Endocranial petrosal anatomy of Bothriogenys (Mammalia, Artiodactyla, Anthracotheriidae), and petrosal volume and density comparisons among aquatic and terrestrial artiodactyls and outgroups

We provide the first detailed endocranial description of the petrosal bone of the ear region of the anthracotheriid artiodactyl Bothriogenys, based on two new specimens from the early Oligocene of the Jebel Qatrani Formation, Fayum, Egypt. The new fossils have petrosals with a hyperinflated (pachyostotic) tegmen tympani (the roof over the middle ear), resembling the condition in certain cetancodontans such as hippopotamids and basal cetaceamorphans (fossil stem taxa to extant Cetacea).The morphology of the petrosal, particularly its relative size and density, has been considered an important indicator of the ability of a marine mammal to localize sound transmitted in water, yet petrosal size (pachyostosis) and density (osteosclerosis) have not previously been quantified independent of each other. We examine the new fossils in the context of a preliminary CT-based study of petrosal density (extant taxa only) and petrosal volume (extant and extinct taxa) in a sample of artiodactyls and outgroups. In our extant comparative sample, the petrosals of cetaceans are both dense and voluminous as has been previously stated. We find, however, that the tegmen tympani is relatively voluminous (pachyostotic) without being particularly dense (osteosclerotic) in Hippopotamus amphibius, an extant taxon that has been documented to show some aquatic hearing behaviors, albeit less derived ones than those seen in cetaceans. A voluminous tegmen tympani, which is present in Bothriogenys, may have specific implications for behavior that are distinct from increases in petrosal density.

Non-trilobite arthropods from the Silver Peak Range, Nevada

Two non-trilobite arthropods are described from the Emigrant Formation (Lower Cambrian-Lower Ordovician) in the Silver Peak Range, Esmeralda County, Nevada. A Middle or Upper Cambrian “arachnomorph” arthropod with a phosphatic exoskeleton has been noted in previous faunal lists, but has not been previously described. This fossil is here named Quasimodaspis brentsae gen. et sp. nov. Q. brentsae belongs in the Aglaspidida, a close outgroup to the true chelicerates; this is the second report of an aglaspidid from the Great Basin. Esmeraldacaris richardsonae gen. et sp. nov. is a newly discovered arthropod from the lower Ordovician, from beds transitional between the Emigrant Formation and the overlying Palmetto Formation. It is a survivor of an early arthropod lineage that does not belong in any extant taxon, but which may also include the Ordovician Corcorania and the Cambrian Mollisonia.

Fossil Woods from the El Cien Formation in Baja California Sur: Leguminosae

Three types of fossil woods with similarities to the Leguminosae are described, Mimosoxylon tenax (Felix) Müller-Stoll ' Mädel, Bajacalijomioxylon cienense Cevallos-Ferriz ' Barajas-Morales, gen. et sp. nov., and Copaijeroxylon matanzensis Cevallos-Ferriz ' Barajas-Morales, sp. nov. These woods are from the EI Cien Formation in Baja California Sur, Mexico, which is dated as Zemorrian-Saucesian, i.e., late Oligocene–early Miocene. Although two of the names of the fossil woods suggest affinity with a particular extant taxon, differences in some quantitative and qualitative features preclude their identification with a single extant taxon. The similarity among wood of some groups of extant Leguminosae and limited knowledge of character variability in woods of this family explains this taxonomie uncertainty. These fossil woods from Baja California underscore the need for an extensive systematic study of the wood anatomy of Leguminosae, add to the poorly known plant history of the Peninsula, suggest a tropical South American influence in the fossil flora of Baja Califomia, and indicate that the climate during the Zemorrian- Saucesian was different from the xeric conditions that prevail today in the area.