Phanerozoic survivors: Actinopterygian evolution through the Permo‐Triassic and Triassic‐Jurassic mass extinction events

Actinopterygians (ray‐finned fishes) successfully passed through four of the big five mass extinction events of the Phanerozoic, but the effects of these crises on the group are poorly understood. Many researchers have assumed that the Permo‐Triassic mass extinction (PTME) and end‐Triassic extinction (ETE) had little impact on actinopterygians, despite devastating many other groups. Here, two morphometric techniques, geometric (body shape) and functional (jaw morphology), are used to assess the effects of these two extinction events on the group. The PTME elicits no significant shifts in functional disparity while body shape disparity increases. An expansion of body shape and functional disparity coincides with the neopterygian radiation and evolution of novel feeding adaptations in the Middle‐Late Triassic. Through the ETE, small decreases are seen in shape and functional disparity, but are unlikely to represent major changes brought about by the extinction event. In the Early Jurassic, further expansions into novel areas of ecospace indicative of durophagy occur, potentially linked to losses in the ETE. As no evidence is found for major perturbations in actinopterygian evolution through either extinction event, the group appears to have been immune to two major environmental crises that were disastrous to most other organisms.     

A new scanilepiform from the Lower Triassic of northern Gansu Province,China, and phylogenetic relationships of non‐teleostean Actinopterygii

A new scanilepiform, Beishanichthys brevicaudalis gen. et sp. nov. , is named and described based on fossils from the Lower Triassic lake deposits exposed in Beishan area, Gansu Province, China. The discovery documents a new record of this group, which is significantly older than other known scanilepiforms from China, and is slightly younger than Evenkia from the Lowest Triassic of Central Siberia. Although the Beishan beds were previously interpreted as Late Permian in age, based on megaplant fossils, this new discovery supports the reinterpretation of the deposits as Early Triassic in age, based on vertebrate fossils from the same locality and horizon. Phylogenetic analysis was conducted to resolve the relationships of Scanilepiformes with other actinopterygian clades, and the inter‐relationships within Scanilepiformes. Contrary to previous thought that scanilepiforms are closely related to the Amiidae, the phylogenetic results of this study recognize the Scanilepiformes as stem‐group neopterygians. Relationships of the Scanilepiformes and Australosomus with other neopterygians remain unresolved. With a characteristic long‐based dorsal fin, scanilepiforms represent a small group that emerged in Early Triassic freshwater environments, inhabited Eurasia and North America during the Middle–Late Triassic, briefly invaded the marine environment by the Late Triassic in Europe, and became extinct at the end of Triassic. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161 , 595–612.     

Supernumerary median fin-rays in teleostean fishes

Supernumerary fin-rays in the dorsal and anal fins are those that articulate directly with the head of the first proximal radial; they lie in front of the ray serially associated with the first radial. The argument presented here is that just as the number of fin-rays per dorsal and anal radial has decreased in actinopterygian history, so the number of dorsal and anal supernumeraries has decreased in teleosts. It is proposed that D > 3 and A > 3 (more than three dorsal and anal supernumeraries) is the condition primitive for teleosts, and that D2 and A3 are primitive for acanthomorphs.     

浙江和江西二叠/三叠系界线层上下的辐鳍鱼类化石与鱼类的绝灭、复苏和辐射

记述了浙江长兴县煤山剖面、江西修水县四都乡东岭剖面和信丰县铁石口镇铁石口剖面二叠/三叠系界线层上下的辐鳍鱼类6个类别的微体化石,包含2新属2新种,它们是:赵氏浙江鱼(Zhejiangichthys zhaoi gen.et sp.nov.)和小齿葆青鱼(Baoqingichthys microdontus gen.et sp.nov.)。这是包括全球二叠/三叠系界线层型剖面和点位(GSSP)在内的全球二叠/三叠系界线层上下辐鳍鱼类微体化石序列的首次报道。在总结煤山剖面已记述的鱼类大化石和微体化石资料的基础上,分析了长兴煤山剖面二叠纪末鱼类的集群绝灭。绝灭发生得很晚,持续的时间很短,规模也很大,绝灭率高达93%。讨论了华南二叠/三叠系之交大绝灭后鱼类的复苏和辐射,认为鱼类和牙形类一样都是大绝灭后在三叠纪最早复苏的类别,最早复苏的鱼类为裂齿鱼类;鱼类从绝灭期到辐射期仅用了1.3 Ma到4 Ma,从地质时间考虑,大绝灭后鱼类的复苏和辐射是相当快的。华南早三叠世以裂齿鱼类的张氏鱼(Zhangina)和软骨鱼类的弓鲛(Hybodus)为代表的组合替代了晚二叠世以古鳕类的中华扁体鱼(sinoplatysomys)和软骨鱼类的中华尖齿鲨(Sinacrodus)为代表的组合。华南晚二叠世海相地层产出的辐鳍鱼类和软骨鱼类的一些土著属与产于特提斯区三叠纪的一些属非常相近,表明华南下扬子区很可能是后来繁盛于特提斯区的三叠纪鱼类的发源地。     

Re‐evaluation of the ontogeny and reproductive biology of the Triassic fish Saurichthys (Actinopterygii,Saurichthyidae)

Viviparity has evolved independently at least 12 times in ray‐finned fishes. However, the fossil record of actinopterygian viviparity is poor, with only two documented occurrences. Both of these are from the non‐teleost actinopterygian Saurichthys, and include S. curionii and S. macrocephalus from the Middle Triassic Meride Limestone (Monte San Giorgio, Switzerland). Here, we present new data on the reproductive biology of these species, giving unprecedented insights into their life‐history. Based on positional and preservational criteria, six specimens were identified as unambiguously gravid. Embryos were positioned dorsal to the gastrointestinal tract, parallel to the axial skeleton and to each other, in the posterior two‐thirds of the abdominal region. A minimum of 16 embryos are preserved in the most fecund females and, based on the largest preserved embryos and smallest preserved neonates, birth must have occurred at 7–12% of maternal fork length. Embryonic crania and teeth are relatively well‐ossified, however ossification of the parietal region is delayed. In the postcranium, the median scale rows and lepidotrichia are ossified, but not the lateral scale rows. Ossified squamation and gradual allometric growth suggests that neonates did not undergo metamorphosis and were relatively precocial. When considered in a phylogenetic context, neither live birth nor internal fertilization appears to represent the primitive state for saurichthyid fishes.     

Middle Triassic paleomagnetic data from northern Bulgaria: constraints on Tethyan magnetostratigraphy and paleogeography

Magnetostratigraphic and biostratigraphic data are presented from the Anisian (Middle Triassic) Peri-Tethyan Edivetur section of northwestern Bulgaria. A dual-polarity component of magnetization carried by magnetite delineates a magnetic stratigraphy of mainly reversed polarity. Magnetozones are dated by means of foraminifer and conodont biostratigraphy. Data from Edivetur are compared with data from Middle Triassic Tethyan limestone sections with the aim of contributing to the completion of the Middle Triassic magnetic polarity time scale. We also propose that paleomagnetic data from Edivetur can be used as proxy data for the paleogeographic position of the Moesian platform. The Moesian platform was located at 21–24°N along the southern margin of Europe. It was probably marginally separated, but not detached or rotated away from Europe by the North Dobrugea transtensional trough, which is interpreted as a back-arc basin resulting from the northward subduction of the Neo-Tethys (Vardar) or Paleo-Tethys ocean. Paleomagnetic data from this study and other minor tectonic elements are used to generate a paleogeographic sketch map of the Pangea-bounded western Tethys and Peri-Tethys at Middle/early Late Triassic time.     

Biogeography of Triassic tetrapods: evidence for provincialism and driven sympatric cladogenesis in the early evolution of modern tetrapod lineages

Triassic tetrapods are of key importance in understanding their evolutionary history, because several tetrapod clades, including most of their modern lineages, first appeared or experienced their initial evolutionary radiation during this Period. In order to test previous palaeobiogeographical hypotheses of Triassic tetrapod faunas, tree reconciliation analyses (TRA) were performed with the aim of recovering biogeographical patterns based on phylogenetic signals provided by a composite tree of Middle and Late Triassic tetrapods. The TRA found significant evidence for the presence of different palaeobiogeographical patterns during the analysed time spans. First, a Pangaean distribution is observed during the Middle Triassic, in which several cosmopolitan tetrapod groups are found. During the early Late Triassic a strongly palaeolatitudinally influenced pattern is recovered, with some tetrapod lineages restricted to palaeolatitudinal belts. During the latest Triassic, Gondwanan territories were more closely related to each other than to Laurasian ones, with a distinct tetrapod fauna at low palaeolatitudes. Finally, more than 75 per cent of the cladogenetic events recorded in the tetrapod phylogeny occurred as sympatric splits or within-area vicariance, indicating that evolutionary processes at the regional level were the main drivers in the radiation of Middle and Late Triassic tetrapods and the early evolution of several modern tetrapod lineages.     

The early evolution of ray‐finned fishes

Ray‐finned fishes (Actinopterygii) constitute approximately half of all living vertebrate species. A stable hypothesis of relationships among major modern lineages has emerged over the past decade, supported by both anatomy and molecules. Diversity is unevenly partitioned across the actinopterygian tree, with most species concentrated within a handful of geologically young (i.e. Cretaceous) teleost clades. Extant non‐teleost groups are portrayed as ‘living fossils’, but this moniker should not be taken as evidence of especially primitive structure: each of these lineages is characterized by profound specializations. Attribution of fossils to the crowns and apical stems of Cladistia, Chondrostei and Neopterygii is uncontroversial, but placements of Palaeozoic taxa along deeper branches of actinopterygian phylogeny are less secure. Despite these limitations, some major outlines of actinopterygian diversification seem reasonably clear from the fossil record: low richness and disparity in the Devonian; elevated morphological variety, linked to increases in taxonomic dominance, in the early Carboniferous; and further gains in taxonomic dominance in the Early Triassic associated with earliest appearance of trophically diverse crown neopterygians.     

Late Paleozoic–early Mesozoic continental biostratigraphy — Links to the Standard Global Chronostratigraphic Scale

Nonmarine biostratigraphic/biochronologic schemes have been created for all or parts of the late Carboniferous–Middle Triassic using palynomorphs, megafossil plants, conchostracans, blattoid insects, tetrapod footprints and tetrapod body fossils, and these provide varied temporal resolution. Cross correlation of the nonmarine biochronologies to the Standard Global Chronostratigraphic Scale has been achieved in some parts of the late Carboniferous–Middle Triassic in locations where nonmarine and marine strata are intercalated, the nonmarine strata produce biochronologically significant fossils and the marine strata yield fusulinids, conodonts and/or ammonoids. Other cross correlations have been aided by magnetostratigraphy, chemostratigraphy and a growing database of radioisotopic ages. A synthetic nonmarine biochronology for the late Carboniferous–Middle Triassic based on all available nonmarine index fossils, integrated with the Standard Global Chronostratigraphic Scale, is presented here. The focus is on the nonmarine biostratigraphy/biochronology of blattoid insects, conchostracans, branchiosaurid amphibians, tetrapod footprints and tetrapod body fossils within the biochronological framework of land-vertebrate faunachrons. Correlation to the Standard Global Chronostratigraphic Scale presented here is divided into seven time intervals: Pennsylvanian, Carboniferous–Permian boundary, Cisuralian, Guadalupian, Lopingian, Permian–Triassic boundary and Early to Middle Triassic. The insects, conchostracans and branchiosaurs provide robust nonmarine correlations in the Pennsylvanian–Cisuralian, and the footprints and tetrapod body fossils provide robust correlations of varied precision within the entire Pennsylvanian–Middle Triassic. Radioisotopic ages are currently the strongest basis for cross correlation of the nonmarine biostratigraphy/biochronology to the Standard Global Chronostratigraphic Scale, particularly for the Pennsylvanian–Cisuralian. Chemostratigraphy and magnetostratigraphy thus far provide only limited links of nomarine and marine chronologies. Improvements in the nonmarine-marine correlations of late Paleozoic–Triassic Pangea require better alpha taxonomy and stratigraphic precision for the nonmarine fossil record integrated with more reliable radioisotopic ages and more extensive chemostratigraphic and magnetostratigraphic datasets.     

New fish assemblages from the Middle Permian from the Guadalupe Mountains,West Texas,USA

Late Wordian/Capitanian (Guadalupian, Middle Permian) fish assemblages are described from the “McKittrick Canyon Limestone”, Lamar Limestone and Reef Trail Members of the Bell Canyon Formation in the Patterson Hills and the PI section (Hegler/Pinery Members) along Highway 62/180 in the Guadalupe Mountains, West Texas. The assemblages contain chondrichthyan teeth of Stethacanthulus meccaensis, Texasodus varidentatus, Cooleyella cf. amazonensis, C. cf. peculiaris, and the new genus and species Lamarodus triangulus; and buccopharyngeal denticles of undetermined symmoriiform; chondrichthyan scales of eight morphotypes; fragment of an actinopterygian jaw, isolated teeth; the scales of Alilepis sp., Varialepis sp. and undetermined elonichthyid and haplolepid fishes. Using microtomography, the vascularization system has been observed for the first time for the teeth of Texasodus varidentatus and a new taxon Lamarodus triangulus. The distribution of chondrichthyan taxa was analyzed for the known fish assemblages of the Early, Middle, and Late Permian of the world. The end-Guadalupian crisis in the evolution of chondrichthyan fishes involved substantially more taxonomic change than the Permian–Triassic mass extinction.     

Locomotor Patterns in the Evolution of Actinopterygian Fishes

SYNOPSIS. Locomotor adaptations in actinopterygian fishes aredescribed for (a) caudal propulsion, used in cruising and sprintswimming, acceleration, and fast turns and (b) median and pairedfin propulsion used for slow swimming and in precise maneuver.Caudal swimming is subdivided into steady (time independent)and unsteady (time dependent acceleration and turning) locomotion. High power caudal propulsion is the major theme in actinopterygianswimming morphology because of its role in predator evasionand food capture. Non-caudal slow swimming appears to be secondaryand is not exploited before the Acanthopterygii. Optimal morphological requirements for unsteady swimming are(a) large caudal fin and general body area, (b) deep caudalpeduncle, often enhanced by posterior dorsal and anal fins,(c) an anterior stabilizing body mass and\or added mass, (d)flexible body and (e) large ratio of muscle mass to body mass.Optimal morphological requirements for steady swimming are (a)high aspect ratio caudal fin, (b) narrow caudal peduncle, (c)small total caudal area, (d) anterior stabilizing body massand added mass, and (e) a stiff body. Small changes in morphologycan have large effects on performance. Exclusive morphological requirements for steady versus unsteadyswimming are partially overcome using collapsible fins, butcompromises remain necessary. Morphologies favoring unsteadyperformance are a recurring theme in actinopterygian evolution.Successive radiations at chondrostean, halecostome and teleosteanlevels are associated with modifications in the axial and caudalskeleton. Strength of ossified structures probably limited maximum propulsionforces early in actinopterygian evolution, so that specializationsfor fast cruising (carangiform and thunmform modes) followedstructural advances especially in the caudal skeleton. No suchlimits apply to eel-like forms which consequently recur in successiveactinopterygian radiations. Slow swimming using mainly non-caudal propulsion probably firstoccurred among neopterygians in association with reduced andneutral buoyancy. Slow swimming adaptations can add to and extendthe scope of caudal swimming, but specialization is associatedwith reduced caudal swimming performance. Marked exploitationof slow swimming opportunities does not occur prior to the anterodorsallocation of pectoral and pelvic girdles and the vertical rotationof the base of the pectoral fin, as found in the Acanthopterygii.     

Facies and biota of Anisian to Carnian carbonate platforms in the Northern Calcareous Alps (Tyrol and Bavaria)

Summary During the Middle and early Late Triassic carbonate ramps and rimmed platforms developed at the northwestern margin of the Tethys ocean. In the Northern Calcareous Alps, Anisian stacked homoclinal ramps evolved through a transitional stage with distally steepened ramps to huge rimmed platforms of Late Ladinian to Early Carnian age. Middle Triassic to early Late Triassic facies and biota of basin, slope and platform depositional systems are described. Special emphasis is given to foraminifers, sponges, microproblematic organisms and algae. The Ladinian to early Carnian reef associations are characterized by the abundance of segmented sponges, microproblematica, biogenic crusts and synsedimentary cements. Among the foraminifers, recifal forms likeHydrania dulloi andCucurbita infundibuliformis (Carnian in age) are reported from the Northern Calcareous Alps for the first time. Some sphinctozoid sponges likeParavesicocaulis concentricus were known until now only from the Hungarian and Russian Triassic.     

Fossil vertebrate faunas of the British Rhaetian (latest Triassic)

Rhaetian fossil vertebrate faunas of Britain represent rich but biased samples of taxonomic diversity during uppermost Triassic time. Review of the Westbury Formation, Penarth Group, in particular, reveals a combination of marine, littoral, and terrestrial elements. Minimally, six species of shark are preserved along with a myriacanthid holocephalan, at least four actinopterygian taxa, a characteristic lungfish, ichthyosaurs, plesiosaurs, dinosaurs, and potentially the earliest representative of the Choristodera. Rare mammalian occurrences in the Westbury beds are also possible. Severnichthys gen. nov. is a large osteichthyan, probably a palaeonisciform chondrostean, which historically has been mistaken for a labyrinthodont amphibian. At least two additional actinopterygian species and a holocephalan are known from die Lilstock Formation, and a mammal or mammallike reptile is recorded from the uppermost Blue Anchor Formation. Analysis of element abundance in the disarticulated Westbury Formation assemblage indicates that many parts of some taxa are never preserved while other elements of the same form are common. Such preservational bias suggests that many species may be missing entirely from this long-studied but poorly understood taphocoenosis. Possibly contemporaneous cave faunas from nearby upland areas give a similarly biased picture of the terrestrial fauna during this time of widespread marine transgression.     

Triassic nannoplankton limestones of deep basin origin in the central mediterranean region

Samples of Triassic pelagic limestones collected in several regions of the Central Mediterranean area were examined with the electron microscope. They show calcareous nannoplankton existing already from Middle Triassic time. The Middle Triassic nannofossils are contained in nodular limestones such as the “Ammonitico Rosso” of Epidaurus (Greece); the Upper Triassic ones are contained in nodular limestones like the Ammonitico Rosso of Hallstatt (Austria), as well as in Halobia cherty limestones of the Pindos basin in Italy, Yugoslavia and Greece. In the Halobia limestones it is possible, in spite of the recrystallization effects, to recognize such an abundance of organic forms — even if in fragments — that we can suppose the original sediment to be a kind of nannoplankton ooze.Because of the very low accumulation rate (few metres/m.y.) of the Middle Triassic Ammonitico Rosso limestones, the coccoliths cannot be considered a significant factor of carbonate pelagic sedimentation at this time; the very high accumulation rate (up to 25 metres/m.y.) of the Upper Triassic cherty limestones in the Pindos basin, on the contrary, allows the nannoplankton to be considered a very important agent of calcareous pelagic sedimentation. The authors hypothesize that the Dogger-Malm, mainly represented by radiolarites, was only a temporary interlude in the Mesozoic pelagic carbonate sedimentation.     

Permian and Triassic Therocephals (Eutherapsida) of Eastern Europe

Cranial morphology of Permian and Triassic Therocephalia of Eastern Europe is revised. The Therocephalia are regarded as an order of the subclass Eutherapsida of the class Theromorpha. Phylogenetic relationships are reconsidered and a tentative taxonomic scheme of the order is proposed. Biomorph evolution of East European Therocephalia from the Middle Permian to the Middle Triassic are discussed.     

Pleuromeia discovered from the Middle Triassic Linjia Formation of Benxi,Northeast China

A new species Pleuromeia shaolinii Zhang et Wang n. sp. was established under the family Pleuromeiaceae, based on eight specimens of stems and leaves, cones, rhizophores, and adventitious roots that were recently collected from the Middle Triassic Linjia Formation in Benxi, Northeast China. P. shaolinii n. sp. is similar to the type species P. sternbergii, in the morphology of the stem and rhizophore, but differs from it by the transversely rounded sporophylls organized in a heterosporous cone, and the two conspicuous triangular scars present on both sides of the vascular bundle scar. The Linjia flora, an only reliable Middle Triassic flora in Northeast China, was discovered 40 years ago. Although the Linjia Formation can be compared with the Middle Triassic Ermaying Formation from another area of the North China plate, its age was questionable due to the absence of the Early to Middle Triassic index fossil Pleuromeia. Based on the flora similarity, the zircon dating, lithologic characteristics, presence of a disconformity, and the occurrence of the Middle Triassic–Early Cretaceous insect fossil Sogdoblatta, the age of the Linjia Formation can be confirmed as Middle Triassic. The new species not only supplements our knowledge in biology and taxonomy of Pleuromeia, but also supports the Middle Triassic age assignment of the Linjia flora.     

渤海沿岸临清坳陷堂古5井中三叠统轮藻化石与地层划分对比

在临清坳陷堂古5井发现轮藻化石Stenochara和Stellatochara两属7种,证实该区存在三叠世地层。根据地层层序、岩石地层特征和区域地质资料分析,该区亦应存在下三叠统,并建议参照区域方案将该区中、下三叠统红层划分为刘家沟组、和尚沟组和二马营组。     

Arizonasaurus and its implications for archosaur divergence

The Moenkopi Formation has yielded partial and isolated remains of important archosaurs including rauisuchian skull fragments and isolated poposaur centra and pelvic girdle elements. A recently discovered skeleton referable to Arizonasaurus babbitti shows that most of these archosaurian remains belong to one taxon. Characteristics of the skeleton of Arizonasaurus show that it belongs to a poorly known group of Middle Triassic (240-230 Myr ago) archosaurs called the ctenosauriscids, and that ctenosauriscids are or are closely related to poposaurs. Furthermore, many characteristics of Arizonasaurus provide evidence that poposaurids and ctenosauriscids are derived rauisuchians. The presence of a poposaurid in the early Middle Triassic suggests that the divergence of birds and crocodiles occurred earlier than previously thought. Middle Triassic ctenosauriscids also allow the correlation of Triassic faunas in Europe, Asia, North America and Africa. The Moenkopi Formation fauna represents a transitional fauna between Early and Late Triassic faunas.     

A new species of basal rhynchosaur (Diapsida: Archosauromorpha) from the early Middle Triassic of South Africa,and the early evolution of Rhynchosauria

Rhynchosauria was an important clade of herbivorous archosauromorph reptiles during the Triassic, with a worldwide distribution. We describe a new genus and species of early rhynchosaur, E ohyosaurus wolvaardti gen. et sp. nov. , from the early Middle Triassic (early Anisian) Cynognathus Assemblage Zone (Subzone B) of the Karoo Supergroup, South Africa. Eohyosaurus wolvaardti is known from a single skull, and is recovered as the sister taxon of Rhynchosauridae in a new phylogenetic analysis. Cynognathus Subzone B has previously yielded the stratigraphically oldest well‐understood rhynchosaur species, Mesosuchus browni and Howesia browni. Eohyosaurus wolvaardti increases the rhynchosaur diversity within this stratigraphical horizon to three species. Intriguingly, all currently confirmed rhynchosaur occurrences from the Early Triassic to earliest Middle Triassic are from South Africa. This may suggest a relatively restricted palaeogeographical distribution for early rhynchosaurs, followed by a global dispersal of rhynchosaurids during the Middle Triassic. © 2015 The Linnean Society of London     

A taxodiaceous seed cone from the Triassic of Antarctica

A silicified seed cone is described from the lower Middle Triassic of A silicified seed cone is described from the lower Middle Triassic of Antarctica. The cone measures up to 3.4 cm long and 1.4 cm wide, and consists of helically arranged cone scales attached to a eustelic axis. Bract and ovuliferous scale are approximately of equal length and fused at the base. The bract is entire and vascularized by a single trace. The ovuliferous scale contains five distal lobes, each vascularized by a terete strand that divides to form a smaller trace to each of the five inverted ovules. Ovules are small and flattened with the three-parted integument attenuated into oppositely positioned lateral wings. The Triassic specimens are compared with both extant and fossil conifer seed cones and believed to have their closest affinities within the Taxodiaceae.