Fossil Record 20(2): 105-127, doi: 10.5194/fr-20-105-2017
Modeling the physiology of the aquatic temnospondyl Archegosaurusdecheni from the early Permian of Germany
expand article infoFlorian Witzmann, Elizabeth Brainerd§
‡ Museum für Naturkunde Berlin, Berlin, Germany§ Department of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912, United States of America
Open Access
Physiological aspects like heat balance, gas exchange, osmoregulation, anddigestion of the early Permian aquatic temnospondyl Archegosaurusdecheni, which lived in a tropical freshwater lake, are assessed basedon osteological correlates of physiologically relevant soft-tissue organsand by physiological estimations analogous to air-breathing fishes. Bodymass (M) of an adult Archegosaurus with an overall body length ofmore than 1 m is estimated as 7 kg using graphic double integration.Standard metabolic rate (SMR) at 20 °C (12 kJ h−1) and activemetabolic rate (AMR) at 25 °C (47 kJ h−1) were estimated accordingto the interspecific allometry of metabolic rate (measured as oxygenconsumption) of all fish (VO2 = 4. 8 M0. 88) and form the basis formost of the subsequent estimations. Archegosaurus is interpreted asa facultative air breather that got O2 from the internal gills at restin well-aerated water but relied on its lungs for O2 uptake in timesof activity and hypoxia. The bulk of CO2 was always eliminated via thegills. Our estimations suggest that if Archegosaurus did not havegills and released 100 % CO2 from its lungs, it would have to breathemuch more frequently to release enough CO2 relative to the lungventilation required for just O2 uptake. Estimations of absorption andassimilation in the digestive tract of Archegosaurus suggest thatan adult had to eat about six middle-sized specimens of the acanthodian fishAcanthodes (ca. 8 cm body length) per day to meet its energydemands. Archegosaurus is regarded as an ammonotelic animal thatexcreted ammonia (NH3) directly to the water through the gills and theskin, and these diffusional routes dominated nitrogen excretion by thekidneys as urine. Osmotic influx of water through the gills had to becompensated for by production of dilute, hypoosmotic urine by the kidneys.Whereas Archegosaurus has long been regarded as a salamander-like animal, there is evidence that its physiology was more fish-than tetrapod-like in many respects.