Fig. 3. Akanthosuchus langstoni O in New data on the anatomy and relationships of the Paleocene crocodylian Akanthosuchus langstoni

Fig. 3. Akanthosuchus langstoni O'Neill, Lucas, and Kues, 1981. Holotype, NMMNH P−8628, from the Middle Paleocene (Torrejonian) Nacimiento Formation, San Juan Basin, New Mexico, USA. Histological section of oval osteoderm. A. Superficial region of compact bone viewed under normal light, showing growth rings composed of multiple zones of lamellar bone (numbers) with intervening annuli, indicating the minimum age of the specimen at eight years. Note lines of arrested growth (arrowheads). B. Middle and deep regions of osteoderm viewed under cross−polarized light, showing primary woven bone, parallel−fibered bone, and elliptical resorption areas indicating obliquely oriented channels within the osteoderm. C. Detail of secondary osteon viewed under cross−polarized light, showing lines of reversal. D. Detail of vascular "pipes", channels that are elongated proximodistally within the spiked expansion of the osteoderm. Abbreviations: lr, line of reversal; pfb, parallel−fibered bone; ra, resorption area; so, secondary osteon; vp, vascular "pipes"; wb, woven bone. Scale bars 500 µm.