Mostrando postagens com marcador Najash rionegrina. Mostrar todas as postagens
Mostrando postagens com marcador Najash rionegrina. Mostrar todas as postagens

quinta-feira, 21 de novembro de 2019

Fóssil de cobra com patas encontrado na Argentina confirma teoria de Darwin

Concepção artística da
 cobra cujo fóssil foi
encontrado na Argentina
Pesquisadores da Universidade de Flinders, Austrália, encontram na Argentina um esqueleto de serpente com patas traseiras, o que seria uma das melhores provas da teoria da evolução de Darwin.

A Najash rionegrina tem seu nome derivado da palavra Nahash (cobra em hebraico) e por seu esqueleto ter sido encontrado na província argentina de Río Negro.

O fóssil possui restos de patas traseiras, o que mostraria o quanto o corpo das cobras evoluiu até se tornar mais flexível como as atuais. Elas seriam uma evolução de antigos lagartos.

Durante os primeiros 70 milhões de anos de evolução, o animal ainda se movia sobre um par de patas traseiras.

De acordo com Alessandro Palci, pesquisador da Universidade de Flinders, além do desaparecimento das patas traseiras, outras mudanças na estrutura do animal teriam surgido ao longo do tempo, como indicaria o fóssil.

"A Najash tem o crânio mais completo, tridimensionalmente preservado de uma serpente antiga. Isto está nos fornecendo uma grande quantidade de novas informações sobre como a cabeça das serpentes evoluiu. Tem algumas, mas não todas as juntas flexíveis encontradas no crânio de serpentes modernas. Sua orelha é intermediária entre a dos lagartos e das cobras atuais, e diferente destas, tem o osso da face bem desenvolvido, que também é remanescente dos lagartos", afirmou Palci.

Ainda segundo Mike Lee, pesquisador do Museu do Sul da Austrália e da Universidade de Flinders, a "Najash encontrada mostra como as cobras evoluíram dos lagartos em passos evolutivos, tal como Darwin predisse".
Com informação da Science Advances, com ilustração de Raúl O. Gómez, da Universidade de Buenos Aires.

quarta-feira, 20 de maio de 2015

 PALEONTOLOGIA 2015

Origem das serpentes

The Origin of Snakes: revealing the Ecology, Behavior, and Evolutionary History of Early Snakes - using Genomics, Phenomics, and the Fossil Record


Reconstruction of the ancestral crown-group snake, based on the new study.
Artwork by Julius Csotonyi.

Abstract
Background
The highly derived morphology and astounding diversity of snakes has long inspired debate regarding the ecological and evolutionary origin of both the snake total-group (Pan-Serpentes) and crown snakes (Serpentes). Although speculation abounds on the ecology, behavior, and provenance of the earliest snakes, a rigorous, clade-wide analysis of snake origins has yet to be attempted, in part due to a dearth of adequate paleontological data on early stem snakes. Here, we present the first comprehensive analytical reconstruction of the ancestor of crown snakes and the ancestor of the snake total-group, as inferred using multiple methods of ancestral state reconstruction. 
 
We use a combined-data approach that includes new information from the fossil record on extinct crown snakes, new data on the anatomy of the stem snakes Najash rionegrina, Dinilysia patagonica, and Coniophis precedens, and a deeper understanding of the distribution of phenotypic apomorphies among the major clades of fossil and Recent snakes. Additionally, we infer time-calibrated phylogenies using both new ‘tip-dating’ and traditional node-based approaches, providing new insights on temporal patterns in the early evolutionary history of snakes.
Results
Comprehensive ancestral state reconstructions reveal that both the ancestor of crown snakes and the ancestor of total-group snakes were nocturnal, widely foraging, non-constricting stealth hunters. They likely consumed soft-bodied vertebrate and invertebrate prey that was subequal to head size, and occupied terrestrial settings in warm, well-watered, and well-vegetated environments. The snake total-group – approximated by the Coniophis node – is inferred to have originated on land during the middle Early Cretaceous (~128.5 Ma), with the crown-group following about 20 million years later, during the Albian stage. Our inferred divergence dates provide strong evidence for a major radiation of henophidian snake diversity in the wake of the Cretaceous-Paleogene (K-Pg) mass extinction, clarifying the pattern and timing of the extant snake radiation. Although the snake crown-group most likely arose on the supercontinent of Gondwana, our results suggest the possibility that the snake total-group originated on Laurasia.
Conclusions
Our study provides new insights into when, where, and how snakes originated, and presents the most complete picture of the early evolution of snakes to date. More broadly, we demonstrate the striking influence of including fossils and phenotypic data in combined analyses aimed at both phylogenetic topology inference and ancestral state reconstruction.

Keywords: Serpentes, Phylogeny, Ancestral state reconstruction, Divergence time estimation, Combined analysis, Fossil tip-dating
Allison Y Hsiang, Daniel J Field, Timothy H Webster, Adam DB Behlke, Matthew B Davis, Rachel A Racicot and Jacques A Gauthier. 2015. The Origin of Snakes: revealing the Ecology, Behavior, and Evolutionary History of Early Snakes using Genomics, Phenomics, and the Fossil Record. BMC Evolutionary Biology. DOI: 10.1186/s12862-015-0358-5.
Limbless triumph: The origin and diversification of snakes - http://go.shr.lc/1HsbUb8
What did the first snakes look like? http://phy.so/351261014 via @physorg_com
Data Suggests Legs and Toes in Ancestor of Living Snakes http://nyti.ms/1JxQewl

sábado, 31 de janeiro de 2015

 Paleontology • 2015 

The Oldest Known Snakes from the Middle Jurassic-Lower Cretaceous provide insights on Snake Evolution

Ancient snakes: (top left) Portugalophis lignites (Upper Jurassic) in a gingko tree, from coal swamp deposits at Guimarota, Portugal;  (top right) Diablophis gilmorei (Upper Jurassic), hiding in a ceratosaur skull, from the Morrison Formation in Fruita, Colorado; (bottom) Parviraptor estesi (Upper Jurassic/Lower Cretaceous) swimming in freshwater lake with snails and algae, from the Purbeck Limestone in Swanage, England.
Illustrations: Julius Csotonyi |  DOI: 10.1038/ncomms6996
ABSTRACT 
The previous oldest known fossil snakes date from ~100 million year old sediments (Upper Cretaceous) and are both morphologically and phylogenetically diverse, indicating that snakes underwent a much earlier origin and adaptive radiation. We report here on snake fossils that extend the record backwards in time by an additional ~70 million years (Middle Jurassic-Lower Cretaceous). These ancient snakes share features with fossil and modern snakes (for example, recurved teeth with labial and lingual carinae, long toothed suborbital ramus of maxillae) and with lizards (for example, pronounced subdental shelf/gutter). The paleobiogeography of these early snakes is diverse and complex, suggesting that snakes had undergone habitat differentiation and geographic radiation by the mid-Jurassic. Phylogenetic analysis of squamates recovers these early snakes in a basal polytomy with other fossil and modern snakes, where Najash rionegrina is sister to this clade. Ingroup analysis finds them in a basal position to all other snakes including Najash.
  


 Michael W. Caldwell, Randall L. Nydam,  Alessandro Palci and Sebastián Apesteguía. 2015. The Oldest Known Snakes from the Middle Jurassic-Lower Cretaceous provide insights on Snake Evolution. Nature Communications. 6. DOI: 10.1038/ncomms6996.

The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution

Published -

Abstract

The previous oldest known fossil snakes date from ~100 million year old sediments (Upper Cretaceous) and are both morphologically and phylogenetically diverse, indicating that snakes underwent a much earlier origin and adaptive radiation. We report here on snake fossils that extend the record backwards in time by an additional ~70 million years (Middle Jurassic-Lower Cretaceous). These ancient snakes share features with fossil and modern snakes (for example, recurved teeth with labial and lingual carinae, long toothed suborbital ramus of maxillae) and with lizards (for example, pronounced subdental shelf/gutter). The paleobiogeography of these early snakes is diverse and complex, suggesting that snakes had undergone habitat differentiation and geographic radiation by the mid-Jurassic. Phylogenetic analysis of squamates recovers these early snakes in a basal polytomy with other fossil and modern snakes, where Najash rionegrina is sister to this clade. Ingroup analysis finds them in a basal position to all other snakes including Najash.