Pathologic tooth deformities in modern and fossil chondrichthians: a consequence of feeding-related injury

Deformed teeth are found as rare components of the dentitions of both modern and fossil chondrichthians. Tooth deformities occur as bent or twisted tooth crowns, missing or misshaped cusps, atypical protuberances, perforations, and abnormal root structures. Deformed tooth files consisting of unusually overlapped or small teeth, or teeth misaligned in the jaw also occur in modern forms, but deformed tooth files generally are not recognizable in fossils due to post-mortem dissociation of teeth and jaws. A survey of 200 modern lamniform and carcharhiniform sharks as well as literature sources indicate that such deformities are produced by feeding-related injury to the tooth-forming tissue of the jaws, particularly by impaction of chondrichthian and teleost fin and tail spines. Tooth counts for several late Cretaceous genera, based on material recovered from coastal plain sites from New Jersey to Alabama, suggest that the frequency of occurrence of deformed teeth in a species varies from about 0.015% in Squalicorax kaupi to about 0.36% in Paranomotodon sp. Tooth counts for modern lamniform and carcharhiniform sharks yield a comparable range in frequency of tooth deformities. Variation in frequency of tooth deformity may reflect interspecific differences in feeding behavior and dietary preferences. There is no suggestion in our data of any strong patterns of temporal variation in tooth deformity frequency, or of patterns ­reflecting chondrichthian phylogenetic history and evolution. Skeletal components of the probable prey of the Cretaceous species are preserved in the same horizons as the deformed teeth, and also are found within co-occurring chondrichthian coprolites.     

Morphology and evolution of the jaw suspension in lamniform sharks

The morphology of the jaw suspension and jaw protrusion mechanism in lamniform sharks is described and mapped onto a cladogram to investigate how changes in jaw suspension and protrusion have evolved. This has revealed that several evolutionary modifications in the musculoskeletal apparatus of the jaws have taken place among lamniform sharks. Galeomorph sharks (Carcharhiniformes, Lamniformes, Orectolobiformes, and Heterodontiformes) have paired ethmopalatine ligaments connecting the ethmoid process of the upper jaw to the ethmoid region of the cranium. Basal lamniform sharks also acquired a novel single palatonasal ligament connecting the symphysis of the upper jaw to the cranium mid-ventral to the nasal capsule. Sharks in the family Lamnidae subsequently lost the original paired ethmopalatine ligament while retaining the novel palatonasal ligament. Thus, basal lamniform taxa (Mitsukurina owstoni, Carcharius taurus, Alopias vulpinnis) have increased ligamentous support of the lateral region of the upper jaw while derived species (Lamnidae) have lost this lateral support but gained anterior support. In previous studies the morphology of the jaw suspension has been shown to play a major role in the mechanism of upper jaw protrusion in elasmobranchs. The preorbitalis is the primary muscle effecting upper jaw protrusion in squalean (sister group to galeomorphs) and carcharhiniform (sister group to lamniforms) sharks. The preorbitalis originates from the quadratomandibularis muscle and inserts onto the nasal capsule in squalean and carcharhiniform sharks. Carcharhiniform sharks have evolved a subdivided preorbitalis muscle with the new division inserting near the ethmoid process of the palatoquadrate (upper jaw). Alopid sharks have also independently evolved a partially subdivided preorbitalis with the new division inserting at the base of the ethmoid process and surrounding connective tissue. Lamnid sharks have retained the two preorbitalis divisions but have modified both of the insertion points. The original ventral preorbitalis division now inserts onto the connective tissue surrounding the mid-region of the upper jaw, while the new dorsal preorbitalis division inserts onto the surrounding connective tissue and skin at a more posterior position on the upper jaw. The retractor muscle of the jaws, the levator hyomandibularis, has also been modified during the evolution of lamniform sharks. In most sharks, including basal lamniforms, the levator hyomandibularis inserts onto the hyomandibula and functions to retract the jaws after protrusion. In alopid and lamnid sharks the levator hyomandibularis inserts primarily onto the upper and lower jaws around the jaw joint and is a more direct route for retracting the jaws. Thus, there has been at least one instance of character loss (ethmopalatine ligament), acquisition (palatonasal ligament), subdivision (preorbitalis), and modification (ventral preorbitalis, dorsal preorbitalis, and levator hyomandibularis) in the ligaments and muscles associated with the jaw suspension and jaw protrusion mechanism in lamniform sharks. While derived lamniform sharks (Lamna nasus, Carcharodon carcharius, and Isurus oxyrinchus) lost the ancestral passive lateral support of the ethmoid articulation of the upper jaw, they simultaneously acquired muscular support by way of the levator hyomandibularis, which provides a dynamic mechanism for lateral support. The evolution of multiple divisions of preorbitalis insertions onto the palatoquadrate and modification of the levator hyomandibularis insertion directly onto the jaws provides an active mechanism for multiple protractions and retractions of the upper jaw, which is advantageous in those sharks that gouge or saw pieces from large oversized prey items.     

Types of morphogenesis of the dermal skeleton in fossil sharks

Four types of morphogenesis of the dermal skeleton can be distinguished. They differ with regard to scale growth, scale replacement and insertion of new scales during ontogeny. Three of the types occur exclusively in fossil sharks and have been found in only a few articulate specimens. In only one case (Jurassic hybodontids) it is possible to trace the phyletic transition from one type to another. The adaptive significance, both of different types of morphogenesis of the dermal skeleton as well as different types of scale shapes, is discussed.     

Sr/Ca and early hominin diets revisited: new data from modern and fossil tooth enamel

A previous study of strontium/calcium (Sr/Ca) ratios in Paranthropus suggested that it consumed more animal foods than was previously believed. However, that study looked at Sr/Ca in fossil bone, which is known to be highly susceptible to diagenesis. Enamel, in contrast, is resistant to post-mortem alteration making it a more appropriate material for Sr/Ca analysis of Plio-Pleistocene fossils. Yet, we know virtually nothing about Sr/Ca in the enamel of modern African mammals, much less fossil taxa. To address this gap, we studied Sr/Ca in tooth enamel from modern mammals in the greater Kruger National Park, South Africa, as well as fossil fauna from the Sterkfontein Valley. Grazing herbivores have the highest Sr/Ca, followed by browsers and carnivores in both modern and fossil fauna. This similarity in ecological Sr/Ca patterning between modern and fossil fauna shows that diagenesis has not obscured the primary dietary signals. Australopithecus has significantly higher Sr/Ca than Paranthropus, and higher Sr/Ca than fossil papionins, browsers, and carnivores. Paranthropus has lower Sr/Ca than grazers, but its Sr/Ca is higher or equal to that of fossil papionins, browsers, and carnivores. Thus, Sr/Ca for both hominins is relatively high, and provides no direct evidence for omnivory in either taxon. The consumption of underground resources or insects are among the possible explanations for the highly elevated Sr/Ca in Australopithecus.     

Post-pleistocene changes in tooth root and jaw relationships

Mandibles of 126 sexed skeletal specimens, from Near Eastern sites dating over the past 12,000 years were radiographed. From the radiographs obtained, digitised tracings were made of crown length (mesiodistal), root height and width, and corpus height mesial to the premolars and first and second molars. The data obtained were analysed using rank transformation procedures. The significance of unidirectional trends in relation to periods sampled was examined graphically and analytically through linear regression analysis of the ranks on the chronological scale, and Spearman's rank correlation was used to compare relationships between different parameters of individual teeth in different periods. Significant reduction was found in crown length between 12,000 B.P. and 6,000 B.P., but no further reduction was found between 6,000 B.P. and 1,000 B.P. Little change was observed in root size, but corpus height showed significant reduction over the past 6,000 years. The differences observed in the timing and extent of reduction in crown, root, and corpus height are associated with a low intrapopulation correlation between them.     

Kinematic analysis of jaw protrusion in orectolobiform sharks: A new mechanism for jaw protrusion in elasmobranchs

Jaw protrusion is an important component of prey capture in fishes, although the mechanics of protrusion have thus far been studied largely in teleosts. Elasmobranchs are also able to protrude their jaws (Tricas and McCosker [1984] Proc. Cal. Acad. Sci. 43: 221–238; Tricas [1985] Mem. S. Calif. Acad. Sci. 8:81–91.; Frazzetta and Prange [1987] Copeia 4:979–993). Several related features of the feeding apparatus contribute to jaw protrusion in sharks. Labial cartilages form an extendible series attached dorsally to the anterolateral face of the palatoquadrate and ventrally to the anteroventral surface of Meckel's cartilage. The labial cartilage chain swings anterolaterally as the lower jaw is depressed, thrusting the labial margins forward to form a circular oral opening and displacing the jaw apparatus towards the food; this pattern is analogous to halecomorph and primitive actinopterygian fishes in which the maxilla swings forward (Lauder [1979] J. Zool. Lond. 187:543–578). The palatoquadrate and Meckel's cartilage also project anteriorly and represent the major contribution to protrusion. These movements occur simultaneously with enlargement of the oral cavity to generate suction. The wobbegong sharks (Orectolobidae) are specialized for jaw protrusion. The spotted wobbegong protrudes its jaw by 33% of its chondrocranial length using two different mechanical systems. In the first mechanism of jaw protrusion, the intermandibularis and interhyoideus muscles medially compress the lower jaw and hyomandibulae. Compression of the lower jaw results in a more acute symphyseal angle so that the anteroposterior alignment of the lower jaw increases due to the rotation of each lower jaw towards a saggital orientation. Distal compression of the hyomandibulae at their attachments to the jaws swings the jaws forward. The second mechanism involves rotation of the ceratohyal around a posterior process of the lower jaw, pushing the hyomandibulae anteroventrally, thereby pushing the jaw articulation ventrally and anteriorly to protrude the jaws. © 1994 Wiley-Liss, Inc.     

Jaw movement and tooth use in recent and fossil primates

Masticatory movements and molar wear facets in species of Tupaia, Galago, Saimiri, and Ateles have been examined using cinefluorography and occlusal analysis. The molars have been compared with those of a fossil series: Palenochtha, Pelycodus and Aegyptopithecus. The extant primates are almost identical in their feeding behaviour, the movements and timing of the masticatory cycle. Food is first puncture-crushed where the cycle is elongated, the power stroke attenuated and abrasion facets are produced on the molars. Chewing follows, the movements are more complex, the power stroke has two distinct parts and attrition facets are produced. In the primitive forms (Tupaia, Palenochtha), shearing blades, arranged in series (en echelon) were used to cut the food during the first part (Phase I) of the power stroke as the lower teeth move into centric occlusion. This mechanism has been progressively replaced by a system of blade-ringed compression chambers which cut and compartmentalise the food in Phase I. This is followed by an anteromedially and inferiorly directed movement away from centric occlusion (Phase II) in which the food is ground. In both extant and fossil series there has been a clear trend towards the elongation of Phase II with a corresponding reduction in Phase I. These results suggest that the observed changes in the morphology of the jaw apparatus have probably occurred within the limits set by a pre-existing behavioral pattern.     

Exploring macroevolution using modern and fossil data

Macroevolution, encompassing the deep-time patterns of the origins of modern biodiversity, has been discussed in many contexts. Non-Darwinian models such as macromutations have been proposed as a means of bridging seemingly large gaps in knowledge, or as a means to explain the origin of exquisitely adapted body plans. However, such gaps can be spanned by new fossil finds, and complex, integrated organisms can be shown to have evolved piecemeal. For example, the fossil record between dinosaurs and Archaeopteryx has now filled up with astonishing fossil intermediates that show how the unique plexus of avian adaptations emerged step by step over 60 Myr. New numerical approaches to morphometrics and phylogenetic comparative methods allow palaeontologists and biologists to work together on deep-time questions of evolution, to explore how diversity, morphology and function have changed through time. Patterns are more complex than sometimes expected, with frequent decoupling of species diversity and morphological diversity, pointing to the need for some new generalizations about the processes that lie behind such patterns.     

Regional variation in tooth size and pathology in fossil hominids.

Tooth size and dental pathology in fossil hominids were studied to test for regional differences in these parameters. The results showed little regional variation in tooth size for the Middle and Upper Pleistocene sites compared (except for Krapina) but considerable differences in the severity of attrition and dental pathology. These differences were considered indicative of regional differences in the functional load borne by the teeth, and in view of the similar technological status of the groups studied, were attributed to environmental differences in the diet. Since, in all regions, reduction in tooth size appeared to continue at the same rate for the periods investigated, no association can be established between presumed selective pressures related to differences in functional demands made on the dentition, and tooth reduction.     

Reasons of micromorphism in modern or fossil brachiopods

Mass samples of the micromorphic recent (Hemithyris psittacea, Eucalathis murrayi, Macandrevia cranium, Megathyris detruncate, Argyrotheca cuneata, Argyrotheca cordata) and fossil Silurian (Microsphaeridiorhynchus sp.) brachiopods were studied. New location of Eucalathis murrayi on the Kitovyi Ridge in the Atlantic Ocean is described. Rates of growth of shells were revealed by the study of the sizes and age of brachiopods. Reasons of dwarfism in brachiopods are discussed. Three strategies of growth of the micromorphic brachiopods are distinguished. Appearance of micromorphic brachiopods is connected with the changes in the rates of shell growth and life expectancy.     

Patterns of ecological diversity in fossil and modern mammalian faunas

Ecological diversity provides a means of analysing the community structure of fossil mammalian faunas in order to obtain information on the habitat of the fauna. As a basis for the analysis, 23 modern mammalian communities from distinct habitats have been used to establish patterns of community structure for tropical African habitats according to their species diversity by taxonomic group, size, locomotor zonal adaptation, and feeding adaptation. All the communities tested were in tropical Africa, but additional analyses on tropical forest communities in Australia, Malaya, and Panama have shown that these communities, which all have completely different species composition, nevertheless have community structures very similar to each other and to those of the African forest communities.     

An analytical approach for estimating fossil record and diversification events in sharks, skates and rays

Background

Modern selachians and their supposed sister group (hybodont sharks) have a long and successful evolutionary history. Yet, although selachian remains are considered relatively common in the fossil record in comparison with other marine vertebrates, little is known about the quality of their fossil record. Similarly, only a few works based on specific time intervals have attempted to identify major events that marked the evolutionary history of this group.

Methodology/Principal Findings

Phylogenetic hypotheses concerning modern selachians’ interrelationships are numerous but differ significantly and no consensus has been found. The aim of the present study is to take advantage of the range of recent phylogenetic hypotheses in order to assess the fit of the selachian fossil record to phylogenies, according to two different branching methods. Compilation of these data allowed the inference of an estimated range of diversity through time and evolutionary events that marked this group over the past 300 Ma are identified. Results indicate that with the exception of high taxonomic ranks (orders), the selachian fossil record is by far imperfect, particularly for generic and post-Triassic data. Timing and amplitude of the various identified events that marked the selachian evolutionary history are discussed.

Conclusion/Significance

Some identified diversity events were mentioned in previous works using alternative methods (Early Jurassic, mid-Cretaceous, K/T boundary and late Paleogene diversity drops), thus reinforcing the efficiency of the methodology presented here in inferring evolutionary events. Other events (Permian/Triassic, Early and Late Cretaceous diversifications; Triassic/Jurassic extinction) are newly identified. Relationships between these events and paleoenvironmental characteristics and other groups’ evolutionary history are proposed.     

Interspecific and intraspecific relationships between tooth size and jaw size in primates

The association between mandibular robusticity, postcanine megadontia, and canine reduction in hominins has led to speculation that large and robust jaws might be required to spatially accommodate large canine and molar teeth in hominins and other primates. If so, then variations in mandibular form that are generally regarded as biomechanical adaptations to masticatory demands might instead be incidental effects of functional requirements of tooth support. While the association between large teeth and deep, robust jaws in hominins is well known, the relationship between tooth size and jaw size has not been systematically evaluated in a comparative sample of primates. We evaluate the relationships between molar tooth size, canine tooth size, and mandibular corpus and symphyseal dimensions in a sample of adult anthropoids in interspecific (n=84 species) and intraspecific (n=36 species) contexts. For intraspecific comparisons, tooth size and jaw size are correlated, but for a majority of species this is a function of sexual size dimorphism. Interspecific comparisons lend little direct support to the hypothesis that jaw breadth directly covaries with molar tooth breadth, but they do support the hypothesis that mandibular depth is associated with canine tooth size in males. The latter observation suggests that if there is a causal association between canine size and mandibular depth, it is subject to a threshold effect. In contrast, neither corpus nor symphyseal robusticity, measured as a shape index of breadth/height, are correlated with tooth size. Our results suggest that further studies of the relationship between tooth size and corpus morphology should focus on tooth root size and corpus bony architecture, and that species-specific factors should have a strong impact on such relationships.     

Dinoflagellates,fossil and modern: certain unresolved problems

We identify a variety of areas and topics that have received relatively little attention hitherto or where there are significant residual problems, following earlier researches. Questions of interest both to palaeontologists and neontologists are emphasized. They are presented in the hope of stimulating new researches on themes presently neglected.     

Woods of the Vitaceae—fossil and modern

Vitaceoxylon tiffneyi gen. et sp. nov. and Vitaceoxylon carlquistii sp. nov. from the Middle Eocene Clarno formation are the oldest known woods with characteristics of the Vitaceae. They are characterized by a tendency to two diameter classes of vessels, wide and tall rays, and a high proportion of their area is vessel. Other characteristics include septate imperforate elements, scanty paratracheal to vasicentric parenchyma, idioblasts in the rays, crowded alternate intervessel pitting, and vessel-parenchyma pits with reduced borders. Wood anatomy of the major extant genera of Vitaceae was examined and compared to the fossils. Features of secondary xylem useful for distinguishing between genera in the Vitaceae include vessel size and arrangement (two distinct diameter classes or not, radial multiples or tendency to tangential multiples), vessel pitting (scalariform or alternate), crystal type (prismatic, druses, and/or raphides) and location (in chambered parenchyma and/or ray parenchyma), cambial variants (present or absent). Wood anatomy supports the proposed close relationship of Cissus to Cayratia. Pronounced vessel dimorphism occurs in temperate Vitaceae; cambial variant structure occurs in tropical Vitaceae. Despite their conformity with Vitaceae at the family level, the two fossil woods are not comparable to any one extant genus. This contrasts with the Vitaceae seeds from Clarno, all of which are referable to extant genera. Two new combinations for fossil woods of the Vitaceae are proposed: Vitaceoxylon ampelopsoides (Schönfeld) comb. nov., and Vitaceoxylon megyazoense (Greguss) comb. nov.     

Color changes in modern and fossil teeth induced by synchrotron microtomography

Studies using synchrotron microtomography have shown that this radiographic imaging technique provides highly informative microanatomical data from modern and fossil bones and teeth without the need for physical sectioning. The method is considered to be nondestructive; however, researchers using the European Synchrotron Radiation Facility have reported that color changes sometimes occur in teeth during submicron scanning. Using the Advanced Light Source, we tested for color changes during micron‐level scanning and for postexposure effects of ultraviolet light. We exposed a 2.0‐mm wide strip (band) to synchrotron light in 32 specimens, using multiple energy levels and scan durations. The sample included modern and fossilized teeth and bone. After scanning, the specimens were exposed to fluorescent and direct ultraviolet light. All teeth showed color changes caused by exposure to synchrotron radiation. The resulting color bands varied in intensity but were present even at the lowest energy and shortest duration of exposure. Color bands faded during subsequent exposure to fluorescent and ultraviolet light, but even after extensive ultraviolet exposure, 67% (8/12) of UV‐exposed teeth retained some degree of induced color. We found that the hydroxyapatite crystals, rather than the organic component, are the targets of change, and that diagenesis appears to impact color retention. Color changes have significance beyond aesthetics. They are visible indicators of ionization (chemical change) and, therefore, of potential physical damage. It is important for researchers to recognize that synchrotron microtomography may damage specimens, but adopting suitable safeguards and procedures may moderate or eliminate this damage. Am J Phys Anthropol 149:172–180, 2012. © Wiley Periodicals, Inc.