Paleonews

Il blog dedicato ai Paleontologi !!!!

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.

————————————————————————————

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)

—————————————————————————————————————-

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

——————————————————————–

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

————————————————————————————-

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.)

—————————————————————————————————————–

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

————————————————————————————-

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.

 

About these ads

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

Non c'è ancora nessun commento.

Rispondi

Inserisci i tuoi dati qui sotto o clicca su un'icona per effettuare l'accesso:

Logo WordPress.com

Stai commentando usando il tuo account WordPress.com. Chiudi sessione / Modifica )

Foto Twitter

Stai commentando usando il tuo account Twitter. Chiudi sessione / Modifica )

Foto di Facebook

Stai commentando usando il tuo account Facebook. Chiudi sessione / Modifica )

Google+ photo

Stai commentando usando il tuo account Google+. Chiudi sessione / Modifica )

Connessione a %s...

Iscriviti

Ricevi al tuo indirizzo email tutti i nuovi post del sito.

%d blogger cliccano Mi Piace per questo: