Search

Our understanding of the evolutionary origin of Chordata, one of the most disparate and ecologically significant animal phyla, is hindered by a lack of unambiguous stem-group relatives. Problematic Cambrian fossils that have been considered as candidate chordates include vetulicolians, 1 Yunnanozoon, 2 and the iconic Pikaia. 3 However, their phylogenetic placement has remained poorly constrained, impeding reconstructions of character evolution along the chordate stem lineage. Here we reinterpret the morphology of Pikaia, providing evidence for a gut canal and, crucially, a dorsal nerve cord-a robust chordate synapomorphy. The identification of these structures underpins a new anatomical model of Pikaia that shows that this fossil was previously interpreted upside down. We reveal a myomere configuration intermediate between amphioxus and vertebrates and establish morphological links between Yunnanozoon, Pikaia, and uncontroversial chordates. In this light, we perform a new phylogenetic analysis, using a revised, comprehensive deuterostome dataset, and establish a chordate stem lineage. We resolve vetulicolians as a paraphyletic group comprising the earliest diverging stem chordates, subtending a grade of more derived stem-group chordates comprising Yunnanozoon and Pikaia. Our phylogenetic results reveal the stepwise acquisition of characters diagnostic of the chordate crown group. In addition, they chart a phase in early chordate evolution defined by the gradual integration of the pharyngeal region with a segmented axial musculature, supporting classical evolutionary-developmental hypotheses of chordate origins 4 and revealing a "lost chapter" in the history of the phylum., Competing Interests: Declaration of interests The authors declare no competing interests., (Crown Copyright © 2024. Published by Elsevier Inc. All rights reserved.)

The freshwater amphipod genus Hyalella Smith, 1874 is widely distributed in the Neotropics, with several biogeographically restricted species and a high cryptic diversity throughout South America. Tens of species of Hyalella have been documented from nearby Brazil and Argentina, but no systematic record of the genus exists for Paraguay. Here we describe two new species of Hyalella : H.mboitui sp. nov. and H.julia sp. nov. from the Ñeembucú wetlands of southwestern Paraguay. Hyalellamboitui sp. nov. and H.julia sp. nov. are characterised by a dorsally smooth body, pigmented eyes, uropod 1 endopod with a curved seta, the dorsal margin of uropod 3 ramus without setae, and uropod 3 peduncle longer than wide and with six setae apically. The two species are distinguished by their diagnostic mouthparts, with a median serrated edge on the lacinia mobilis in H.mboitui sp. nov. and two elongated lateral denticles with a serrated edge in H.julia sp. nov. , and by the presence of a pronounced cup for the dactylus on gnathopod 2 in H.mboitui sp. nov . In addition, they show differences in the number of articles on antennae 1 and 2, in the relative length of the pereiopods, and in the numbers and types of setae on their gnathopods and uropods 1-3. Hyalellamboitui sp. nov. and H.julia sp. nov. represent the first taxonomically documented occurrence of Paraguayan freshwater amphipods. These new taxa attest to the largely unmapped species richness of freshwater invertebrates in the Humid Chaco of Paraguay. This potential biodiversity hotspot is currently under threat from land conversion, highlighting the need for more systematic studies and effective conservation of the local invertebrate biodiversity., Competing Interests: The authors have declared that no competing interests exist., (Giovanni Mussini, Nicole D. Stepan, Gersey Vargas.)

The end-Neoproterozoic transition marked a gradual but permanent shift between distinct configurations of Earth's biosphere. This interval witnessed the demise of the enigmatic Ediacaran Biota, ushering in the structured trophic webs and disparate animal body plans of Phanerozoic ecosystems. However, little consensus exists on the reality, drivers, and macroevolutionary implications of end-Neoproterozoic extinctions. Here we evaluate potential drivers of late-Neoproterozoic turnover by addressing recent findings on Ediacaran geochronology, the persistence of classical Ediacaran macrobionts into the Cambrian, and the existence of Ediacaran crown-group eumetazoans. Despite renewed interest in the possibility of Phanerozoic-style 'mass extinctions' in the latest Neoproterozoic, our synthesis of the available evidence does not support extinction models based on episodic geochemical triggers, nor does it validate simple ecological interpretations centred on direct competitive displacement. Instead, we argue that the protracted and indirect effects of early bilaterian innovations, including escalations in sediment engineering, predation, and the largely understudied impacts of reef-building, may best account for the temporal structure and possible selectivity of late-Neoproterozoic extinctions. We integrate these processes into a generalised model of early eumetazoan-dominated ecologies, charting the disruption of spatial and temporal isotropy on the Ediacaran benthos as a consequence of diversifying macrofaunal interactions. Given the nature of resource distribution in Ediacaran ecologies, the continuities among Ediacaran and Cambrian faunas, and the convergent origins of ecologically disruptive innovations among bilaterians we suggest that the rise of Phanerozoic-type biotas may have been unstoppable., (© 2023 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.)

The late Ediacaran Jiangchuan biota, from the Dengying Formation in eastern Yunnan, is well-known for its diverse macroalgal fossils, opening a window onto eukaryotic-dominated ecosystems from the late Neoproterozoic of South China. Although multiple lines of evidence suggest that metazoans had already evolved by the late Ediacaran, animal fossils have not yet been formally described from this locality. Here, we report a putative disc-shaped macrofossil from the Jiangchuan biota, Lobodiscus tribrachialis gen. et sp. nov. This specimen shows the triradial symmetry characteristic of trilobozoans, a group of Ediacaran macrofossils previously documented in Australia and Russia. Lobodiscus could record the youngest known occurrence of trilobozoans, strengthening taxonomic and ecological continuities between the Ediacaran "White Sea" and "Nama" assemblages. Our findings may expand the known paleogeographical distribution of trilobozoans and provide data for Ediacaran biostratigraphic correlations across the Yangtze block and globally, helping to track the diversification of early metazoan-grade organisms., Competing Interests: The authors declare no competing interests., (© 2024 The Author(s).)

BACKGROUND: In June 1993, the authors started performing the Vertical Banded Gastroplasty (VBG) via laparoscopy. METHODS: Since June 1993, 25 patients have undergone laparoscopic VBG. RESULTS: Weight loss did not differ from the traditional open VBG. CONCLUSIONS: The laparoscopic procedure, which can be performed simply, permits minimal trauma compared to the traditional open operation, with a reduction in hospitalization and in short-term as well as long-term complications.

A patient with ovarian carcinoma and splenic metastasis who underwent cytoreductive surgery is described. Since the patient had liver cirrhosis the authors hypothesize that the hepatic problem could have been a risk factor for splenic metastasis.

Gastric banding as a laparoscopic procedure was performed on 40 morbidly obese patients. This operation matches the advantages of the gastric banding (efficacy, reversibility and low invasivity) with the advantages of the laparoscopic procedure (low surgical risk, short hospital stay and less complications in the short and long term). The maximum follow-up is 6 months and so far the weight loss results are the same as we obtained by the vertical banded gastroplasty of Mason. The greatest problem of laparoscopic gastric banding is to get the right tightness of the band for a stoma of 12-13 mm. In three patients the band was replaced due to stenosis, in two of them by a laparoscopic procedure. The adjustable band of Kuzmak should exclude the risk of stenosis and its use will be tried by the laparoscopic procedure.