolution. Our results suggest that cetacean brain and body mass evolved under strong directional trends to increase through time, but decreases in EQ were widespread. Mysticetes have significantly lower EQs than odontocetes due to a shift in brain:body allometry following the divergence of the suborders, caused by rapid increases in body mass in Mysticeti and a period of body mass reduction in Odontoceti. The pattern in Cetacea contrasts with that in primates, which experienced strong trends to increase brain mass and relative brain size, but not body mass. We discuss what these analyses reveal about the convergent evolution of large brains, and highlight that until recently the most encephalized mammals were odontocetes, not primates.     

Cope's rule in cryptodiran turtles: do the body sizes of extant species reflect a trend of phyletic size increase?

Cope's rule of phyletic size increase is questioned as a general pattern of body size evolution. Most studies of Cope's rule have examined trends in the paleontological record. However, neontological approaches are now possible due to the development of model-based comparative methods, as well as the availability of an abundance of phylogenetic data. I examined whether the phylogenetic distribution of body sizes in extant cryptodiran turtles is consistent with Cope's rule. To do this, I examined body size evolution in each of six major clades of cryptodiran turtles and also across the whole tree of cryptodirans (n = 201 taxa). Extant cryptodiran turtles do not appear to follow Cope's rule, as no clade showed a significant phyletic body size trend. Previous analyses in other extant vertebrates have also found no evidence for phyletic size increase, which is in contrast to the paleontological data that support the rule in a number of extinct vertebrate taxa.     

Cope's rule in the Ordovician trilobite family Asaphidae (order Asaphida): patterns across multiple most parsimonious trees

Cope's rule defines lineages that trend towards an increase in body size through geological time. The trilobite family Asaphidae is one of the most diverse of the class Trilobita and ranges from the Upper Cambrian through to the Upper Ordovician. The group is one trilobite clades that displays a large size range and contains several of the largest trilobite species. Reduced major axis correlations between the lengths of cephala and pygidia and the total sagittal length of complete individuals have high support and were used to standardise all incomplete specimens to total axial length. Phylogenetic studies into Cope's rule tend to use supertrees, composite trees or a single tree selected through a fit criterion. Here, for the first time, all trees recovered from a maximum parsimony analysis were analysed equally. Maximum likelihood was used to fit four evolutionary models: random walk, directional, Ornstein–Uhlenbeck (evolution towards an adaptive optimum) and stasis. These were compared equally using Akaike weights. Fitting of evolutionary models by maximum likelihood supports stasis as consistently the most likely model across all trees with low support for directionality.     

The age and phylogeny of wood boring weevils and the origin of subsociality

A large proportion of the hyperdiverse weevils are wood boring and many of these taxa have subsocial family structures. The origin and relationship between certain wood boring weevil taxa has been problematic to solve and hypotheses on their phylogenies change substantially between different studies. We aimed at testing the phylogenetic position and monophyly of the most prominent wood boring taxa Scolytinae, Platypodinae and Cossoninae, including a range of weevil outgroups with either the herbivorous or wood boring habit. Many putatively intergrading taxa were included in a broad phylogenetic analysis for the first time in this study, such as Schedlarius, Mecopelmus, Coptonotus, Dactylipalpus, Coptocorynus and allied Araucariini taxa, Dobionus, Psepholax, Amorphocerus-Porthetes, and some peculiar wood boring Conoderini with bark beetle behaviour. Data analyses were based on 128 morphological characters, rDNA nucleotides from the D2-D3 segment of 28S, and nucleotides and amino acids from the protein encoding gene fragments of CAD, ArgK, EF-1α and COI. Although the results varied for some of the groups between various data sets and analyses, one may conclude the following from this study: Scolytinae and Platypodinae are likely sister lineages most closely related to Coptonotus; Cossoninae is monophyletic (including Araucariini) and more distantly related to Scolytinae; Amorphocerini is not part of Cossoninae and Psepholax may belong to Cryptorhynchini. Likelihood estimation of ancestral state reconstruction of subsociality indicated five or six origins as a conservative estimate. Overall the phylogenetic results were quite dependent on morphological data and we conclude that more genetic loci must be sampled to improve phylogenetic resolution. However, some results such as the derived position of Scolytinae were consistent between morphological and molecular data. A revised time estimation of the origin of Curculionidae and various subfamily groups were made using the recently updated fossil age of Scolytinae (100 Ma), which had a significant influence on node age estimates.     

Giant lizards occupied herbivorous mammalian ecospace during the Paleogene greenhouse in Southeast Asia

Mammals dominate modern terrestrial herbivore ecosystems, whereas extant herbivorous reptiles are limited in diversity and body size. The evolution of reptile herbivory and its relationship to mammalian diversification is poorly understood with respect to climate and the roles of predation pressure and competition for food resources. Here, we describe a giant fossil acrodontan lizard recovered with a diverse mammal assemblage from the late middle Eocene Pondaung Formation of Myanmar, which provides a historical test of factors controlling body size in herbivorous squamates. We infer a predominately herbivorous feeding ecology for the new acrodontan based on dental anatomy, phylogenetic relationships and body size. Ranking body masses for Pondaung Formation vertebrates indicates that the lizard occupied a size niche among the larger herbivores and was larger than most carnivorous mammals. Paleotemperature estimates of Pondaung Formation environments based on the body size of the new lizard are approximately 2–5°C higher than modern. These results indicate that competitive exclusion and predation by mammals did not restrict body size evolution in these herbivorous squamates, and elevated temperatures relative to modern climates during the Paleogene greenhouse may have resulted in the evolution of gigantism through elevated poikilothermic metabolic rates and in response to increases in floral productivity.     

Phylogeny of the mega-diverse Gelechioidea (Lepidoptera): adaptations and determinants of success

The Gelechioidea, with 18,000 described and many more unnamed species ranks among the most diverse lepidopteran superfamilies. Nevertheless, their taxonomy has remained largely unresolved, and phylogenetic affinities among gelechioid families and lower taxa have been insufficiently understood. We constructed, for the first time, a comprehensive molecular phylogeny for the Gelechioidea. We sampled seven genes, in total 5466 base pairs, of 109 gelechioid taxa representing 32 of 37 recognized subfamilies, and two outgroup taxa. We used maximum likelihood methods and Bayesian inference to construct phylogenetic trees. We found that the families Autostichidae, Lecithoceridae, Xyloryctidae, and Oecophoridae s. str., in this order, are the most basally arising clades. Elachistidae s. l. was found to be paraphyletic, with families such as Gelechiidae and Cosmopterigidae nested within it, and Parametriotinae associated with several families previously considered unrelated to them. Using the phylogenetic trees, we examined patterns of life history evolution and determinants of the success of different lineages. Gelechioids express unusually wide variability in life-history strategies, including herbivorous, saprophagous, fungivorous, and carnivorous lineages. Most species are highly specialized in diet and other life history traits. The results suggest that either saprophagy was the ancestral feeding strategy from which herbivory evolved independently on multiple occasions, or that the ancestor was herbivorous with repeated origins of saprophagy. External feeding is an ancestral trait from which internal feeding evolved independently several times. In terms of species number, saprophages are dominant in Australia, while elsewhere several phytophagous lineages have extensively specialized and diversified. Internal feeding has remained a somewhat less generally adopted feeding mode, although in a few lineages significant radiations of leaf mining species have occurred. We conclude that diverse feeding modes, specialization among saprophages, repeated shifts to phytophagy, and a generally high specialization rate on single plant species (monophagy) are the major factors behind the success of the Gelechioidea.     

Flies on thistles: support for synchronous speciation?

Synchronous speciation of hosts and herbivorous insects predicts a congruent topology of host and insect phylogenies and similar evolutionary ages of host and insect taxa. To test these predictions for the specialized herbivorous fly genus Urophora (Diptera: Tephritidae), we used three different approaches. (i) We generated a phylogenetic tree of 11 European Urophora species from allozyme data and constructed a phylogeny of their hosts from published sources. Superimposing the Urophora tree on the host-plant tree we found no evidence for general congruence. (ii) We correlated genetic distances (Nei distances) of the host plants vs. the genetic distances of associated Urophora species. Overall, the relationship was not positive. Nevertheless, for some pairs of Urophora species and host plants genetic distances were in the same order of magnitude. (iii) We collected allozyme data for pairs of thistle taxa and pairs of herbivores on thistles together with independent time estimates. With these data we calibrated a molecular clock. There was a non-linear relationship between phylogenetic age and genetic distance, rendering the dating of deep events in thistle–insect evolution difficult. Nevertheless the derived molecular clock showed that the split of insect taxa lagged behind the split of hosts.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 775–783.     

Body Size Evolution in Extant Oryzomyini Rodents: Cope's Rule or Miniaturization?

At the macroevolutionary level, one of the first and most important hypotheses that proposes an evolutionary tendency in the evolution of body sizes is "Cope's rule". This rule has considerable empirical support in the fossil record and predicts that the size of species within a lineage increases over evolutionary time. Nevertheless, there is also a large amount of evidence indicating the opposite pattern of miniaturization over evolutionary time. A recent analysis using a single phylogenetic tree approach and a bayesian based model of evolution found no evidence for Cope's rule in extant mammal species. Here we utilize a likelihood-based phylogenetic method, to test the evolutionary trend in body size, which considers phylogenetic uncertainty, to discern between Cope's rule and miniaturization, using extant Oryzomyini rodents as a study model. We evaluated body size trends using two principal predictions: (a) phylogenetically related species are more similar in their body size, than expected by chance; (b) body size increased (Cope's rule)/decreased (miniaturization) over time. Consequently the distribution of forces and/or constraints that affect the tendency are homogenous and generate this directional process from a small/large sized ancestor. Results showed that body size in the Oryzomyini tribe evolved according to phylogenetic relationships, with a positive trend, from a small sized ancestor. Our results support that the high diversity and specialization currently observed in the Oryzomyini tribe is a consequence of the evolutionary trend of increased body size, following and supporting Cope's rule.     

Combinatorial model for the formation of body plans in higher metazoan taxa: Paleontological insight

The body plans of higher metazoan taxa were formed during a short time (on the geological time scale) by combination of the previously developed characters. The combinations were realized as a result of manifestation of latent characters in adults through various heterochronies. This resulted in mosaic evolution and concealment of intermediate forms. Many characters of new body plans appeared in the ancestral taxon and their various combinations in the newly established taxa formed the archaic diversity. The maximum rank of newly appearing higher taxa decreased with geological time. The evolution of metazoans passed from the development of the general body plan to less significant details and appearance of body plans describing taxa of lower ranks. New body plans of higher taxa were superposed on the old body plan rather than replaced it, extending with time the subordination of body plans and respective hierarchy of taxa. Aromorphoses are always connected with the appearance of a new body plan. The appearance of new taxa and an increase in morphological diversity mostly occurred at certain boundaries in the development of the biota, which were connected with a sharp increase in the previously limited resources.     

Body size effects and rates of cytochrome b evolution in tube-nosed seabirds

Variation in rates of molecular evolution now appears to be widespread. The demonstration that body size is correlated with rates of molecular evolution suggests that physiological and ecological factors may be involved in molecular rate variation, but large-scale comparative studies are still lacking. Here, we use complete cytochrome b sequences from 85 species of tube-nosed seabirds (order Procellariiformes) and 5 outgroup species of penguins (order Sphenisciformes) to test for an association between body mass and rates of molecular evolution within the former avian order. Cladistic analysis of the 90 sequences estimates a phylogeny largely consistent with the traditional taxonomy of the Procellariiformes. The Diomedeidae, Procellariidae, and Pelecanoididae are monophyletic, while the Hydrobatidae are basal and paraphyletic. However, the two subfamilies within the Hydrobatidae (Hydrobatinae and Oceanitinae) are monophyletic. A likelihood ratio test detects significant deviation from clocklike evolution in our data. Using a sign test for an association between body mass and branch length in the seabird phylogeny, we find that larger taxa tend to have shorter terminal branch lengths than smaller taxa. This observation suggests that rates of mitochondrial DNA evolution are slower for larger taxa. Rate calibrations based on the fossil record reveal concordant body size effects. We interpret these results as evidence for a metabolic rate effect, as the species in this order exhibit large differences in metabolic rates, which are known to be highly correlated with body mass in this group. Our results support previous findings of body size effects and show that this effect can be significant even within a single avian order. This suggests that even lineage-specific molecular clocks may not be tenable if calibrations involve taxa with different metabolic rates.      

Body length of bony fishes was not a selective factor during the biggest mass extinction of all time

The Permo‐Triassic mass extinction devastated life on land and in the sea, but it is not clear why some species survived and others went extinct. One explanation is that lineage loss during mass extinctions is a random process in which luck determines which species survive. Alternatively, a phylogenetic signal in extinction may indicate a selection process operating on phenotypic traits. Large body size has often emerged as an extinction risk factor in studies of modern extinction risk, but this is not so commonly the case for mass extinctions in deep time. Here, we explore the evolution of non‐teleostean Actinopterygii (bony fishes) from the Devonian to the present day, and we concentrate on the Permo‐Triassic mass extinction. We apply a variety of time‐scaling metrics to date the phylogeny, and show that diversity peaked in the latest Permian and declined severely during the Early Triassic. In line with previous evidence, we find the phylogenetic signal of extinction increases across the mass extinction boundary: extinction of species in the earliest Triassic is more clustered across phylogeny compared to the more randomly distributed extinction signal in the late Permian. However, body length plays no role in differential survival or extinction of taxa across the boundary. In the case of fishes, size did not determine which species survived and which went extinct, but phylogenetic signal indicates that the mass extinction was not a random field of bullets.