The edentulous giant anteater (Myrmecophaga tridactyla) ingests food using a slender, elongated sticky tongue which can project to a distance greater than the cranial length. A large and elongated hyoid apparatus, including a long stylohyal, epihyal, reduced ceratohyal and fused basihyal-thyrohyal fused to a partially ossi®ed thyroid cartilage, supports the tongue. The fusion pattern and relative hyoid element sizes in adult Myrmecophaga differ from those in other xenarthran anteaters, tree and ground sloths, and armadillos. The hyoid bones have synovial joints with articular surfaces permitting great freedom of movement. A unique hyoid muscle arrangement enables Myrmecophaga to project the tongue with great speed and precise positional control. This muscle arrangement combined with an elongated secondary palate, accommodates the retracted tongue within the oropharynx without compromising the animal's ability to breathe. Maximum gape is reached at a few degrees of mandibular depression, but the oral opening is increased to 2 cm by the extreme length of the anterior facial region. Gape is further increased by medial rotation and depression of the unfused mandibular rami at the mental symphysis. This movement, even without mandibular depression, permits protraction and retraction of the elongated tongue. Mandibular rotation in lieu of depression and elevation simpli®es jaw movements made by a smaller uniquely modi®ed muscle mass over shorter distances, therefore increasing the speed with which anteaters can ingest food, and complements the extremely rapid tongue protrusion±retraction cycle.
The tree sloths, Bradypus and Choloepus, show unusual masticatory specializations, compared to each other and to other mammals. Both have an incomplete zygomatic arch with descending jugal process, a complex superficial masseter, a large temporalis and medial pterygoid musculature, and a lateral pterygoid with two heads. In Choloepus the deep masseter and zygomaticomandibularis are typical when compared to other mammals. However, in Bradypus there is an ascending jugal process from which enlarged and vertically oriented deep masseter and zygomaticomandibularis muscles originate. Although both sloths are folivores, the anterior teeth in Choloepus are caniniform, while those of Bradypus have lost such elongation. In both sloths the glenoid cavity is similarly located; however, in Bradypus the craniomandibular joint is raised above the occlusal plane, and the pterygoid flanges are elongated. Prediction of the evolutionary sequence of cranial changes from Choloepus-like (primitive) to Bradypus-like (derived) morphology is based upon the most parsimonious model of masseter-medial pterygoid complex changes for masticatory efficiency improvement. The model proposes that the condylar neck in Bradypus was elongated and that this single change predicated a series of other structural changes. Mandibular movement patterns in both sloths showed anteromedially directed unilateral power strokes as in other mammals. Puncture-crushing, tooth-sharpening, and chewing cycles are distinct in Choloepus, less so in Bradypus. The masticatory rate is slow in sloths compared to other mammals of similar body size, averaging 590 ms per cycle for Choloepus and 510 ms for Bradypus.
Based on morphological analyses, hippos have traditionally been classified as Suiformes, along with pigs and peccaries. However, molecular data indicate hippos and cetaceans are sister taxa (see review in Uhen, 2007, this issue). This study analyzes soft tissue characters of the pygmy hippo forelimb to elucidate the functional anatomy and evolutionary relationships of hippos within Artiodactyla. Two specimens from the National Zoological Park in Washington, D.C. were dissected, revealing several adaptations to an aquatic lifestyle. However, these adaptations differ functionally from most aquatic mammals as hippos walk along river or lake bottoms, rather than swim. Several findings highlight a robust mechanism for propelling the trunk forward through the water. For example, mm. pectoralis superficialis and profundus demonstrate broad sites of origin, while the long flexor tendons serve each of the digits, reflecting the fact that all toes are weight-bearing. Pygmy hippos also have eight mm. interossei and a well-developed m. lumbricalis IV. Retention of intrinsic adductors functions to prevent splaying of the toes, an advantageous arrangement in an animal walking on muddy substrates. Published descriptions indicate common hippos share all of these features. Hippo and ruminant forelimbs share several traits; however, hippos are unique among artiodactyls in retaining several primitive muscles (e.g., mm. palmaris longus and flexor digitorum brevis). These findings are consistent with the hypothesis that hippos diverged from other Artiodactyla early in the history of this group. Additional analyses of hindlimb and axial muscles may help determine whether this trajectory was closely allied to that of Cetacea. Anat Rec, 290:673-693, 2007. 2007 WileyLiss, Inc.Key words: pygmy hippopotamus; common hippopotamus; myology; forelimbThere are two extant species of hippopotami, the common hippo (Hippopotamus amphibius) and the pygmy hippo (Choeropsis liberiensis). Based on morphological analyses, hippos have traditionally been classified as Suiformes, along with pigs and peccaries (Simpson, 1945). However, molecular studies indicate hippos and cetaceans are sister taxa (e.g., Irwin and Arnason, 1994;Gatesy et al., 1996;Nikaido et al., 1999). In addition, many molecular analyses support a close relationship between ruminants and the hippo and whale clade, further separating hippos from suids and tayassuids (e.g., Shimamura et al
Saber-toothed carnivores, until now, have been divided into two groups: scimitar-toothed cats with shorter, coarsely serrated canines coupled with long legs for fast running, and dirk-toothed cats with more elongate, finely serrated canines coupled to short legs built for power rather than speed. In the Pleistocene of North America, as in Europe, the scimitar-cat was Homotherium; the North American dirk-tooth was Smilodon. We now describe a new sabercat from the Early Pleistocene of Florida, combining the scimitar-tooth canine with the short, massive limbs of a dirk-tooth predator. This presents a third way to construct a saber-toothed carnivore.
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