Palaeocast

Gavialoids are a superfamily of crocodilians with distinctive elongated snouts specialised for the capture of fish. Today, the family is represented by just two species: the gharial, Gavialis gangeticus, and the false gharial, Tomistoma schlegelii. Despite their current low diversity and limited geographical range, the fossil record of gavialoids contains significantly more taxa with fossils discovered on nearly every continent. In this episode, we speak to Dr Paul Burke, Swedish Museum of Natural History, who has been working on the placement of a particularly problematic species from the Eocene of Egypt within the gavialoid tree. 'Tomistoma' cairense was originally described in 1927, so what could modern imaging techniques tell us about its anatomy almost a century on? We look at how redescriptions of old fossils can allow new family trees to be drawn and what we can learn about the evolution of gavialoids through time.

The Cambrian Explosion is one of the most significant events in evolutionary history. Classically, it describes the sudden appearance of complex fossils (including all major animal groups) at the beginning of the Cambrian Period. Before then it was thought that only relatively simple single-celled or multicellular life existed. We now understand this event to be a lot more nuanced, recognising many of the geological biases at play and having discovered complex fossils in the earlier Ediacaran Period. Many researchers therefore consider the term 'Cambrian Radiation' to be a better representation of the event. Whether an explosion or a radiation, determining the events of the Ediacaran and Early Cambrian and their causes is a constant area of palaeontological research. Numerous drivers behind this event have been hypothesised ranging from oxygen availability and nutrient cycling to an arms race between predators and prey. It is likely that no single factor will be identified as an underlying cause, but the relative extent to which each contributed to the event will be debated for many years to come. In this interview, we are joined by Dr Julien Kimmig, Staatliches Museum für Naturkunde Karlsruhe, Germany, who recently authored a study on the coprolites of the Early Cambrian, the evolution of guts, and the influence the 'Cambrain Fecal Revolution' may have had on the wider Cambrian Radiation.

The Carboniferous period is host to some of the largest arthropods to have ever lived. Giant taxa such as the griffenfly Meganuera and the millipede Arthropleura are almost talismanic and are often depicted in reconstructions of the period. Since many other groups also have giant representatives in the Carboniferous, what is it about this time that allows for arthropods to grow to such large sizes? Arthropods breathe very differently to how we do with many using a series of branching hollow tubes called trachea for gas exchange throughout the body. This tracheal system uses diffusion and advection to exchange oxygen and carbon dioxide from areas of higher concentration to lower concentrations. In 1995, a study in the journal Nature suggested that elevated oxygen concentrations in the Carboniferous (approximately 30%, as opposed to 21% today) allowed for gigantism in arthropods since oxygen could diffuse deeper/further into their larger bodies. A recently published study in the same journal is now casting doubt on that interpretation and in this interview, we are joined by one of the authors, insect physiologist Prof. Jon Harrison from Arizona State University. He introduces us to the tracheal system and its link to the size of insects in the Carboniferous.

The Carboniferous period is host to some of the largest arthropods to have ever lived. Giant taxa such as the griffenfly Meganuera and the millipede Arthropleura are almost talismanic and are often depicted in reconstructions of the period. Since many other groups also have giant representatives in the Carboniferous, what is it about this time that allows for arthropods to grow to such large sizes? Arthropods breathe very differently to how we do with many using a series of branching hollow tubes called trachea for gas exchange throughout the body. This tracheal system relies upon the process of diffusion where oxygen and carbon dioxide will be exchanged from areas of higher concentration to lower concentrations. In 1995, a study in the journal Nature suggested that elevated oxygen concentrations in the Carboniferous (approximately 30%, as opposed to 21% today) allowed for gigantism in arthropods since oxygen could diffuse deeper/further into their larger bodies. A recently published study in the same journal is now casting doubt on that interpretation and in this interview, we are joined by one of the authors, insect physiologist Prof. Jon Harrison from Arizona State University. He introduces us to the tracheal system and its link to the size of insects in the Carboniferous.

Prof. Paul Barrett of the Natural History Museum, London, recently authored A History of Dinosaurs in 50 Fossils. We took this as an opportunity to get an overview of what we really know about dinosaurs and how it's even possible to tell their story with just 50 specimens. In this episode, Paul discusses the history of dinosaur research, the current state of the science and what are still some of the big unknowns.

Petrified Forest National Park in northeastern Arizona, USA is a hub for Triassic palaeontology and has exposures representing 20 million years of the Late Triassic Chinle Formation. Visitors marvel at the colourful fossilised trees from which the park takes its name, but a whole host of animals called these swampy forests home 225 million years ago. In this episode, we talk to Dr. Adam Marsh, lead palaeontologist at the National Park. We explore the history, geology, and palaeontology of Petrified Forest, along with exciting research centred around specimens from the park. Research is ongoing, with many groups of palaeontologists working on Petrified Forest specimens, and we hear about directions it might go in the future.

Today, there is only one living species of rhynchocephalian: the tuatara of Aotearoa/New Zealand. Despite today's paucity of species, this was once a diverse group of reptiles, with a wide range of lifestyles from swimming in the ocean to climbing trees. Once highly abundant around the world, reasons for their decline are still debated and may have had to do with competition from their relatives, the squamates, or changing environments. Rhynchocephalians are related to lizards and snakes within Lepidosauria, but despite their outward appearance, are not lizards themselves and have a number of differences that make them distinct. In this interview, we speak to Dr. Victor Beccari, an expert in rhynchocephalians, and discuss this and more about this fascinating group of reptiles.

We've been given exclusive access to a brand new study examining the chemistry of a mosasaur tooth found within the Late Cretaceous Hell Creek Formation, North Dakota. The remarkable circumstances of how this tooth was discovered meant that multiple lines of chemical evidence could be reliably gathered, each acting as a powerful palaeoenvironmental proxy providing clues as to how and where this giant aquatic predator lived. The results of the study now mean that a revision of mosasaur palaeoecology is required and that food webs in one of the world's most famous fossil deposits might need redrawing. Joining us in this episode are the lead authors Nathan Van Vranken (Eastern West Virginia Community and Technical College) and Melanie During (Uppsala University & Vrije Universiteit Amsterdam). Their study "King of the Riverside", a multi-proxy approach offers a new perspective on mosasaurs before their extinction is open access and available in BMC Zoology now!  

The iguanodontians were an incredibly successful group within the Cretaceous. They could reach incredible sizes, with the largest species even matching the proportions of some sauropods, and they also had an incredible palaeogeographic range, meaning that their remains are found all over the world today. In the late Jurassic, they were a lot less diverse and much smaller, so the late Jurassic and early Cretaceous are key times for understanding the evolution of this group. Cariocecus bocagei is a newly described iguanodontian from the Early Cretaceous of Praia do Areia do Mastro, Portugal. Whilst it is only know from a partial skull, there are numerous useful characteristics that help identify it as a new species and fill in our understanding of iguanodontians in this important time in their evolution. Joining us in this episode is Dr Filippo Bertozzo of the Royal Belgian Institute of Natural Sciences.