This paper describes the petrosal (periotic) and the inner ear of Herpetocetus sp., an archaic mysticete whale (Mysticeti, Mammalia) from the Yorktown Formation (Pliocene) of North Carolina, USA. [9], Köhler & Fordyce 1997 described an incomplete skull, four vertebrae, two teeth, and small fragments in early Bartonian sediments in New Zealand which they tentatively identified as Zygorhiza sp.. The new Indocetus specimens included a piece of pelvic bone, tibia and femur, but no foot bones. It might indicate that Zygorhiza represents a stage in archaeocete evolution where skeletal maturation was delayed like in modern cetaceans. P2–3 are two-rooted. Anatomical evidence for low frequency sensitivity in an archaeocete whale: comparison of the inner ear of Zygorhiza kochii with that of crown Mysticeti. [16], The vertebral formula is 7 cervicals, 15 thoracics, probably 13 lumbars, 2 sacrals, and at least 21 caudals. Hoyte, D. A. N. (1961). P1 is caniniform with a single root. The head consisted of a very wolf-like structure, with … Throughout these changes, cetaceans have maintained a unique auditory structure: the pachyosteoslerotic tympanic bulla. (i) Pinna: ADVERTISEMENTS: The pinna is […] Four major divisions of auditory system - Anatomy 1. The ear consists of three major regions: Outer ear - picks up the sound; Middle ear - transmits the sound to the inner ear via the eardrum and three ossicles (incus, malleus, stapes) Inner ear - transforms the sound into nervous impulses via the cochlea and maintains balance via the semicircular canals; The ear anatomy doesn’t finish here. Zygorhiza differs from all other dorudontines in the presence of well-developed cuspules on the cingula of the upper premolars. [14], The elbow is a hinge joint without rotary movements and the forelimbs are relatively short. Ekdale, E. G. and R. A. Racicot. The postnatal growth of the ear capsule in the Bisconti, M. (2015). The centra of the posterior thoracic, lumbar, sacral, and anterior caudal are slightly elongated. However, the lack of The centra of the cervicals are compressed and the flexibility in the neck is limited by the interlocked lateral processes. Skeleton [ edit | edit source ] The skull is elongated with a narrow rostrum and a flattened forehead; the premaxillae are laterally convex. The axis, a small odontoid (tooth-like) process, short and narrow transverse processes, and an elongated neural spine. The atlas has a hypapophysial (ventral) process. Zygorhiza differs from all other dorudontines in the presence of well-developed cuspules on the cingula of the upper premolars. [14], The hyoid apparatus consists of a small, central, and hexagonal basihyoid bone. Whale Evolution Data Table Name Mesonychids e.g. The centra of the posterior thoracic, lumbar, sacral, and anterior caudal are slightly elongated. Zygorhiza (and Dorudon) replaced their upper and lower deciduous first premolars with permanent teeth. [2], The skull is elongated with a narrow rostrum and a flattened forehead; the premaxillae are laterally convex. 2015. ], the significance of this finding is limited by the methods employed and taxa sampled. locomotion. [7], Seeley 1876 named and described the species Zeuglodon wanklyni based on a skull that is friend Dr. Arthur Wanklyn had found in the Barton Clays in southern England. 2000 estimated the adult body mass for Zygorhiza to 3,351 kg (7,388 lb) based on an estimated body length of 520 cm (200 in). ual petrosal. Journal of Anatomy. Pachyaena Pakicetus Ambulocetus Rodhocetus Basilosaurus Zygorhiza Year reported Country where found Geological From this bone project a pair of thyrohyoid bones (homologous with the greater cornua in humans) that are slightly expanded anteriorly and tapper off posteriorly, and another pair of slender and elongated bones, the epihyoid and stylohyoid bones.