Jaw Morphology Research Articles

Relative impact of parrotfish grazing scars on massive Porites corals at Lizard Island, Great Barrier Reef

Scraping and excavating parrotfishes are well known for their marked differences in jaw morphology and feeding behaviour. Despite the importance of parrotfishes to reef systems and the well-known differences within the group, few studies have compared the functional importance of scraping versus excavating parrotfishes in shaping coral reef benthic communities. We compared the abundance, depth and dynamics of scraping and excavating parrotfish grazing scars on massive Porites spp. colonies along a reef gradient at Lizard Island, northern Great Barrier Reef. Scraping grazing scars were more abundant at most study sites than excavating scars. Excavating grazing scars were relatively rare but exposed more coral skeleton than scraping scars. Approximately 70% of excavating scars had some degree of filamentous algal growth in the scar compared with just 5% of scraping scars. Scraping grazing scars on massive Porites spp. completely disappeared after 2 mo whereas excavating grazing scars remained almost unchanged over this period. Groups of excavat- ing scars were more tightly clustered, exposed more coral skeleton and presented higher algal cover than grouped scraping scars. The deep, long-lasting excavating scars probably provide more suitable sites for the settlement of benthic algae and other invasive taxa on coral colonies. In contrast, the abundant and frequent grazing scars of scraping parrotfish may represent a more constant drain on energy supplies for coral colonies. These results highlight the differences between parrotfishes with distinct feeding modes and indicate that they differently impact not only algal communities but also coral colonies.

Phylogeny of triconodonts and symmetrodonts and the origin of extant mammals

zoic and Paleogene †Multituberculata), and Theria. The last subclass included the infraclasses †Pantothe� ria (Mesozoic orders of †Pantotheria and †Symmetr� odonta), Metatheria (marsupials), and Eutheria (pla� centals). Mesozoic triconodonts (order †Tricon� odonta) were referred to as Mammalia incertae subclassis. The classification of Mesozoic mammals proposed by Simpson was based exclusively on struc� tural features of their molars. In the midtwentieth cen� tury, Late Triassic–Early Jurassic mammal faunas were discovered, which included taxa with tricon� odont and symmetrodont types of molars combined with primitive morphology of the lower jaw, which, along with the dentary, included postdentary and paradentary bones, suggesting the presence in these taxa of a rudimentary reptilian jaw joint between the quadrate and articular. In the modern classification of Mesozoic mammals based on cladistic analysis of 275 morphological characters [2], the class Mamma� lia is divided into three subclasses: Australosphenida (orders †Ausktribosphenida and Monotremata), †Allotheria (orders †Haramiyida and †Multitubercu� lata), and Boreosphenida (infraclasses Metatheria and Eutheria). Many Mesozoic groups, including tricon� odonts and symmetrodonts, with the double jaw joint (†Morganucodonta and †Kuehneotheriidae, respec� tively), have not been assigned to any of these sub� classes. This system postulates homoplasy in the development of certain characters, such as appearance

Lack of Correlation Between Duration of Osteonecrosis of the Jaw and Sequestra Tissue Morphology: What It Tells Us About the Condition and What It Means for Future Studies

More studies have begun to investigate properties of tissue obtained from patients with osteonecrosis of the jaw (ONJ). Because of the relatively low incidence of ONJ, these studies necessitate the use of specimens from patients who have had ONJ for various durations. The goal of this study was to determine if properties, specifically bone morphology assessed by microcomputed tomography, were influenced by the duration of ONJ. Sequestra from 31 patients with confirmed ONJ for 3 weeks to 42 months before obtaining the tissue were scanned using microcomputed tomography to determine bone volume/tissue volume and bone surface/tissue volume. There was no significant correlation between the sequestra bone morphology (bone volume/tissue volume or bone surface/tissue volume) and the duration of ONJ. The findings indicated that studies should not be concerned about assessing tissue properties from patients who have had ONJ for different durations. In addition, the lack of difference in morphology with continued duration of ONJ suggests that most changes to bone tissue occur early in the disease progression.

The experimental study of seed dispersal by fish (ichthyochory)

1. The last few years have seen an increased interest in the experimental study of seed dispersal by fish (ichthyochory). This paper reviews such experiments, aiming to determine what functional aspects of ichthyochory have been investigated, what experimental designs have been used and what the potential pitfalls are. 2. The process of seed dispersal by fish can be divided into six discrete stages, each with its own probability of occurrence and each individually quantifiable in seed feeding trials: (i) seed uptake, (ii) ingestion, (iii) retention time, (iv) survival, (v) germination probability and (vi) germination rate after gut passage. 3. Inter- and intraspecific variation in seed traits (e.g. size, coat hardness, coat morphology, colour, presence and chemical composition of fruit pulp) and characteristics of fish (e.g. gape width, jaw morphology, presence of teeth, length of the digestive tract and digestive capability) can significantly affect the probability of one or more of the six stages of ichthyochory, thereby affecting the probability and distance of seed dispersal by fish. 4. To date only seven studies, which together investigated a total of nine fish species and 25 plant species, have used feeding experiments to study one or more of these quantifiable stages in the ichthyochory process. There is a clear bias in the research questions towards assessing seed survival during passage through the gut and subsequent viability. Only a few studies focus on seed retention in the digestive tract and germination rate, and even fewer address seed ingestion. 5. There is also considerable variation in experimental design among studies: Some have used groups of fish, while others used fish that are individually housed; some have fed seeds to hungry fish, while others used sated fish; some studied germination of seeds dissected from the alimentary tract, rather than seeds recovered from the faeces. 6. I present a number of recommendations for a more standardised protocol for future experimental studies of zoochory in general, and ichthyochory in particular, and highlight areas of interest for future research.

Quantitative analyses link modulation of sonic hedgehog signaling to continuous variation in facial growth and shape

Variation is an intrinsic feature of biological systems, yet developmental biology does not frequently address population-level phenomena. Sonic hedgehog (SHH) signaling activity in the vertebrate forebrain and face is thought to contribute to continuous variation in the morphology of the upper jaw, but despite its potential explanatory power, this idea has never been quantitatively assessed. Here, we test this hypothesis with an experimental design that is explicitly focused on the generation and measurement of variation in multivariate shape, tissue growth, cellular behavior and gene expression. We show that the majority of upper jaw shape variation can be explained by progressive changes in the spatial organization and mitotic activity of midfacial growth zones controlled by SHH signaling. In addition, nonlinearity between our treatment doses and phenotypic outcomes suggests that threshold effects in SHH signaling may play a role in variability in midfacial malformations such as holoprosencephaly (HPE). Together, these results provide novel insight into the generation of facial morphology, and demonstrate the value of quantifying variation for our understanding of development and disease.

Is intraspecific variation in diet and morphology related to environmental gradients? Exploring Liem's paradox in a cichlid fish

Interspecific studies have demonstrated that trophic morphology and ecology are not always tightly matched: a phenomenon rarely reported at the intraspecific level. In the present study, we explored relationships among diet, morphology and the environment in a widespread cichlid fish, Astatoreochromis alluaudi (Pellegrin 1904), from 6 sites in southern Uganda to test for evidence of eco-morphological matching at the interdemic level. Previous studies of Astatoreochromis alluaudi have demonstrated developmental plasticity in trophic morphology in response to diet: a mollusk diet produces specimens with large pharyngeal jaws and muscles, whereas a soft-food diet produces smaller pharyngeal jaws and corresponding changes in musculature. Sites were chosen to maximize variability in environmental variables that might directly or indirectly affect trophic morphology. We found significant differences in pharyngeal jaw and muscle morphology among populations. Similarly, we found differences in diets among sites: mollusks were found in the stomachs of fish from only 2 populations sampled, despite the presence of mollusks in 5 of the 6 sites. Although trophic morphology did match the observed diet in 2 sites, diet did not correlate with either morphology or environmental variables across sites, nor were environmental variables correlated with morphological variation among sites. These results suggest that mismatch can occur among different populations of a single species for reasons such as seasonality in resources, developmental plasticity and/or complex indirect interactions. Intraspecific mechanisms should be further studied in order to better understand the complex relationships between morphological specialization and ecological generalization.

Disparate feeding strategies used by syntopic Antillean nectarivorous bats to obtain dietary protein

Protein is essential for growth and reproduction. We used nitrogen stable isotope analysis to reconstruct protein (i.e., nitrogen) dietary origin in 2 Antillean nectarivorous bats with contrasting morphology of the masticatory apparatus: the Greater Antillean long-tongued bat (Monophyllus redmani, Glossophaginae) and Poey's flower bat (Phyllonycteris poeyi, Phyllonycterinae). M. redmani has a masticatory apparatus that is more adapted to feed on flowers, whereas P. poeyi has a feeding structure that resembles the structure of frugivorous bats. M. redmani relied on a mixture of nitrogen derived from insects and plants, and P. poeyi depended more on plant nitrogen. Based on previous findings in fecal contents, we concluded that M. redmani obtained plant nitrogen mainly from pollen, and P. poeyi obtained it predominantly from fruits. Our study suggests that jaw morphology plays a major role in dietary diversification among nectarivorous bats to obtain protein.

Weaning Strategies for Striped Trumpeter, Latris lineata, Postlarvae Culture

The striped trumpeter, Latris lineata, is a native fish being developed for aquaculture in Tasmania, Australia. Striped trumpeter have a long postlarval stage and rearing has been reliant on the long-term use of Artemia. Two experiments were conducted to investigate weaning strategies. The first experiment used 52 d posthatch (dph) postlarvae previously reared on Artemia from 16 to 52 dph enriched with either low or high ascorbic acid. The treatments were Artemia, a microdiet, or cofeeding. The postlarvae were reared until 67 dph. The Artemia treatment yielded significantly higher mean survival, followed by cofeeding, and the microdiet. Feeding Artemia yielded significantly heavier postlarvae and the microdiet produced significantly smaller postlarvae. A second experiment used 41 dph postlarvae and investigated the effect of cofeeding duration prior to feeding with Artemia and microdiet as controls. Cofeeding periods of 5, 10, and 15 d were tested. Cofeeding for 5 d and microdiet feeding yielded significantly poorer survival compared with Artemia. Artemia feeding yielded significantly heavier postlarvae. In both experiments, the diets did not have a significant effect on jaw morphology. These experiments are the first to examine weaning strategies for striped trumpeter postlarvae and suggest cofeeding postlarvae from 40 dph and feeding microdiet exclusively at 50 dph.

Feeding and breathing: trait correlations in an African cichlid fish

Environmental factors can directly influence phenotype such that a tight correlation between morphological and environmental variation is expected. However, morphological response to environmental variation may also reflect constraints imposed by interactions between adjacent structures such as the gills and the trophic apparatus in fishes. Such complex interactions help to explain why an organism's phenotype may appear mismatched with its environment. This study quantified relationships between morphological traits related to feeding and respiration and the physico-chemical environment in a widespread cichlid fish Astatoreochromis alluaudi, from six sites in Uganda. This species is known to be plastic in jaw morphology with enlarged jaw morphs specialized for mollusk eating, and reduced jaw morphs for insect eating. However, recent studies suggest a mismatch between the trophic morphology and feeding ecology in field populations of this species that could reflect interactions with the branchial apparatus; the development of large gills in low-oxygen habitats may constrain or affect pharyngeal jaw size. MANCOVA results for morphometric data showed a strong population effect for both gill and jaw traits. We found a significant negative correlation between composite morphological variables (principle components) relating to the size and shape of gill apparatus and pharyngeal jaw size across all populations. Furthermore, gill traits generated from principle component analysis were positively correlated with water conductivity, which was highly correlated with dissolved oxygen (DO) across the six sites. These results suggest that a particular morphological trait (pharyngeal jaw size) can be indirectly altered by the physico-chemical environment (conductivity and DO) due to correlated effects on a functionally unrelated morphology (gill size). These results have important implications for understanding species distribution patterns because trade-offs between suites of traits may constrain an individual's ability to exploit an otherwise suitable habitat or resource.

Comparative rates of lower jaw diversification in cichlid adaptive radiations

The lower jaw (LJ) provides an ideal trophic phenotype to compare rates and patterns of macroevolution among cichlid radiations. Using a novel phylogeny of four genes (ND2, dlx2, mitfb, and s7), we examined the evolutionary relationships among two of the most phylogenetically disparate cichlid radiations: (i) the Central America Heroines; and (ii) the East African Lake Malawi flock. To quantify jaw morphology, we measured two LJ lever systems in approximately 40 species from each lineage. Using geologic calibrations, we generated a chronogram for both groups and examined the rates of jaw evolution in the two radiations. The most rapidly evolving components of the LJ differed between the two radiations. However, the Lake Malawi flock exhibited a much faster rate of evolution in several components of the LJ. This rapid rate of divergence is consistent with natural selection, promoting unparalleled trophic diversification in Lake Malawi cichlids.

The case of an insular molarless black rat: Effects on lifestyle and mandible morphology

We report a specimen of an insular black rat ( Rattus rattus) from Illa den Colom (Menorca, Western Mediterranean) displaying a singular dental characteristic. It has no molar teeth but displays regular incisors. Its mere occurrence as a regular adult rat is puzzling and we attempted to evaluate what diet and morphological changes in jaw shape were promoted by the total lack of molars, and allowed the successful survival of this specimen. Two approaches were performed: first, bone tissue was analysed to obtain δ 15N and δ 13C values in order to estimate dietary preferences of the rat. Second, the shape of the jaw was analysed through elliptic Fourier analysis, using outlines as markers of diet. The values for C and N fractionation (−19.89‰ and 10.06‰, respectively) suggest that the molarless rat included animal food in the diet and not exclusively plant material as observed in other mainland rat populations. The morphometric analysis in which the shape of the molarless mandible falls into the range of omnivorous groups leads to a similar conclusion. The adult age of the specimen suggests that it fed efficiently enough with its incisors to allow a normal growth. Although displaying a lack of molar teeth, no deep changes in remodelling jaw morphology can be observed and its shape falls into the variation of regular murines. The molarless rat exemplifies that special ecological features on small islands allow the survival of aberrant morphotypes.

A New Pterosaur (Pterodactyloidea: Azhdarchidae) from the Upper Cretaceous of Morocco

The Kem Kem beds in South Eastern Morocco contain a rich early Upper (or possibly late Lower) Cretaceous vertebrate assemblage. Fragmentary remains, predominantly teeth and jaw tips, represent several kinds of pterosaur although only one species, the ornithocheirid Coloborhynchus moroccensis, has been named. Here, we describe a new azhdarchid pterosaur, Alanqa saharica nov. gen. nov. sp., based on an almost complete well preserved mandibular symphysis from Aferdou N'Chaft. We assign additional fragmentary jaw remains, some of which have been tentatively identified as azhdarchid and pteranodontid, to this new taxon which is distinguished from other azhdarchids by a remarkably straight, elongate, lance-shaped mandibular symphysis that bears a pronounced dorsal eminence near the posterior end of its dorsal (occlusal) surface. Most remains, including the holotype, represent individuals of approximately three to four meters in wingspan, but a fragment of a large cervical vertebra, that probably also belongs to A. saharica, suggests that wingspans of six meters were achieved in this species. The Kem Kem beds have yielded the most diverse pterosaur assemblage yet reported from Africa and provide the first clear evidence for the presence of azhdarchids in Gondwana at the start of the Late Cretaceous. This, the relatively large size achieved by Alanqa, and the additional evidence of variable jaw morphology in azhdarchids provided by this taxon, indicates a longer and more complex history for this clade than previously suspected.

Unusual kinematics and jaw morphology associated with piscivory in the poeciliid, Belonesox belizanus

Piscivory in fishes is often associated with the evolution of highly elongate jaws that achieve a large mouth opening, or gape. Belonesox belizanus, the pike killifish, has independently evolved this morphology, which is derived from short-jawed poeciliids within the Cyprinodontiformes. Using kinematic analysis of high-speed video footage, we observed a novel aspect of the elongate jaws of Belonesox; the premaxilla rotates dorsally during mouth opening, while the lower jaw rotates ventrally. Anatomical study revealed that this unusual motion is facilitated by the architecture of the premaxillomandibular ligament, prominent within cyprinodontiforms. In Belonesox, it allows force to be transferred from the lower jaw directly to the premaxilla, thereby causing it to rotate dorsally. This dorsal rotation of the premaxilla appears to be assisted by a mediolateral twisting of the maxilla during jaw opening. Twisting maxillae are found in members of the group such as Fundulus, but are lost in Gambusia. Models revealed that elongate jaws partially account for the enlarged gape, but enhanced rotation at the quadrato-mandibular joint was equally important. The large gape is therefore created by: (i) the convergent evolution of elongate jaws; (ii) enhanced jaw rotation, facilitated by loss of a characteristic cyprinodontiform trait, the lip membrane; and (iii) premaxilla rotation in a novel direction, facilitated by the retention and co-option of additional cyprinodontiform traits, the premaxillomandibular ligament and a twisting maxilla.

The ecological morphology of darter fishes (Percidae: Etheostomatinae)

Darters are a species-rich radiation of small benthic and benthic-associated stream fishes that comprise approximately 20% of the diversity of the North American freshwater fish fauna. Here, we gather data from 165, or 87%, of described species and use this information to characterize the morphological diversity of the darter radiation. We focus on characters of the oral jaws known to function in prey capture and consumption in other perciform taxa in order to explicitly link morphological diversity to ecological diversity. In addition to a quantitative description of the morphospace occupied by darters, we identify several instances of significant morphological convergence. We also describe three groups of darter species that exhibit unusual jaw morphologies that are used in previously undescribed prey capture behaviours. Despite these new ecomorphs, we find that darters exhibit relatively low variation in trophic morphology when compared with two other radiations of teleost fishes, and that the observed variation is related more to differences in microhabitat use than to differences in prey type.

Geographic variation in lower pharyngeal jaw morphology in the Shiner Perch Cymatogaster aggregata (Embiotocidae, Teleostei)

Correlations of feeding morphology with body morphology reflect ecological variation of a species and the geographic or ontogenetic scales over which it occurs. In this study, evidence was found for geographic variation in lower pharyngeal jaw (LPJ) morphology of Cymatogaster aggregata Gibbons (Embiotocidae, Teleostei) in the Pacific Northwest, U.S.A. Correlations of LPJ morphology with body morphology were more obvious in adulthood than the juvenile stage. Morphological patterns corresponded better with environmental variables and gut contents than geographic proximity, indicating that they were most likely caused by habitat differences. Qualitative common garden experiments indicated the nature and direction of plastic responses, and indicate a likely plastic origin to most naturally observed differences. Recognizing ecological patterns via morphology is an important first step in understanding how and when ecological mechanisms influence the functional role of an organism within its environment.

Shark scavenging behavior in the presence of competition

Abstract The distribution of organisms within a community can often be determined by the degree of plasticity or degree of specialization of resource acquisition. Resource acquisition is often based on the morphology of an organism, behavior, or a combination of both. Performance tests of feeding can identify the possible interactions that allow one species to better exploit a prey item. Scavenging behaviors in the presence or absence of a competitor were investigated by quantifying prey selection in a trophic generalist, spiny dogfish Squalus acanthias, and a trophic specialist, smooth-hounds Mustelus canis, in order to determine if each shark scavenged according to its jaw morphology. The diet of dogfish consists of small fishes, squid, ctenophores, and bivalves; they are expected to be nonselective predators. Smooth-hounds primarily feed on crustaceans; therefore, they are predicted to select crabs over other prey types. Prey selection was quantified by ranking each prey item according to the order it was consumed. Dietary shifts were analyzed by comparing the percentage of each prey item selected during solitary versus competitive scavenging. When scavenging alone, dogfish prefer herring and squid, which are easily handled by the cutting dentition of dogfish. Dogfish shift their diet to include a greater number of prey types when scavenging with a competitor. Smooth-hounds scavenge on squid, herring, and shrimp when alone, but increase the number of crabs in the diet when scavenging competitively. Competition causes smooth-hounds to scavenge according to their jaw morphology and locomotor abilities, which enables them to feed on a specialized resource.

Buoyancy studies of three morphs of the Antarctic fish Trematomus newnesi (Nototheniidae) from the South Shetland Islands

Phenotypic plasticity, a widespread phenomenon in boreal freshwater fishes, is less apparent in the marine realm and the organism–environment interactions producing this variation are undetermined. A sample of 40 specimens of Trematomus newnesi, an inshore Antarctic fish from King George/25 de Mayo Island in the South Shetlands, was composed of 52.5% typical morphs, 27.5% large-mouth morphs and 20% intermediate morphs. Measurements of percentage buoyancy on the morphs of this sample were 3.73, 3.84 and 3.83%, respectively with no significant differences among means. Both mean dry skeletal weight as a percentage of body weight and mean oral jaw weight as a percentage of dry skeletal weight were significantly greater in large-mouth morphs compared to typical morphs. Diversification in head and jaw morphology is not accompanied by diversification in ecology as represented by buoyancy and, in spite of external appearances, measurements of buoyancy offer no support for the hypothesis that the large-mouth morph is more benthic than the typical semipelagic morph. Although a trophic basis for this polymorphism is possible, it has not yet been documented. Our discussion centers on the status of key open questions regarding morphism and highlights areas requiring more research.

Palaeoecology of Placodus gigas (Reptilia) and other placodontids — Middle Triassic macroalgae feeders in the Germanic Basin of central Europe — and evidence for convergent evolution with Sirenia

The classical descriptions of Middle Triassic marine Placodus gigas Agassiz, 1833 (Reptilia) from the Germanic Basin of central Europe as being shell-crushing durophagous placodontids are revised in this paper through analyses in convergent anatomy. In particular, the jaw morphologies of three placodontid genera, Paraplacodus, Placodus and Cyamodus, are compared to those of dugongs (Mammalia) such as the central European Tertiary Halitherium schinzii and the modern Dugong dugon of the Arabian Gulf. The anatomies of Paraplacodus, Placodus and Cyamodus exhibit convergences to Halitherium and Dugong. Whereas mammalian dugongs developed pachyostotic thoracic ribs to enhance their body weight, the placodontid reptiles achieved a similar result in different ways: Paraplacodus developed enlarged thoracic ribs; Placodus had pachyostotic gastral ribs, and Cyamodus had a thoracic osteoderm shield. The teeth of the placodontids are also convergent with those of Halitherium and Dugong in their general function and jaw morphology. Whereas Halitherium and the modern Dugong possess a horny oral pad and counterpart, and a specialized rasp-like tongue with which to grind the seagrass and its roots, placodontids had large teeth that covered the whole of their upper and lower jaws forming a similar crushing or grinding pad. Both of the extinct groups must have fed on sea-plants, as does the modern Dugong, although Halitherium possibly fed on both seagrass and macroalgae. A study of the wear stages of many Placodus teeth, skulls and jaws has revealed a large proportion of highly worn anterior teeth, indicating a usage similar to that of the procumbent front teeth of modern Dugong which are used to scrape plant roots from the sea-floor. In contrast, highly worn (wear stage 3) teeth are rare (0.5%) amongst all other upper palatal, maxillary, or lower-jaw dentary teeth, suggesting a relatively soft diet. Placodus must have used their broadly spaced anterior teeth, to dig macroalgae from carbonate sands in shallow marine, sand bar environments; indirect evidence for the existence of such environments is provided by the benthic communities of the Germanic Basin and the northern Tethys. Sea-plants would have been only crushed and swallowed by the placodontids and not chewed with jaw rotation, in a similar feeding strategy to that used by modern Dugong feeding on seagrass.

Jaw morphology and ontogeny in five species of Ophryotrocha

Detailed scanning electron microscopy of jaws within the genus Ophryotrocha (Dorvilleidae, Annelida) was performed on 871 jaw parts. The investigations resulted in new understandings of the ontogeny and jaw morphology and have systematic implications for the family. Five species in the genus (Ophryotrocha alborana, O. diadema, O. gracilis, O. hartmanni, and O. labronica pacifica) were kept in culture, and the development of the jaws was studied by sampling throughout their life history. Ophryotrocha species have mandibular plates that remain the same throughout ontogeny, whereas the posterior shafts elongate. Both mandibular plate morphology and shaft ontogeny have species-specific distinctions. In Ophryotrocha, the maxillae can be assigned to three to four distinct types, which are replaced by moulting. The maxillary morphology and developmental stages at which moults occur are species specific, although with broad intervals. A redefinition is given for some of the basic jaw elements, and new homologies are proposed for structures that are also present across other dorvilleid taxa.

The occurrence of Contogenys-like lizards in the Late Cretaceous and Early Tertiary of the western interior of the U.S.A.

ABSTRACT Based on diagnostic jaw and dental material from the Cenomanian–middle Paleocene of the western U.S.A., we erect a new fossil lizard taxon, Contogeniidae taxon nov., that contains the following species: Contogenys sloani Estes, 1969 (Maastrichtian–early Paleocene, Montana); Contogenys ekalakaensis sp. nov. (middle Paleocene, Montana); Palaeoscincosaurus middletoni Sullivan and Lucas, 1996 (early Paleocene, Colorado); Palaeoscincosaurus pharkidodon sp. nov. (Campanian, Utah); Utahgenys evansi gen. et sp. nov. (Turonian, Utah); and Utahgenys sp. indet. (Cenomanian, Utah). These taxa share unique characteristics of tooth and jaw morphologies (e.g., tooth crowns truncate and bearing longitudinal apical grooves; hypertrophied inferior alveolar canal). Phylogenetic analysis indicates that among squamates, Contogeniidae taxon nov. is most closely related to Xantusiidae.