01 luglio 2011

Scoperto occhio del Cambriano (mezzo milione di anni fa): era in un museo. Nature, 30 Giugno 2011

eye Un fossile da catalogare. Uno sguardo attento. Ed ecco la scoperta sensazionale: un occhio complesso come quello di alcuni insetti odierni. Ciò significa che alcuni dei primi abianti della Terra possedevano una vista potente. Forse è la conferma attesa da tempo: all'origine dello sviluppo improvviso della vista nel Cambriano ci potrebbe essere proprio la pressione evolutiva esercitata in quell'era. In altre parole sarebbe proprio lo straordinario vantaggio adattivo determinato dalla comparsa dei primi occhi ad aver indotto la cosiddetta Esplosione Cambriana.
La scoperta, avvenuta casualmente nel corso della ricatalogazione di alcuni pezzi del museo di Adelaide, è pubblicata su Nature del 30 giugno 2011 e porta la firma di Michael Lee (South Australian Museum, University of Adelaide's School of Earth & Environmental Sciences).

Modern optics in exceptionally preserved eyes of Early Cambrian arthropods from Australia Nature 631–634 (30 June 2011)

Abstract
Despite the status of the eye as an “organ of extreme perfection”1, theory suggests that complex eyes can evolve very rapidly2. The fossil record has, until now, been inadequate in providing insight into the early evolution of eyes during the initial radiation of many animal groups known as the Cambrian explosion. This is surprising because Cambrian Burgess-Shale-type deposits are replete with exquisitely preserved animals, especially arthropods, that possess eyes3, 4, 5. However, with the exception of biomineralized trilobite eyes, virtually nothing is known about the details of their optical design. Here we report exceptionally preserved fossil eyes from the Early Cambrian (~515 million years ago) Emu Bay Shale of South Australia, revealing that some of the earliest arthropods possessed highly advanced compound eyes, each with over 3,000 large ommatidial lenses and a specialized ‘bright zone’. These are the oldest non-biomineralized eyes known in such detail, with preservation quality exceeding that found in the Burgess Shale and Chengjiang deposits. Non-biomineralized eyes of similar complexity are otherwise unknown until about 85 million years later6, 7. The arrangement and size of the lenses indicate that these eyes belonged to an active predator that was capable of seeing in low light. The eyes are more complex than those known from contemporaneous trilobites and are as advanced as those of many living forms. They provide further evidence that the Cambrian explosion involved rapid innovation in fine-scale anatomy as well as gross morphology, and are consistent with the concept that the development of advanced vision helped to drive this great evolutionary event.


L'architettura della vita spiegata dall'Evo-Devo (L'Unione Sarda, 15 febbraio 2007)

Nessun commento: