Iterative ontogenetic development of ammonoid conch shapes from the Devonian through to the Jurassic

We measured longitudinal growth in conch cross‐sections of 177 Devonian to Jurassic ammonoid species to test whether conch ontogenetic development parallels the iterative evolution of pachyconic or globular conch shapes. Ontogenetic trajectories of two cardinal conch parameters, conch width index and umbilical width index, show a few common recurring ontogenetic pathways in terms of the number of ontogenetic phases. The most common, with three phases in the conch width index (decrease–increase–decrease) and umbilical width index (increase–decrease–increase), is termed here C‐mode ontogeny (after the Carboniferous genus Cravenoceras). Many of the studied globular Palaeozoic and Triassic species (of the latter, particularly the arcestid ammonoids) share principal patterns in the triphasic C‐mode conch ontogeny in closely related groups but also between unrelated groups as well. The repetition of conch growth patterns is an example of convergent evolution of the entire life history of globular ammonoids. The studied Jurassic globular shaped ammonoids deviate from the growth patterns seen in earlier groups showing less pronounced ontogenetic trajectories with nearly isometric or weakly asymmetric growth without distinct phases. This trajectory is termed here M‐mode ontogeny (after the Jurassic genus Macrocephalites). No major change in the ontogenetic modes of pachyconic and globular ammonoids occurred moving from the Palaeozoic into the Mesozoic; the survivors of the end‐Permian extinction event iteratively developed conch ontogenies similar to those of Palaeozoic forms. In contrast, the Triassic–Jurassic boundary marks the major event with the evolution of some cardinal conch parameters relating to globular ammonoid ontogeny.     

Diversity dynamics of post‐Palaeozoic crinoids – in quest of the factors affecting crinoid macroevolution

Following the end‐Permian biotic crisis which led to the near extinction of crinoids, this echinoderm class rebounded rapidly during the Mesozoic, resulting in forms with important morphological and behavioural novelties. However, quantitative patterns of crinoid diversity during the Mesozoic remain largely unexplored. Here, we report results of analyses of the evolutionary dynamics of post‐Palaeozoic crinoid genera spanning a time interval between 250 and 70 Myr. We show that crinoids reached their Mesozoic peak of genus‐level richness during the Late Jurassic. We also document a major reorganization of different ecological crinoid groups in the Mesozoic. More specifically, the diversity of sessile forms generally increased towards the mid‐Mesozoic but decreased significantly starting in the Cretaceous, whereas the number of motile crinoid genera increased linearly during the Mesozoic. The possible role of biotic and abiotic factors in crinoid evolution is discussed.     

Permian–Triassic Osteichthyes (bony fishes): diversity dynamics and body size evolution

The Permian and Triassic were key time intervals in the history of life on Earth. Both periods are marked by a series of biotic crises including the most catastrophic of such events, the end‐Permian mass extinction, which eventually led to a major turnover from typical Palaeozoic faunas and floras to those that are emblematic for the Mesozoic and Cenozoic. Here we review patterns in Permian–Triassic bony fishes, a group whose evolutionary dynamics are understudied. Based on data from primary literature, we analyse changes in their taxonomic diversity and body size (as a proxy for trophic position) and explore their response to Permian–Triassic events. Diversity and body size are investigated separately for different groups of Osteichthyes (Dipnoi, Actinistia, ‘Palaeopterygii’, ‘Subholostei’, Holostei, Teleosteomorpha), within the marine and freshwater realms and on a global scale (total diversity) as well as across palaeolatitudinal belts. Diversity is also measured for different palaeogeographical provinces. Our results suggest a general trend from low osteichthyan diversity in the Permian to higher levels in the Triassic. Diversity dynamics in the Permian are marked by a decline in freshwater taxa during the Cisuralian. An extinction event during the end‐Guadalupian crisis is not evident from our data, but ‘palaeopterygians’ experienced a significant body size increase across the Guadalupian–Lopingian boundary and these fishes upheld their position as large, top predators from the Late Permian to the Late Triassic. Elevated turnover rates are documented at the Permian–Triassic boundary, and two distinct diversification events are noted in the wake of this biotic crisis, a first one during the Early Triassic (dipnoans, actinistians, ‘palaeopterygians’, ‘subholosteans’) and a second one during the Middle Triassic (‘subholosteans’, neopterygians). The origination of new, small taxa predominantly among these groups during the Middle Triassic event caused a significant reduction in osteichthyan body size. Neopterygii, the clade that encompasses the vast majority of extant fishes, underwent another diversification phase in the Late Triassic. The Triassic radiation of Osteichthyes, predominantly of Actinopterygii, which only occurred after severe extinctions among Chondrichthyes during the Middle–Late Permian, resulted in a profound change within global fish communities, from chondrichthyan‐rich faunas of the Permo‐Carboniferous to typical Mesozoic and Cenozoic associations dominated by actinopterygians. This turnover was not sudden but followed a stepwise pattern, with leaps during extinction events.     

Sinaspidoneura magnifica nov. gen., nov. sp., first Chinese Caloneurodea (Insecta: Archaeorthoptera)

We describe the first Chinese Caloneurodea, Sinaspidoneura magnifica nov. gen., nov. sp., from the middle Permian Yinping Formation. This new genus and species belongs to the small family Aspidoneuridae, previously known from two genera and species, one from the latest Carboniferous of France and another from the late early Permian of North America. This discovery shows that this order was more widespread during the middle Permian than previously supposed, under a great variety of palaeoclimates. This clade is still unknown in the late Permian, and possibly became extinct because of the crisis of biodiversity that happened at the end of the middle Permian.     

Why was there a delayed radiation after the end‐Palaeozoic extinctions?

Data from widespread dysaerobic facies, carbon/sulphur ratios and cerium anomalies suggest that the early Triassic was a time when anoxic conditions spread widely over epicontinental seas. These conditions, associated with marine transgression following the latest Permian regression, are likely to be a prime cause of the mass extinction of Palaeozoic marine faunas. The occurrence of many Lazarus taxa in the Middle and Upper Triassic indicates, however, that the extinctions at the end of the Permian were less severe than has been widely assumed, and that the turnover from Palaeozoic to Mesozoic faunas was considerably extended in time, being finally accomplished only after the end‐Triassic mass extinction event.     

Predatory asteroids and the decline of the articulate brachiopods

Various causes, such as increased predation pressure, the lack of planktotrophic larvae, a 'resetting' of diversity, increased competition from benthic molluscs and the decline of the Palaeozoic fauna, have been suggested to explain the failure of the brachiopods to reradiate following the Permo-Triassic mass extinction. Increased predation pressure has hitherto appeared improbable, because typical predators of brachiopods, such as teleostean fish, brachyuran crabs and predatory gastropods, did not undergo major radiation until the late Mesozoic and early Cenozoic. However, new evidence strongly suggests that one important group of predators of shelly benthic organisms, the asteroids, underwent a major radiation at the beginning of the Mesozoic. Although asteroids appeared in the early Ordovician, they remained a minor element of the marine benthos during the Palaeozoic acme of the brachiopods. However, these early asteroids lacked four important requirements for active predation on a bivalved epifauna: muscular arms (evolved in the early Carboniferous); suckered tube feet, a flexible mouth frame and an eversible stomach (all evolved in the early Triassic). Thus radiation of the Subclass Neoasteroidea coincided with both their improved feeding capability and the decline of the articulates. The asteroids were the only group of predators of brachiopods that underwent a major adaptive radiation in the earliest Mesozoic. The asteroids may therefore have contributed to inhibiting a Mesozoic reradiation of the brachiopods. Epifaunal species lacking a muscular pedicle may have been particularly vulnerable. Unlike bivalve molluscs, modern brachiopods show only a limited range of adaptations to discourage asteroid predation. □ Asteroidea, Brachiopoda, evolution, predation, functional morphology.     

Late paleozoic atmospheres and biotic evolution

The latter half of the Paleozoic era is marked by notable evolutionary advances, followed by the greatest of all mass extinctions and the subsequent establishment of Mesozoic‐Cenozoic faunas of very different aspect. Current models suggest marked changes in concentration of oxygen and carbon dioxide in the Paleozoic atmosphere. Atmospheric oxygen is thought to have increased from 15% in the mid‐Devonian to near 35% by the end of the Carboniferous, followed by a decline to 17% near the end of the Permian. Atmospheric carbon dioxide was near 0.5% in the early Paleozoic, declining to less than 0.3% in the Devonian, and then more steeply downward to a minimum near 0.04% at the end of the Carboniferous. The principal causes of these changes were the advent and expansion of land plants, deposition of carbonates and continental weathering. Notwithstanding quantitative uncertainties, it seems clear that a major pulse of high oxygen concentration and associated shifts in carbon dioxide characterized the late Paleozoic atmosphere. Atmospheres with such different compositions have markedly different physical characteristics. These changes have major implications for the physiologies of contemporary organisms. The fossil records of various taxa indicate dramatic changes in the biosphere that coincide in time with the inferred changes in composition of the atmosphere. Major changes in phenotype observed in numerous lineages of animals and plants, including accelerated radiations in fresh water and on the land, are inferred to have occurred in response to these changes in the atmosphere. The morphologies, physiologies, and inferred behavior of many organisms preserved in the fossil record are in good accord with expectations based on hyperoxic, low carbon dioxide conditions of the Carboniferous atmosphere and with a return to lower oxygen levels by the end of the Permian.     

Battenizyga, a new Early Triassic gastropod genus with a discussion of the caenogastropod evolution at the Permian/Triassic boundary

Battenizyga, a new Early Triassic gastropod genus from the Moenkopi Formation of Utah, is described and the speciesAnoptychia eotriassica Batten & Stokes, 1986 is placed in it. The new genus has an axially ribbed planktonic larval shell and a teleoconch with an angulated periphery. This character combination is unknown from the Palaeozoic. Therefore,Battenizyga represents additional evidence that recovery from the end-Permian mass extinction was connected with a faunal turnover. Additionally, the extinction of diverse Palaeozoic groups of the Caenogastropoda in the Permian (e.g., the Pseudozygopleuridae) suggest a turnover. All caenogastropod genera that hold Early Triassic species, have post-Palaeozoic type species and most were not reported from the Palaeozoic. This corroborates the view that there was an intense faunal turnover within the Caenogastropoda.Battenizyga is probably a caenogastropod that is closely related to the superfamily Zygopleuroidea which is abundant in the late Palaeozoic and early Mesozoic.      

A supertree of temnospondyli: cladogenetic patterns in the most species-rich group of early tetrapods

As the most diverse group of early tetrapods, temnospondyls provide a unique opportunity to investigate cladogenetic patterns among basal limbed vertebrates. We present five species-level supertrees for temnospondyls, built using a variety of methods. The standard MRP majority rule consensus including minority components shows slightly greater resolution than other supertrees, and its shape matches well several currently accepted hypotheses of higher-level phylogeny for temnospondyls as a whole. Also, its node support is higher than those of other supertrees (except the combined standard plus Purvis MRP supertree). We explore the distribution of significant as well as informative changes (shifts) in branch splitting employing the standard MRP supertree as a reference, and discuss the temporal distribution of changes in time-sliced, pruned trees derived from this supertree. Also, we analyse those shifts that are most relevant to the end-Permian mass extinction. For the Palaeozoic, shifts occur almost invariably along branches that connect major Palaeozoic groups. By contrast, shifts in the Mesozoic occur predominantly within major groups. Numerous shifts bracket narrowly the end-Permian extinction, indicating not only rapid recovery and extensive diversification of temnospondyls over a short time period after the extinction event (possibly less than half a million years), but also the role of intense cladogenesis in the late part of the Permian (although this was counteracted by numerous 'background' extinctions).     

Peronosporomycetes (Oomycota) from a Middle Permian Permineralised Peat within the Bainmedart Coal Measures,Prince Charles Mountains,Antarctica

The fossil record of Peronosporomycetes (water moulds) is rather sparse, though their distinctive ornamentation means they are probably better reported than some true fungal groups. Here we describe a rare Palaeozoic occurrence of this group from a Guadalupian (Middle Permian) silicified peat deposit in the Bainmedart Coal Measures, Prince Charles Mountains, Antarctica. Specimens are numerous and comprise two morphologically distinct kinds of ornamented oogonia, of which some are attached to hyphae by a septum. Combresomyces caespitosus sp. nov. consists of spherical oogonia bearing densely spaced, long, hollow, slender, conical papillae with multiple sharply pointed, strongly divergent, apical branches that commonly form a pseudoreticulate pattern under optical microscopy. The oogonia are attached to a parental hypha by a short truncated stalk with a single septum. Combresomyces rarus sp. nov. consists of spherical oogonia bearing widely spaced, hollow, broad, conical papillae that terminate in a single bifurcation producing a pair of acutely divergent sharply pointed branches. The oogonium bears a short truncate extension where it attaches to the parental hypha. We propose that similarities in oogonium shape, size, spine morphology and hyphal attachment between the Permian forms from the Prince Charles Mountains and other reported Peronosporomycetes from Devonian to Triassic strata at widely separated localities elsewhere in the world delimit an extinct but once cosmopolitan Palaeozoic to early Mesozoic branch of the peronosporomycete clade. We name this order Combresomycetales and note that it played an important role in late Palaeozoic and early Mesozoic peatland ecosystems worldwide.     

A NEW RECONSTRUCTION OF ONYCHOSELACHE TRAQUAIRI, COMMENTS ON EARLY CHONDRICHTHYAN PECTORAL GIRDLES AND HYBODONTIFORM PHYLOGENY

Abstract:  A new, third, specimen of Onychoselache traquairi from the Viséan (Holkerian) of Scotland allows a significant revision of the anatomy of this stem-group elasmobranch. This first report of material from the Mumbie Quarry exposure of the Glencartholm fish beds presents a new reconstruction of Onychoselache showing broad-based cephalic and nuchal spines, and exceptionally large pectoral fins. Details of the jaws, braincase and postcranial skeleton demonstrate that Onychoselache is a well-characterized member of the Hybodontiformes. Comparisons of the pectoral skeleton with other early chondrichthyan examples, including new material of Tristychius arcuatus and Plesioselachus macracanthus , highlight a range of early chondrichthyan conditions that are incorporated into a revised hybodontiform phylogeny. Close resemblance between Onychoselache and Mesozoic and late Palaeozoic hybodonts implies that these clades diverged within the Carboniferous and Permian. Major differences between Onychoselache and the coeval Tristychius (a modified reconstruction of which is included) indicate that the Neoselachii-Hybodontiformes split is probably Late Devonian, consistent with records of isolated teeth. The pectoral fins of Onychoselache , while unique among Palaeozoic forms, resemble those of Recent bamboo and epaulette sharks (Orectolobiformes). The functional corollary of this convergence is that Onychoselache represents an instance of a non-tetrapod early vertebrate with a near-walking gait.     

Composition and dynamics of the great Phanerozoic Evolutionary Floras

Factor analysis of a data set representing the global distribution of vascular plant families through time shows the broad pattern of vegetation history can be explained in terms of five Evolutionary Floras. The Rhyniophytic (=Eotrachyophytic) Flora represents the very earliest (Silurian and earliest Devonian) vascular plants, notably the Rhyniophytopsida. The Eophytic Flora represents the early (Early–Middle Devonian) mainly homosporous land plants, notably the Zosterophyllopsida, Trimerophytopsida and early Lycopsida. The Palaeophytic Flora represents the Late Devonian and Carboniferous vegetation, which saw the introduction of heterospory among the spore producing plants and of early gymnosperms. The Mesophytic Flora first appeared in the Late Carboniferous and Permian macrofossil record, although there is palynological evidence of these plants having grown earlier in extra‐basinal habitats and was dominated by gymnosperms with more modern affinities. The Cenophytic Flora that first appeared during Cretaceous times was overwhelmingly dominated by angiosperms. The end‐Devonian, end‐Triassic and end‐Cretaceous mass‐extinction events recognized in the marine fossil record had little impact on the diversity dynamics of these Evolutionary Floras. Rather, the changes between floras mainly reflect key evolutionary innovations such as heterospory, ovules and angiospermy.     

Wall structure and evolution in cyclostomate Bryozoa

The Stenolaemata comprise both basically single-walled forms (Cyclostomata) and doublewalled forms (Trepostomata, Cystoporata and Cryptostomata) from their first appearance in the geological record. At the end of the Palaeozoic the main groups of apparently double-walled stenolaemates died out, and only the single-walled cyclostomates survived. During the Mesozoic, evolution within the Stenolaemata was apparently repeated by the further development of double-walled forms such as cerioporids, lichenoporids and cancelloids, from single-walled ancestors. These double-walled groups are all remarkable homeomorphs of the major Palaeozoic groups of Bryozoa. A monophyletic origin of the post-Palaeozoic Cyclostomata from Palaeozoic single-walled forms is thus suggested.     

Late Carboniferous intra-arc sediments in the north Chilean Andes: Stratigraphy,paleogeography and paleoclimate

Summary Thick terrestrial Late Carboniferous to Triassic volcanosedimentary successions, a prominent feature of the Chilean and Argentinian High Andes, were formed on the active continental margin of Gondwanaland. Their stratigraphic position and the paleogeographic and paleoclimatic relations to neighbouring successions are poorly defined. A more precise age has been obtained for alluviolimnic intra-arc sediments (Miembro Medio), which are intercalated in the Late Carboniferous-Triassic volcano-sedimentary successions in the Salar de Atacama area of northern Chile. The ostracodesCarbonita cf.pungens andParaparchites sp., which occur in the lower part of the Miembro Medio, are of Late Carboniferous, probably Westphalian age. The diverse taphoflora, which occurs in a higher stratigraphic level than the ostracodes, includes sphenophytes, ferns, gymnosperms and pteridophylls, for which we assume a late Westphalian-Early Permian age. Considering radiometric data of under-and overlying volcanic rocks, a Westphalian-Stephanian (to? Early Permian) age is inferred for the Miembro Medio. Fauna and flora indicate that warm-humid and seasonal climatic conditions existed during the deposition of the lower fossiliferous part of the Miembro Medio. This coincides with the sedimentary paleoclimatic indicators of the Miembro Medio and the climate which was assumed to have predominated in wide parts of the Central and Southern Andes during the Latest Carboniferous.     

Evolutionary patterns in early tetrapods. I. Rapid initial diversification followed by decrease in rates of character change

Although numerous studies have examined morphological diversification during major radiations of marine taxa, much less attention has been paid to terrestrial radiations. Here, we examine rates of character change over phylogeny and over time for Palaeozoic limbed tetrapods. Palaeozoic tetrapods show significant decreases in rates of character change whether the rate is measured per sampled cladistic branch or per million years along phylogeny. Given changes per branch, rates decrease significantly from the Devonian through the Pennsylvanian, but not from the Pennsylvanian through the Permian. Given changes per million years, rates decrease significantly over each boundary, although the decrease is least significant over the Pennsylvanian-Permian boundary. Decreasing rates per million years through the Permian might be an artefact of the method being able to ascribe longer durations to Permian branches than to Carboniferous ones; however, it is difficult to ascribe the general pattern of decreasing rates of change over time to sampling biases or methodological biases. Thus, the results implicate biological explanations for this pattern.     

Cambrian to Cretaceous changes in hardground communities

The changing nature of the communities of boring and encrusting taxa found on upward-facing hard-grounds has been studied from the standpoints of (a) diversity, (b) faunal composition, and (c) nature of the niches occupied. After a rapid initial increase in the early Palaeozoic, diversity remained at much the same level from the Middle Ordovician until the late Cretaceous. However, there is a considerable turnover in the identity of the individual taxa between successive sample intervals. The incoming and outgoing of the major groups parallel their fortunes in the marine realm as a whole. Niche analysis suggests that the same feeding levels are occupied for most of the history of hardground communities, but Mesozoic faunas contain a much higher proportion of species with true exoskcletons, or which lived infaunally. The evolution of these forms was probably influenced by the Mesozoic radiation of marine predators and duriphages, but it also resulted in Mesozoic hardground faunas being more resistant than their Palaeozoic counterparts to episodic corrasion. Resulting higher population densities in the Mesozoic were probably one reason why cavity faunas beneath some of these hardground surfaces are more diverse than those beneath Palaeozoic examples. □ Hardground, community, evolution.     

Foraminiferal zonation of late Paleozoic depositional sequences

From the later part of the Devonian through the Permian, calcareous foraminifers became abundant and evolved rapidly. This rapid evolution of taxa forms the basis of a detailed zonation through the Carboniferous and Permian. Comparison of this evolutionary history of foraminifers, their biostratigraphic zonation, and the depositional sequences in which they occur suggests that sea-level events in late Paleozoic depositional history contributed significantly in subdividing a fairly continuous evolutionary record into a succession of about 75 identifiable foraminiferal zones during a 100–125 Myr time span. Although variable in terms of duration and vertical occurrences, the more completely recorded high-stand intervals give brief histories of the foraminiferal evolutionary record and are sandwiched between the poorly recorded or unrecorded low-stand intervals. Many of the individual foraminiferal zones are confined to a single depositional sequence.The late Paleozoic carbonate foraminiferal fossil record, as with the rest of the fossil record, is strongly affected by sediment deposition-nondeposition as a result of major changes in sea level. This incomplete fossil record is the result of repeated depositional breaks because of the way that depositional sequences form. It is not possible to ascribe macromutations, ‘punctuated’ evolution or ‘punctuated gradualism’ as the cause of this evolutionary pattern of the shelf-carbonate fossil record. This pattern is distinctive and we refer to it as ‘sequence evolution’ and ‘sequence extinction’. In the later part of the Middle Permian and in the Late Permian, the fossil record clearly illustrates that a series of faunal losses through ‘sequence extinctions’ progressively exceeded faunal replacements and new species through ‘sequence evolution’, but not a ‘mass extinction’ as is commonly ascribed to the end of the Permian Period. Most Permian faunas became extinct in the interval of 8 to 4 million years before the end of the Late Permian.     

Diversity of exine structure in Upper Carboniferous (Westphalian) selaginellalean megaspores

Studies of wall structure in Mesozoic and Recent selaginellalean megaspores have been well documented. However, Palaeozoic examples have received minimal attention. The principal Palaeozoic megaspore genus of likely selaginellalean affinity is Triangulatisporites, extending from the Upper Devonian to the Upper Carboniferous. The particulate wall ultrastructure of a previously published Carboniferous (Duckmantian) megaspore assigned to this genus suggested that this form of wall construction may have been the ancestral wall structure of the group, an observation which posed difficulties in relating selaginellalean ultrastructure to that of other contemporaneous lycopsid megaspores. Subsequent investigation showed that the genus also contains more laminate exines similar to those of other extinct lycopsids and extant Selaginella species. Our new examples of Triangulatisporites ultrastructure from the Langsettian, Duckmantian and Westphalian D yield more information regarding early variation of wall structure within Carboniferous selaginellalean megaspores and suggest that a more laminate wall composition is at least as old as the particulate form. However, without further investigation of Lower Carboniferous forms, we are unable to state which is indeed ancestral. The laminate structure reported here and elsewhere is, none the less, more easily related to comparable ultrastructure in other groups of Carboniferous lycopsid megaspores and could suggest a link with such genera as Zonalesporites and early Lagenicula. This would be in keeping with current concepts regarding the most primitive ultrastructural type within lycopsid megaspore walls.     

Latitudinal diversity gradients for brachiopod genera during late Palaeozoic time: links between climate, biogeography and evolutionary rates

Aim The latitudinal diversity gradient, in which taxonomic richness is greatest at low latitudes and declines towards the poles, is a pervasive feature of the biota through geological time. This study utilizes fossil data to examine how the latitudinal diversity gradient and associated spatial patterns covaried through the major climate shifts at the onset and end of the late Palaeozoic ice age. Location Data were acquired from fossil localities from around the world. Methods Latitudinal patterns of diversity, mean geographical range size and macroevolutionary rates were constructed from a literature‐derived data base of occurrences of fossil brachiopod genera in space and time. The literature search resulted in a total of 18,596 occurrences for 991 genera from 2320 localities. Results Climate changes associated with the onset of the late Palaeozoic ice age (c. 327 Ma) altered the biogeographical structure of the brachiopod fauna by the preferential elimination of narrowly distributed, largely tropical genera when glaciation began. Because the oceans were left populated primarily with widespread genera, the slope of the diversity gradient became gentle at this time, and the gradient of average latitudinal range size weakened. In addition, because narrowly distributed genera had intrinsically high rates of origination and extinction, the gradients of both of these macroevolutionary rates were also reduced. These patterns were reversed when the ice age climate abated in early Permian time (c. 290 Ma): narrowly distributed genera rediversified at low latitudes, restoring steep gradients of diversity, average latitudinal range size and macroevolutionary rates. Main conclusions During late Palaeozoic time, these latitudinal gradients for brachiopods may have been linked by the increased magnitude of seasonality during the late Palaeozoic ice age. Pronounced seasonality would have prevented the existence of genera with narrow latitudinal ranges. These results for the late Palaeozoic ice age suggest a climatic basis for the present‐day latitudinal diversity gradient.     

Origins and early evolution of herbivory in tetrapods

The first herbivorous tetrapods date from the Late Carboniferous, about 300 million years ago. By the Late Permian, continental ecosystems of `modern' aspect had been established, with a vast standing crop of herbivores supporting relatively few carnivores. Processing of high-fibre plant material requires (1) structural modifications of the dentition, jaw apparatus and digestive tract and (2) the acquisition of microbial endosymbionts that produce the enzymes needed for fermentative digestion of cellulose, the principal compound of cell walls in plants. Recent phylogenetic analyses of tetrapods indicate that endosymbiotic cellulysis was acquired independently in a number of lineages during the late Palaeozoic.