Another brainy paper

It has been a good month with another paper published last week. This one “Brain Reconstruction Across the Fish-Tetrapod Transition; Insights From Modern Amphibians” forms part of a special research topic in the Frontiers in Ecology & Evolution journal on soft tissue reconstruction (you guessed it!) over the fish-tetrapod transition.

I was very happy, along with my co-authors, to contribute to this special issue. My co-authors included Flinders PhD candidate, Corinne Mensforth, Dr Tom Challands from the University of Edinburgh in the UK, Prof. Shaun Collin from La Trobe University (Victoria, Australia) and Prof. John Long, also from Flinders University.

In this work we looked at the relationship between the brain and it’s “endocast” in some amphibians (frogs and caecilians), to compare with earlier work on lungfish and salamanders. The endocast is a cast or mould of the internal space of a hollow structure, in this case, the space inside the skull that usually houses the brain in life.

We did this to try and better inform our interpretation of fossil endocasts when the soft parts of the brain haven’t been preserved and only the hard, bony parts remain. I also wrote an article for The Conversation about this research, so if you’d like to know more please CLICK HERE!

Brains (pink) and endocasts (grey) of lobe-finned fish and amphibians.

New paper on fossil limb bones and bone marrow

We had a paper published today in the journal, eLife. The article, “New light shed on the early evolution of limb-bone growth plate and bone marrow” was written by an international team of researchers from Uppsala University in Sweden (Sophie Sanchez, Jordi Estefa, Grzegorz Niedźwiedzki), the European Synchrotron Radiation Facility in France (Paul Tafforeau, Camille Berruyer), Comenius University in Bratislava, Slovakia (Jozef Klembara), and of course, Flinders University in Australia (that’s me!)

Do you know where in the body your red blood cells are produced? For most of us, this occurs in the bone marrow within our “long bones” (in our arms and legs). But what about animals without arms and legs, like fish? They tend to produce blood cells (in a process known as haematopoiesis) in other body organs, such as their kidney or liver. This raises the question: at which point in evolution did blood cell production shift from body organs into long bones?

How tetrapods acquired new bone characteristics as they transitioned from water to land.
Image from article by Holly Woodward:

Some researchers thought this might have occurred in the bones of the earliest backboned animals to evolve limbs (yes, you guessed it, we are talking about early tetrapods again!) before they moved from water onto land. To test this hypothesis, my good friend and colleague, virtual palaeohistology queen Dr Sophie Sanchez, together with PhD student Jordi Estefa, led this investigation into the microarchitecture of animals spanning the fish-tetrapod transition (stem-tetrapods, batrachians, and amniotes).

Classical histology, as well as three-dimensional synchrotron virtual histology, was used to identify which animals had humeri (upper arm bones) with an internal organization that would enable blood cells to be produced (similar to what we see in living reptiles and mammals). The earliest animals we investigated with open marrow cavities where haematopoiesis could have occurred, are 300 million-year-old stem amniotes called Seymouria and Discosauriscus. Contrary to previous hypotheses, this is significantly (at least ~60-70 million years) later than the first tetrapods that evolved limbs and crawled out of water and onto land!

Left: The 380-million-year-old lobe-finned fish, Eusthenopteron upper arm bone (humerus) has marrow processes forming a simple enclosed mesh of tubular structures that probably only served for the elongation of the bone. 
Right: The 300-million-year-old tetrapod, Discosauriscus, upper arm bone (humerus). Discosauriscus has marrow processes forming a complex mesh of tubular structures and small cavities that open up onto the large empty medullary cavity at midshaft, where a centralized blood-vessel mesh could allow the production of blood cells.