Croaking Science: Evolutionary Origins Part 1-The Age of Amphibians

Becky Austin our Croaking Science Volunteer, finds out about the evolutionary origons of our species in this two part post...look out for part two on reptiles in a few weeks time.

Picture the scene: A hot, humid environment, with huge forests of mosses and ferns and swampy mangroves. It sounds like a far cry from what we know today but this was what Britain was like in the Devonian era, around 400 million years ago, when it was part of a huge land mass close to the equator. It was a time of great change: the massive drop in atmospheric CO₂ due to these early forests paved the way for fishes of the time to take to the land, and become the very first amphibians.

The Devonian is often termed “the age of fishes”, as Osteichthyes, or “bony fishes” ruled the earth’s aquatic environments. One branch, the “lobe-finned fishes”, is the ancestor group of amphibians and all other terrestrial vertebrates. The closest modern-day example is the African lungfish, which can survive long periods of drought by breathing air with a primitive lung. However, it was a group of lobe-finned fishes called the Osteolepiformes which were the pioneers of the land.

A number of fossil discoveries have helped decipher how Osteolepiformes moved from water to land. Panderichthys, from 385mya onwards, had nostrils for breathing air, and eyes on top of its head to see out of the water. A flatter body and stronger bones helped protect against the crush of gravity out of water, and it had two sets of fins. 3 million years later, Tiktaalik had wrist bones and digits on its limbs, and by 365mya the first real amphibian-like creatures roamed the land, such as Ichthyostega and the later Eryops.

These first amphibians had tough skin to avoid drying out, lungs evolved from swim-bladders for use instead of gills, and hind-limbs extending from the newly evolved pelvis. But, like modern amphibians, they still had to return to water to lay eggs, which is why they retained their aquatic lifestyle. It is possible that this path of evolution was followed to adapt to life in and between woodland swamps of the Devonian – a path which led to the formation of all terrestrial vertebrate life seen today, over 350 million years later.
 

References:

Ahlberg, P.E. and Milner, A.R. (1994). The origin and early diversification of tetrapods. Nature, 368: 507-514.

Clack, J.A. (2012). Gaining ground: the origin and evolution of tetrapods. 2^nd edition. Indiana University Press, Indiana, USA.

Retallack, G.J. (2011). Woodland hypothesis for Devonian tetrapod evolution. The journal of geology, 119: 235-258.

Froglife gets ready for leap off

In two weeks Froglife is holding an event to celebrate the efforts of a number of experts committed to saving amphibians from extinction, both in the UK and abroad. You can be a part of it!

‘Year of the Frog – a big leap forward’ will be held on the evening of Friday 14th November at Edinburgh Zoo. The event will be chaired by the eminent Professor Aubrey Manning, authority on animal behaviour and renowned BBC broadcaster.

The exciting evening gives you a chance to hear the story of some of the hard-working fieldworkers, scientists, landscape-shapers, and campaigners who will be continuing the fight for amphibians long after Year of the Frog 2008 ends.

Speakers at the event will include respected herpetologists Professor Tim Halliday and Professor Roger Downie, Glasgow City Council’s Jim Coyle MBE speaking alongside individuals from Froglife and The Royal Zoological Society of Scotland.

Limited tickets remain - book early!

Tickets (£5 each) can be paid by cheque (made payable to ‘The Froglife Trust’ and posted to Froglife, 9 Swan Court, Cygnet Park, Peterborough PE7 8GX) or by credit/debit card over the phone (01733 558844 - office hours). For additional information please email: info@froglife.org.

For more information: http://www.froglife.org/year_of_the_frog_event.htm

Amphibian populations could halve by 2050

Half of Europe's frogs and toads and newts could be wiped out in the next 40 years, scientists from the Zoological Society of London (ZSL) have warned.

Factors including climate change, habitat destruction and disease are having a serious effect, said ZSL scientists at a special event hosted by Sir David Attenborough on 25th September 2008.

Speaking at the lecture, Dr Trent Garner, a Research Fellow at ZSL, said climate change will dramatically affect the living conditions of amphibians and survival of populations:

“Published projections show that climate change alters amphibians’ habitats so we expect a large number of amphibian species to be faced with loss of habitat and ultimately extinction.” said Dr Garner.

“In the UK we are already seeing common toads losing condition and experiencing reduced survival. As climate change continues to impact habitats, the situation gets far worse for these native species.” he added.

In addition to identifying climate change as a threat, Dr Garner and his colleagues also highlighted two infectious diseases affecting survival rates, a chytrid fungus and ranaviruses. Ranavirus kills thousands of amphibians in the UK each year and the chytrid fungus, implicated in extinctions of amphibian species around the world, has recently been identified in the UK.

Froglife and the Institute of Zoology (based at ZSL) have been working on the issue of amphibian disease in the UK since 1992, through our Frog Mortality Project. Currently Froglife are running a Frog Disease Appeal so that the Frog Mortality Project can expand and better inform scientists of the disease threat, working toward a safer future for the UK's amphibians >>> Frog Disease Appeal…

Later this year solutions to the imminent extinction crisis facing the world’s amphibians will be discussed at another ZSL event: ‘Halting the Global Decline in Amphibians: research and practice’ – a two-day symposium being held on 20 & 21st of November 2008 >>> More details…