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?
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!