Paleonews

Il blog dedicato ai Paleontologi !!!!

2009-05-12 – Darwinius masillae: l’anello mancante dell’evoluzione umana? (missing link of human evolution?)

Trovato l’anello mancante dell’evoluzione: un Adapide di oltre 37 milioni di anni fa

LONDRA (10 maggio) – La Bbc ha preparato uno straordinario documentario, presentato da David Attenborough, in cui rivelerà la scoperta di uno scheletro fossilizzato che rappresenterebbe l’anello mancante dell’evoluzione umana. Secondo il Mail on Sunday il documentario è top secret, ma fonti negli Usa dicono che la rivoluzionaria scoperta verrà presentata il prossimo 19 maggio da un gruppo di scienziati e documentaristi a New York. In quell’occasione verrà presentato il primo scheletro intero mai trovato di un particolare tipo di un animale che si chiamava Adapide, battezzato Darwinius masillae: le ossa fossilizzate, che hanno dai 37 ai 47 milioni di anni, sono stati trovati nella cava Messel in Germania, un sito famoso per i suoi fossili.

L’animale, una femmina, somiglia a un lemure (il mammifero dalla lunga coda che vive in Madagascar). Attenborough spiegherà che i ricercatori hanno concluso che quell’animale non è semplicemente un antenato dei lemuri (mancano diverse caratteristiche), ma fa parte di un gruppo collegato di primati che si sarebbero evoluti in scimmie ed esseri umani.

Lo studio cui fa riferimento la Bbc verrà pubblicato dalla rivista angloamericana “Public library of science”. Philip Gingerich, presidente della Us paleontological society, co-autore dello studio, ha detto al Mail: «Ho esaminato questo scheletro, è incredibilmente completo e datato con precisione. Lo abbiamo tenuto nascosto perché non si può parlare di qualcosa finché non la capisci a fondo. Ora abbiamo capito, farà progredire la nostra conoscenza dell’evoluzione». Interpellato sul documentario Bbc, Sir David ha risposto: «Temo di non essere autorizzato a parlarne».

fonte: IlMessaggero.it

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Is David Attenborough set to reveal the Missing Link in human evolution?

By Sharon Churcher

The BBC has made an extraordinary new documentary, presented by Sir David Attenborough, which will reveal the discovery of a fossilised skeleton that may be a vital ‘missing link’ in human evolution.

The 90-minute programme is top secret but The Mail on Sunday has learned from sources in America that the results of the study on which it is based will be revealed by a team of scientists and broadcasters in New York on May 19.

The centrepiece of the programme is the unveiling of the first-ever complete skeleton of an extinct animal called an adapid.

david attenborough

Relative values: Sir David Attenborough with a lemur – one of the creatures at the centre of the fossil debate

The fossilised bones, which are thought to be between 37 and 47million years old, were found in Germany’s Messel Shale Pit, a disused quarry near Frankfurt famous for its fossils.

The team who examined the young female animal say it has some resemblance to a lemur, a mammal with a distinctive tail that is found to this day in the forests of Madagascar.

But Sir David’s documentary will explain that the researchers have, controversially, concluded the fossil ‘is not simply a lemur’ but from a related group of primates which evolved into monkeys, apes and human beings.

The BBC programme is based on a scientific study to be published by the Public Library of Science, a leading academic journal with offices in Cambridge and San Francisco.

Last night, the study’s co-author, Philip Gingerich, the president-elect of the US Paleontological Society, said: ‘I examined this skeleton. It is exceptionally complete and it is well-dated.

We have kept it under wraps because you can’t blither about something until you understand it. We now understand it. It is going to advance our knowledge of evolution.’

Prof Gingerich confirmed he had spoken to Sir David.

The significance of the discovery, according to New York’s academic community, is that it could resolve the fierce debate about which kind of primates humans are descended from.

graphic

Some palaeontologists believe we evolved from the adapids – but that theory is hotly contested. The new skeleton appears to be a previously unknown type of adapid which would be the ‘missing link’ between small mammals and the apes which evolved into humans.

The study’s authors insist that the fossil can’t be a lemur because it lacks two features: the ‘toothcomb’, a set of lower front teeth used to groom fur; and ‘toilet claws’, toes on the hind feet used for scratching.

Half of the fossil was found a few years ago, but it was only when the rest of the body was discovered last year that scientists realised its importance.

The ground-breaking research was only possible after Norway’s National History Museum managed to buy the two parts of the fossil from private collectors.

The study, led by Norway’s Professor Jorn Hurum, says the fossil is so well-preserved that its soft tissues and stomach contents can be analysed.

Christened Darwinius masillae, it belonged to an extinct group of primates which lived in rainforests.

It was a female that was less than a year old but had been weaned and had developing teeth. It had nails rather than claws and would have weighed just 2lb when fully grown.

When asked about the BBC documentary, Sir David said: ‘I’m afraid I am not allowed to talk about it.’ Prof Hurum also refused to comment.
Why a wet nose could ruin research

While all the experts agree that the Messel fossil is an exciting discovery, some doubt that it will settle the debate about mankind’s ancestors.

Professor Matt Cartmill of Boston University, a leading authority on primates, said: ‘What remains to be shown is that this animal had features which link it decisively to higher primates.

If it turns out that it had a dry nose, like monkeys and people, rather than a wet nose like dog or a lemur, that could have a big impact on ideas about the origins of monkeys, apes and humans.’

Roger Thomas, secretary of the US Paleontological Society, said: ‘According to one group of thought, we are descended from the same primates as lemurs. Another argument is that hominids evolved from another small primate, the tarsiidae.’

Prof Cartmill added: ‘This specimen could settle that debate but, if I had to put my money on it, my expectation would be that they will not be able to tell one way or another.’

source: http://www.mailonsunday.co.uk/sciencetech/article-1179926/Is-David-Attenborough-set-reveal-Missing-Link-human-evolution.html

Annunci

maggio 12, 2009 Posted by | - Mammiferi, - Ominidi, - Primati, 6 Eocene, An. Vertebrates, Articolo sc. di riferimento, Cenozoic, Europa, Lang. - Italiano, P - Evoluzione, P - Paleoantropologia, P - Ritrovamenti fossili, Paleontology / Paleontologia | , , , , , , , , , , , , , , , , , | 2 commenti

2009-04-23 – Puijila darwini: Anello mancante nell`evoluzione dei Pinnipedi (missing link in pinniped evolution)

recommended links:

http://nature.ca/puijila/index_e.cfm (Official home page)

http://www.eurekalert.org/pub_releases/2009-04/cmon-feo042009.php (good scientific description of the discovery)

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 Fossil of a walking seal found

Remains of a previously unknown mammal could represent a missing link in pinniped evolution
Web edition : Wednesday, April 22nd, 2009 
Researchers discovered remains of a previously unknown pinniped in the Canadian Arctic. (Inset shows bones that were found.) The fossilized skeleton was about 65 percent complete. (Illustration fills in the missing pieces.)
Researchers discovered remains of a previously unknown pinniped in the Canadian Arctic. (Inset shows bones that were found.) The fossilized skeleton was about 65 percent complete. (Illustration fills in the missing pieces.)

A fossilized skeleton of what researchers are calling a walking seal has been uncovered in the Canadian Arctic. The remains of this previously unknown mammal could shed light on the evolution of pinnipeds, the group that includes seals, sea lions and walruses, researchers report in the April 23 Nature.

The animal, named Puijila darwini, had a long tail and an otterlike body with webbed feet and legs like a terrestrial animal, the researchers report. But P. darwini also had a pinniped-like skull.

“We realized there was no way this was an otter,” says study coauthor Natalia Rybczynski of the Canadian Museum of Nature in Ottawa. The walking seal probably lived about 20 million years ago and was adept at moving both on land and in water, the team reports. 

 
Researchers describe Puijila darwini (illustration shown) as a walking seal, with the legs of a terrestrial animal, a seal-like skull and webbed feet.

Researchers describe Puijila darwini (illustration shown) as a walking seal, with the legs of a terrestrial animal, a seal-like skull and webbed feet.

 Scientists had theorized that pinnipeds evolved from land-dwelling ancestors but had little fossil evidence to support that claim. The new finding could be the missing link in pinniped evolution, the researchers report.

“This is a fantastic discovery,” comments evolutionary biologist Annalisa Berta of San Diego State University.

The finding may also indicate that the Arctic was a geographic center for pinniped evolution, the researchers speculate.

But, Berta notes, other early pinnipeds have been discovered in the North Pacific and Eurasia. “We can’t yet conclude the Arctic was the area of origin for pinnipeds,” Berta says.

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Otter-like fossil reveals early seal evolution

The Associated Press – ‎22-apr-2009‎
One expert called it “a fantastic discovery” that fills a crucial gap in the fossil record. The 23 million-year-old creature was not a direct ancestor of

aprile 23, 2009 Posted by | - Mammiferi, America Northern, An. Vertebrates, Articolo sc. di riferimento, P - Evoluzione, P - morfologia funzionale, P - Ritrovamenti fossili, Paleontology / Paleontologia, X - Nature | , , , , , , , , , , | Lascia un commento

2009-03-13 – Evoluzione: I denti del pesce “Dracula” (evolution, “Dracula” fish)

SCOPERTO PESCE-DRACULA MISURA SOLO 16 MILLIMETRI

PD*27442385

• Per gli scienziati è straordinario
Ha due denti aguzzi come i canini di un vampiro il “Danionella Dracula”, un pesce un cui esemplare è stato scoperto in un fiume in Birmania. Il pesce, piccolissimo – misura poco più di 16 millimetri di lunghezza – è stato trovato vicino Mogaung, nel Myanmar, e gli scienziati hanno subito definito la scoperta “straordinaria”. “E’ una delle creature più interessanti scoperte negli ultimi decenni”, hanno detto al quotidiano britannico “Telegraph”. I denti aguzzi di cui è dotato il piccolo pesciolino, che altro non sono che un prolungamento della lisca, gli hanno regalato il soprannome, dal notissimo romanzo di Bram Stoker. Ralf Britz, zoologo al museo di storia naturale di Londra, ha detto: “Questo pesce è una delle scoperte più straordinarie degli ultimi cinquant’anni. I denti che il Danionella Dracula ha sono molto particolari, perché delle oltre 3700 specie di pesci di questo tipo, nessun esemplare aveva i denti. I loro antenati preistorici persero i loro denti più di 50 milioni di anni fa”. La squadra di ricerca di Britz sta già lavorando ad analizzare il piccolo pesce, alla St. Louis University del Missouri (Usa).

FONTE: http://www.leggonline.it/articolo.php?id=16197

 

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PHOTO IN THE NEWS: New “Dracula” Fish Discovered

2009-03-12-dracula-fish-01

March 11, 2009–While he may not vant to suck your blood, the male fish seen above does sport spooky-looking fangs that have earned it the name Danionella dracula.

Researchers at London’s Natural History Museum found several of the new species (bottom) in a tank of aquarium fish. Initially museum staff had thought the 0.7-inch-long (1.7-centimeter-long) creatures, caught in Myanmar (Burma), were part of an already known, related species.

“After a year or so in captivity, they started dying,” museum scientist Ralf Britz told BBC News.

“When I preserved them and looked at them under the microscope, I thought, my God, what is this, they can’t be teeth.”

In fact, the fangs are not true teeth—the line of fish that gave rise to D. dracula is thought to have lost teeth around 50 million years ago.

By staining the bone and dissolving away tissue to reveal the full jawbones of dead specimens (top), Briz found that the odd species has rows of bony jaw protrusions (inset) that lack the pulp cavities and enamel caps of true teeth.

Despite their ghoulish appearance, the fangs likely aren’t used for feeding.

“We did not study stomach contents, but we know that its close relatives live on small crustaceans … and other small invertebrates,” Britz said in an email to National Geographic News. “In captivity it readily accepts brine shrimp [larvae], tiny nematodes, and even very fine flake food.”

Based on the behavior of live “Dracula” fish, the researchers think the males use their extralong fangs to spar with each other during aggressive displays. The findings are described this week in the online edition of the Proceedings of the Royal Society B.

—Victoria Jaggard

Photographs courtesy Ralf Britz, Natural History Museum

SOURCE: nationalgeographic.com

marzo 13, 2009 Posted by | - Pesci / Fishes, An. Vertebrates, Asia, Attuale, Bio-Zoology / Bio-Zoologia, Lang. - Italiano, P - Evoluzione | , , , , , , | Lascia un commento

2009-03-06 – Macropinna microstoma: Il pesce con la testa trasparente (transparent-head fish)

 Il mistero del pesce trasparente

Macropinna microstoma
Ingrandisci la foto

Abita negli abissi marini, anche a 800 metri di profondità e da quelle parti non c’è molta luce. Per questo ha sviluppato una vista molto speciale. (Federica Ceccherini 2 marzo 2009)

Avvistato per la prima volta nel 1939 il pesce Macropinna microstoma, che abita nel mare al largo della California, con il suo cranio trasparente era rimasto un mistero a lungo.
Ma dopo vari studi un gruppo di ricercatori di Monterey Bay Aquarium Research Institute ha finalmente svelato i suoi segreti.
Vivendo negli oscuri fondali marini, fino a 800 metri, questo buffo pesce ha sviluppato una vista speciale, grazie alla forma degli occhi e al cranio trasparente. Che gli permettono di raccogliere e immagazzinare tutta la luce necessaria per vedere anche nella semi oscurità. Gli occhi inoltre possono muoversi, secondo gli scienziati, all’interno della copertura trasparente, permettendo di controllare tutto quello che gira loro intorno. In particolare le prede, piccoli pesci di cui si nutrono e che catturano con manovre molto veloci e precise.
La calotta trasparente rende perfettamente visibili tutti gli organi interni della sua testa, conferendo all’animale un buffo aspetto. I ricercatori hanno potuto riprendere l’animale grazie a un veicolo comandato a distanza.
Gurda anche il video (in inglese)

fonte: focus.it

 

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Copeia 2008(4):780-784. 2008 – doi: 10.1643/CG-07-082

Macropinna microstoma and the Paradox of Its Tubular Eyes

Bruce H. Robison1 and Kim R. Reisenbichler1

Abstract:

The opisthoproctid fish Macropinna microstoma occupies lower mesopelagic depths in Monterey Bay and elsewhere in the subarctic and temperate North Pacific. Like several other species in the family, Macropinna has upward-directed tubular eyes and a tiny, terminal mouth. This arrangement is such that in their upright position, the visual field of these highly specialized eyes does not include the mouth, which makes it difficult to understand how feeding takes place. In situ observations and laboratory studies reveal that the eyes of Macropinna can change position from dorsally-directed to rostrally-directed, which resolves the apparent paradox. The eyes are contained within a transparent shield that covers the top of the head and may provide protection for the eyes from the tentacles of cnidarians, one of the apparent sources of the food of Macropinna.

Full TextPDF (2931 KB)

marzo 6, 2009 Posted by | - Pesci / Fishes, America Northern, An. Vertebrates, Articolo sc. di riferimento, Attuale, Bio-Zoology / Bio-Zoologia, FREE ACCESS, Lang. - Italiano, P - Evoluzione | , , , , , , | Lascia un commento

2009-03-03 – L’origine del sesso (sex origin) 2: Multimedia

Multimedia and scientific article from Nature:

The mother fish

Ancient fish fossils shed light on the origins of sex.

see also previous post: 2009-02-28 – L’origine del sesso (sex origin)

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Scientific publication, Info and Abstract:

Devonian arthrodire embryos and the origin of internal fertilization in vertebrates

John A. Long, Kate Trinajstic & Zerina Johanson

Nature 457, 1124-1127 (26 February 2009) | doi:10.1038/nature07732;

 

Evidence of reproductive biology is extremely rare in the fossil record. Recently the first known embryos were discovered within the Placodermi1, an extinct class of armoured fish, indicating a viviparous mode of reproduction in a vertebrate group outside the crown-group Gnathostomata (Chondrichthyes and Osteichthyes). These embryos were found in ptyctodontids, a small group of placoderms phylogenetically basal to the largest group, the Arthrodira2, 3. Here we report the discovery of embryos in the Arthrodira inside specimens of Incisoscutum ritchiei from the Upper Devonian Gogo Formation of Western Australia4 (approximately 380 million years ago), providing the first evidence, to our knowledge, for reproduction using internal fertilization in this diverse group. We show that Incisoscutum and some phyllolepid arthrodires possessed pelvic girdles with long basipterygia that articulated distally with an additional cartilaginous element or series, as in chondrichthyans, indicating that the pelvic fin was used in copulation. As homology between similar pelvic girdle skeletal structures in ptyctodontids, arthrodires and chondrichthyans is difficult to reconcile in the light of current phylogenies of lower gnathostomes2, 3, 5, we explain these similarities as being most likely due to convergence (homoplasy). These new finds confirm that reproduction by internal fertilization and viviparity was much more widespread in the earliest gnathostomes than had been previously appreciated.

marzo 3, 2009 Posted by | - Pesci / Fishes, An. Vertebrates, Articolo sc. di riferimento, Bl - Top posts, Multimedia, P - Ritrovamenti fossili, Paleontology / Paleontologia, Video, X - Nature | , , , , , , , , , , | Lascia un commento

2009-01-29 – Dinosauri ed evoluzione (Dinosaur fossils fit perfectly into the evolutionary tree of life)

Studi statistici confermano che la nostra conoscenza sui dinosauri è molto avanzata (cioè conosciamo molto riguardo la loro diversità e le loro linee evolutive)

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Dinosaur fossils fit perfectly into the evolutionary tree of life

Press Release – 26 January 2009

A recent study by researchers at the University of Bath and London’s Natural History Museum has found that scientists’ knowledge of the evolution of dinosaurs is remarkably complete.

Evolutionary biologists use two ways to study the evolution of prehistoric plants and animals: firstly they use radioactive dating techniques to put fossils in chronological order according to the age of the rocks in which they are found (stratigraphy); secondly they observe and classify the characteristics of fossilised remains according to their relatedness (morphology).

Dr Matthew Wills from the University of Bath’s Department of Biology & Biochemistry worked with Dr Paul Barrett from the Natural History Museum and Julia Heathcote at Birkbeck College (London) to analyse statistical data from fossils of the four major groups of dinosaur to see how closely they matched their trees of evolutionary relatedness.

The researchers found that the fossil record for the dinosaurs studied, ranging from gigantic sauropods to two-legged meat eaters such as T. rex, matched very well with the evolutionary tree, meaning that the current view of evolution of these creatures is very accurate.

Dr Matthew Wills explained: “We have two independent lines of evidence on the history of life: the chronological order of fossils in the rocks, and ‘trees’ of evolutionary relatedness.

“When the two tell the same story, the most likely explanation is that both reflect the truth. When they disagree, and the order of animals on the tree is out of whack with the order in the rocks, you either have a dodgy tree, lots of missing fossils, or both.

“What we’ve shown in this study is that the agreement for dinosaurs is remarkably good, meaning that we can have faith in both our understanding of their evolution, and the relative completeness of their fossil record.

“In other words, our knowledge of dinosaurs is very, very good.”

The researchers studied gaps in the fossil record, so-called ‘ghost ranges’, where the evolutionary tree indicates there should be fossils but where none have yet been found. They mapped these gaps onto the evolutionary tree and calculated statistical probabilities to find the closeness of the match.

Dr Wills said: “Gaps in the fossil record can occur for a number of reasons. Only a tiny minority of animals are preserved as fossils because exceptional geological conditions are needed. Other fossils may be difficult to classify because they are incomplete; others just haven’t been found yet.

“Pinning down an accurate date for some fossils can also prove difficult. For example, the oldest fossil may be so incomplete that it becomes uncertain as to which group it belongs. This is particularly true with fragments of bones. Our study made allowances for this uncertainty.

“We are excited that our data show an almost perfect agreement between the evolutionary tree and the ages of fossils in the rocks. This is because it confirms that the fossil record offers an extremely accurate account of how these amazing animals evolved over time and gives clues as to how mammals and birds evolved from them.”

The study, published in the peer-reviewed journal Sytematic Biology, was part of a project funded by the Biotechnology & Biological Sciences Research Council (BBSRC) that aimed to combine different forms of evolutionary evidence to produce more accurate evolutionary trees.

source: http://www.bath.ac.uk/news/2009/1/26/dinosaur-fossils.html

Journal reference:

  1. Wills et al. The Modified Gap Excess Ratio (GER*) and the Stratigraphic Congruence of Dinosaur Phylogenies. Systematic Biology, 2008; 57 (6): 891 DOI: 10.1080/10635150802570809

gennaio 29, 2009 Posted by | - R. Dinosauri, An. Vertebrates, P - Evoluzione, Paleontology / Paleontologia | , , , , | Lascia un commento

2008-12 – TAC for Archaeopteryx

Stanford scientists scan birdlike dinosaur for evolution clues

dicembre 31, 2008 Posted by | - R. Dinosauri, - Uccelli / Birds, 1, Bl - Top posts, P - Evoluzione, P - morfologia funzionale, Paleontology / Paleontologia | , , , , , , , , , | Lascia un commento

2008-12-08 – Cordyceps ed altri parassiti

 Vedendo un documentario sono venuto a conoscenza di un parasita (cordyceps) che uccide le vittime nutrendosene e poi fuoriuscendo dalla testa (… quasi un film di fantascienza !!!!!)

  Se vi interessa l’argomento date un occhiata ai seguenti link …. Incredibile !!!!

  • Parasite manipulates host’s sense of smell
  • Insect strategies for avoiding parasitic infections
  • Brainwashed by a parasite
  • Cordyceps on wikipedia (ENG, ITA)
  • Cordyceps on Google video
  • Links for photos:

    http://www.mycokey.com/Ecuador.html

    dicembre 8, 2008 Posted by | Bio-Zoology / Bio-Zoologia, Italiano (riassunto), P - Evoluzione | , , , , | Lascia un commento

    2008-11-25 – Uno straordinario esempio di organismi simbionti (Elysia chlorotica, Vaucheria litorea, symbionts)

    più di ogni spiegazione guardatevi i video ….. incredibile !!!!!!

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     see free access videos from Supporting Information !!!!!

    Horizontal gene transfer of the algal nuclear gene psbO to the photosynthetic sea slug Elysia chlorotica

    Mary E. Rumpho, Jared M. Worful, Jungho Lee, Krishna Kannan, Mary S. Tyler, Debashish Bhattacharya, Ahmed Moustafa, and James R. Manhart

    Abstract

    The sea slug Elysia chlorotica acquires plastids by ingestion of its algal food source Vaucheria litorea. Organelles are sequestered in the mollusc’s digestive epithelium, where they photosynthesize for months in the absence of algal nucleocytoplasm. This is perplexing because plastid metabolism depends on the nuclear genome for >90% of the needed proteins. Two possible explanations for the persistence of photosynthesis in the sea slug are (i) the ability of V. litorea plastids to retain genetic autonomy and/or (ii) more likely, the mollusc provides the essential plastid proteins. Under the latter scenario, genes supporting photosynthesis have been acquired by the animal via horizontal gene transfer and the encoded proteins are retargeted to the plastid. We sequenced the plastid genome and confirmed that it lacks the full complement of genes required for photosynthesis. In support of the second scenario, we demonstrated that a nuclear gene of oxygenic photosynthesis, psbO, is expressed in the sea slug and has integrated into the germline. The source of psbO in the sea slug is V. litorea because this sequence is identical from the predator and prey genomes. Evidence that the transferred gene has integrated into sea slug nuclear DNA comes from the finding of a highly diverged psbO 3′ flanking sequence in the algal and mollusc nuclear homologues and gene absence from the mitochondrial genome of E. chlorotica. We demonstrate that foreign organelle retention generates metabolic novelty (“green animals”) and is explained by anastomosis of distinct branches of the tree of life driven by predation and horizontal gene transfer.

    • PNAS November 18, 2008 vol. 105 no. 46 17867-17871

    novembre 25, 2008 Posted by | - Molluschi, Articolo sc. di riferimento, Attuale, Bio-Zoology / Bio-Zoologia, Bl - Top posts, Italiano (riassunto), Multimedia, P - Evoluzione, Video, X - PNAS | , , , , , , , | Lascia un commento

    2008-11-01 – L’evoluzione di ragni e scorpioni (spider and scorpion evolution)

    Un nuovo studio condotto sul DNA mitocondriale di 25 taxa di artropodi ha permesso di stimare un’età più antica di quella che ci raccontano i fossili per la differenziazione del taxa dei Chelicherata di cui fanno parte ragni e scorpioni.

    L’età stimata del progenitore comune varia da 400 a 450 milioni di anni fa, mentre fino ad ora i reperti fossili ci dicono che il più antico ragno fossile ritrovato è stato datato 120-135 milioni di anni fa, mentre per gli scorpioni si scende a 200 milioni di anni fa.

    Il dato è di per sè significativo, anche se probabilmente estendendo l’analisi a più taxa in futuro si avranno risultati più precisi.

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    UF study suggests spiders, scorpions, ticks, mites far older than fossil record indicates

    GAINESVILLE, Fla. – Halloween is the only holiday when spiders and other arachnids get a little respect from humans, and a new University of Florida study suggests they deserve more, because they’ve apparently managed to survive a very, very long time. By analyzing gene sequences in modern-day spiders, scorpions, ticks and mites, researchers have estimated that these invertebrates first appeared on Earth roughly 400 million to 450 million years ago.

    GAINESVILLE, Fla. — Halloween is the only holiday when spiders and other arachnids get a little respect from humans, and a new University of Florida study suggests they deserve more, because they’ve apparently managed to survive a very, very long time.

    By analyzing gene sequences in modern-day spiders, scorpions, ticks and mites, researchers have estimated that these invertebrates first appeared on Earth roughly 400 million to 450 million years ago.

    The study, published online this month by the journal Experimental and Applied Acarology, is the first large-scale attempt to use genetic analysis to make projections suggesting when various arachnids evolved, said entomologist Marjorie Hoy, an eminent scholar with UF’s Institute of Food and Agricultural Sciences.

    “This is a first estimate, it’s not the be-all and end-all,” said Hoy, who co-authored the paper with Ayyamperumal Jeyaprakash, a senior biological scientist with the entomology department.

    “It suggests for the first time that these creatures are much older than the fossil record indicates,” Hoy said.

    Fossil arachnids are rare because their bodies contain no bones and typically decompose altogether, so many questions remain unanswered about their early history.

    The oldest known fossil spider is 125 million to 135 million years old; the oldest fossil scorpion is about 200 million years old, Hoy said.

    Jeyaprakash and Hoy used a relatively new type of computer software in their study, analyzing all the genetic sequences from the mitochondria, cell components sometimes called “cellular power plants” because they produce chemical energy. Mitochondria provide a good yardstick for calculating when related organisms diverged from a common ancestor.

    “Not too many people are using this strategy,” Hoy said. “It’s been used on fish but not on invertebrates.”

    The UF researchers obtained complete genetic sequences for the mitochondria of 25 different invertebrates, including four spiders, three scorpions, 10 ticks and four mites. Then Jeyaprakash identified genetic sequences common to the organisms and used two sophisticated computer models to calculate how much time had passed since the sequences evolved from a common origin.

    The results also supported the hypothesis that spiders, scorpions, ticks and mites all descended from a common ancestor, something scientists have generally believed for decades, Hoy said. The study didn’t provide any hints regarding that creature’s appearance, but it probably lived in the ocean, she said.

    Although the findings are subject to debate, the UF study will be helpful to researchers making similar estimates in the future, said Hans Klompen, an associate professor with The Ohio State University’s entomology department.

    “I think this is a great start,” said Klompen, who studies mite evolution. “Now we have something specific to test, and that’s always a good thing.”

    The computer models Hoy and Jeyaprakash used may not fully compensate for variations in the speed of mitochondrial evolution, he said. So the results may indicate that some arachnids appeared on Earth earlier or later than they actually did.

    “It might work better if the sampling size was bigger,” Klompen said. “But we can’t wait for the perfect data set. We have to work with what’s available.”

    Credits
    Writer
    Tom Nordlie, tnordlie@ufl.edu, 352-392-0400
    Source
    Marjorie Hoy, mahoy@ifas.ufl.edu, 352-392-1901, ext. 153
    Ayyamperumal Jeyaprakash, margret@ufl.edu, 352-392-1901, ext. 170
    Hans Klompen, Klompen.l@osu.edu

    link: http://media-newswire.com/release_1077847.html

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    Scientific article:

    Experimental and Applied Acarology, Saturday, October 18, 2008

    First divergence time estimate of spiders, scorpions, mites and ticks (subphylum: Chelicerata) inferred from mitochondrial phylogeny

    Ayyamperumal Jeyaprakash and Marjorie A. Hoy
    A. Jeyaprakash e-mail: ajey@ifas.ufl.edu

    PDF (365.8 KB), HTML, Supplemental HTML

    Abstract  Spiders, scorpions, mites and ticks (chelicerates) form one of the most diverse groups of arthropods on land, but their origin and times of diversification are not yet established. We estimated, for the first time, the molecular divergence times for these chelicerates using complete mitochondrial sequences from 25 taxa. All mitochondrial genes were evaluated individually or after concatenation. Sequences belonging to three missing genes (ND3, 6, and tRNA-Asp) from three taxa, as well as the faster-evolving ribosomal RNAs (12S and 16S), tRNAs, and the third base of each codon from 11 protein-coding genes (PCGs) (COI-III, CYTB, ATP8, 6, ND1-2, 4L, and 4-5), were identified and removed. The remaining concatenated sequences from 11 PCGs produced a completely resolved phylogenetic tree and confirmed that all chelicerates are monophyletic. Removing the third base from each codon was essential to resolve the phylogeny, which allowed deep divergence times to be calculated using three nodes calibrated with upper and lower priors. Our estimates indicate that the orders and classes of spiders, scorpions, mites, and ticks diversified in the late Paleozoic, much earlier than previously reported from fossil date estimates. The divergence time estimated for ticks suggests that their first land hosts could have been amphibians rather than reptiles. Using molecular data, we separated the spider-scorpion clades and estimated their divergence times at 397 ± 23 million years ago. Algae, fungi, plants, and animals, including insects, were well established on land when these chelicerates diversified. Future analyses, involving mitochondrial sequences from additional chelicerate taxa and the inclusion of nuclear genes (or entire genomes) will provide a more complete picture of the evolution of the Chelicerata, the second most abundant group of animals on earth.

    Electronic supplementary material  The online version of this article (doi:10.1007/s10493-008-9203-5) contains supplementary material, which is available to authorized users.

    novembre 1, 2008 Posted by | - Artropodi, Articolo sc. di riferimento, Genetic / Genetica, Italiano (riassunto), P - Evoluzione, Paleontology / Paleontologia | , , , , , , , , , , , , , , , | Lascia un commento