PATHOLOGY OF TWO FOSStL SEA COWS (MAMMALIA: STRENIA) BY DARYL P. DOMNING AND FREDR1C L. FRYE ABSTRACT Pathological conditions in two fossil sirenian skeletons from California include imperfectly healed fractures, osteomyelitis, and ossifying spondylosis in Metaxytherium jordani (Late Miocene), and an unidentified condition grossly resembling osteitis defor- mans or osteitis fibrosa in Hydrodamalis Sp. nov. (Late Pliocene). This is the first natural occurrence of osteomyelitis noted in a sirenian. INTRODUCTION In recent years numerous specimens of fossil sirenians, includ- ing ancestors of the recently (oa. 1768) exterminated Steller's sea cow, Hydrodamalis gigas (Zimmermann, 1780), have been found in the North Pacific region (Domning, 1975). Among these ancestral forms are two skeletons from California showing particularly in- teresting and extensive pathological conditions. Both are depos- ited in the University of California Museum of Paleontology, Berkeley (UCMP). Metaxytherium jordani KELLOGG, 1925 An old adult individual (4.32 m long) of Metaxytherium jordani (UCMP 77037), from the Late Miocene (Clarendonian, Cierbo-Neroly, or Mohnian-Delmontian in West Coast provincial biostratigraphic chronologies; Domning, 1975) Santa Margarita Formation of Santa Cruz County (UCMP locality V6376), shows several types of osteo- pathology. The corresponding zygapophyses on the right sides of thoracic vertebrae 7-8 and the left sides of T10-11 are vestigially devel- oped. Caudal vertebrae at the base of the flukes (especially caudals 13-15) show ossifying spondylosis in the form of lipping of the centra, probably as a result of frequent flexion at this point in the tail. The lips do not cross joints but are recurved over the centra bearing them. The same individual suffered a series of fractures, some ex- hibiting evidence of osteomyelitis^ of the rostrum, sternum, and Museum of Paleontology, University of California, Berkeley, California 94720. 2 Berkeley Dog and Cat Hospital, Berkeley, California 94704. 1. ribs. Most of these exhibit exuberant callus formation. The base of the rostrum (Plate 1A) was completely fractured through the premaxillae and maxillae along an anteroventrad-slop- ing plane (suggesting a blow from beneath), and had partly healed with development of large carious exostoses and necrotic sinuses on the premaxillae and an irregular hole about 2.5 cm in diameter in the center of the palatal surface. The premaxillae are incom- pletely healed, the maxillae not at all healed; the rostrum is deflected slightly to the left. A fracture in the midsection of the left eleventh rib (Plate IB) has formed some callus and a pseudarthrosis whose surface passes ventrolaterad; wide dorsad-directed lips have formed on the medial sides of both portions. Fractures of the right twelfth and possibly left fifth and sixth ribs have completely healed, forming smaller amounts of callus. The xiphisternum is transversely fractured about 6 cm from its junction with the manubrium. Its dorsal side his completely healed, but its ventral side shows severe osteomyelitis with large open necrotic sinuses extending onto the ventral and even dorsal sides of the posterior end of the manubrium (Plate 1C, D). The two sternal segments are not fused, possibly as a result of this infection. The sternum is bent sharply upward at the site of the fracture, the anterior and posterior parts of the xiphisternum forming a 235° angle on the dorsal side (Plate ID). Anatomical apposition in most of these fractures appears to have been adequate for normal function. Exceptions are the stern- ebral and eleventh rib fractures, which in the former case healed with marked displacement, and in the latter, healed with a well- developed pseudarthrosis. A non-union involving a weight-bearing long bone would usually create some degree of dysfunction, whereas such a lesion affecting a rib or sternebra may be essentially a- symptomatic except for moderate anatomical distortion. These injuries may have been caused by the animal's being thrown against rocks by surf. Steller (1899:198) observed of Hydrodamalis ,'igas that sometimes "they get caught among the rocks and are clashed by the waves violently upon them". As the Late Miocene species probably depended significantly on kelp for food and there- fore, like Hydrodamalis, spent considerable time feeding near rocky shores (Domning, 1975), this would not have been an unlikely occur- rence. A large wave, lifting the animal and dropping it onto jag- ged rocks, could have caused the upward displacement of the snout and sternal fractures and the inward displacement of the broken ends of the ribs, as well as wounds open to infection. The in- juries could all have occurred in a single accident, or in similar accidents at different times. 2. Plate 1. Lesions in skeleton of Metaxytherium jovdani (UCMP 77037). A. Dorsolateral view of rostrum, showing exostoses on premaxillae. B. Anterior view of pseudarthrosis in left eleventh rib, parts separ- ated. C & 1). Ventral and left lat- eral views of sternum, showing necrotic sinuses on ventral side and sharp bend in xiphisternum. In C manubrium and xiphisternum are slightly separated. Scales in centimeters and inches. Plate 2. Lesions in skeleton of Hydrodamalio sp. nov. (UCMP 86A Tl>. A. Posterior view of skull lacking basioccipital and right exoccipital, showing dorsoventral thinness and pitting on dorsal side of basisphen- oid (bs), and atrophied condition of pterygoid processes (pp) (tips broken). B. Proximal parts of ribs; top to bottom: posterior views of right ribs 6, 8, and 11, and anterior view of left posterior rib; show- ing pitting and thinning of proximal ends or (on left rib) entire shaft. Although fractures (of unknown cause) have been reported in manatees and dugongs (Loth, 1940; Korschelt, 1932; Freund, 1904; Crane, 1881), and human-inflicted wounds caused osteomyelitis in a manatee (Frye and Herald, 1969), this is the first record of naturally-occurring osteomyelitis in a sirenian, as well as of ossifying spondylosis in a form other than fusion of vertebrae. The latter condition, as well as abnormalities of zygapophyses, has already been noted by Reinhart (1959) in a specimen of Metaxytheviwn jordani (his Halianassa vanderhoofi; for synonymy see Domning, 1975). The latter specimen, UCMP 3794, came from the same area and stratigraphic unit as UCMP 77037, but it would be unwarranted to conclude from the available sample of this local population (one complete and three partial skeletons and many iso- lated bones) that the incidence of pathology was unusually high, especially in view of the lack of data on incidence of pathology in Recent sirenian populations. One case of fusion of two thor- acic vertebrae and of the dorsal halves of the corresponding left ribs has been noted in Hydrodamalis gigas (Pales, 1930: pi. 27, fig. 2); similar conditions probably also occur in Dugong and Trichechus, but no records have come to our attention. Hydrodamalis sp. nov. The second individual is an immature Hydrodamalis (UCMP 86433) of a new species which will be described by Domning in the near future; this specimen is from the Late Pliocene (Blancan; Domning, 1975) Squire Member of the Pismo Formation, San Luis Obispo County (UCMP locality V70148). It suffered from an unidentified disabl- ing affliction of bones, joints, and muscles of the jaw, neck, and back regions. Bone resorption, leaving irregularly pitted surfaces, has taken place on the dorsal side of the basisphenoid (Plate 2A), on the proximal ends of right ribs 4, 6, 8, and 11 (the interven- ing ribs are almost or entirely unaffected; the corresponding left ribs are not preserved), and on the entire lengths of several pos- terior left ribs (Plate 2B). Cervical vertebrae 2 and 3 are fused on the left side; the right side of C3 was evidently partly re- sorbed. The pterygoid processes and basisphenoid (Plate 2A) and the dorsolateral border of the exoccipital show subnormal growth and thickness, suggesting atrophy of the attached muscles (ptery- goidei, longus capitis, and semispinalis capitis, respectively). The rostrum and the posterior parts of the mandibles show no ab- normalities, but the anterior ends of the latter, though only partly preserved, seem to have tapered rather abruptly instead of showing the expected robust development of the symphyseal region, suggesting atrophy possibly attributable to the weakness of the pterygoid muscles. Although the lesions grossly resemble those of osteitis defor- mans or osteitis fibrosa, these could not be distinguished on the basis of the fossil material. Much of the bone microarchitecture is well preserved, but a thin section of compact bone from one of the affected posterior left ribs, examined under plane and polar- 3. ized light microscopy, revealed apparently normal Haversian sys- tems, lacunae, and irregular cement lines. While fusion of cer- vicals 2 and 3 sometimes occurs in manatees (Petit, 1928), the other symptoms seen here have not been reported in Recent siren- ians; thus the disease remains unidentified. ACKNOWLEDGEMENTS We thank Bruce Welton for making a thin section of the sea cow rib, and the Kaiser Sand and Gravel Co., Felton, California, Cuesta College, San Luis Obispo, California, and J. E. Bowen for donation of the specimens. LITERATURE CITED Crane, A., 1881. Notes on the habits of the manatees {Manatus australis) in captivity in the Brighton Aquarium. Proc. Zool. Soc. London 1881: 456-460. Domning, D. P., 1975. Systematics, morphology, and evolution of North Pacific sirenians. Ph.D. Thesis, Univ. of California, Berkeley, x + 398. Freund, L., 1904. Die Osteologie der Halicoreflosse. Zs. wiss. Zool. 77(3): 363-397, pis. 14-15. Frye, F. L., and E. S. Herald, 1969. Osteomyelitis in a manatee. J. Amer. Vet. Med. Assoc. 155(7): 1073-1076. Korschelt, E., 1932. Ueber Frakturen und Skelettanomalien der Wirbeltiere. Erster Teil: SHugetiere. Beitr. path. Anat. allg. Path. 89(2): 419-483. Loth, E., 1940. Sur les fractures gueries des os des Cetaces et des Sireriiens. Res. Camp. sci. Monaco Fasc, 103: 247-254. Pales, L., 1930. Pale*opathologie et pathologie comparative. Masson et Cie, Paris: vii + 352, 63 pis. Petit, G., 1928. Sur la synostose de l'axis et de la troisieme vertebre cervicale chez les Lamantins. Bull. Mus. Nat. Hist. Nat. Paris 34(6): 429-431. Reinhart, R. H., 1959. A review of the Sirenia and Desmostylia. Univ. Calif. Publ. Geol. Sci. 36(1): iii + 145, 14 pis. Steller, G. W., 1899. The beasts of the sea. In: D. S. Jordan, ed.. The fur seals and fur-seal islands of the North Pacific Ocean. Govt. Printing Office, Washington, D. C, Part 3, Art. 8: 179-218. (Translation by W. and J. E. Miller of Steller, 1751, De bestiis marinis, Nov. Comm. Acad. Sci. Petropolitanae 2: 289-398, pis. 14-16.) PALE0BI0S, No. 18, 1975. 4. This series of papers is published under the supervision of the Graduate Students in Paleontology at the University of California, Berkeley, with the technical assistance of the academic and non- academic staff of the Museum of Paleontology. To purchase this article or previous numbers, send money to the Managing Editor, PALEOBIOS, University of California, Museum of Paleontology, Berkeley, California, 94720. Nos. 1 through 12 (available). $0.15 or $0.30 each No. 13. A Pliocene colubrid snake (Reptilia: Colubridae) from west- central Nevada. By John Ruben, 1 pp. (1971). $0.30 No. 14. Miocene mammals, stratigraphy and environment of Muruarot Hill, Kenya. By Cary T. 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