THE XENARTHRA FROM THE ITABORAÍ BASIN (ITABORAIAN, UPPER PALE- disappear as amelogenesis progresses. OCENE) RIO DE JANEIRO, BRAZIL Several lines of evidence demonstrate that siderose enamel is harder than hydroxya- ABRANTES, Erika Aparecida Leite, BERGQVIST, Lílian, and AVILLA, Leonardo, paptite enamel and it is distributed where resistance to dental abrasion would be critical to Universidade Federal do Rio de Janeiro, Rua Jiquiba, 60/301, Maracanã Rio de maintenance of puncturing and shearing functions. This appears to contradict the fact that the Janeiro, 20271-250 Brazil. majority of shrew prey items are soft bodied invertebrates. However, scattered data indicate The discovery of xenarthran remains in Itaboraí Basin was reported in 1949, but they were that soricine shrews not only ingest a larger percentage of earthworms and subterranean lar- only formally studied in the mid-seventies. Two osteoderms were first assigned to vae but also chew them more thoroughly than do crocidurine shrews. We believe that siderose Prostegotherium astrifer Ameghino, 1902, but latter reviewed and considered a new taxon— enamel serves to minimize dental abrasion during mastication of prey items with silt and sand Riostegotherium yanei Oliveira & Bergqvist, 1998—based on the presence of more than ten adhering to them or in their guts. pits in the groove around the central figure of fixed scutes. It is difficult to trace similar iron mineralization in fossil teeth because seconday iron In the early eighties, two cingulate astragali were described and assigned to a dasypodid (the staining is so common but numerous examples of Lambdopsalis bulla, a Paleocene multitu- larger) and to a glyptodontid. A posterior review of those astragali suggested that the features berculate, bear bright red enamel on their incisors and second molars and the color of fossil argued as suggestive of glyptodontid affinities are also presented in several other “edentate” rodent incisors and soricine teeth can persist for millions of years. Various iron oxide com- tarsals. pounds have been reported in ectodermally derived dental cuticle or in the outermost dental In the nineties, new xenarthran remains were discovered among the fossils recovered layers of extant fish, salamanders, snakes and rodents suggesting that iron compunds were from the basin. The revision and description of the postcranium are the goals of this contri- important throught much of vertebrate history. bution. As in other xenarthrans, the humeri presents a developed deltopectoral shelf, a promi- CRANIAL STRUCTURE AND AFFINITIES OF THE LOWER PERMIAN CAPTORHINID nent supinatory crest and a broad distal end, but also bear several features shared by other REPTILE CAPTORHINIKOS PARVUS (REPTILIA, CAPTORHINIDAE) “edentates”: a pectoral crest medially directed, pectoral and deltoid tuberosities developed, ALBRIGHT, Gavan, California State University, San Bernardino, 3653 Watkins Dr., deltopectoral shelf extending more than halfway of total length, supinatory crest with a Riverside, CA 92507. straight border and wide and shallow bicipital groove. The ulna preserved only the proximal The cranial morphology of the Lower Permian captorhinid reptile Captorhinikos parvus part. As in most Dasypodidae, the olecranon is long in thin, but the epiphysis is transversely (Reptilia, Captorhinidae) is re-interpreted. Re-examination and further preparation of 7 spec- large and curved, as in Metacheiromys. Two different patterns of xenarthrans astragali are con- imens from the original study characterizing the species, as well as preparation and examina- firmed for Itaboraí. The smaller has a more primitive morphology—body and neck slender tion of 16 new specimens, all from the Hennessy Formation of Central Oklahoma provide sig- and longer, though lacking astragalar foramen. The larger resembles dasypodids with a broad nificant new information bearing on the characterization of C. parvus. This study shows it to and short trochlea and a more oblique neck. Both bear sustentacular and ectal facets aligned be a valid and distinct taxon based on very small adults with multiple maxillary and mandibu- on the same axis of rotation, considered by some authors as a synapomorphy of Xenarthra and lar tooth rows. This determination supports Olson’s original characterization in the broadest Palaeonodonta. sense, but significant revision and additions to cranial morphology and relationships can now Although the scutes surely indicate the presence of cingulates in Itaboraí, the same can- be offered. Fine scale preparation of these excellently preserved specimens has yielded one of not be assumed by the limb bones, as several features are shared by other “edentates”. A care- the most complete pictures of cranial structure in a basal reptile, including the morphology ful review is urged for a better definition of each edentate-like group. and interrelationships of palatal as well as braincase, and stapedial elements. Three single rows of small palatal teeth radiate anteriorly, anterolaterally, and laterally from the medial THE BRAINCASE AND EAR REGION OF ICHTHYOSTEGA: A UNIQUELY SPE- edge of the transverse flange. In addition, the suture connecting the vomer and palatine bones CIALISED EAR IN AN EXCEPTIONALLY PRIMITIVE TETRAPOD BRAINCASE bisects the facet marking the contact between the palate and the maxilla anterior-posteriorly. AHLBERG, Per Erik, The Natural History Museum, Dept. of Palaeontology Cromwell Visualization of individual braincase elements, including opisthotic, basioccipital, and stapes Rd London, SW7 5BD United Kingdom; CLACK, Jennifer, University Museum bones allows for a much more complete braincase reconstruction. Preliminary phylogenetic of Zoology Cambridge CB2 3EJ United Kingdom; KETCHAM, Richard, analysis reinforces the validity of the taxon and hints at possible affinities with the small, sin- University of Texas Austin, TX, 78712-1101; DOMINGUEZ ALONSO, Patricio, gle rowed captorhinid reptile Saurorictus australis. Confirmation that C. parvus is indeed The Natural History Museum London, SW7 5BD United Kingdom. based on adult specimens also invites speculation that the taxon represents an example of Surface preparation and CT scanning of new Ichthyostega specimens has allowed the first miniaturization within the Captorhinidae. anatomically plausible interpretation of the braincase and ear region. The highly autapomor- phic otic structure suggests specialisation for underwater audition, but it also shows some very THE PHYLOGENETIC RELATIONSHIPS OF MEGALOSAURIDAE WITHIN BASAL primitive features. The otoccipital region is unusually long for a stem tetrapod but the saccu- TETANURINE THEROPODS (DINOSAURIA). lar chambers are remarkably small and anteriorly placed. The combination of a tiny ear and ALLAIN, Ronan, Museum National d’Histoire Naturelle, Laboratoire de long hindbrain is unique among tetrapods. The otoccipital bears deep posterior flanges sutur- Paléontologie, UMR 8569 CNRS 8 rue Buffon Paris, F-75005 France. ing to the skull roof and there are no posttemporal fossae. The vestibular fontanelle is not con- The discovery of Poekilopleuron? valesdunensis from the Middle Bathonian of Normandy fluent with the fenestra vestibuli; this may be a primitive trait, but is unique among early provides us cranial and postcranial characters that are crucial for reconstructing the phyloge- tetrapods. ny of basal tetanurine theropods commonly related to poorly known Megalosauridae. Large chambers on each side of the braincase, constrained by flanges of the braincase Phylogenetic analyses of a data matrix of 107 characters and 22 ingroup taxa (includ- and skull roof, extend above the otic capsules almost to the midline. With its reinforced walls, ing 9 European taxa) in a branch and bound search in PAUP support the monophyly of the chamber is unique to Ichthyostega, but may correspond in part to a spiracular recess iden- Megalosauridae within a monophyletic Spinosauroidea (Megalosauridae + Spinosauridae + tified in other early tetrapods. The stapes appears to have two heads separated by large stape- Torvosaurus) which is the sister taxon to Neotetanurae (Allosauroidea + Coelurosauria). dial foramen. The ventral head articulates with the basioccipital, while the dorsal head inserts Ceratosaurus lies closer to Tetanurae than to Coelophysis. Poekilopleuron? valesdunensis, into a hole in the braincase wall near the saccular chamber. The stapedial shaf’ is an almost Eustreptospondylus, Streptospondylus and Afrovenator are united within Megalosauridae. circular, anterodorsally curved lamina of very thin bone projecting dorsolaterally into the Lourinhanosaurus is found to be another Megalosauridae, while Metriacanthosaurus and chamber alongside the braincase, almost contacting the transverse proötic buttress. The cham- Erectopus, commonly referred to that clade, are more closely related to Allosauroidea. ber likely housed a diverticulum of the spiracular tract (or middle ear). If air-filled but seal- Neovenator is a basal allosauroid. able, it could have acted as a transducer for water-borne sound, transmitting it to the stapes if The resulting strict consensus tree superimposed on the geochronologic time scale sug- the latter were incorporated into a ventral, soft tissue wall to the chamber. This would be func- gests that Ceratosauria, Spinosauroidea, Allosauroidea and Coelurosauria were distinct as tionally comparable to ear function in underwater sound reception in Xenopus and ostario- early as the Early Jurassic. With nine valid