Oldest broken bone reveals our ancestors' switch to life on land

[muriel_volestrangler]

IT WAS one small fall for a tetrapod, but it signals one giant leap for tetrapod kind. A broken leg bone pushes back the emergence of our four-legged ancestors from water on to land by at least 2 million years.

A gap in the tetrapod fossil record means we know little about what happened between the time when limbs evolved from fish fins some 360 million years ago and the first land-adapted tetrapods appeared 330 million years ago.

To find out, Peter Bishop at the Queensland Museum in Hendra, Australia, and his colleagues analysed a rare tetrapod fossil from that gap, a 1.5-metre-long Ossinodus which lived some 333 million years ago in what is now Australia. They found that Ossinodus's forearm bones were strong enough to support the animal's body on land.

It also has what Bishop believes is the world's oldest known broken tetrapod bone. When the team used computer software to reconstruct the forces required to cause the break, they found the magnitude of the force was so large relative to the size of the animal that the accident must have occurred on land.

http://www.newscientist.com/article/mg22630224.900-oldest-broken-bone-reveals-our-ancestors-switch-to-life-on-land.html

Oldest Pathology in a Tetrapod Bone Illuminates the Origin of Terrestrial Vertebrates

Abstract

The origin of terrestrial tetrapods was a key event in vertebrate evolution, yet how and when it occurred remains obscure, due to scarce fossil evidence. Here, we show that the study of palaeopathologies, such as broken and healed bones, can help elucidate poorly understood behavioural transitions such as this. Using high-resolution finite element analysis, we demonstrate that the oldest known broken tetrapod bone, a radius of the primitive stem tetrapod Ossinodus pueri from the mid-Viséan (333 million years ago) of Australia, fractured under a high-force, impact-type loading scenario. The nature of the fracture suggests that it most plausibly occurred during a fall on land. Augmenting this are new osteological observations, including a preferred directionality to the trabecular architecture of cancellous bone. Together, these results suggest that Ossinodus, one of the first large (>2m length) tetrapods, spent a significant proportion of its life on land. Our findings have important implications for understanding the temporal, biogeographical and physiological contexts under which terrestriality in vertebrates evolved. They push the date for the origin of terrestrial tetrapods further back into the Carboniferous by at least two million years. Moreover, they raise the possibility that terrestriality in vertebrates first evolved in large tetrapods in Gondwana rather than in small European forms, warranting a re-evaluation of this important evolutionary event.

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0125723

[AZ Mike]

1. So cool!

The moment man fell from heaven! 6,000 years ago!!!

[denbot]

2. I've broken a bone, and had a fairly severe neck injury surfing.

The forces encountered in the intertidal zone are often extremely violent, so it would seem to me that animals transitioning from sea to land would spend a good deal of time exposed to these forces.

I would question the assumption that the injury was caused on land.