Dental Eruption Sequence Research Articles

Evaluation of the Relationship between the BMI and the Sequence and Chronology of Eruption in Permanent Dentition in Spanish Population.

The aim was to analyze the relationship between BMI (body mass index) and the sequence and chronology of the eruption of permanent teeth in a sample of Spanish children. Methods: The study design was descriptive, cross-sectional, observational, and epidemiological. Patients of pediatric age were included. Emerged teeth, and patient’s age, race, and sex were recorded. The nutritional status of the child was assessed by calculating the BMI, according to the WHO parameters. Statistical analysis was carried out with a confidence interval of 95%. A prediction model with logistic regression models was obtained. Results: A total of 725 pediatric patients between 4 and 14 years old were analyzed. BMI acts as a predictor variable for eruption symmetry, as it was most frequent in overweight children (p < 0.001). The probability of symmetry in dental eruption increases for South American children, for an extra month of age, and each meter of height. BMI had an influence in the first tooth to appear only in the fourth quadrant. BMI did not seem to influence present teeth, and the sequence of permanent dental eruption was not influenced by the BMI category. Conclusions: Age, weight, height, and BMI act as significant predictors for eruption symmetry. BMI does not produce alterations in the eruption sequence of the permanent dentition.

Cronología y secuencia de erupción dentaria permanente en niños de 5 a 12 años

Background: Tooth eruption is the movement of teeth through the bone and overlying mucosa to emerge and function in the oral cavity. Aim: To characterize the variability in the sequence and chronology of eruption of the permanent dentition in children aged 5 to 12 years. Method: A descriptive observational cross-sectional study was carried out in the "Briones Montoto" Primary School of the municipality of Guanabacoa, in the period between September 2019 and June 2020. The universe was constituted by 239 children and to determine the chronology of dental eruption, a sample of 216 children who attended classes on the day of the evaluation were taken, who fulfilled the inclusion and exclusion criteria. Results: At 5 years of age, most of the children were found with their primary dentition completed, representing 61.5%, at 6 years of age 85.5% presented all the incisors plus the first molar and 57.1% of the total studied at the age of 11 years had all the permanent teeth up to the second molar, with a predominance of the female sex, which represented 66.7%. Conclusions: There is an advance in the sequence and chronology of permanent dental eruption in this school, becoming more evident in the female sex with the central incisor being the first tooth to erupt before the first molar.

Deciduous dentition and dental eruption sequence in Interatheriinae (Notoungulata, Interatheriidae): implications in the systematics of the group

AbstractStudies focused on deciduous dentition, ontogenetic series, and tooth eruption and replacement patterns in fossil mammals have lately increased due to the recognized taxonomic and phylogenetic weight of these aspects. A study of the deciduous and permanent dentition of Interatherium and Protypotherium (Interatheriinae) is presented, based mainly on unpublished materials. Deciduous cheek teeth are brachydont and placed covering the apex of the respective permanent tooth; in addition, some morphological and metrical differences are observed along the crown height. Five dental ontogenetic stages are distinguished among the juvenile specimens on the basis of the degree of wear, the replacement of the deciduous premolars, and the eruption of the molars. The crown height and the wear degree of different Interatheriinae taxa show: (1) eruption pattern of molars in an anterior–posterior direction (M/m1 to M/m3); (2) pattern of replacement of deciduous premolars and eruption of permanent premolars in a posterior–anterior direction (dP/dp4 to dP/dp2 and P/p4 to P/p2); and (3) eruption of M/m3 before the replacement of dP/dp4. Results allow evaluating the diagnostic dental characteristics used to describe some interatheriines, as well as reinterpreting some taxonomic assumptions: the holotype of Protypotherium diversidens Ameghino, 1891 is recognized as a juvenile of another species of the genus, and the species is not validated, considering it as Protypotherium sp.; the holotype of Eudiastatus lingulatus Ameghino, 1891 falls in the variability of Protypotherium, becoming P. lingulatus new combination, tentatively maintaining the species and implying the synonymy between Eudiastatus and Protypotherium; and the holotype of Eopachyrucos ranchoverdensis Reguero, Ubilla, and Perea, 2003 is reinterpreted as bearing deciduous premolars.

Contributions of the pars lateralis, pars basilaris and femur to age estimations of the immature skeleton within a South African forensic setting

Dental development and eruption sequences have prevailed as the gold standard in age estimations of previously unidentified immature individuals within a legal context. However, in the absence of the dentition, skeletal assessments have served as a frequently applied alternative. While various cranial and postcranial skeletal elements have been used in estimating age of the immature skeleton, little is known about the anthropometric value of the pars basilaris, pars lateralis and femur as skeletal age estimation tools. Thus, this study aimed to assess if these bones of the immature human skeleton were useful elements in estimating the age of prenatal and postnatal individuals. These bones were excised from the remains of 74 unclaimed human immature individuals and evaluated using traditional anthropometric methods. The study sample was sourced from the Johannesburg Forensic Pathology Services (JFPS) and the Johannesburg Forensic Paediatric Collection (JFPC), University of the Witwatersrand and subdivided into an early prenatal (younger than 30 gestational weeks); late prenatal (30 to 40 gestational weeks) and postnatal (birth to 7.5months) age ranges. Statistically significant differences (p ≤0.05) were found when assessing the maximum length, sagittal length, maximum width and distal width of the bones across each of the age ranges (30 gestational weeks to 7 postnatal months). The cranial and postcranial skeletal elements investigated in this study provide a valuable contribution to skeletal ageing in African individuals.

Clinical and x-ray oral evaluation in patients with congenital Zika Virus.

Objective:The aim of this study was to investigate possible malformations in the soft, bone and/or dental tissues in patients with congenital Zika Virus (ZIKV) by clinical and x-ray evaluation.Methodology:Thirty children born with ZIKV and 30 children born without ZIKV (control group) were included in the study. Patients were evaluated over 24 consecutive months according to the variables: sex, age, cleft palates, soft tissue lesions, alveolar ridge hyperplasia, short labial and lingual frenums, inadequate posture of the lingual and perioral muscles at rest, micrognathia, narrow palatine vaults, changes in the teeth shape and/or number, sequence eruption, spasms, seizures and eruption delay were evaluated. Chi-square test, Student's t-test and nominal logistic regression were used (p<0.05).Results:Among the 30 babies examined, the mean age of the first dental eruption was 10.8±3.8 with almost two-thirds of the children (n=18, 60%) experiencing eruptions of their first tooth after 9 months of age, nine children (30%) had inadequate lingual posture at rest, more than half of the children (n=18, 60%) had short labial or lingual frenums. ZIKV babies showed a high prevalence of clef palate (p<0.001), inadequate lingual posture at rest (p=0.004), micrognathia (p=0.002), changes in the shape and/or number of teeth (p=0.006), alteration in sequence of dental eruption (p<0.001) and muscles spasms (p=0.002). The delay eruption was associated with inadequate lingual posture at rest (p=0.047), micrognathia (p=0.002) and changes in the shape and/or number of teeth (p=0.021). The delayed eruption (p=0.006) and narrow palatine vaults (p=0.008) were independently associated with ZIKV. Moreover, female patients showed the most narrow palatine vaults (p=0.010).Conclusions:The children with ZIKV showed a greater tendency to have delayed eruption of the first deciduous tooth, inadequate lingual posture and short labial and lingual frenums.

Breaking the rules: Phylogeny, not life history, explains dental eruption sequence in primates.

Although a great deal is known about the biology of tooth development and eruption, there remains disagreement about the factors driving the evolution of dental eruption sequence. We assessed postcanine eruption sequence across a large sample of primates to test two hypotheses: (1) Dental eruption sequence is significantly correlated with life history and body size variables that capture postnatal growth and longevity (Schultz's Rule), and (2) Dental eruption sequence is conserved phylogenetically. We assessed postcanine dental eruption sequence for 194 individuals representing 21 primate genera spanning eight families. With the inclusion of an additional 29 primate genera from the literature, this is the most comprehensive report on dental eruption sequence in primates to date. We used a series of phylogenetic analyses to statistically compare dental eruption sequence to life history and body size and test for phylogenetic signal in these traits. Dental eruption sequence is conserved phylogenetically in primates, and body and brain size are both significantly associated with dental eruption sequence. Ancestral state reconstruction supports the hypothesis that the third molar erupted before one or more of the premolars in the ancestor of primates and derived clades within primates evolved an eruption sequence in which the third molar erupts after the premolars. Schultz's Rule, as it is currently written and applied, is not supported by this extended data set. Our results demonstrate that dental eruption sequence is a far better predictor of phylogeny and will likely prove useful in phylogenetic hypotheses about relationships between extinct and extant mammalian taxa. The evolution of dental eruption sequence is likely driven by factors that significantly influence body size and mandibular symphyseal fusion.

First Radiological Study of a Complete Dental Ontogeny Sequence of an Extinct Equid: Implications for Equidae Life History and Taphonomy

The sequence of cheek teeth mineralization, eruption, and replacement of an extinct horse species is here documented with radiological techniques for the first time thanks to the exceptional preservation of Hipparion sp. mandibles from Cerro de los Batallones (Madrid Basin, Spain). The sequence of dental ontogeny in mammals provides valuable insights about life history traits, such as the pace of growth, and about the mode of formation of fossiliferous assemblages. We have determined that the order of permanent cheek teeth mineralization and eruption of hipparionine horses is m1, m2, (p2, p3), p4, m3. Cheek teeth mineralization timing of hipparionine horses coincides with the one observed in modern equids. In turn, there are differences in the eruption timing of the p4 and m3 between horses belonging to the Anchitheriinae and Hipparionini compared to equids of the Equus genus that might be related to the shorter durability of the deciduous tooth dp4 in anchitheriine and hipparionine horses and, more broadly, to an increased durability of equid teeth through their evolutionary history. Based on the dental eruption sequence, hipparionine horses are slow-growing, long-living mammals. The Hipparion sp. assemblage from Batallones-10 conforms to an attritional model, as individuals more vulnerable to natural mortality predominate.

Unrevealed Caries in Unerupted Teeth: A Prevalence Study.

Background:Preeruptive caries are an abnormal, well-circumscribed, radiolucent area, occurring within the coronal dentinal tissue close to the dentinoenamel junction of unerupted teeth. OPGs are commonly taken in children for assessing the dental age and eruption sequence. It can be used as a good diagnostic source for detection of PEIR defects.Aim:The aim of this study is to determine the prevalence of Preeruptive intracoronal dentin radiolucencies in unerupted permanent teeth from orthopantomogram.Settings and Design:A total of 1000 standard orthopantomographs of children below 12 years of age were collected and examined.Methodology:The OPGs were examined for PIER defects in the unerupted teeth. The prevalence of PEIR defects was assessed with respect to age, sex, tooth, and the arch involved.Statistical Analysis:The data obtained were tabulated and analyzed. The prevalence was calculated in percentage.Results:The participant prevalence was 13.6%. The teeth prevalence was 1.20%. The majority (38.9%) of defects were seen in the in the mandibular first premolar. Almost half of the lesions were located on the mesial side (52.3%), with a size less than one-third of dentine thickness (53%).Conclusion:PIER defects constitutes an important part of anomalies associated with unerupted teeth and thus needs a proper understanding of its prevalence, etiology, manifestations, and complications. These defects are usually overlooked by clinicians while interpreting radiographs; however, it is of utmost importance to promptly diagnose these defects thus preventing further complications.

Ameloblastic Fibroma Associated With Impacted 3rd Molar: A Case Report

Ameloblastic fibroma is an uncommon mixed neoplasm of odontogenic origin with a relative frequency between 1.5 – 4.5%. It can occur either in the mandible or maxilla, but predominantly seen in the posterior region of the mandible. It occurs in the first two decades of life. Most of the times it is associated with tooth enclosure, causing a delay in eruption or altering the dental eruption sequence. The common clinical manifestation is a slow growing painless swelling and is detected during routine radiographic examination. There is controversy in the mode of treatment, whether conservative or aggressive. Here we reported a 38 year old male patient referred for evaluation of painless swelling on the right posterior region of the mandible associated with clinically missing 3rd molar. The lesion was completely enucleated under general anesthesia along with the extraction of impacted molar.

Dental eruption sequence and hypsodonty index of a Pleistocene macraucheniid from the Brazilian Intertropical Region

AbstractLitopterna is represented in the Pleistocene of the Brazilian Intertropical Region by a monospecific genus of Macraucheniidae, Xenorhinotherium. Although most of the knowledge about this family is derived from the dentition, some dental features still remain unknown. This study describes the eruption sequence of permanent dentition and classifies the hypsodonty status of X. bahiense. The specimens studied are from Toca dos Ossos, a limestone cave located in Bahia State. We perform qualitative macroscopic analysis to describe the eruption dental sequence. Additionally, we perform quantitative analysis to determine the hypsodonty index. The dental eruption sequence of the juvenile specimen is M1, M2, I1, I2, M3, I3, P1, P2, P3, and P4. In addition, the analysis of tooth wear in adult specimens provides similar results. The hypsodonty index assigns a mesodont tooth crown for X. bahiense. The dental eruption sequence is most similar to a rapid-growth extant mammal. Moreover, our results do not support afrotherian-like delayed dental eruption to Litopterna. The hypsodonty index can be related to data on vegetation of the Brazilian Intertropical Region and the shape of the premaxilla of X. bahiense, both of which suggest a browsing diet for this macraucheniid.

Wear reconstruction of the teeth of Yindirtemys deflexus (Ctenodactylidae, Rodentia) and evolution of its dental pattern

The dental pattern of Yindirtemys deflexus from Mongolia has been analysed using a Micro-CT scanner. This ctenodactylid exhibits a peculiar dental pattern, characterised by a mesodont dentition with some degree of selenodonty, an intricate enamel folding and elevated connections between cusps. Furthermore, the wear sequence in the upper tooth row shows very worn M1 even before other teeth emerge. The descriptive parameters used in the analyses (Area, Perimeter and structural density) allowed us to determine the relative wear stage in the different dental elements. The study reveals for Yindirtemys deflexus a wear pattern typical of mesodont teeth in which the maximum perimeter of the enamel is relatively constant over a large part of the crown height, and the Structural density decreases progressively until the senescence of the tooth. This peculiar dental morphology and eruption sequence of Y. deflexus is interpreted as the result of the evolution towards a relatively more durable dentition caused by the adaptation to more arid environments.

Patterns of dental emergence in early anthropoid primates from the Fayum Depression, Egypt

Paleontological field work in the Fayum Depression of Egypt has produced a remarkable diversity of fossil anthropoids, and this, combined with advances in genetic analyses of living anthropoids, has led to establishment of a temporal and phylogenetic framework for anthropoids that is achieving some degree of consensus. Less well understood are the evolutionary mechanisms and selective factors behind the origin and early diversification of anthropoids. One area that has remained under explored is investigation into the life history patterns of early anthropoids, a major omission given that understanding patterns of growth and development is essential for interpreting the paleobiology of fossil species. Here we detail dental emergence sequences for five species in four families of early anthropoid primates from the Fayum, and use these data to test Schultz’s Rule concerning the timing of emergence of molars versus premolars in mammals. Two important results are generated: (1) only one species had a dental eruption sequence identical to that observed among crown catarrhine primates; and (2) in all cases, the permanent canine was the last post-incisor dental element to fully erupt, a finding that may be significant for interpreting early anthropoid behavioral strategies.

The Evolution of Dental Eruption Sequence in Artiodactyls

The sequence of eruption of the second generation of teeth varies across taxa, is highly functional, and is strongly influenced by genetic effects. We assessed postcanine dental eruption sequence across artiodactyls in order to test two hypotheses: 1) dental eruption sequence is a good phylogenetic character for artiodactyls; and, 2) eruption sequence is adaptive and associated with life history variables like postnatal growth and longevity in artiodactyls (Schultz’s Rule). We examined postcanine eruption sequence in 81 genera (100 species) spanning ten families of Artiodactyla. Our ancestral state reconstruction supports the interpretation that the third molar erupted last in the ancestor of Artiodactyla, and that the fourth premolar erupted after the third molar in the ancestor of Ruminantia. Our results indicate that eruption of the third molar last evolved secondarily in the caprines, likely sometime in the Miocene. Overall, our results support the hypothesis that dental eruption sequence is phylogenetically conserved in artiodactyls. Caprines occupy high elevation habitats, and we hypothesize that evolution of their unique dental eruption sequence may be associated with limited resource availability in high elevation mountain systems and the necessity to process a wide range of vegetation types.

Displasia odontomascellare segmentale: revisione della letteratura e descrizione del primo caso italiano

ObjectivesThe aim of this paper is to present a literature review regarding the Segmental Odontomaxillary Dysplasia (SOD) and to report the first Italian case of such condition. Materials and methodsThe PubMed database was consulted with the following keywords: segmental odontomaxillary dysplasia, hemimaxillofacial dysplasia, hemimaxillary enlargement. After collecting 32 results, 18 case reports and 10 case series were selected, published in English from 1987 to 2014. No prospective clinical trial was found. ResultsSOD is an uncommon developmental disorder, characterized by an unknown aetiology and a variable clinical presentation. Clinical signs, like bone growth alterations of the maxilla, lack of one or both premolars and delayed tooth eruption on the affected side, alteration of adjacent gingival tissue with or without facial cutaneous lesions, may be observed. Histopathological examination of bone samples is at present the only reliable diagnostic tool. ConclusionsSOD is a rare unilateral maxillary condition which may alter the dental eruption sequence and jeopardize the achievement of occlusal stability.

Life history of the most complete fossil primate skeleton: exploring growth models for Darwinius.

Darwinius is an adapoid primate from the Eocene of Germany, and its only known specimen represents the most complete fossil primate ever found. Its describers hypothesized a close relationship to Anthropoidea, and using a Saimiri model estimated its age at death. This study reconstructs the ancestral permanent dental eruption sequences for basal Euprimates, Haplorhini, Anthropoidea, and stem and crown Strepsirrhini. The results show that the ancestral sequences for the basal euprimate, haplorhine and stem strepsirrhine are identical, and similar to that of Darwinius. However, Darwinius differs from anthropoids by exhibiting early development of the lower third molars relative to the lower third and fourth premolars. The eruption of the lower second premolar marks the point of interruption of the sequence in Darwinius. The anthropoid Saimiri as a model is therefore problematic because it exhibits a delayed eruption of P2. Here, an alternative strepsirrhine model based on Eulemur and Varecia is presented. Our proposed model shows an older age at death than previously suggested (1.05–1.14 years), while the range for adult weight is entirely below the range proposed previously. This alternative model is more consistent with hypotheses supporting a stronger relationship between adapoids and strepsirrhines.

Free-ranging Cayo Santiago rhesus monkeys (Macaca mulatta): III. Dental eruption patterns and dental pathology.

This article describes the dental eruption patterns, dentition, and dental wear, including tooth loss and breakage, of the free-ranging population of rhesus monkeys (Macaca mulatta) on Cayo Santiago (CS), Puerto Rico, ranging from 24 hr to 25 years old. Of the 694 monkeys on the island in the year 1985, 688 (99.1%; 366 males, 322 females) were captured and the dentition of 685 subjects (98.7% of the total population; 366 males, 319 females) was examined. Animals ranged in age from less than 24 hr to 331 months (27.58 years), encompassing the entire life span of the CS macaques. Results demonstrated that the first deciduous teeth appeared as early as the third day of life and that the sequence of dental eruption was comparable to the pattern observed in laboratory rhesus. However, there were slight differences in the age of eruption of individual teeth. For example, the canines and third molars erupted about a year later in the CS macaques compared to some laboratory rhesus. Overall, CS rhesus had good oral health and dental condition although tooth wear, loss, and breakage were common in aged animals, especially in males. This report, combined with earlier studies on morphological characteristics and skeletal remains of the CS macaques, provides the basis for further studies on the biology, genetics, life history, and effects of the environment on rhesus monkeys.

Oldest known cranium of a juvenile New World monkey (Early Miocene, Patagonia, Argentina): Implications for the taxonomy and the molar eruption pattern of early platyrrhines

A juvenile cranium of Homunculus patagonicus Ameghino, 1891a from the late Early Miocene of Santa Cruz Province (Argentina) provides the first evidence of developing cranial anatomy for any fossil platyrrhine. The specimen preserves the rostral part of the cranium with deciduous and permanent alveoli and teeth. The dental eruption sequence in the new specimen and a reassessment of eruption patterns in living and fossil platyrrhines suggest that the ancestral platyrrhine pattern of tooth replacement was for the permanent incisors to erupt before M1, not an accelerated molar eruption (before the incisors) as recently proposed.Two genera and species of Santacrucian monkeys are now generally recognized: H. patagonicus Ameghino, 1891a and Killikaike blakei Tejedor et al., 2006. Taxonomic allocation of Santacrucian monkeys to these species encounters two obstacles: 1) the (now lost) holotype and a recently proposed neotype of H. patagonicus are mandibles from different localities and different geologic members of the Santa Cruz Formation, separated by approximately 0.7 million years, whereas the holotype of K. blakei is a rostral part of a cranium without a mandible; 2) no Santacrucian monkey with associated cranium and mandible has ever been found. Bearing in mind these uncertainties, our examination of the new specimen as well as other cranial specimens of Santacrucian monkeys establishes the overall dental and cranial similarity between the holotype of Killikaike blakei, adult cranial material previously referred to H. patagonicus, and the new juvenile specimen. This leads us to conclude that Killikaike blakei is a junior subjective synonym of H. patagonicus.

First Fossil Evidence for the Advance of Replacement Teeth Coupled with Life History Evolution along an Anagenetic Mammalian Lineage

In mammals that grow up more slowly and live longer, replacement teeth tend to appear earlier in sequence than in fast growing mammals. This trend, known as ‘Schultz's Rule’, is a useful tool for inferring life histories of fossil taxa. Deviations from this rule, however, suggest that in addition to the pace of life history, ecological factors may also drive dental ontogeny. Myotragus balearicus is an extinct insular caprine that has been proved to be an excellent test case to correlate morphological traits with life history. Here we show that Myotragus balearicus exhibits a slow signature of dental eruption sequence that is in agreement with the exceptionally slow life history of this species, thus conforming to ‘Schultz's Rule’. However, our results also show an acceleration of the absolute pace of development of the permanent incisors in relation to that of the posterior teeth. The rodent-like incisors of Myotragus balearicus erupted early not only in relative but also in absolute terms (chronological age), suggesting that feeding characteristics also plays an important role in dental ontogeny. This is in agreement with ecological hypotheses based on primates. Our study documents a decoupling of the pace of development of teeth in mammals that is triggered by different selection pressures on dental ontogeny. Moreover, we show that Myotragus kopperi from the early Pleistocene (a direct ancestor of the late Pleistocene-Holocene M. balearicus) follows the pattern of first incisor replacement known in living bovids. Hence, the advance in the eruption sequence of the first incisors occurs along the Myotragus evolutionary lineage over a period of about 2.5 Myr. To our knowledge, this is the first fossil evidence of an advance of the emergence of the permanent first incisor along an anagenetic mammalian lineage.

Dental eruption sequence and eruption times in Erythrocebus patas

Erythrocebus patas has a short inter-birth interval, juveniles become independent from their mother early, females are young at first birth, and adult females have a high mortality rate. According to Schultz's rule, the molars of fast-growing and shorter-lived primate species erupt early relative to the replacement teeth. Based on the life history of E. patas, we hypothesized that the molars would erupt before the replacement teeth and/or that the eruption time of its molars would be early. The purpose of the present study was to determine the dental eruption sequence and eruption times for E. patas and to test our hypothesis. The eruption sequence for the permanent teeth of E. patas is M1 I1 I2 M2 P3 P4 [C M3]/M1 I1 I2 M2 P4 [P3 C]M3 in males and M1 I1 I2 [M2 P4 P3 C]M3/M1 I1 I2 [M2 P4 P3 C]M3 in females. Because these sequences constitute the general pattern seen in cercopithecines, Schultz's rule could not be applied to E. patas. The emergence time of upper and lower first molar (M1) is earlier in E. patas than in macaques, baboons, and mandrills and is similar to that in Chlorocebus aethiops. The emergence time of deciduous upper and lower fourth premolar (dp4) is similar to that in the above-mentioned cercopithecines but is later than that in Ch. aethiops. The emergence times of upper and lower second molar (M2) and upper and lower third molar (M3) in E. patas are earlier than those in the above-mentioned cercopithecines but later than those in Ch. aethiops. However, the intervals of the emergence time between each permanent molar in E. patas are similar to those of the above-mentioned cercopithecines. The early appearance of M2 and M3 in E. patas is related to the short interval of emergence time between dp4 and M1.

A Paleopopulation of Coryphodon lobatus (Mammalia: Pantodonta) from Deardorff Hill Coryphodon Quarry, Piceance Creek Basin, Colorado

A unique early middle Wasatchian paucispecific bone bed from Deardorff Hill in the Piceance Creek Basin of Colorado contains a minimum of 12 individuals of Coryphodon lobatus that range in age from subadult “yearlings” to senescent individuals. The preponderance of Coryphodon material in this assemblage (92% of the 700 complete bones represent a single species of Coryphodon) argues for a “catastrophic” origin for this assemblage. The Deardorff Hill Coryphodon Quarry preserves one of the most complete dental eruption sequences reported to date for Coryphodon and allows interpretation of demographic and life history attributes not ordinarily observable, such as evidence of seasonality in births. In addition, females are disproportionate in number to males, further confirming that this species had a polygynous social structure. Mass mortality assemblages are useful in eliciting a better understanding of the range of variation in single populations. Metrically, the molars of C. lobatus specimens from Deardorff Hill Coryphodon Quarry have coefficients of variation ranging from 4 to 11, which are comparable to metric variation observed in other mass death Coryphodon assemblages. An understanding of the range of variation in this highly variable taxon is of particular importance in the taxonomy and phylogenetic relationships of this ubiquitous Eocene mammal.