mesonychids skull teeth, ear structure

1998. Fractures of the occipital bone at the base of the skull can occur in this manner, producing a basilar fracture that can damage the artery that passes through the carotid canal. (Walking whale). Mesonychid dentition consisted of molars modified to generate vertical shear, thin blade-like lower molars, and carnassial notches, but no true carnassials. [7] Some genera may need revision to clarify the actual number of species or remove ambiguity about genera (such as Dissacus and Ankalagon).[5]. Geisler, J. H. 2001. The chorda tympani branches off from the facial nerve in its vertical segment of the temporal bone (the main skull bone that houses the inner ear). Or, weirder still, the lumpsucker (both the blobfish and lumpsucker have names that betray their unappetizing beginnings--although all that has changed with overfishing): I exchanged a bunch of emails a week or two ago with a journalist who was working on a story involving the possibility of faster-than-light travel. - . [1] These "wolves on hooves" were probably one of the more important predator groups (although they may have been scavengers) in the late Paleocene and Eocene ecosystems of Europe (which was an archipelago at the time), Asia (which was an island continent) and North America. to breed and give birth. 292-331. Though mesonychids have skulls similar to canids, the two are quite different. Goodbye Tet Zoo ver 2. While later mesonychids evolved a suite of limb adaptations for running similar to those in both wolves and deer, their legs remained comparatively thick. Lateral to either side of this bump is asuperior nuchal line(nuchal = nape or posterior neck). Within the nasal cavity, the perpendicular plate of the ethmoid bone forms the upper portion of the nasal septum. They were also most diverse in Asia where they occur in all major Paleocene faunas. [4] A later genus, Pachyaena, entered North America by the earliest Eocene, where it evolved into species that were at least as large. The septal cartilage fills the gap between these bones and extends into the nose. wzi88?&wXo. On the interior of the skull, the petrous portion of each temporal bone forms the prominent, diagonally orientedpetrous ridgein the floor of the cranial cavity. These are paired bones, with the right and left parietal bones joining together at the top of the skull. (1988) to name a new clade, Hapalodectini, which they regarded as the sister-taxon to a (mesonychid + (Andrewsarchus + cetacean)) clade (that's right, they regarded Andrewsarchus as the sister-taxon to Cetacea). The molars were laterally compressed and often blunt, and were probably used for shearing meat or crushing bones. As I recall Prothero et al. The ethmoid bone and lacrimal bone make up much of the medial wall and the sphenoid bone forms the posterior orbit. Geisler & McKenna (2007) found Ankalagon to be nested within a clade of Dissacus species, suggesting that it doesn't deserve generic separation after all. The foot was compressed for efficient running with the axis between the third and fourth toes (paraxonic); it would have looked something like a hoofed paw. The frontal bone is thickened just above each supraorbital margin, forming rounded brow ridges. Inside the skull, the base is subdivided into three large spaces, called theanterior cranial fossa,middle cranial fossa, andposterior cranial fossa(fossa = trench or ditch) (Figure4). ear structure of He has also worked for the The lesser wings of the sphenoid bone form the prominent ledge that marks the boundary between the anterior and middle cranial fossae. Mesonychids e.g. It is a small U-shaped bone located in the upper neck near the level of the inferior mandible, with the tips of the U pointing posteriorly. The ethmoid bone also forms the lateral walls of the upper nasal cavity. So, in the sheep figure, anterior is to the left and above. Skulls and teeth have similar features to early whales, and the family was long thought to be the ancestors of cetaceans. It is subdivided into the facial bonesand thebrain case, or cranial vault (Figure1). Skull of a new mesonychid (Mammalia, Mesonychia) from the Late Paleocene of China. Good remains of P. ossifraga show that it was a large animal of 60-70 kg [skull of Sinonyx jiashanensis from Late Paleocene China shown below, from Zhou et al. These are located just behind your eyebrows and vary in size among individuals, although they are generally larger in males. [6] Most paleontologists now doubt the idea that whales are descended from mesonychians, and instead suggest that whales are either descended from or share a common ancestor with the anthracotheres, the semi-aquatic ancestors of hippos. & Geisler, J. H. 1999. These include the paired parietal and temporal bones, plus the unpaired frontal, occipital, sphenoid, and ethmoid bones. However, as the order is also renamed for Mesonyx, the term "mesonychid" is now used to refer to members of the entire order Mesonychia and the species of other families within it. The largest of the conchae is the inferior nasal concha, which is an independent bone of the skull. (f`0eib6bP! kA endstream endobj 16 0 obj 54 endobj 5 0 obj << /Type /Page /Parent 1 0 R /Resources 6 0 R /Contents 11 0 R /Rotate -90 /MediaBox [ 0 0 612 792 ] /CropBox [ 0 0 612 792 ] >> endobj 6 0 obj << /ProcSet [ /PDF /Text /ImageC /ImageI ] /Font << /F2 8 0 R /F3 7 0 R /F4 9 0 R >> /XObject << /Im1 13 0 R >> /ExtGState << /GS1 14 0 R >> /ColorSpace << /Cs9 10 0 R >> >> endobj 7 0 obj << /Type /Font /Subtype /Type1 /Encoding /WinAnsiEncoding /BaseFont /Times-Roman >> endobj 8 0 obj << /Type /Font /Subtype /Type1 /Encoding /WinAnsiEncoding /BaseFont /Times-Bold >> endobj 9 0 obj << /Type /Font /Subtype /Type1 /Encoding /WinAnsiEncoding /BaseFont /Times-Italic >> endobj 10 0 obj [ /Indexed /DeviceRGB 255 12 0 R ] endobj 11 0 obj << /Length 1039 /Filter /FlateDecode >> stream An Unforgettable Time-Lapse Volcano (Synopsis). It is formed by the junction of two bony processes: a short anterior component, thetemporal process of the zygomatic bone(the cheekbone) and a longer posterior portion, thezygomatic process of the temporal bone, extending forward from the temporal bone. 1988, the feature they thought united Andrewsarchus and Cetacea (they include a cladogram with a list of synapomorphies for each node (or at least for many)) was arrangement of incisors in a fore-and-aft line: early whales (and I'm not sure how many really early Cetaceans were known when they wrote) have all three incisors in a line, Andrewsarchus has M3 behind rather than beside M2, which they saw as an intermediate step towards the Cetacean condition. They first appeared in the Early Paleocene and went into a sharp decline at the end of the Eocene and died out entirely when the last genus, Mongolestes became extinct in the Early Oligocene. There is evidence to suggest that some genera were sexually dimorphic. Theparietal boneforms most of the upper lateral side of the skull (seeFigure3). determine paleoecology in secondary aquatic mammals. The teeth were also very similar to other early cetaceans and a chemical [11] The similarity in dentition and skull may be the result of primitive ungulate structures in related groups independently evolving to meet similar needs as predators; some researchers have suggested that the absence of a first toe and a reduced metatarsal are basal features (synapomorphies) indicating that mesonychids, perissodactyls, and artiodactyls are sister groups. Asutureis an immobile joint between adjacent bones of the skull. Fujiwara - 2016. The The position of Cetacea within Mammalia: phylogenetic analysis of morphological data from extinct and extant taxa. It is divided at the midline by the large foramen magnum (great aperture), the opening that provides for passage of the spinal cord. Early mesonychids probably walked on the flats of their feet (plantigrade), while later ones walked on their toes (digitigrade). Figure8. COMPARATIVE ANATOMY OF THE CRANIUM IN MESONYCHIDAE AND HAPALODECTIDAE The Hapalodectidae (sensu Ting and Li, 1987) in- > predators might have some credit after all. These features suggest to some authors that Harpagolestes was a carrion feeder (Szalay & Gould 1966, Archibald 1998). [8], harvnb error: no target: CITEREFJordiAnton2002 (, J. D. Archibald. The middle cranial fossa has several openings for the passage of blood vessels and cranial nerves (seeFigure6). It is subdivided into the facial bones and the brain case, or cranial vault ( Figure 7.3 ). The hyoid bone is located in the upper neck and does not join with any other bone. Theparanasal sinusesare hollow, air-filled spaces located within certain bones of the skull (Figure16). Many species are suspected of being fish-eaters, though some of these reconstructions may be influenced by earlier theories that the group was ancestral to cetaceans. Thezygomatic archis the bony arch on the side of skull that spans from the area of the cheek to just above the ear canal. Each of these spaces is called anethmoid air cell. Mesonychians were once long considered to be creodonts but have now been removed from that order and placed in three families (Mesonychidae, Hapalodectidae, Triisodontidae), either within their own order, Mesonychia (or in older text, "Acreodi"), or within the order Condylarthra. The large, diagonally positioned petrous ridges give the middle cranial fossa a butterfly shape, making it narrow at the midline and broad laterally. Paranasal Sinuses. This duct then extends downward to open into the nasal cavity, behind the inferior nasal concha. Anteriorly, the anterior fossa is bounded by the frontal bone, which also forms the majority of the floor for this space. Its limbs indicate a cursorial lifestyle [Charles Knight's Mesonyx shown below]. Currently, it is believed that the mesonychians are descended from the Condylarths (the first hoofed animals) and are part of the cohort or superorder Laurasiatheria. The pterion is located approximately two finger widths above the zygomatic arch and a thumbs width posterior to the upward portion of the zygomatic bone. They were also larger in general, with some species exceeding the size of bears. Harpagolestes and Mesonyx appear to be sister-taxa, and the most derived of mesonychids (O'Leary & Geisler 1999, Geisler 2001, Thewissen et al. Cranial Fossae. was more aquatic than There were bone-cracking scavengers, small jackal or fox-like generalists, large wolf-like hunters, and so on. On the lateral side of the brain case, above the level of the zygomatic arch, is a shallow space called thetemporal fossa. Basilosaurus (meaning "king lizard") is a genus of large, predatory, prehistoric archaeocete whale from the late Eocene, approximately 41.3 to 33.9 million years ago (mya). long webbed feet. Mesonychidae was named by Cope (1880). Figure17. This opening provides for passage of the nerve from the hearing and equilibrium organs of the inner ear, and the nerve that supplies the muscles of the face. In this view, the vomer is seen to form the entire height of the nasal septum.

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