Virginia L. Naples

Three ways to be a saber-toothed cat.

Abstract 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.

Forelimb myology of the pygmy hippopotamus (Choeropsis liberiensis)

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.

The Morphology and Function of the Hyoid Region in the Tree Sloths, Bradypus and Choloepus

The sloth hyoid region has unique structural features, associated with inverted feeding and dependence upon the tongue and lips for food manipulation and ingestion. The hyoid apparatus functions as a unit and is large and robust. The basihyal is strongly bound to the skull posterior in comparison to other mammals. The anterior digastric is enlarged and fused medially, covering the mylohyoid in Choloepus but exposing its anterior aspect in Bradypus . Posteriorly, the muscle fuses with the sternohyoid to form a wide sternomandibularis with a loose tendinous connection to the basihyal. The proposed model of hyoid function predicts that this arrangement aids an inverted sloth in opening the mouth fully against gravity while permitting the hyoid to move anteriorly during tongue extension independent of the sternomandibularis. In upright feeding, contraction of the posterior digastric-sternomandibularis complex allows a similar function. In all postures, increasing gape improves the ability of the hyoglossus and styloglossus muscles to act jointly in moving the tongue laterally. Hyoid retraction, in all postures, occurs with contraction of the modified sternothyroid, which arises from the mid-dorsum of the manubrium sternum and inserts on the ossified thyroid cartilage. The sloth palate also facilitates inverted feeding. The mucosa shows tubercles and grooves which channel food particles toward a central groove. Food is then returned to the toothrows by the tongue for further mastication or passed along a posteriorly deepening groove for bolus formation prior to swallowing.

Morphological changes in the facial region and a model of dental growth and wear pattern development in Nothrotheriops shastensis

ABSTRACT Specimens of Nothrotheriops shastensis (25 juvenile mandibles or fragments, and 22 maxillae and fragments) from San Josecito Cave, Mexico, Shelter Cave, Conkling Cavern, Rampart Cave, and the tar seeps at Rancho La Brea were examined to determine (1) the patterns of tooth growth, eruption, and wear, and (2) the pattern of anterior facial growth. Although they lack enamel, sloth teeth have a hard outer layer of dentine structurally distinct from the softer central dentine. These two dentine types were present in all specimens, including the smallest juvenile (length of mandibular tooth row = 20.3 mm). Some tooth wear was present in all specimens. The alveoli for the ever-growing teeth extend to the ventral border of the mandibular ramus in adult sloths but not in juveniles. Both maxillary and mandibular tooth roots in juvenile sloths are tilted and curved, but in adults are more vertical and straight. Changes in tooth size and orientation during growth result in size and shape changes in the occlu...

The Power of the Claw

Scratches on bones have routinely been attributed to tooth marks (a predominantly untested speculation), ignoring the effects of claws, perhaps because of the general assumption that claws are too soft to damage bone. However, some pathologies appears to be more compatible with claw rather than tooth impacts. Therefore, it is critical to determine if the claws of any animal are capable of scratching into the surface of any bone – a test and proof of concept. A tiger enrichment program was used to document actual bone damage unequivocally caused by claws, by assuring that the tiger had access to bones only by using its paws (claws). The spectrum of mechanisms causing bone damage was expanded by evidentiary analysis of claw-induced pathology. While static studies suggested that nails/claws could not disrupt bone, specific tiger enrichment activities documented that bones were susceptible to damage from the kinetic energy effect of the striking claw. This documents an expanded differential consideration for scratch marks on bone and evidences the power of the claw.

Evolution of Hystricomorphy in the Nimravidae (Carnivora; Barbourofelinae): Evidence for complex character convergence with rodents

Barbourofelis fricki is a saber‐tooth with canines approximately 22 cm long and the largest mandibular flange among nimravids. The jaw‐rotation for canine clearance and biting exceeded 115°. This gape was coupled with extensive cranial musculoskeletal reorganization, including extension of the deep masseter through a greatly enlarged infraorbital foramen onto the muzzle (hystricomorphy). This condition was previously described in rodents, wherein the anteriorly originating deep masseter improved the mechanical advantage of anterior mandibular movements involved in gnawing. The anterior origin of the deep masseter in barbourofelins facilitated jaw closure from gapes over 90° in four ways: 1) a lengthened muscle excursion permitted greater contraction distance; 2) the line of action at all gapes improved, particularly for those over 90°; 3) anteroposterior masseter origin length increased; and 4) sequential muscle segment activation provided smooth muscular contraction and the ability to control mandibular position precisely. An occipital inclination of 90° or more and an elongated axis spinous process in barbourofelins and some rodents also permitted increased snout elevation.

Sex determination in lions (Panthera leo, Felidae): a novel method of distinguishing male and female skulls

Abstract Examination of skulls and mandibles reveals a consistent and previously undocumented means of distinguishing sex in lions (Panthera leo), on the basis of a phenomenon unique among Carnivora. Male lions show a pattern of increased pore-like porosity in the maxillary region, superficial and proximal to the root of the upper canine teeth. Although some porosity is present in females, pores are less common, smaller, less obvious and primarily restricted to the bulge in the maxilla that marks the root of the upper canine tooth. Increased porosity (fine pores) is also a gender-independent feature of young individuals. This feature remains prominent throughout the lives of males, whereas porosity diminishes as females approach adult size. Juvenile male lions show a rapid increase in head size, correlated with the time immediately prior to dispersal from the natal pride. Specifically, increases in the rate of growth of cranial features, including the dentition and facial musculature are reflected in these changes. The rapid alteration of these features in maturing male lions indicates readiness to compete for social status with adult pride males. It is hypothesized that maxillary porosity is the anatomical correlate of this phenomenon.

Reconstruction of the cranial musculature and masticatory function of the Pleistocene panamerican ground sloth Eremotherium laurillardi (Mammalia, Xenarthra, Megatheriidae)

Cranial musculature, dental function and mandibular movement patterns in Eremotherium laurillardi were reconstructed from the examination of crania and dentitions. Size, shape and pattern of muscle divisions were reconstructed from the examination of bony rugosities indicating muscle attachments. Details of masticatory muscle structure and function were based on dissections of the tree sloths Bradypus and Choloepus. Among sloths, masticatory muscles in E. laurillardi demonstrate a different synergist–antagonist pattern, reflecting greater emphasis on mediolateral mandibular movements. Eight cranial character complexes (anterior facial, zygomatic arch, superficial masseter, deep masseter–zygomaticomandibularis, pterygoid, temporal, occipital and occlusal) determined by interrelated contributions of each component made to group functions were identified. An elongate anterior face and predental spout in E. laurillardi allowed protrusion of a long narrow tongue at small degrees of gape, reflecting a probably ancestral xenarthran condition. Gape minimisation, in conjunction with the mediolaterally directed masticatory stroke in E. laurillardi, was a unique solution to increase masticatory efficiency by permitting molariform tooth shearing surfaces to remain in or near occlusion for a greater percentage of each chewing cycle.

Decompression Syndrome and Diving Behavior in Odontochelys, the First Turtle

Odontochelys semitestacea, the oldest known turtle, from the Late Triassic of China, shows a pathology. Sharply defined, focal depressions were noted on the articular surfaces of both humeri, documenting avascular necrosis. Diving habits of Mesozoic marine reptiles have been characterized on the basis of this localized form of bone death attributed to decompression syndrome. Pursuit by a predator was likely the cause of dangerously rapid depth changes by swimming turtles. The prevalence of avascular necrosis decreased geometrically from the Cretaceous to the Pleistocene. This study suggests that the habit of repetitive diving in turtles was already present in the Late Triassic, but that protective physiological and behavioral adaptations had not yet evolved.

Do ribs actually have a bare area? A new analysis

Recognition of macroscopic rib pathology requires an in-depth understanding of anatomy, especially of the attachment of muscle tendons and aponeuroses. Distinguishing periosteal reaction from residual aponeurotic tissues and the rugosity associated with muscle attachments, requires knowledge of these structures. The ribs of twenty cadavers were examined to establish the distribution of muscle attachments and aponeuroses, and their variations. A unique observation was that the entire rib surface is covered by tendon attachments and aponeuroses, without evidence of bare areas that are so prominent in other parts of the skeleton. Discrepancies between rugose regions and the extent of tendon attachments were occasionally noted, with the tendons or aponeuroses extending beyond the areas of attachments of the muscle fibers. Variable dessication of aponeurotic tissues can compromise appearance of normal bone, and may be responsible for past overdiagnosis of periosteal reaction.