A new spalacolestine mammal from the Early Cretaceous Jehol Biota and implications for the morphology,phylogeny, and palaeobiology of Laurasian ‘symmetrodontans’

‘Symmetrodontans’ are extinct mammals characterized by having a reversed‐triangle molar pattern in which three main cusps define a triangular molar crown. This dental morpholgy has been regarded as being intermediate between the ‘triconodont’ tooth and the tribosphenic pattern characterizing therians; it is a key feature in taxonomy of Mesozoic mammals and one to understand mammalian evolution and palaeobiology. Here we report a new genus and species of ‘symmetrodontan’ mammal, Lactodens sheni, from the Early Cretaceous Jehol Biota, represented by a partial skeleton with dentary and upper and lower teeth with dental morphologies well‐preserved. The new species has a dental formula of three upper incisors, one canine, three premolars, and six molars/three lower incisors, one canine, five premolars and six lower molars, double‐rooted canines, extremely low‐crowned and transversely thin premolars, and acute angled molars. The dental morphologies of molars and peculiar deciduous premolars are similar to those of Spalacolestes from North America. The associated upper and lower dentitions from one individual animal helped to clarify tooth identification of some spalacotheriids represented only by fragmentary material. Phylogenetic analyses indicate a close relationship of the new species to North American spalacolestines and faunal interchanges between Eurasia and North America, thus supporting the notion that small‐bodied spalacotheriids were diverse and had a pan‐Laurasian distribution during the Early Cretaceous. Absence of the Meckelian groove suggests acquisition of the definitive mammalian middle ear in spalacolestines, and deciduous canines and premolars in the slim and extremely long dentary imply a faunivorous diet.     

Unique inhibitory cascade pattern of molars in canids contributing to their potential to evolutionary plasticity of diet

Developmental origins that guide the evolution of dental morphology and dental formulae are fundamental subjects in mammalian evolution. In a previous study, a developmental model termed the inhibitory cascade model was established. This model could explain variations in relative molar sizes and loss of the lower third molars, which sometimes reflect diet, in murine rodents and other mammals. Here, I investigated the pattern of relative molar sizes (inhibitory cascade pattern) in canids, a taxon exhibiting a wide range of dietary habits. I found that interspecific variation in canid molars suggests a unique inhibitory cascade pattern that differs from that in murine rodents and other previously reported mammals, and that this variation reflects dietary habits. This unique variability in molars was also observed in individual variation in canid species. According to these observations, canid species have greater variability in the relative sizes of first molars (carnassials), which are functionally important for dietary adaptation in the Carnivora. In conclusion, an inhibitory cascade that differs from that in murine rodents and other mammals may have contributed to diverse dietary patterns and to their parallel evolution in canids.     

Patterns of size variation and correlation in the dentition of the red colobus monkey (Colobus badius)

There have been numerous studies on variability and correlation in dental crown size, but the significance of the resulting patterns remains unclear. Regions of low variation and high correlation have been hypothesized to represent the poles of Butler's morphological fields, to be related to absolute tooth size, or to be related to morphological complexity of the teeth and functional efficiency. Variation and correlation of tooth lengths and breadths were investigated in 138 red colobus monkeys to further assess the relations among size associations, crown morphology, and absolute tooth size. In the maxilla and mandible, the postcanine teeth are the most highly correlated and least variable, followed by the incisors, then the canines. There are also lower correlations between premolars and molars than within either group. While there appears to be a relation between degree of morphological differentiation and levels of correlation and variation, there are no notable differences in the correlation of opponents along the dental arcade, which is the most important functional consideration. This suggests that different levels of correlation and variation within upper or lower teeth are “artifacts” of tooth dimensions that contribute to different geometric designs in different tooth groups as the germs develop. This morphological effect is coupled with the influence of integration fields, indicated by higher variability and lower correlations of the third molar, the largest or most molarized tooth. It is concluded that there are wide functional tolerances in occlusion with respect to the gross dimensions of dental crowns and their interrelationships.     

Oral and craniofacial morphology of a patient with Larsen syndrome

A case is reported of a 15 years old Chinese female with Larsen syndrome exhibiting many characteristic facial and skeletal features plus hitherto unreported orofacial anomalies including delayed dental development; hypodontia affecting all the permanent canines, second and third molars, maxillary lateral incisors and second premolars; morphological anomalies of the maxillary first premolars and molars; a class 3 skeletal pattern and reduced upper facial height. Cephalometric radiographs showed the skull bones to have an appearance similar to that of osteopetrosis.     

Survey of antibodies to Trypanosoma cruzi and Leishmania spp. in gray and red fox populations from North Carolina and Virginia

American trypanosomiasis and leishmaniasis are caused by related hemoflagellate parasites, Trypanosoma cruzi and Leishmania spp., which share several common host species. Both zoonotic protozoans are endemic in the United States. Canines, including domestic and wild canids, are reservoir hosts for human infections with T. cruzi and Leishmania spp. The present study examined the seroprevalence of T. cruzi and Leishmania spp. in wild canids from North Carolina and Virginia. Wild canine species tested in this work included 49 gray foxes (Urocyon cinereoargenteus) and 5 red foxes (Vulpes vulpes). Overall, sera samples from 54 foxes (North Carolina = 43; Virginia = 11) were tested by immunochromatographic strip assays (ICT). Antibodies to T. cruzi were found in 4 (9%) gray foxes from North Carolina and 2 (18%) gray foxes from Virginia. Antibodies to Leishmania spp. were detected in 1 (2%) gray fox from North Carolina. Our results indicate that wild canids are exposed more frequently to T. cruzi in North Carolina than Leishmania spp. and only T. cruzi in Virginia.     

Genetic and morphological divergence among sympatric canids

Numerous studies have suggested that the extent of character divergence observed between two sympatric species reflects the intensity of competition for resources or space. However, the influence of time on divergence is often overlooked. We examined the relationship between time and character divergence in two groups of congeneric, sympatric canids on two continents: South American foxes and African jackals. Character divergence was assessed from measurements of body mass and dental and cranial shape. Divergence time was estimated from data on mitochondrial DNA restriction site polymorphisms. Our findings indicate that African jackals are morphologically similar despite having diverged more than 2 million years ago. By contrast, South American foxes differ substantially in both size and morphology after only 250,000 years of evolution. Thus, the lack of character divergence among the African jackals cannot be explained as a result of very recent common ancestry.     

Schultz's unruly rule: dental developmental sequences and schedules in small-bodied, folivorous lemurs

Schultz's rule (as reconstructed by Smith) states that there is a relationship between the pattern (or relative order) of eruption of molar versus secondary (replacement) teeth and the overall pace (or absolute timing) of growth and maturation. Species with 'fast' life histories (rapid dental development, rapid growth, early sexual maturation, short life spans) are said to exhibit relatively early eruption of the molars and late eruption of the secondary replacement teeth (premolars, canines, incisors), whereas species with 'slow' life histories are said to exhibit relatively late eruption of the molars and early eruption of the secondary dentition. In a recent review, B.H. Smith noted that primates with tooth combs might violate this rule because tooth combs tend to erupt early, regardless of the pace of life history. We show that exceptions to Schultz's rule among lemurs are not limited to the relative timing of eruption of the tooth comb. Rather, among lemurs, some species with extremely accelerated dental development exhibit a pattern of eruption of molars and of secondary teeth in direct opposition to the expectations of Schultz's rule. We focus particularly on the pattern (order) and pace (absolute timing) of dental development and eruption in Avahi and Lepilemur - two relatively small, nocturnal folivores with rapid dental development. These taxa differ markedly in their eruption sequences (the premolars erupt after M2 and M3 in Lepilemur but not Avahi ). We offer an explanation for the failure of Schultz's rule to predict these differences. Schultz's rule presumes that eruption timing is dependent on the size of the jaw and that, therefore, molar crown formation and eruption will be delayed in species with slow-growing jaws. We show that a variety of processes (including developmental imbrication) allows the crowns of permanent teeth to form and to erupt into jaws that might appear to be too small to accommodate them.     

Morphology of the lower deciduous premolars of South American hystricomorph rodents and age of the Octodontoidea

Abstract

We analyse the crest homologies of lower deciduous premolars (Dp4) of South American caviomorphs in a comparative context including other hystricomorphs and under a dynamic topological criterion. An hexalophodont pattern in which the three anteriormost crests are assumed to be the anterolophid, metalophulid I and metalophulid II, respectively, is proposed as ancestral morphology. Simplified pentalophodont morphologies would have resulted from loss of the metalophulid I, and distinct transformation pathways are recognised especially for Octodontoidea and Cavioidea. A basal octodontoid morphological pattern can be recognised in the fossil record from as early as the middle Eocene, supporting that an initial divergence among major clades of caviomorphs had already occurred by this time. Programs for identifying potentially useful dental characters in phylogeny and taxonomy of caviomorphs need to be revised. Interpreting lophids as dynamic components in the morpho-functional variation of molars, rather than as static landmarks, is central for understanding dental evolution in these rodents.     

Formation of the permanent dentition in Arikara Indians: timing differences that affect dental age assessments

This report concerns one problem encountered with application of American white dental formation standards to age assessment of sub-adults of archaeological context. Dental ages for eight mandibular permanent teeth and maxillary central and lateral incisors of Arikara Indian immature skeletons were determined according to degree of crown or root mineralization. Ages assigned to the various teeth of the same individual were compared. They showed similarities as well as patterned differences. First premolar, second premolar, and mandibular incisor ages closely approximated one another. In relation to this complex, dental ages for maxillary incisors and mandibular second molars were older by 0.5 to 1.1 years. Developmental ages assigned to individuals on the basis of third molars showed relative advancement by more than 2 years. The systematic occurrence of these observations reflects more than just individual variability; it shows the presence of population differences in tooth-formation timing. Timing differences complicate assessment of dental ages needed for growth or demographic studies.     

Small tooth sizes in a nineteenth century South Carolina plantation slave series

Sub-Saharan African (and derived) populations typically exhibit larger mean tooth crown diameters than whites in spite of considerable population variability. We report on a 19th century series of American black slaves from a single cemetery near Charleston, South Carolina, that possessed notably smaller crown sizes. Analysis identifies a characteristic set of differences compared to caucasians, including retention of large maxillary lateral incisors and disproportionately large premolars and molars. Regression of principal components scores (derived from the mesiodistal diameters) on the sum of all diameters (used here as a measure of overall tooth mass) confirms a basic ethnic difference between black and white odontometrics: significantly more of the tooth mass is apportioned to the cheek teeth (premolars, molars) in blacks than whites. The difference (expressed as residuals from linear regression on tooth mass) holds for the several groups assessed here despite considerable intergroup variability in tooth sizes. Potential explanations for the notably small diameters of this plantation series are speculative, but may involve kin-based divergences and/or reflect the natural intergroup differences extant in the African slave sources.     

Brief communication: enamel thickness trends in the dental arcade of humans and chimpanzees

In addition to evidence for bipedality in some fossil taxa, molar enamel thickness is among the few characters distinguishing (thick-enameled) hominins from the (thin-enameled) African apes. Despite the importance of enamel thickness in taxonomic discussions and a long history of scholarship, measurements of enamel thickness are performed almost exclusively on molars, with relatively few studies examining premolars and anterior teeth. This focus on molars has limited the scope of enamel thickness studies (i.e., there exist many fossil hominin incisors, canines, and premolars). Increasing the available sample of teeth from which to compare enamel thickness measurements from the fossil record could substantially increase our understanding of this aspect of dental biology, and perhaps facilitate greater taxonomic resolution of early hominin fossils. In this study, we report absolute and relative (size-scaled) enamel thickness measurements for the complete dentition of modern humans and chimpanzees. In accord with previous studies of molars, chimpanzees show lower relative enamel thickness at each tooth position, with little overlap between the two taxa. A significant trend of increasing enamel thickness from anterior to posterior teeth is apparent in both humans and chimpanzees, indicating that inter-taxon comparisons should be limited to the same tooth position in order to compare homologous structures. As nondestructive imaging techniques become commonplace (facilitating the examination of increasing numbers of fossil specimens), studies may maximize available samples by expanding beyond molars.     

Deciduous dental morphology and the biological affinities of a late Chalcolithic skeletal series from western India

Morphological variations of the dental crown and roots provide valuable data for determining the genetic affinities and evolutionary adaptedness of prehistoric human skeletal populations. This paper documents morphological variations of a sample of deciduous teeth from the late Chalcolithic farming village of Inamgaon (1600-700 B.C.) in western India. Hanihara's (1963) grading system of deciduous dental traits was employed in assessing the degree of expression of shovel-shape of incisors, cusp number of upper and lower first molars, hypocone variation, Carabelli's trait, cusp number of lower second molars and the protostylid. Turner's (1970) classification was used to determine presence and size of accessory cusps: entoconulid (C-6) and metaconulid (C-7). Comparative evaluation of the Inamgaon deciduous dental data is hampered by the absence of data for dental features of living and prehistoric South Asian populations. Many of the traits observed in the Inamgaon series exhibit a frequency of occurrence intermediate between figures characteristic of the "Mongoloid" dental complex and the "Caucasoid" dental complex.     

A molecular phylogeny of the Canidae based on six nuclear loci

We have reconstructed the phylogenetic relationships of 23 species in the dog family, Canidae, using DNA sequence data from six nuclear loci. Individual gene trees were generated with maximum parsimony (MP) and maximum likelihood (ML) analysis. In general, these individual gene trees were not well resolved, but several identical groupings were supported by more than one locus. Phylogenetic analysis with a data set combining the six nuclear loci using MP, ML, and Bayesian approaches produced a more resolved tree that agreed with previously published mitochondrial trees in finding three well-defined clades, including the red fox-like canids, the South American foxes, and the wolf-like canids. In addition, the nuclear data set provides novel indel support for several previously inferred clades. Differences between trees derived from the nuclear data and those from the mitochondrial data include the grouping of the bush dog and maned wolf into a clade with the South American foxes, the grouping of the side-striped jackal (Canis adustus) and black-backed jackal (Canis mesomelas) and the grouping of the bat-eared fox (Otocyon megalotis) with the raccoon dog (Nycteruetes procyonoides). We also analyzed the combined nuclear + mitochondrial tree. Many nodes that were strongly supported in the nuclear tree or the mitochondrial tree remained strongly supported in the nuclear + mitochondrial tree. Relationships within the clades containing the red fox-like canids and South American canids are well resolved, whereas the relationships among the wolf-like canids remain largely undetermined. The lack of resolution within the wolf-like canids may be due to their recent divergence and insufficient time for the accumulation of phylogenetically informative signal.     

Prevalence of Toxoplasma gondii infection diagnosed by PCR in farmed red foxes, arctic foxes and raccoon dogs

The aim of this study was to compare Toxoplasma gondii infection in three canid species: red fox Vulpes vulpes, arctic fox Vulpes lagopus and raccoon dog Nyctereutesprocyonoides kept at the same farm. Anal swabs were taken from 24 adult and 10 juvenile red foxes, 12 adult arctic foxes, three adult and seven juvenile raccoon dogs. Additionally, muscle samples were taken from 10 juvenile red foxes. PCR was used to detect T. gondii DNA. T. gondii infection was not detected in any of the arctic foxes; 60% ofraccoon dogs were infected; the prevalence of the parasite in material from red fox swabs was intermediate between the prevalence observed in arctic foxes and raccoon dogs. It is possible that susceptibility and immune response to the parasite differ between the three investigated canid species. T. gondii DNA was detected in muscle tissue of five young foxes. The results of this study suggest that T. gondii infection is not rare in farmed canids.     

Variation in enamel thickness within the genus Homo

Recent humans and their fossil relatives are classified as having thick molar enamel, one of very few dental traits that distinguish hominins from living African apes. However, little is known about enamel thickness in the earliest members of the genus Homo, and recent studies of later Homo report considerable intra- and inter-specific variation. In order to assess taxonomic, geographic, and temporal trends in enamel thickness, we applied micro-computed tomographic imaging to 150 fossil Homo teeth spanning two million years. Early Homo postcanine teeth from Africa and Asia show highly variable average and relative enamel thickness (AET and RET) values. Three molars from South Africa exceed Homo AET and RET ranges, resembling the hyper thick Paranthropus condition. Most later Homo groups (archaic European and north African Homo, and fossil and recent Homo sapiens) possess absolutely and relatively thick enamel across the entire dentition. In contrast, Neanderthals show relatively thin enamel in their incisors, canines, premolars, and molars, although incisor AET values are similar to H. sapiens. Comparisons of recent and fossil H. sapiens reveal that dental size reduction has led to a disproportionate decrease in coronal dentine compared with enamel (although both are reduced), leading to relatively thicker enamel in recent humans. General characterizations of hominins as having ‘thick enamel’ thus oversimplify a surprisingly variable craniodental trait with limited taxonomic utility within a genus. Moreover, estimates of dental attrition rates employed in paleodemographic reconstruction may be biased when this variation is not considered. Additional research is necessary to reconstruct hominin dietary ecology since thick enamel is not a prerequisite for hard-object feeding, and it is present in most later Homo species despite advances in technology and food processing.     

Variables affecting dental fluctuating asymmetry in human isolates

The aims of the present study are to 1) determine and describe levels of dental fluctuating asymmetry (FA) in a highly endogamous human group; 2) evaluate the effects of various FA measures on perceived FA levels and their interrelationships; 3) study the connections between dental variables (tooth size, class, position, type, location and dimension) and FA levels; and 4) estimate the interrelationships between dental FA measures. The study was carried out on 242 Bedouin boys aged 5 to 14 years. The results demonstrate that the main variables influencing dental FA levels within this population are tooth class (incisors, canine, premolars, molars) and position (mesial, distal) and that the interaction between the two is significant. When sample sizes are large enough and individual measures are needed for the statistical analysis, the use of a computational method based on absolute values is legitimate. Clear relationships between some FA dental traits are discerned though principal-components analysis. © 1993 Wiley-Liss, Inc.     

Masculinization of the eruption pattern of permanent mandibular canines in opposite sex twin girls

The aim of this study is to explore the effect of prenatal androgenization on the clinical eruption of permanent teeth expressing dimorphism and bimaturism. The eruption curves of permanent teeth (except third molars), including those that make up the canine complex (permanent canines, lower first premolars), are compared among opposite sex twins (OS twins) relative to single‐born boys and girls. The comparisons are made with regard to three phases of eruption (pierced mucosa, half‐ erupted, and completely erupted) from a cross‐sectional sample of dental casts, using Kaplan–Meier survival and Cox regression analyzes. The casts were collected from 2159 school children from the US Collaborative Perinatal Project, including 39 pairs of OS‐twins, of which 12 pairs (30.8%) were Euro‐Americans and 27 pairs (69.2%) were of African‐American ancestry. The eruption patterns of the incisors, upper first molars, and lower canines were found to be significantly masculinized (delayed) among OS twin girls. The differences in most other teeth were either not significant, or the number of observations of active eruption phases were too few, such as in the upper first molars and incisors, to yield strong evidence and meaningful results. The masculinization of the tooth eruption pattern in OS twin girls is intriguing because of the lower canine responses during puberty, as well as canine primordial formation during early fetal androgenization of their co‐twin during the 8th to 14th gestational weeks. The present results offer a challenge for future research exploring tooth eruption mechanisms, and may also highlight some cases of delayed or ectopic canines, which are biased toward females. Am J Phys Anthropol 151:566–572, 2013. © 2013 Wiley Periodicals, Inc.     

Population dynamics and epidemiology of Toxocara canis in Danish red foxes

Toxocara canis, an intestinal helminth of canids with zoonotic potential, was found in 618 (59%) of 1,040 red foxes (Vulpes vulpes) collected from all Danish provinces (1997-2002). The prevalence and average worm burden were significantly higher for cubs than older foxes and in males than in females. A multiple logistic regression demonstrated that the prevalence was influenced significantly by sex and age of foxes in addition to location, season, and year of collection. The highest prevalence and worm burden were found in rural areas. The size and number of female worms was positively correlated to the fecal egg excretion. The length and fecundity of the worms was significantly higher in male foxes, and a general intensity dependence was suggested from a negative correlation between worm numbers and worm lengths. As compared to intestinal recovery of worms, somatic larvae were recovered from 20% of muscle samples and fecal eggs in 41% of fecal samples. The consistent finding of T. canis larvae in somatic tissues of naturally infected foxes is new.     

Tooth morphology and other aspects of the Teso dentition

The teeth of over 5,000 Teso schoolchildren members of a Nilo-Hamitic tribe in East Africa, were examined for morphological traits. There was a significant difference between the sexes in the number of cusps on the lower first and second molars, in the prevalence of the cusp of Carabelli, and in variability and agenesis of the upper lateral incisor. The results showed that females consistently favoured tooth reduction. There was also a tendency among those possessing extra cusps on one molar to have extra cusps or other molars. Records kept of the prevalence of the tribal custom of extracting lower central incisors indicated that this practise is rapidly dying out. On another group of teeth which had been extracted from adults common variations of root morphology were noted, together with the fissure pattern of the lower molars. Measurements were made of those teeth which were unworn and were not broken down by dental decay, and the lower third molar was found to be the largest tooth of the series. Observations on the pattern of molar tooth wear showed that the buccal as well as the occlusal surface was strongly affected.     

A new correction procedure for calibrating dental caries frequency

The incisors and canines and the premolars and molars show differential resistance to cariogenic factors. The anterior teeth have a lower caries frequency than the posterior teeth. However, these tooth classes are lost differentially in postmortem stages due to their anatomical structures. This differential postmortem tooth loss distorts proportions between the anterior and posterior tooth classes. The disproportionality can affect the calculation of total caries prevalence. In this paper, we propose a new calibration procedure which removes this disproportionality and call it the proportional correction factor. For this procedure, the caries rates of anterior and posterior teeth are corrected by multiplying the anterior teeth by three-eighths and the posterior teeth by five-eighths. These fractions are derived from the human dental formula which contains three anterior and five posterior teeth by side. The correction factor is more effective if the proportion of anterior to the posterior teeth is extremely distorted. When this procedure is used with the caries correction factor, it provides a useful way to approach to an almost true caries prevalence. Am J Phys Anthropol 108:237–240, 1999. © 1999 Wiley-Liss, Inc.