Vol.3, No.1, 9-27 (2011) Natural Science http://dx.doi.org/10.4236/ns.2011.31002 Fossil middle triassic “sea cows” – placodont reptiles as macroalgae feeders along the north-western Tethys coastline with Pangaea and in the Germanic basin Cajus G. Diedrich Paleologic, Nansenstr, Germany;
[email protected] Received 19 October 2010; revised 22 November 2010; accepted 27 November 2010. ABSTRACT this plant-feeding adaptation and may even ex- plain the origin or at least close relationship of The descriptions of fossil Triassic marine pla- the earliest Upper Triassic turtles as toothless codonts as durophagous reptiles are revised algae and jellyfish feeders, in terms of the through comparisons with the sirenia and basal long-term convergent development with the si- proboscidean mammal and palaeoenvironment rens. analyses. The jaws of placodonts are conver- gent with those of Halitherium/Dugong or Mo- Keywords: Placodont Reptiles; Triassic; eritherium in their general function. Whereas Convergent Evolutionary Ecological Adaptation; Halitherium possessed a horny oral pad and Sirenia; Macroalgae Feeders; NW Tethys Shelf; counterpart and a special rasp-like tongue to Palaeoecology grind seagrass, as does the modern Dugong, placodonts had large teeth that covered their 1. INTRODUCTION jaws to form a similar grinding pad. The sirenia also lost their anterior teeth during many Mil- The extinct reptile group of the placodonts found in lions of years and built a horny pad instead and Germany and other European sites (Figure 1), a group specialized tongue to fed mainly on seagrass, of diverse marine diving reptiles, had large teeth cover- whereas placodonts had only macroalgae availa- ing the lower and complete upper jaws (Figsure 2-5) ble.