Linglongtriton daxishanensis, gen. et sp. nov.Â
Jia Jia & Ke-Qin Gao (2019)
A new stem hynobiid salamander (Urodela, Cryptobranchoidea) from the Upper Jurassic (Oxfordian) of Liaoning Province, China.
Journal of Vertebrate Paleontology Article: e1588285Â
Hynobiids are a group of small- to moderate-sized salamanders living primarily in Asia. They are a primitive crown-group clade, with a poor fossil record. Several hynobiid-like taxa have been discovered from the Lower Cretaceous strata of northern China during the last 20 years, with Liaoxitriton zhongjiani and Nuominerpeton aquilonaris identified as the oldest known stem hynobiids. However, the record of pre-Cretaceous hynobiid-like taxa is only known by Liaoxitriton daohugouensis, of which both the morphology and the congeneric status with L. zhongjiani remain problematic. Here, we report on a new hynobiid-like salamander, Linglongtriton daxishanensis, gen. et sp. nov., on the basis of two specimens from the Upper Jurassic Lanqi/Tiaojishan Formation (~160 Ma) of Liaoning Province, China. Linglongtriton is diagnosed by a unique combination of features revealed by both observation under microscope and micro-computed tomography (ÎCT) scan of the holotype, including nasals separated from each other at the midline; prootic, opisthotic, and exoccipital retained as discrete elements; dentary with a lateral groove; articular not ossified; metacarpal III enlarged; a single centrale; and distal tarsals 4 and 5 fused into a single element. Phylogenetic analysis identified Linglongtriton and several other hynobiid-like taxa, including Liaoxitriton daohugouensis, as stem hynobiids, thereby extending the temporal range of the stem by at least 40 Ma--from the Early Cretaceous (AptianâBarremian) to the Middle Jurassic (Bathonian). Comparative study of Linglongtriton with living and fossil hynobiids sheds new lights on the evolution and developmental mechanisms of several characters, including nasal separation and tarsal elements.
David P. Groenewald,Â Michael O. DayÂ & Bruce S. Rubidge (2019)
Vertebrate assemblages from the northâcentral Main Karoo Basin, South Africa, and their implications for midâPermian biogeography
Lethaia (advance online publication)
The rich fossil vertebrate record from the Beaufort Group, Main Karoo Basin, provides a global standard for midâPermian to MidâTriassic continental faunas. However, recent studies have demonstrated variability in the composition of contemporaneous faunas across Gondwana. This raises the question of how much the vertebrate faunas differ within the Karoo, where the taxonomic composition of vertebrate assemblage zones (AZs) is mostly considered to be uniform. Although fossil material is known from across the outcrop of the Beaufort Group, the lowest Beaufort strata have received little attention, particularly north of S31Â10â. Here, we report two fossil tetrapod assemblages from the lowest Beaufort Group in the southern Free State Province, which represent the northernmost point at which the lowest Beaufort has been targeted for collecting. The lower assemblage is characterized by an abundance of the small dicynodont Eosimops and can thus be attributed to the Tapinocephalus AZ (Guadalupian), but the absence of dinocephalian or pareiasaurian material is unlike contemporaneous assemblages found further south. This suggests that the Tapinocephalus AZ was not uniform across the entire basin and highlights that the abundance, distribution and taxonomic composition of Karoo biozones may vary more than currently appreciated. The upper assemblage, characterized by the dicynodonts Oudenodon, Aulacephalodon and Dinanomodon, is attributable to the upper Cistecephalus AZ to lower Daptocephalus AZ. The juxtaposition of the lower Tapinocephalus AZ and upper Cistecephalus\lower Daptocephalus AZ in the southern Free State implies a stratigraphic gap from the Middle to Late Permian of up to 6 million years.
Francisco J. Correa-Martins (2019)
The Neostratotype of Itapecuru Formation (Lower-Middle Albian) and Its Impact for Mesozoic Stratigraphy of ParnaÃba Basin.
Anais da Academia Brasileira de CiÃncias 91, suppl.2: e20180730
This study defines the neostratotype of the Lower-Middle Albian Itapecuru Formation in the ParnaÃba Basin, Northeast Brazil. In this sedimentary succession along the right bank of the Itapecuru River near the Itapecuru-Mirim City, MaranhÃo State, three lithofacies associations are recognized. The first is silty claystone with some very fine sand, micaceous, reddish color, thin laminated, showing a tabular aspect, interpreted as floodplain fines in a distal position. The second is clayey siltstone, reddish color, with ripple cross-lamination, very thin cross-laminated wacke lenses, grading to thin parallel lamination, in apparently tabular layers, interpreted as crevasse splay and distributive channels deposits in successive avulsion events. The third is fine quartz wacke, reddish to grayish color, showing grouped trough cross bedding, interpreted as channel filling deposits. These facies associations correspond to part of a fluvial depositional system, with predominantly fine-grained rocks, and small lakes in the floodplain, in an oxidizing environment and marked by seasonality. These field data, reinforced by grain size and petrographic analyses showed that, contrary to previous descriptions, the Itapecuru Formation consists mainly of mudrocks. This research also shows that the medium to coarse sandstones and conglomerates, previously included in the Itapecuru Formation, belong to the underlying GrajaÃ Formation.
Andreas T. Matzke & Michael W. Maisch (2019)
The braincase of Syllomus aegyptiacusLydekker, 1899 (Reptilia, Testudines) from the Middle Miocene Calvert Formation of Virginia.
Palaeodiversity 12(1): 31-39
The braincase of the marine turtle Syllomus aegyptiacus (Calvert Formation, Virginia, Middle Miocene) is described and figured in detail for the first time. It reveals a ventral crest on the basisphenoid, a high dorsum sellae, an almost subequal diameter of the canals for the internal and lateral carotid arteries at a cross break and a canalis caroticus lateralis and internus that are still far separated from each other at level of the dorsum sellae. The braincase is compared to other known braincases of fossil and extant chelonioid turtles.
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Hong-Tao Li, Ting-Shuang Yi, Lian-Ming Gao, Peng-Fei Ma, Ting Zhang, Jun-Bo Yang, Matthew A. Gitzendanner, Peter W. Fritsch, Jie Cai, Yang Luo, Hong Wang, Michelle van der Bank, Shu-Dong Zhang, Qing-Feng Wang, Jian Wang, Zhi-Rong Zhang, Chao-Nan Fu, Jing Yang, Peter M. Hollingsworth, Mark W. Chase, Douglas E. Soltis, Pamela S. Soltis & De-Zhu Li (2019)
Origin of angiosperms and the puzzle of the Jurassic gap.
Nature Plants (2019)Â
Angiosperms are by far the most species-rich clade of land plants, but their origin and early evolutionary history remain poorly understood. We reconstructed angiosperm phylogeny based on 80âgenes from 2,881âplastid genomes representing 85% of extant families and all orders. With a well-resolved plastid tree and 62âfossil calibrations, we dated the origin of the crown angiosperms to the Upper Triassic, with major angiosperm radiations occurring in the Jurassic and Lower Cretaceous. This estimated crown age is substantially earlier than that of unequivocal angiosperm fossils, and the difference is here termed the 'Jurassic angiosperm gap'. Our time-calibrated plastid phylogenomic tree provides a highly relevant framework for future comparative studies of flowering plant evolution.
Zerina Johanson, Kate Trinajstic, Stephen Cumbaa, and Michael J. Ryan (2019)
Fusion in the vertebral column of the pachyosteomorph arthrodire Dunkleosteus terrelli ('Placodermi').Â
Palaeontologia Electronica 22.2.20A 1-13.Â
Fusion in the vertebral column has evolved multiple times within jawed vertebrates and for these taxa represents normal physiology, with structures such as the sacrum, notarium and pygostyle providing rigidity and support. The synarcual represents the fusion of the anterior part of the vertebral column and occurs in a number of jawed vertebrates, including a variety of placoderms, chondrichthyans and mammals. Placoderms are an entirely fossil group of armoured fishes (Silurian-Devonian), resolved phylogenetically to the base of the jawed vertebrate clade, with vertebrae comprising neural and haemal arches composed of perichondral bone. The placoderm synarcual preserves substantial developmental information from anterior (oldest) to posterior, where new vertebrae are incorporated. This developmental sequence was described recently in the phyllolepid arthrodire Cowralepis mclachlani and ptyctodonts such as Materpiscis attenboroughi, although finer developmental details were not visible. We describe the synarcual in a subadult specimen of the pachyosteomorph arthrodire Dunkleosteus terrelli, preserving 16 paired vertebral elements showing varying degrees of anteroposterior fusion along the vertebral column. Micro-CT scanning of the synarcual provides details of a transitional zone of vertebral modification (involving four of these paired vertebrae, posteriorly), providing unprecedented information on how each vertebra is altered and incorporated into the synarcual. Some of the synarcual elements still retain substantial vertebral identity, showing less fusion overall, thus being more comparable to other arthrodires such as Compagopiscis. By comparison, synarcuals of other taxa, such as the ptyctodont placoderms, along with batoids, holocephalans (Chondrichthyes) and mammals (syncervical) show more complete fusion of vertebral elements.