The early ontogeny of Jurassic thecideoid brachiopods and its contribution to the understanding of thecideoid ancestry

Abstract: A collection of very early brephic juveniles from the Upper Aalenian of the Cotswolds, England, has provided the first opportunity to study the ontogeny of thecideoids prior to the recognizable development of a median septum. Traced towards their origin, the enduring characters of thecideides appear to be cementation, a delthyrium closed by a pseudodeltidium, an almost circular dorsal valve with a prominent erect bilobed cardinal process, well‐defined inner socket ridges, widely spaced lateral adductor muscle fields, tubercles, fibrous secondary shell lining both valves and probably endopunctae. The subperipheral rim and median septum so characteristic of adult thecideoids are undeveloped in the earliest juveniles. Initiation of the development of the free ventral wall in the ventral valve is identified as an important event in thecideoid ontogeny. Further important discoveries arising from the study are that the crura‐like outgrowths which form the brachial bridge in thecideides are not structurally homologous with the crura of spiriferides or terebratulides and that during their earliest ontogenetic development thecidellinids and thecideids are indistinguishable. Also, the identification of morphological characters correlative with both palaeontological and neontological approaches to thecideoid phylogeny has important implications for thecideide taxonomy. Interpretation of the morphology exhibited by the Cotswold specimens introduces the probability that during their earliest ontogeny moorellinin, thecidein and lacazellin dorsal valves follow the same development pattern and the described ontogenetic sequence has been corroborated by evidence from Jurassic rocks of Argentina, North America and France, from Cretaceous rocks of England, Central Europe and Czechoslovakia, also from extant species from the Atlantic, Indian and Pacific oceans, and to an extent which suggests the pattern of ontogenetic development revealed has been typical of thecideoids throughout their history.     

Pleurotomaria DeFrance, 1826 (Gastropoda,Mollusca) from the Lower Bajocian (Middle Jurassic) sediments of Luxembourg,with considerations on its systematics,evolution and palaeobiogeographical history

Abstract: Pleurotomaria species from lower Bajocian (Middle Jurassic) sediments of south‐western Luxembourg housed in the National Natural History Museum of Luxembourg are described. Seven species are recognized, one of which is new, Pleurotomaria faberi sp. nov. A more detailed definition of the diagnostic characters of the genus is proposed and the morphological continuity between Talantodiscus and Pleurotomaria is demonstrated, suggesting that the former cannot be considered as a distinct taxon. The palaeoecology, evolution and palaeobiogeographical history of Pleurotomaria are outlined. Pleurotomaria presumably first appeared in late Middle Triassic of New Zealand where it underwent a relative diversification up to the Hettangian (Early Jurassic). From early Hettangian, most of its evolutionary history took place in Europe and western Tethys. In the European epicontinental seas, Pleurotomaria experienced two important radiations. The first occurred in the Early Jurassic, with a peak in the late Pliensbachian, and was marked by an expansion of the distribution to the central part of western Tethys. After a collapse in species diversity, probably related to the early Toarcian anoxic event, a second radiation occurred. This culminated in the early Bajocian and was mainly confined in a region encompassing southern England, Paris Basin and southern Germany. Low‐spired species, formerly attributed to Talantodiscus, probably originated independently and iteratively during the history of Pleurotomaria. The facies and associated benthic faunas suggest that Pleurotomaria probably lived on shallow soft bottoms composed of mixed calcareous–siliciclastic sediments. The two main Early Jurassic and early Middle Jurassic radiations of the genus took place in these environments. Records of the genus in Jurassic carbonate platform deposits are very few and concern mainly post‐Bajocian species.     

A New Basal Sauropod Dinosaur from the Middle Jurassic of Niger and the Early Evolution of Sauropoda

Background

The early evolution of sauropod dinosaurs is poorly understood because of a highly incomplete fossil record. New discoveries of Early and Middle Jurassic sauropods have a great potential to lead to a better understanding of early sauropod evolution and to reevaluate the patterns of sauropod diversification.

Principal Findings

A new sauropod from the Middle Jurassic of Niger, Spinophorosaurus nigerensis n. gen. et sp., is the most complete basal sauropod currently known. The taxon shares many anatomical characters with Middle Jurassic East Asian sauropods, while it is strongly dissimilar to Lower and Middle Jurassic South American and Indian forms. A possible explanation for this pattern is a separation of Laurasian and South Gondwanan Middle Jurassic sauropod faunas by geographic barriers. Integration of phylogenetic analyses and paleogeographic data reveals congruence between early sauropod evolution and hypotheses about Jurassic paleoclimate and phytogeography.

Conclusions

Spinophorosaurus demonstrates that many putatively derived characters of Middle Jurassic East Asian sauropods are plesiomorphic for eusauropods, while South Gondwanan eusauropods may represent a specialized line. The anatomy of Spinophorosaurus indicates that key innovations in Jurassic sauropod evolution might have taken place in North Africa, an area close to the equator with summer-wet climate at that time. Jurassic climatic zones and phytogeography possibly controlled early sauropod diversification.     

The radiation of cynodonts and the ground plan of mammalian morphological diversity

Cynodont therapsids diversified extensively after the Permo-Triassic mass extinction event, and gave rise to mammals in the Jurassic. We use an enlarged and revised dataset of discrete skeletal characters to build a new phylogeny for all main cynodont clades from the Late Permian to the Early Jurassic, and we analyse models of morphological diversification in the group. Basal taxa and epicynodonts are paraphyletic relative to eucynodonts, and the latter are divided into cynognathians and probainognathians, with tritylodonts and mammals forming sister groups. Disparity analyses reveal a heterogeneous distribution of cynodonts in a morphospace derived from cladistic characters. Pairwise morphological distances are weakly correlated with phylogenetic distances. Comparisons of disparity by groups and through time are non-significant, especially after the data are rarefied. A disparity peak occurs in the Early/Middle Triassic, after which period the mean disparity fluctuates little. Cynognathians were characterized by high evolutionary rates and high diversity early in their history, whereas probainognathian rates were low. Community structure may have been instrumental in imposing different rates on the two clades.     

The first euthemistid damsel-dragonfly?from the Middle Jurassic of China (Odonata,Epiproctophora,?Isophlebioptera)

Sinoeuthemis daohugouensis gen. et sp. n. is the first record of the isophlebiopteran family Euthemistidae from Middle Jurassic of northeast China, while previously this family was restricted to the early Late Jurassic Kazakhstan. This new finding allows us to emend the family diagnosis with hindwing characters. This new species shows a mixture of characters alternatively present in different genera of the two families Euthemistidae and Sphenophlebiidae.     

Una nueva especie de Weltrichia (Bennettitales) del Jurásico Medio de la Formación Tecomazuchil (Oaxaca, México)

A new species of Weltrichia (Williamsoniaceae: Bennettitales) is described from the Middle Jurassic of Oaxaca. The specimens come from the Tecomazuchil Formation in the Ayuquila region, at the border between the Oaxaca and Puebla states. Fossils are preserved as impressions and compressions, in a fine-grained sublitharenite sequence deposited in a fluvial environment. Preserved diagnostic characters include: large size; a cup-shaped receptacle showing seven radially arranged and basically fused microsporophylls bearing synangia. Microsporophylls are ornamented with longitudinal striations and fine brittled hairs on the edge of their wide base, and taper into a narrow distal tip. In the adaxial part of the microsporophylls seven to nine synangia are observed. These characters differentiate the new species Weltrichia mixtequensis from all previously recorded species from Mexico or elsewhere. The presence of this new species in the Middle Jurassic strata of the Ayuquila region add to the scarce fossil record of microsporangiate structures in the Jurassic flora of Mexico.     

The early evolution of titanosauriform sauropod dinosaurs

Titanosauriformes was a globally distributed, long‐lived clade of dinosaurs that contains both the largest and smallest known sauropods. These common and diverse megaherbivores evolved a suite of cranial and locomotory specializations perhaps related to their near‐ubiquity in Mesozoic ecosystems. In an effort to understand the phylogenetic relationships of their early (Late Jurassic–Early Cretaceous) members, this paper presents a lower‐level cladistic analysis of basal titanosauriforms in which 25 ingroup and three outgroup taxa were scored for 119 characters. Analysis of these characters resulted in the recovery of three main clades: Brachiosauridae, a cosmopolitan mix of Late Jurassic and Early Cretaceous sauropods, Euhelopodidae, a clade of mid‐Cretaceous East Asian sauropods, and Titanosauria, a large Cretaceous clade made up of mostly Gondwanan genera. Several putative brachiosaurids were instead found to represent non‐titanosauriforms or more derived taxa, and no support for a Laurasia‐wide clade of titanosauriforms was found. This analysis establishes robust synapomorphies for many titanosauriform subclades. A re‐evaluation of the phylogenetic affinities of fragmentary taxa based on these synapomorphies found no body fossil evidence for titanosaurs before the middle Cretaceous (Aptian), in contrast to previous reports of Middle and Late Jurassic forms. Purported titanosaur track‐ways from the Middle Jurassic either indicate a substantial ghost lineage for the group or – more likely – represent non‐titanosaurs. Titanosauriform palaeobiogeographical history is the result of several factors including differential extinction and dispersal. This study provides a foundation for future study of basal titanosauriform phylogeny and the origins of Titanosauria. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166 , 624–671.     

New fossil hangingflies (Insecta: Mecoptera: Raptipedia: Cimbrophlebiidae) from the Middle Jurassic of Inner Mongolia,China

Abstract: Two new genera with six new species of hangingflies (Mecoptera: Raptipedia: Cimbrophlebiidae) are described. They were collected from the Middle Jurassic nonmarine sedimentary strata of the Jiulongshan Formation in Daohugou, Inner Mongolia, north‐eastern China. This report of Cimbrophlebiidae from the Yanliao Biota provides detailed morphological information and evidence of a broad diversity of Cimbrophlebiidae during the Middle Jurassic. A key to the known species of Cimbrophlebiidae is provided.     

湖北秭归盆地中侏罗世陈家湾组孢粉组合的发现及其意义

本文首次报道了湖北秭归盆地陈家湾组孢粉组合,该组合可归入Cyathidites minor-Classopollis Callialasporites为代表的组合,时代属中侏罗世。陈家湾组孢粉组合的特征反映了秭归盆地中侏罗世泄滩组、陈家湾组和沙溪庙组三个组的孢粉组合的面貌基本一致,仅早期组合与中、晚期组合略有差别。建议以Gyathidites minor-classopollis-callialasportes组合代表湖北西部——重庆地区中侏罗世孢粉组合,早期为Lunzisporites pallidus亚组合,中晚期为Converrrcosisporites venitus亚组合。根据孢粉植物群在本区侏罗纪垂直分布情况,提出早侏罗世时期属亚热带一热带炎热潮湿气候环境,植物生长茂盛;早侏罗世之后,潮湿的气候仍占主导地位,但出现了干旱的先兆;中侏罗世早期进入了半干旱阶段,随后即为炎热干旱的气候所笼罩;至晚侏罗世达到非常干旱的程度,植物种类十份单调,唯有掌鳞杉科植物占据着统治地位。     

First record of Eretmophyllum (Ginkgoales) with well-preserved cuticle from the Middle Jurassic of the Ordos Basin,Inner Mongolia,China

The genus Eretmophyllum, a characteristic and widespread taxon of the order Ginkgoales, is restricted in the Mesozoic floras of Eurasia. In China, although some specimens were assigned to Eretmophyllum based on gross leaf morphology, none have epidermal structure, which is essential for species delimitation within this genus. In this paper, we describe a new species, Eretmophyllum neimengguensis n. sp., from the Middle Jurassic Yan’an Formation of the Ordos Basin, China. This is the first record of the genus Eretmophyllum (Ginkgoales) from the Ordos Basin as well as from China based upon the gross leaf morphology and the epidermal structure. The new record significantly extends the stratigraphic and geographic distribution of Eretmophyllum in China and Eurasia. It also improves our understanding of its leaf morphology, epidermal structure, and past diversity. The taxonomic position and the stratigraphic and geographical range of the genus Eretmophyllum are discussed. Briefly, leaf morphological and epidermal characters of the new species, associated plant assemblages, and sedimentology indicate that the regional climate of the Ordos Basin was warm and humid with seasonal temperature and precipitation fluctuations in warm-temperate zone during the Middle Jurassic. Furthermore, given the relationship between the distribution/diversity of the genus and the climate, the genus Eretmophyllum may be confined to the warm-temperature climate, is intolerant of heat and frost, and can be considered as an indicator of humid and warm climatic conditions.     

The complex nature of progenetic species — examples from Mesozoic ammonites

Several examples of progenetic species among Mesozoic ammonites are investigated. The ammonites are Middle Jurassic kosmoceratids, Upper Jurassic oppeliids, and Upper Cretaceous scaphites. As assessed through outgroup comparison, the progenetic species in each of these examples is characterized by small size at maturity and the presence of morphological features typical of those of the juveniles of more primitive species. However, in none of these examples is the progenetic species a duplicate form of the juvenile stage of more primitive species. There are at least three kinds of features of progenetic species that differ from those of the juveniles of more primitive species: (1) symplesiomorphous features associated with maturation, (2) unique features whose presence is not clearly related to progenetic processes, and (3) unique features that may represent epigenetic outgrowths of juvenile morphology. This novel combination of juvenile. adult. and unique features may endow progenetic species with the evolutionary potential to play a role in the origin of higher taxa. □ Progenesis, heterochrony, Ammon-oidea. Jurassic, Cretaceous.     

内蒙古宁城道虎沟地区中侏罗世非海相双壳类Ferganoconcha

Ferganoconcha是广泛分布于我国北部、中亚、西伯利亚和乌拉尔地区下、中侏罗统的一类非海相双壳类。Ferganoconchasibirica的产出表明道虎沟地区道虎沟层与辽西地区的海房沟组和冀北地区的九龙山组层位相当,时代介于早侏罗世晚期至中侏罗世之间。结合昆虫和叶肢介化石反映的时代,认为道虎沟层的时代可能为中侏罗世早中期。综合近年来在Ferganoconchidae的分类方面取得的进展,对F.sibirica进行了重新厘定。     

Stratigraphic distribution and ecology of European Jurassic bivalves

Documentation of bivalve generic and species diversity and times of first and last appearance through successive Jurassic stages in Europe, together with data on turnover and changes in taxonomic and ecological composition of the faunas, indicate an approximation to the establishment of an equilibrium fauna by early Middle Jurassic times. Subsequently faunal change was slight compared with the early Jurassic. A diversity increase through the Lower into the Middle Jurassic correlates with an increase in the area of epicontinental seas, while a major species extinction in the early Toarcian is bound up with the onset of widespread stagnation associated with a rise of sea level. An increase of the generic extinction rate at the end of the period correlates with a regional marine regression. The mean species longevity is estimated at 15×10⁶ years. The ecological factors thought to control bivalve distribution are reviewed and four ecological associations distinguished: the reefal, lagoonal and nearshore and basinal marine.     

New Phoenicopsis leaves (Czekanowskiales) from the Middle Jurassic Daohugou Biota,China and their roles in phytogeographic and paleoclimatic reconstruction

The Middle Jurassic Jiulongshan Formation, distributed in the Daohugou area, Ningcheng County, Inner Mongolia, China, is famous for yielding abundant, well-preserved fossil vertebrates and invertebrates. However, only a few fossil plants have been reported to date. In this paper, one new species of Czekanowskiales, Phoenicopsis (Windwardia) daohugouensis n. sp. is described based upon leaf morphology and epidermal characters. The new species represents the first record of Czekanowskiales from the Daohugou Biota. The discovery of the new species reveals the significance of the Daohugou flora as one of the deciduous forests in the temperate-warm temperate zone of Eurasia during the Middle Jurassic.     

Middle Jurassic Spore- pollen Assemblages from Turpan- Shanshan Area,Xinjiang

The Middle Jurassic palynoflora from the two wells of PUl and CN1 of Turpan-Shanshan area in Xinjiang consists of 97 species of fossil spores and pollen grains referred to 45 genera, of which 2 species are newly described. Three palynological assemblages including: 1) Cyathidites-Cycadopites-Quadraeculina (CCQ), 2) Cyathidites-Classopollis-Picites (CCP) and 3 ) Granu-latisporites-Classopollis-Podocarpidites (GCP) assemblages are established in the Xishanyao, Sanjianfang and Qiketai Formations, respectively. Comparisons have been made between these assemblages with those of the adjacent regions in Xinjiang and other domestic areas and at abroad. The geological age of the CCQ assemblage is suggested to be at early Middle Jurassic (corresponding to Aalenian to Bajocian age); while the CCP and GCP assemblages are considered to be at late Middle Jurassic (corresponding to early to late Bathonian age, respectively).     

新疆准噶尔盆地白杨河中侏罗世植物化石新材料

系统描述了准噶尔盆地西北缘白杨河地区西山窑组植物化石15属25种,首次在新疆地区发现侏罗纪真蕨类重要分子Coniopteris hymenophylloides的原位孢子及其孢子囊群,并对Phoenicopsis ( Phoenicopsis) an-gustifolia的叶角质层进行了研究。白杨河地区西山窑组迄今已知植物化石24属39种,以富含蕨类、茨康类、银杏类及松柏类,少见苏铁类等为特征,属于较为典型的内陆型、温带或暖温带植物群;其时代为中侏罗世,且可能为中侏罗世早期。该植物群应属于欧亚大陆早、中侏罗世植物地理区系中的西伯利亚区,反映了温暖潮湿、具季节性变化、并有利成煤的环境。     

新疆吐鲁番—鄯善地区中侏罗世孢粉组合

研究新疆吐鲁番鄯善地区葡１井和草南１井中侏罗世孢子花粉化石４５属９７种,包括２个新种。建立西山窑组、三间房组和七克台组共３个孢粉组合,其地质时代相当于中侏罗世早期和晚期。     

Rapid transformation in the braincase of sauropod dinosaurs: integrated evolution of the braincase and neck in early sauropods?

Sauropod dinosaurs were quadrupedal herbivores with a highly specialized body plan that attained the largest masses of any terrestrial vertebrates. Recent discoveries have shown that key traits associated with sauropod gigantism appeared stepwise during the Late Triassic and Early Jurassic in evolutionary ‘cascades’ of associated changes, in which a ‘head and neck’ cascade has been suggested as an important module. Here, we investigate the evolutionary transformation of the sauropodomorph braincase, using discrete anatomical characters, prompted by the reanalysis of a Middle Jurassic (Bathonian) sauropodiform braincase from England. Our analysis shows that sauropod braincases are highly distinct, and occupy a different region of morphospace than their evolutionary relatives. This resulted from anatomical transformations including a set of changes in the surface attachments of craniocervical musculature, which may indicate integrated evolution between neck elongation and transformation in braincase anatomy. Neck elongation in Late Triassic and Early or Middle Jurassic taxa is potentially associated with episodes of skull reduction, indicating that the ‘head and neck’ cascade was activated more than once in the evolutionary history of Sauropodomorpha. The re‐activation of this cascade in the Jurassic may have impacted on the differential survival of sauropodomorph lineages through the Early and Middle Jurassic.     

A new long-proboscid genus of Pseudopolycentropodidae (Mecoptera) from the Middle Jurassic of China and its plant-host specializations

We describe a new genus and species of Mecoptera with siphonate mouthparts, Sinopolycentropus rasnitsynigen. et sp. n., assigned to the family Pseudopolycentropodidae Handlirsch, 1925. The specimen was collected from late Middle Jurassic nonmarine strata of the Jiulongshan Formation in Inner Mongolia, northeastern China. The new material provides additional evidence for an early diversification of pseudopolycentropodids that was ongoing during the Middle Jurassic. This diversity also adds to the variety of known pseudopolycentropodids with tubular proboscides that apparently fed on ovulate fluids produced by Mesozoic gymnosperms.