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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.

Annunci

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

2008-10-15 – Nuovi studi su Tiktaalik roseae (evolution, tetrapod, “Fishapod”)

Nuovi studi sul Tiktaalik roseae forniscono nuove evidenze dell’evoluzione da uno stile di vita acquatico ad uno anfibio.

Già nel primo studio del 2006 i ricercatori avevano evidenziato peculiartà anatomiche che ne facevano un precursore dei più moderni tetrapodi. Ora i ricercatori hanno presentato uno studio più approfonito, pubblicato su nature, dal quale emergono nuovi adattamenti relativi all’area craniale.

In estrema sintesi le osservazioni più significative sono:

a) le ossa degli arti interiori e della spalla che permettevano una variazione nel movimento degli arti da quello orizzontale (per il nuoto) a quella verticale (col quale poteva fare forza per muoversi su un fondo fangoso [vedi pterioftalmi attuali])

b) l’articolzione del collo e della testa erano diverse da quelle dei suoi predecessori permettendogli muovere la testa in verticale, e quindi fuori dall’acqua

c) gli occhi sono posti in alto sul cranio (altro adattamento ad uno stile di vita anfibio, [vedi ad esempio i coccodrilli])

Tutte queste caratteristiche costituiscono un chiaro esempio dell’adattamento ad uno stile di vita fuori dall’acqua.

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vedi pure precedenti post:

2008-09-22 – Pesce fossile con dita (Panderichthys, 1) (Abstract from Nature)

2008-09-22 – Pesce fossile con dita (Panderichthys, 2) (podcast from Scientific American)

2008-09-22 – Pesce fossile con dita (Panderichthys, 3) (divulgazione sc.)

2008-09-22 – Pesce fossile con dita (Panderichthys, 4) (divulgazione sc. ITA)

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Vedi pure su Le Scienze:

L’evoluzione del collo e del cranio

Nella transizione dalla vita acquatica a quella terrestre la testa ha progressivamente assunto una struttura più solida e al contempo più mobile

Le dita dei pesci primordiali

L’assenza nei pesci dei meccanismi genetici per lo sviluppo delle dita aveva fatto ritenere che esse si fossero sviluppate solo dopo la colonizzazione della terraferma

L’anello mancante fra pesci e animali terrestri

Scoperti sull’isola di Ellesmere numerosi fossili che mostrano i tratti della transizione dalla vita acquatica a quella terricola

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Scientists release findings in study of 375 million-year-old fossil

Posted by John Mangels/Plain Dealer Science Writer October 15, 2008 13:50PM

 

Tiktaalik roseae is an intermediate between fish that lived in water and animals that evolved to walk on land. Its fin is like that of fish but it was capable of propping the body of the animal up, much like a limb.

CLEVELAND – The enigmatic 375 million-year-old fossils of a fish in the midst of adapting to life on land are giving up more of their secrets.

Scientists first described the stubby aquatic predator they named Tiktaalik in 2006, focusing on the anatomical features that showed its front fins were on their way to becoming limbs, and were capable of lifting the animal in a kind of push-up out of the ancient muck.

A new study on the internal anatomy of the skull of Tiktaalik roseae uncovers transitioned from water to land. The findings are reported in the October by Jason Downs, Ted Daeschler, Farish A. Jenkins, Jr. and Neil Shubin.

Today, the team that discovered Tiktaalik in the Canadian Arctic provided new details of its transition from water to solid ground. Further examination of the fossils shows a coordinated series of changes underway not just in the creature’s limbs, but in its crocodile-like skull, neck and gills, all helping prepare it for a less aquatic, shallow-water lifestyle. 

The researchers published their results today in the journal Nature and discussed them publicly during a symposium at this morning’s meeting of the Society of Vertebrate Paleontology meeting in Cleveland.

“We designed an expedition to find a transitional fossil and, bingo, we found it. And it was loaded with surprises,” said project co-leader Neil Shubin of the University of Chicago, who spoke at the Cleveland Museum of Natural History Monday night. “We’re learning so much
about the history of life.”

The scientists initially dug three Tiktaalik partial skeletons from shale outcrops on Canada’s Ellesmere Island, more than 600 miles above the Arctic Circle. (Tiktaalik, pronounced tick-TAH-lick, is an Inuit word meaning large fresh-water fish.)

The landscape is harsh, cold and barren, with winds that can shred tents. Researchers carry guns in addition to their digging tools to protect against roaming polar bears.

In Tiktaalik’s time, though, the area was part of a giant landmass that lay much closer to the equator and was a sub-tropical floodplain. The fossilized remains show Tiktaalik ranged from 4 to 9 feet long, with sharp teeth for flesh-eating and eyes on the top of its flat head.

The fossil site where Tiktaalik roseae was discovered is high in the Canadian Arctic on Ellesmere Island. A new study on the internal anatomy of the skull of Tiktaalik roseae appears in the October 16th issue of Nature.
It had some features of its lobe-finned ancestors, such as scales, webbed fins and primitive jaws. But it also bore similarities to later, four-legged, land-dwelling animals called tetrapods. It had both lungs and gills. 

Tiktaalik’s shoulders and upper arm bones were in the process of rotating from a rearward, swimming orientation to a forward-facing direction, and its elbows and wrists could bend to enable a propped-up posture and perhaps some limited, dragging locomotion.

By painstakingly removing the surrounding rock in which the Tiktaalik specimens were embedded, the researchers were able to study more features of an animal caught in transition, particularly in the skull and gill area. Guided by genes, its skeleton was reorganizing itself.

Tiktaalik lacked the rigid gill-covering bones of its ancestors. That made its head more flexible; it’s the first time a neck appears in the fossil record. Because they can quickly flick their bodies in any direction in the water, fish have no pressing need for independent head motion.

But an animal like Tiktaalik that’s rooted to the ground by its developing limbs would need more head mobility to snare prey or catch a glimpse of an attacker.

The Tiktaalik fossils showed evidence of more changes tied to an aquatic exit strategy. The skulls of fishes have lots of connected, hinge-like moving bones that help the head skeleton function like a pump to move water across the gills during breathing.

In Tiktaalik, one of those head bones, called the hyomandibula, was shrinking in size compared to the creature’s fish ancestors. In those primitive creatures, the boomerang-shaped hyomandibula links parts of the skull and the gill bones, coordinating how those elements move
during underwater breathing and eating.

A new study of Tiktaalik roseae (middle), a 375-million-year-old transitional fossil, highlights an ntermediate step between the condition in fish like Eusthenopteron (bottom) and that in early limbed forms like Acanthostega (top). The new data are described in a paper by Jason Downs, Ted Daeschler, Farish A. Jenkins, Jr. and Neil Shubin in the October 16th edition of Nature.

 

Tiktaalik’s hyomandibula is smaller and in a different position, perhaps because the animal was living in shallow water and relying less on its gills to breathe. In mammals, which don’t need gills at all, the hyomandibula is freed up for another role: it’s become a tiny middle-ear
bone involved in hearing. 

“It’s just one piece of the puzzle,” said paleontologist Jason Downs, the Nature paper’s lead author and a research fellow at Philadelphia’s Academy of Natural Sciences. “One reason why people are intrigued by Tiktaalik is that it isn’t some oddball animal that went extinct. It’s on the
lineage leading to limbed tetrapods,” an ancestral line that leads to humans.

Ahead for the researchers is analysis of Tiktaalik’s pelvis and rear fins, and more trips to the Canadian Arctic to collect additional fossils.

Tiktaalik’s discovery has caused consternation for anti-evolutionists, who previously insisted that scientists could not produce fossils that showed evidence of species in transition.

Ironically, the research team’s initial examination of Tiktaalik coincided with a landmark 2005 federal trial in Dover, Penn., which barred the local school district from teaching intelligent design, an updated version of creationism.

“I remember reading about the Dover trial with a cast of Tiktaalik sitting on my desk, wishing I could tell somebody about it,” Shubin said.

source: http://blog.cleveland.com/metro/2008/10/scientists_release_findings_in.html

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see also previous posts (in English):

2008-09-22 – Pesce fossile con dita (Panderichthys, 1) (Abstract from Nature)

2008-09-22 – Pesce fossile con dita (Panderichthys, 2) (podcast from Scientific American)

2008-09-22 – Pesce fossile con dita (Panderichthys, 3) (divulgazione sc.)

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Other links: updated to 2008-10-18 (11:35 Italy)

Fishapod had ‘world’s first neck’
Nature.com (subscription) – 16 ott 2008
A fossil of the strange Tiktaalik fish has been giving up more of its secrets this week. In a paper in Nature Jason Downs of the Academy of Natural Sciences
Evolutionary transition from fish to land animals revealed
Hindu – 16 ott 2008
Washington (PTI): Scientists have brought out the first detailed evolutionary transition from fish to land animals, a key development that helps resolve the
“Walking fish” reveals fresh evolutionary insights
Reuters – 9 ore fa
By Will Dunham WASHINGTON (Reuters) – An extraordinary fish that existed 375 million years ago had unique features in its head that helped pave the way for
How Tiktaalik got its neck
Science News – 10 ore fa
By Susan Milius NOT FISH HEADSThe fossilized skull of Tiktaalik roseae holds internal details that show the shallow-water fishy predator was already
Earthly Animals Owe Necks to ‘Fishapod’
Wired News – 11 ore fa
By Brandon Keim October 15, 2008 | 3:06:06 PMCategories: Animals The internal skull structure of a creature that bridges the gap between fishes and the
Details of Evolutionary Transition from Fish to Land Animals Revealed
Science Daily (press release) – 13 ore fa
ScienceDaily (Oct. 15, 2008) — New research has provided the first detailed look at the internal head skeleton of Tiktaalik roseae, the 375-million-year-old
“Fishapod” Had World’s First Known Neck, Study Says
National Geographic – 13 ore fa
The skull of a 375-million-year-old Arctic fossil fish reveals that the “fishapod” could nod its head up and down and may have breathed air,
Nunavut fossil captures evolutionary transition
Canada.com – 13 ore fa
Newly exposed parts of Tiktaalik roseae – an exquisitely preserved fossil uncovered in the Canadian Arctic in 2006 – are revealing how the first creatures
‘Missing link’ fossil stuck its neck out
New Scientist (subscription) – 14 ore fa
It didn’t just have protolimbs, it had a mobile neck as well. More details have emerged about the anatomy of Tiktaalik, the “fishopod” that bridges the gap
Fossil Fish Shows Complexity of Transition to Land
New York Times – 14 ore fa
By JOHN NOBLE WILFORD In a new study of a fossil fish that lived 375 million years ago, scientists are finding striking evidence of the intermediate steps
Inside the head of the fishapod
Australian Life Scientist – 47 minuti fa
A daily e-mail from Australian Biotechnology News, with the latest, most important headlines from Australia and around the world. The braincase, palate and
Fish fossil offers clues to evolution
United Press International – 4 ore fa
PHILADELPHIA, Oct. 15 (UPI) — US researchers say a new look at the skull of a 375-million-year-old fish fossil provides clues to the evolutionary process.
Fossil helps understand evolution from fish to land animals
InTheNews.co.uk – 8 ore fa
A 375 million-year-old fossil discovered in Canada is helping shed light on the evolutionary transition between fish and land animals.
‘First fish had wrists and elbows’
Metro – 10 ore fa
The first ‘fish’ to walk out of the sea 375million years ago was able to survive out of water because it had developed a neck, wrist and elbow.
How a fish got its legs: Scientists reveal more details of ancient
The Plain Dealer – cleveland.com – 11 ore fa
by John Mangels/Plain Dealer Science Writer Illustration by Kalliopi MonoyiosTiktaalik roseae is an intermediate between fish that lived in water and
Details of evolutionary transition from fish to land animals revealed
Eureka! Science News – 13 ore fa
New research has provided the first detailed look at the internal head skeleton of Tiktaalik roseae, the 375-million-year-old fossil animal that represents
The Shoulder Bone’s Connected to the Ear Bone…
Discover Magazine – 14 ore fa
When our ancestors moved ashore some 360 million years ago, they underwent a lot of changes as they evolved from ocean-swimming fish to land-walking

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Original Article:

Nature, Volume 455 Number 7215 pp835-1006, (16 October 2008)

The cranial endoskeleton of Tiktaalik roseae p925

Jason P. Downs, Edward B. Daeschler, Farish A. Jenkins & Neil H. Shubin

Correspondence to: Jason P. Downs1Neil H. Shubin3,4 Correspondence and requests for materials should be addressed to J.P.D. (Email: downs@ansp.org) or N.H.S. (Email: nshubin@uchicago.edu).

doi:10.1038/nature07189

See also: Editor’s summary

Abstract

Among the morphological changes that occurred during the ‘fish-to-tetrapod’ transition was a marked reorganization of the cranial endoskeleton. Details of this transition, including the sequence of character acquisition, have not been evident from the fossil record. Here we describe the braincase, palatoquadrate and branchial skeleton of Tiktaalik roseae, the Late Devonian sarcopterygian fish most closely related to tetrapods. Although retaining a primitive configuration in many respects, the cranial endoskeleton of T. roseae shares derived features with tetrapods such as a large basal articulation and a flat, horizontally oriented entopterygoid. Other features in T. roseae, like the short, straight hyomandibula, show morphology intermediate between the condition observed in more primitive fish and that observed in tetrapods. The combination of characters in T. roseae helps to resolve the relative timing of modifications in the cranial endoskeleton. The sequence of modifications suggests changes in head mobility and intracranial kinesis that have ramifications for the origin of vertebrate terrestriality.

 

ottobre 15, 2008 Posted by | - Pesci / Fishes, America Northern, Articolo sc. di riferimento, Bl - Top posts, Italiano (riassunto), P - Evoluzione, Paleontology / Paleontologia | , , , , , , , , , , | Lascia un commento

I pesci fossili di Bolca forniscono nuovi esempi di asimmetria [Amphistium, Heteronectes, Pleuronectiformes]


I pesci fossili di Bolca forniscono nuovi esempi di asimmetria[vedi numero di Settembre 2008 di “Le Scienze”]


Links:

http://www.telegraph.co.uk/earth/main.jhtml?view=DETAILS&grid=&xml=/earth/2008/07/09/sciflat109.xml

Video from Youtube:

http://www.youtube.com/watch?v=qSYl4aMe0BE

Links from Nature.com 

1. The evolutionary origin of flatfish asymmetry

Matt Friedman

SUMMARY: All adult flatfishes (Pleuronectiformes), including the gastronomically familiar plaice, sole, turbot and halibut, have highly asymmetrical skulls, with both eyes placed on one side of the head.

CONTEXT: …Naturhistorisches Museum, Vienna (NHMW). Total length is 142 mm; standard length is 111 mm. Horizon and locality. Bolca, possibly Monte Postale locality, northern Italy. Lower Eocene (Ypresian; SBZ11). Diagnosis. Stem pleuronectiform…

Nature 454, 209 – 212 (10 Jul 2008), doi: 10.1038/nature07108, Letter

2. The eyes have it

Daniel Cressey

SUMMARY: Fossilized flatfish settle evolutionary conundrum.

CONTEXT: …I first noticed the fossil, it was sitting unidentified in a drawer of indeterminate fossil fish pieces from Monte Bolca [in Italy],” he says. “And believe me, it didn t look like much at the time it was an incomplete specimen…

Nature News (09 Jul 2008), doi: 10.1038/news.2008.946, News

3. Palaeontology: Squint of the fossil flatfish

Philippe Janvier

SUMMARY: Evolutionary biologists have floundered when trying to explain how the asymmetrical head of flatfishes came about. ‘Gradually’ is the answer arising from exquisite studies of 45-million-year-old

CONTEXT: …(which has been known for a long time). The specimens all come from the exceptional fossil-fish locality of Bolca, Italy, and were once regarded as possible flatfish relatives on the basis of their postcranial skeleton. However, this…

Nature 454, 169 – 170 (09 Jul 2008), doi: 10.1038/454169a, News and Views

settembre 23, 2008 Posted by | - Italia, - Pesci / Fishes, 6 Eocene, Articolo sc. di riferimento, P - Evoluzione, P - Ritrovamenti fossili, Paleontology / Paleontologia, Video | , , , , , , , , , , , , , , | Lascia un commento

Più antico resto fossile di maternità – Materpiscis attenboroughi

Straordinaria scoperta fossile in Australia, ritrovato infatti un reperto fossile testimoniante un parto in un esemplare di pesce placoderma attribuito al genere: Materpiscis attenboroughi

Articolo da Agi news:

SCIENZA: LA NASCITA PIU’ ANTICA IN FOSSILE DI 380 MILIONI ANNI

(AGI/AFP) – Parigi, 28 mag. –  In Australia e’ stata scoperta traccia della piu’ antica maternita’ mai documentata: un fossile di pesce di 380 milioni di anni, fa con attaccato al cordone ombelicale un minuscolo embrione. Il ritrovamento del “Materpiscis attenboroughi”, come e’ stato ribattezzato il fossile della “madre-pesce” in onore del naturalista David Attenborough, e’ opera di John Long e Kate Trinajstic del museo di Victoria.
  Oltre a portare alla luce una specie animale finora sconosciuta, il fossile e’ la piu’ antica testimonianza di una nascita nel regno animale. “E’ uno piu’ straordinari reperti fossili mai rinvenuti e ci porta a ridiscutere tutte le convinzioni fin ora raggiunte sull’evoluzione dei vertebrati”, ha commentato Long.
  La cosa piu’ interessante per i ricercatori e’ stato il fatto di poter certificare un metodo di riproduzione cosi’ sofisticato in un reperto cosi’ antico. “Questa scoperta ci dimostra che il parto e la schiusa delle uova sono due processi riproduttivi che si svilupparono forse in contemporanea e non in successione come si e’ sempre pensato”, ha spiegato la dottoressa Kate Trinajstic.
  L’esistenza dell’embrione e di un cordone ombelicale certifica anche il piu’ antico caso di fertilizzazione interna nel mondo animale, in pratica il primo esempio di sesso con penetrazione. Lunga circa 25 centimetri la “madre pesce” apparteneva a un gruppo estinto di vertebrati, i placodermi, diffusi nell’era medio paelozoica che va dai 420 ai 350 milioni di anni fa. I placodermi erano dei dinosauri marini che dominarono i mari, i fiumi e i laghi della terra per 70 milioni di anni. Nel fossile ritrovato si possono distinguere nitidamente le forme dell’embrione all’interno dell’utero materno e il cordone ombelicale calcificato che unisce la madre al piccolo. Solo dopo una delicatissima opera di pulitura del fossile tramite speciali acidi i due ricercatori si sono resi conto della particolarita’ del reperto. Come racconta la dottoressa Trinajstic: “Una volta pulito il fossile abbiamo visto l’embrione seduto nella pancia della madre, era conservato in maniera perfetta”. Dopo una successiva analisi del fossile col microscopio elettronico e una termografia computerizzata gli scienziati hanno potuto vedere anche i vasi sanguigni del cordone ombelicale. Secondo le ricostruzione degli scienziati il pesce e il suo piccolo morirono a causa di un improvviso abbassamento dei livelli di ossigeno nell’acqua.
  Caduta sul fondale, la “madre pesce” sarebbe poi stata ricoperta da un fango limaccioso che ne ha consentito la conservazione nei secoli.(AGI)

CORREZIONI:

Ovviamente i placodermi non erano dinosauri marini, bensì pesci.

LINKS:

1 – Video presentazione del reperto – youtube

2 – Articolo scientifico di riferimento – Live birth in the Devonian period (Nature)

3 – Foto e illusttrazioni – Nature.com

maggio 31, 2008 Posted by | - Pesci / Fishes, Articolo sc. di riferimento, Oceania, P - Ritrovamenti fossili, Paleontology / Paleontologia, Video | , , , , | Lascia un commento