Réptil extinto lembra mamífero
5/8/2010
Agência FAPESP – Uma nova espécie de crocodiliano do Período Cretáceo (de cerca de 145,5 milhões a 65,5 milhões de anos atrás) foi descoberta no sudoeste da Tanzânia, com pernas mais finas e dentes que até então eram considerados exclusivos de mamíferos.
Os crocodilianos formam uma ordem de répteis aquáticos e ovíparos, que inclui os crocodilos, jacarés e o gavial, e são encontrados especialmente em regiões tropicais do mundo. Os crocodiliformes do Cretáceo, chamados de notossúquios, eram parentes distantes dos crocodilos e jacarés modernos.
Os notossúquios, que viviam nas massas terrestres do supercontinente Gondwana, tinham um nível de diversidade tanto morfológica como ecológica muito maior do que a encontrada nos atuais crocodilos. Um exemplo está na boca: em vez de fileiras de caninos cônicos e iguais, seus dentes eram divididos em tipos especializados em morder e em outros feitos para esmagar.
A descoberta da nova espécie, cujo fóssil foi encontrado em rochas de 105 milhões de anos, foi publicada na edição desta quinta-feira (5/8) da revista Nature.
Segundo Patrick O’Connor, do Ohio University College of Osteopathic Medicine, e colegas, na espécie, denominadaPakasuchus kapilimai, as fileiras superior e inferior de dentes entravam em contato de modo semelhante ao que até hoje havia sido observado apenas em mamíferos.
O animal também tinha o tamanho aproximado de um gato doméstico e era mais magro do que os crocodilianos atuais. Possuía ainda um pescoço flexível. Apesar das características inusitadas para a ordem, os cientistas afirmam que se tratava de um crocodiliforme.
Credit/Crédito: Mark Witton, University of Portsmouth / Copyrighted underAttribution-Non-Commercial-Share Alike 2.0 Generic Creative Commons License)
A dentição mais complexa indica uma capacidade de processar alimentos que os crocodilos atuais – que simplesmente mordem e engolem – não possuem, mas os mamíferos sim.
De acordo com o estudo, o Pakasuchus kapilimai e outros notossúquios podem ter ocupado nichos ecológicos na Gondwana (supercontinente ao sul) que correspondiam aos preenchidos por mamíferos no hemisfério Norte.
“Um número de características dessa nova espécie – incluindo a redução no número de dentes e uma dentição especializada e similar à divisão em caninos, premolares e molares – é muito semelhante a características que foram críticas durante o curso da evolução dos mamíferos do Mesozóico para o Cenozóico”, disse O’Connor.
O artigo The evolution of mammal-like crocodyliforms in the Cretaceous Period of Gondwana (doi:10.1038/nature09061), de Patrick M. O’Connor e outros, pode ser lido por assinantes da Nature em www.nature.com.
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Letter
Nature 466, 748-751 (5 August 2010) | doi:10.1038/nature09061; Received 22 December 2009; Accepted 25 March 2010
The evolution of mammal-like crocodyliforms in the Cretaceous Period of Gondwana
Patrick M. O’Connor1,2, Joseph J. W. Sertich3, Nancy J. Stevens1,2, Eric M. Roberts4,5, Michael D. Gottfried6, Tobin L. Hieronymus7, Zubair A. Jinnah8, Ryan Ridgely1, Sifa E. Ngasala6,9 & Jesuit Temba10
Department of Biomedical Sciences, Ohio University College of Osteopathic Medicine, 228 Irvine Hall, Athens, Ohio 45701, USA
Ohio Center for Ecology and Evolutionary Studies, Irvine Hall, Ohio University, Athens, Ohio 45701, USA
Department of Anatomical Sciences, Stony Brook University, Stony Brook, New York 11794, USA
Department of Physical Sciences, Southern Utah University, Cedar City, Utah 84720, USA
School of Earth and Environmental Sciences, James Cook University, Townsville Qld 4811, Australia
Department of Geological Sciences, Michigan State University, East Lansing, Michigan 48824, USA
Department of Anatomy and Neurobiology, Northeastern Ohio Universities Colleges of Medicine and Pharmacy, Rootstown, Ohio 44272, USA
School of Geosciences, University of the Witwatersrand, Private Bag 3, Wits, Johannesburg, South Africa
Geology Department, University of Dar es Salaam, PO Box 35052, Dar es Salaam, Tanzania
Tanzania Antiquities Unit, PO Box 2280, Dar es Salaam, Tanzania
Correspondence to: Patrick M. O’Connor1,2Email: oconnorp@ohio.edu
Fossil crocodyliforms discovered in recent years1, 2, 3, 4, 5have revealed a level of morphological and ecological diversity not exhibited by extant members of the group. This diversity is particularly notable among taxa of the Cretaceous Period (144–65 million years ago) recovered from former Gondwanan landmasses. Here we report the discovery of a new species of Cretaceous notosuchian crocodyliform from the Rukwa Rift Basin6of southwestern Tanzania. This small-bodied form deviates significantly from more typical crocodyliform craniodental morphologies, having a short, broad skull, robust lower jaw, and a dentition with relatively few teeth that nonetheless show marked heterodonty. The presence of morphologically complex, complementary upper and lower molariform teeth suggests a degree of crown–crown contact during jaw adduction that is unmatched among known crocodyliforms, paralleling the level of occlusal complexity seen in mammals and their extinct relatives7,8, 9, 10, 11, 12. The presence of another small-bodied mammal-like crocodyliform in the Cretaceous of Gondwana indicates that notosuchians probably filled niches and inhabited ecomorphospace that were otherwise occupied by mammals on northern continents.
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Professores, pesquisadores e alunos de universidades públicas e privadas com acesso ao site CAPES/Periódicos podem ler gratuitamente este artigo da Nature e de mais 22.440 publicações científicas.
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NOTA DESTE BLOGGER:
Estranhamente os autores deixaram de mencionar o Chimaerasuchus paradoxus, um crococilo aparentemente vegetariano, reportado na carta "A plant-eating crocodyliform reptile from the Cretaceous China" de Xiao-chu Wu et al, Nature, vol. 376, 27 August 1995, p.678.
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Letters to Nature
Nature 376, 678-680 (24 August 1995) | doi:10.1038/376678a0; Accepted 30 June 1995
A plant-eating crocodyliform reptile from the Cretaceous of China
Xiao-chun Wu*†, Hans-Dieter Sues†‡§ & Ailing Sun*
*Institute of Vertebrate Paleontology and Paleoanthropology, Academia Sinica, Beijing 100044, China
†Department of Vertebrate Palaeontology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada
‡Department of Zoology, University of Toronto, Toronto, Ontario M5S 1A1, Canada
§To whom correspondence should be addressed at the Royal Ontario Museum
WITH few exceptions, tooth shape among crocodyliform reptiles (Crocodylia of traditional use) is rather uniform1. We report here on the presence of multicuspid molariform teeth in a remarkable new crocodyliform from the Lower Cretaceous of China, which may represent the first known herbivorous member of that group. The overall structure of these teeth is very similar to that of the postcanine teeth of tritylodontid synapsids and represents a particularly striking example of convergent evolution. It indicates back-to-front (proal) motion of the mandible produced by the posterior pterygoid muscle during jaw closing, much as in the extant tuatara, Sphenodon2,3. Certain derived features indicate that the new Chinese crocodyliform is closely related to the Notosuchidae from the Cretaceous of Gondwana4. Its discovery thus casts further doubts on claims5 concerning an endemic Gondwanan tetrapod fauna during the Cretaceous.
PDF grátis na USP. Pena que o arquivo está parcialmente danificado.
+++++A plant-eating crocodyliform reptile from the Cretaceous of China
Xiao-chun Wu*†, Hans-Dieter Sues†‡§ & Ailing Sun*
*Institute of Vertebrate Paleontology and Paleoanthropology, Academia Sinica, Beijing 100044, China
†Department of Vertebrate Palaeontology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada
‡Department of Zoology, University of Toronto, Toronto, Ontario M5S 1A1, Canada
§To whom correspondence should be addressed at the Royal Ontario Museum
WITH few exceptions, tooth shape among crocodyliform reptiles (Crocodylia of traditional use) is rather uniform1. We report here on the presence of multicuspid molariform teeth in a remarkable new crocodyliform from the Lower Cretaceous of China, which may represent the first known herbivorous member of that group. The overall structure of these teeth is very similar to that of the postcanine teeth of tritylodontid synapsids and represents a particularly striking example of convergent evolution. It indicates back-to-front (proal) motion of the mandible produced by the posterior pterygoid muscle during jaw closing, much as in the extant tuatara, Sphenodon2,3. Certain derived features indicate that the new Chinese crocodyliform is closely related to the Notosuchidae from the Cretaceous of Gondwana4. Its discovery thus casts further doubts on claims5 concerning an endemic Gondwanan tetrapod fauna during the Cretaceous.
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