Fossil from most primitive 4-legged creature found

[SolInvictusMithras]

The Schenectady Gazette
By Seth Borenstein
The Associated Press

WASHINGTON -- Scientists unearthed a skull of the most primitive four-legged creature in Earth's history, which should help them better understand the evolution of fish to advanced animals that walk on land.

The 365 million-year old fossil skull, shoulders and part of the pelvis of the water-dweller, Ventastega curonica, were found in Latvia, researchers report in a study published in today's issue of the journal Nature.  Even though Ventastega is likely an evolutionary dead end, the finding sheds new details on the evolutionary transition from fish to tetrapods.  Tetrapods are animals with four limbs and include such descendants as amphibians, birds and mammals.

While an earlier discovery found a slightly older animal was more fish than tetrapod, Ventastega is more tetrapod than fish.  The fierce-looking creature probably swam through shallow brackish waters, measured about three or four feet long and ate other fish.  It likely had stubby limbs with an unknown number of digits, scientists said.

"If you saw it from a distance, it would look like a small alligator, but if you look closer, you would find a fin on the back," said lead author Per Ahlberg, a professor of evolutionary biology at Uppsala University in Sweden.

This all happened more than 100 million years before the first dinosaurs roamed the earth.

[Evolved]

Cool looking creature.  It reminds me of a coelacanth.



Welcome to the forum, SolInvictusMithras.  Can I call you Sol?

[curiosityandthecat]

Sauce?

...er, I mean, link to the source article?

[SolInvictusMithras]

Sauce?

...er, I mean, link to the source article?

This was reported in a local newspaper, not online, so I'm afraid I don't have a link to share.  I received the article as a clipping, but I'll try to find out what page it was originally on etc.

EDIT: I found out from the person who gave me the clipping that this was reported June 26th on page A2 of the Schenectady Daily Gazette.  Many thanks to crocofish for the news.google links in the meantime.

[SolInvictusMithras]

Cool looking creature.  It reminds me of a coelacanth.



Welcome to the forum, SolInvictusMithras.  Can I call you Sol?

Yes, you may.  Nice to meet you and nice to be here.

[crocofish]

While an earlier discovery found a slightly older animal was more fish than tetrapod, Ventastega is more tetrapod than fish.

I assume the "slightly older animal" is Tiktaalik, which happens to be my avatar.  Tiktaalik was from about 375 million years ago.  It's not surprising that there would many different lifeforms in the spectrum between fish to amphibians to reptiles.

news.google.com hits on lots of links for Ventastega.

[Loffler]

Evolutionary questions: why do modern fish have scales, and modern reptiles have scales, but modern amphibians have skin? Did they lose scales or did fish and reptiles gain them?

Or are modern amphibians not truly descended from the "amphibious species" that brought fish to the land?

[crocofish]

Evolutionary questions: why do modern fish have scales, and modern reptiles have scales, but modern amphibians have skin?

It appears that amphibians and reptiles branched off from a common tetrapod ancestor, as seen in this simplified tree from a Wikipedia article.  Reptiles didn't descend directly from amphibians.  Amniotes are the group of animals that includes reptiles, birds, and mammals, based on embryonic development.  Amphibians and fish are not amniotes.  

Code Select Expand

--Tetrapods--------------------------------------------------
      |
      +-- Amphibians ---------------------------------------
      |
      `--Amniotes-----
             |
             +--Sauropsids------------------------------------
             |
             `--Synapsids------
                    |
                    `--Pelycosaurs----
                           |
                           `--Therapsids-----
                                  |
                                  `--Mammals------------------

What makes the early tetrapods so interesting is that they are the common ancestors to all land animals (not including insects).  They were the pioneers that ventured out of the water and led to all the reptiles, birds, and mammals, including us.

[Kylyssa]

There are also fish that do not have scales such as puffers and dragonets.  Hair, feathers, scales - it's fascinating how similar they all are.

[Recusant]

Did a site search for "tetrapod" and got only this thread. I recognise several of the usernames. 

A revision in the proposed timeline of tetrapod evolution appears to be in order. Cool stuff!

Years ago Dr Ahlberg (principle author of the paper and co-author of the article below) was a member of a different rationalist/atheist discussion board. He's a witty gent with a respectably wide knowledge of biology and evolution as well as being on the sharp edge of investigating early tetrapods.

"Two lizard-like creatures crossed tracks 355 million years ago. Today, their footprints yield a major discovery" | The Conversation

The emergence of four-legged animals known as tetrapods was a key step in the evolution of many species today – including humans.

Our new discovery, published today in Nature, details ancient fossil footprints found in Australia that upend the early evolution timeline of all tetrapods. It also suggests major parts of the story could have played out in the southern supercontinent of Gondwana.

This fossil trackway whispers that we have been looking for the origin of modern tetrapods in the wrong time, and perhaps the wrong place.

Tetrapods originated a long time ago in the Devonian period, when strange lobe-finned fishes began to haul themselves out of the water, probably around 390 million years ago.

This ancestral stock later split into two main evolutionary lines. One led to modern amphibians, such as frogs and salamanders. The other led to amniotes, whose eggs contain amniotic membranes protecting the developing foetus.

Today, amniotes include all reptiles, birds and mammals. They are by far the most successful tetrapod group, numbering more than 27,000 species of reptiles, birds and mammals.

They have occupied every environment on land, have conquered the air, and many returned to the water in spectacularly successful fashion. But the fossil record shows the earliest members of this amniote group were small and looked rather like lizards. How did they emerge?

The oldest known tetrapods have always been thought to be primitive fish-like forms like Acanthostega, barely capable of moving on land.

Most scientists agree amphibians and amniotes separated at the start of the Carboniferous period, about 355 million years ago. Later in the period, the amniote lineage split further into the ancestors of mammals and reptiles-plus-birds.

Now, this tidy picture falls apart.

Key to our discovery is a 35 centimetre wide sandstone slab from Taungurung country, near Mansfield in eastern Victoria.

The slab is covered with the footprints of clawed feet that can only belong to early amniotes, most probably reptiles. It pushes back the origin of the amniotes by at least 35 million years.

[Continues . . .]

The paper is open access:

"Earliest amniote tracks recalibrate the timeline of tetrapod evolution" | Nature

Abstract:

The known fossil record of crown-group amniotes begins in the late Carboniferous with the sauropsid trackmaker Notalacerta1, and the sauropsid body fossil Hylonomus. The earliest body fossils of crown-group tetrapods are mid-Carboniferous, and the oldest trackways are early Carboniferous. This suggests that the tetrapod crown group originated in the earliest Carboniferous (early Tournaisian), with the amniote crown group appearing in the early part of the late Carboniferous.

Here we present new trackway data from Australia that challenge this widely accepted timeline. A track-bearing slab from the Snowy Plains Formation of Victoria, Taungurung Country, securely dated to the early Tournaisian, shows footprints from a crown-group amniote with clawed feet, most probably a primitive sauropsid. This pushes back the likely origin of crown-group amniotes by at least 35–40 million years. We also extend the range of Notalacerta into the early Carboniferous.

The Australian tracks indicate that the amniote crown-group node cannot be much younger than the Devonian/Carboniferous boundary, and that the tetrapod crown-group node must be located deep within the Devonian; an estimate based on molecular-tree branch lengths suggests an approximate age of early Frasnian for the latter.

The implications for the early evolution of tetrapods are profound; all stem-tetrapod and stem-amniote lineages must have originated during the Devonian. It seems that tetrapod evolution proceeded much faster, and the Devonian tetrapod record is much less complete, than has been thought.