4TH ANNUAL MEETING OF THE EUROPEAN ASSOCIATION OF VERTEBRATE PALAEONTOLOGISTS

A preserved distal articular cartilage capsule at a humerus of the sauropod dinosaur Cetiosauriscus greppini and its taphonomical and palaeobiological implications

Oliver WINGS1, Daniela SCHWARZ2 & Christian A. MEYER2

1 Institut für Geowissenschaften, Universität Tübingen, Sigwartstrasse 10, D-72076 Tübingen, Germany, e-mail: [email protected]; 2 Naturhistorisches Museum Basel, Augustinergasse 2, CH-4001 Basel, Switzerland, e-mail: [email protected], [email protected]

Re-examination of the holotype of the sauropod explained by different diagenetical conditions, patho- dinosaur Cetiosauriscus greppini Huene, 1922 (Reuche- logic mineralization at this bone caused by a meta- nette Formation; Kimmeridgian, Late Jurassic) from bolic disease, or an accidental removal of preserved northwestern Switzerland has revealed a well-pre- cartilage during the original preparation. served cartilage capsule at the distal extremity of the The position of the cartilage around the distal right humerus (Naturhistorisches Museum Basel MH limb surface allows its interpretation as a remnant of 260). The studied forelimb belongs to an adult the articular cartilage of the distal humerus. In life, individual of approximately 10 m body length. The this cartilage would most probably have been in cartilage tissue was studied macroscopically and contact with similar articular cartilage of the ulna and microscopically. For a histological study, a core of radius. The reconstructed articular cartilage capsule cartilage and bone material was extracted from the extends approximately from one sixth to one third of cranial face of the distal extremity of the humerus, the distal side of the humerus, and suggests that processed into a standard petrographic thin section, sauropod dinosaurs possessed large articular limb and examined with light microscopy and SEM-EDX. capsules. The capsule represents hydrocartilage together The reconstructed articular cartilage capsule with fibrocartilage and can be distinguished by covers all insertion scars (e.g. medial and lateral ridge, colour, surface structure, and histology from the olecranon fossa, ent- and ectepicondylus) present at periosteum of the bone. It is plausible that the the distal humerus. Limb muscles must have inserted preserved cartilage represents the growth zone of the at the distal humerus tendinously or aponeurotically. bone with only the underlying layer of mineralized If the mineralization of the hyaline cartilage and cartilage being fossilized. This is the first evidence for tendon fibres is not pathologic, it might have been an fossil articular cartilage in a sauropodomorph dino- adaptative mechanism in response to mechanical saur. Hitherto, mineralized cartilage in sauropods was forces acting on this joint. only known from sternal or distal rib elements. None The present humerus verifies the assumption that of the other limb bones shows similar cartilage limb lengths of sauropods must have been larger preservation, although it its most likely that all limb than apparent from the bones alone. Although the bones in sauropods were covered by articular distal cartilage capsule is not completely preserved, cartilage at their epiphyses. we estimate an overall cartilage thickness of at least The taphonomical reasons leading to the cartilage 3-5 cm between humerus and antebrachium. preservation are puzzling. The bones of C. greppini are Comparisons with extant archosaurs imply that the strongly compressed and fractured, but the surround- humerus length of C. greppini was 6 to 10% larger ing sediment with rhizoliths indicates very limited than previously thought. It is plausible that the height transport. In vivo mineralization of the cartilage surely to shoulder, and possibly hip, of all sauropod dino- enhanced its preservation potential. The missing saurs has been hitherto under-estimated, making cartilage on other bones of C. greppini may be these largest of land animals even larger.

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