Incisor Enamel Microstructure Research Articles

A small assemblage of early Oligocene rodents and insectivores from the Sivas basin, Turkey

The assemblage of small mammals from a site near Yeniköy (Anatolia) is described. The assemblage was collected by screen-washing a sample from a locality in the Selimye Formation (Sivas basin). The site has a magneto-stratigraphic calibrated age of 29 Ma (younger part of the early Oligocene). The murids dominate in this relatively small collection with Eucricetodon and Pseudocricetodon. In addition, a dipodid, an unidentified erinaceide and the new baluchimyin hystricognath genus and species Zorania milosi nov. gen. et nov. sp. are present. The study of Eucricetodon, Pseudocricetodon and Zorania nov. sp. includes an analysis of incisor enamel microstructure. The incisor microstructure of Eucricetodon shows that there are several parallel long-living lineages within the genus. The Anatolia-Balkans biogeography of the late Eocene-Oligocene is reviewed. Its rodent assemblages are characterised by dominance of murids and presence of taxa that are known from low-latitude Asia. The Paleogene Anatolia-Balkans biogeographic province, is therefore rather different from those of western European and the Indian subcontinent.

Incisor enamel microstructure of West Indian caviomorph hystricognathous rodents (Octodontoidea and Chinchilloidea)

Analysis of the incisor enamel microstructure of extinct and extant West Indian caviomorph rodents emphasizes a clear microstructural distinction between the Echimyidae (Capromyinae and Heteropsomyinae) among Octodontoidea and the “Heptaxodontidae”, whose phylogenetic affinities are debated. All capromyines and heteropsomyines have a pattern of enamel characterized by a rectangular crystallite arrangement, which is biomechanically strongest in limiting crack propagation most efficiently (subtype [Sbt.] 3 of multiserial Hunter-Schreger bands [HSBs]). This enamel condition is exclusive to all mainland octodontoids. In stark contrast, “heptaxodontids” sampled here exhibit much less derived enamel subtypes of multiserial HSBs, with parallel to acute angular crystallite arrangement (Sbt. 1 [Clidomys], Sbt. 1–2 [Elasmodontomys], and low acute Sbt. 2 [Amblyrhiza]), less well adapted for prevention of crack propagation. The incisor enamel microstructure of Amblyrhiza and Clidomys is consistent with a chinchilloid assignment, as reflected by the anatomy of their auditory region and their unusual dental pattern. For Elasmodontomys, the primitive condition of its incisor enamel is difficult to reconcile with its highly nested phylogenetic position within the Octodontoidea clade (among the Capromyinae), as recently inferred from aDNA analyses. The different enamel patterns among extinct and extant West Indian caviomorphs indicate distinct high-level taxonomic groups, but restricted to the Octochinchilloi (Octodontoidea and Chinchilloidea) among Caviomorpha. The great diversity of caviomorphs on the Caribbean islands resulted from intra-archipelago diversification through time, but their high-level phylogenetic diversity can only be explained by distinct sources, implying de facto multiple (potentially time-staggered) natural colonizations of the West Indies. The chinchilloid-compatible enamel and dental pattern characterizing Borikenomys from lower Oligocene deposits in Puerto Rico strongly suggest a link with some of the recently-extinct “heptaxodontids”, which would substantiate their much greater antiquity in the Caribbean islands.

Incisor enamel microstructure of some Neogene muroid rodents of India: taxonomic, evolutionary and biomechanical implications

Incisor enamel microstructure of some Neogene muroid rodents of India: taxonomic, evolutionary and biomechanical implications

Incisor enamel microstructure places New and Old World Eomyidae outside Geomorpha (Rodentia, Mammalia)

AbstractThe lower incisor enamel microstructure of the fossil rodent family Eomyidae was believed to be three‐layered and highly derived but rather uniform throughout the clade. Here, we describe a new four‐layered schmelzmuster in Eomyidae consisting of a three‐fold portio interna with longitudinal oriented, uniserial Hunter‐Schreger bands and a one‐fold portio externa, accounting for a unique enamel microstructure character combination in Rodentia. This new schmelzmuster type has developed early in eomyid evolution and is detectable already in the late Eocene (Chadronian) of North America. In European eomyids, it first occurs in the early Miocene (MN 3), implying that this four‐layered schmelzmuster was not present in all members of the family but restricted to species included in Eomyini and some genera currently considered Eomyidae incertae sedis within Eomyidae. Additionally, our analysis recognizes three taxa with schmelzmuster divergent from all other eomyids. Incisor enamel microstructure does not advocate a close phylogenetic relationship of Eomyidae to either fossil or extant Heteromyidae and Geomyidae, nor to fossil Heliscomyidae and Florentiamyidae. Our results rather support the view that Eomyidae are placed outside Geomorpha.

On the status of early Eucricetodontinae (Muroidea, Rodentia) with a special focus on the Atavocricetodon vs Eucricetodon issue: morphometrical and microstructural aspects

Among the flourishing Muroidea, the Eucricetodontinae constitute the most diversified subfamily of the Eurasian Palaeogene. Early representatives, such as Atavocricetodon and Eucricetodon, are notably characterized by their simple and primitive dental morphology. As a result, it appears very difficult to discriminate these genera according to their dental morphology, and that is emphasized by their imprecise diagnosis. Here, we aim at challenging the taxonomic validity of Atavocricetodon, frequently considered as a grade of Eucricetodon. We chose to investigate the outline of first upper molars for four species of Atavocricetodon and seven of Eucricetodon, to avoid confusions made by their occlusal dental characters. The outline analysis involves samples of ten molars and was realized by using Elliptic Fourier Transforms. Incisor enamel microstructures were investigated as well in four species. Results revealed that if a significant difference exists between the global dental shape of Atavocricetodon and Eucricetodon, outline morphospaces of the considered species generally overlap as displayed by the multivariate analysis and the hierarchical clustering. This is partly explained by the high intrageneric shape variation, which might correspond to different Oligocene lineages of Eucricetodontinae. Such variation is also due to Atavocricetodon paaliense, which could rather belong to another genus, the pseudocricetontine Kerosinia. More generally, there is no real apomorphy which permits to distinguish these genera, because incisor enamel microstructure patterns are highly variable and a few types are shared by both genera. Atavocricetodon cannot thus be retained neither as a genus, nor as a morphosubgenus of Eucricetodon

Evolutionary and Functional Implications of Incisor Enamel Microstructure Diversity in Notoungulata (Placentalia, Mammalia)

Notoungulates are an extinct clade of South American mammals, comprising a large diversity of body sizes and skeletal morphologies, and including taxa with highly specialized dentitions. The evolutionary history of notoungulates is characterized by numerous dental convergences, such as continuous growth of both molars and incisors, which repeatedly occurred in late-diverging families to counter the effects of abrasion. The main goal of this study is to determine if the acquisition of high-crowned incisors in different notoungulate families was accompanied by significant and repeated changes in their enamel microstructure. More generally, it aims at identifying evolutionary patterns of incisor enamel microstructure in notoungulates. Fifty-eight samples of incisors encompassing 21 genera of notoungulates were sectioned to study the enamel microstructure using a scanning electron microscope. We showed that most Eocene taxa were characterized by an incisor schmelzmuster involving only radial enamel. Interestingly, derived schmelzmusters involving the presence of Hunter-Schreger bands (HSB) and of modified radial enamel occurred in all four late-diverging families, mostly in parallel with morphological specializations, such as crown height increase. Despite a high degree of homoplasy, some characters detected at different levels of enamel complexity (e.g., labial versus lingual sides, upper versus lower incisors) might also be useful for phylogenetic reconstructions. Comparisons with perissodactyls showed that notoungulates paralleled equids in some aspects related to abrasion resistance, in having evolved transverse to oblique HSB combined with modified radial enamel and high-crowned incisors.

Relationships Between Enamel Prism Decussation and Organization of the Ameloblast Layer in Rodent Incisors.

Rodent enamel microstructure has been extensively investigated, primarily on the basis of 2D electronic microscopy data. The nature and dynamics of the ameloblasts (the enamel-secreting cells) have also been well studied. However, critical issues still remain surrounding exactly how the ameloblasts produce the astonishing microstructural complexity of enamel, and how this subtle architecture evolved through time. In this article, we used a new methodology based on confocal laser microscopy to reconstruct the enamel microstructure of rodent incisors in three dimensions (3D) with the ameloblasts in situ. We proposed interpretations regarding the possible relationships between the workings of the ameloblasts and the resulting enamel prisms, especially how the phenomenon of decussation is generated. Finally, we were able to represent the two main types of modern rodent incisor microstructures (uniserial and multiserial decussations), as a set of parameters that have been entered into the 3D enamel simulation software Simulenam to generate 3D models that can be digitally manipulated. Associating 2D data of incisor enamel microstructure of fossil rodents and Simulenam, it was then possible to better understand how the various decussation parameters evolved through time and gave rise to the two modern microstructure types from the same ancestral type (pauciserial). This study also confirmed that rodent and artiodactyl enamel do not share the same mechanism of decussation formation. Anat Rec, 302:1195-1209, 2019. © 2018 Wiley Periodicals, Inc.

Incisor Enamel Microstructure of Paleogene Caviomorph Rodents from Contamana and Shapaja (Peruvian Amazonia)

Fil: Boivin, Myriam. Institut Des Sciences de L'evolution de Montpellier; Francia. Centre National de la Recherche Scientifique; Francia. Universite de Montpellier; Francia

Incisor Enamel Microstructure of Hystricognathous and Anomaluroid Rodents from the Earliest Oligocene of Dakhla, Atlantic Sahara (Morocco)

Seven hystricognaths and five anomaluroids have been recently described from the earliest Oligocene of the Dakhla (DAK C2) region of Morocco, based primarily on isolated cheek teeth. Here, we analyzed the enamel microstructure of thirty associated isolated fragments of incisors. Among these specimens, only three display an early stage of uniserial Hunter-Schreger bands (HSBs), with mostly a single prism per band, but also occasionally two prisms per band (in two specimens), and a thin interprismatic matrix (IPM) that runs parallel to the prism direction, thereby documenting incisors of anomaluroids. All other sampled incisors display an enamel with multiserial HSBs, thereby documenting hystricognaths. For these latter, we recorded primarily an IPM crystallite arrangement describing the subtype 2 of multiserial HSBs, but with variation including a wide amplitude in the angle (acute) formed between the crystallites of IPM and those of the prisms, some variations in the frequency of the IPM sheet anastomoses, in the number of prisms per HSBs, and variations in the inclination of the HSBs. The absence of the subtypes 2–3 and 3 of multiserial HSBs in DAK C2 suggests that African hystricognathous rodents had still not achieved these most resistant multiserial HSBs at that time. The drier, cooler climatic regime of the early Oligocene, having increased the fragmentation and opening of habitats, might have played a role in the subsequent selection of taxa having acquired a more resistant incisor enamel.

A new large beaver (Mammalia, Castoridae) from the early Miocene of Japan

ABSTRACTA new early Miocene large castorid, Minocastor godai gen. et sp. nov., from the Dota locality, Gifu Prefecture in central Japan, is described on the basis of dentaries and teeth. The material comes from the Kani basin, where limnofluviatile clay and sandstones of the Nakamura Formation (Mizunami Group) are exposed on the southern (left) bank of the Kiso River. It represents the richest sample of a Miocene small mammal in the Japanese fossil record thus far known. Based on jaw and tooth morphology, this new castorid most likely represents a primitive anchitheriomyine. However, it lacks the marked striations on the incisors that are characteristic of the advanced large, middle Miocene anchitheriomyines like Anchitheriomys and Amblycastor. The new castorid shares this dental feature with other primitive anchitheriomyines from Asia and North America, like Propalaeocastor, Oligotheriomys, and Miotheriomys. For these genera, a new tribe, Minocastorini, is proposed as sister group to the Anchitheriomyini. The incisor enamel microstructure of the new castorid largely exhibits plesiomorphic characters but also apomorphic features such as pseudo-pauciserial Hunter-Schreger bands. Additionally, the outer portion of the enamel band is rather thick in comparison to that of other beavers. Based on the rodent taxa associated with Minocastor godai gen. et sp. nov., Dota can be correlated with European Neogene mammal units MN 3/4. Magnetostratigraphic studies and radiometric dates obtained from the Mizunami Group indicate that Dota is more likely correlated with MN 3, with an absolute age of around 18.5 Ma.http://zoobank.org/urn:lsid:zoobank:org:pub:B1886424-1759-4BDA-A5CC-D122436E1A76 Citation for this article: Mörs, T., Y. Tomida, and D. C. Kalthoff. 2016. A new large beaver (Mammalia, Castoridae) from the early Miocene of Japan. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1080720.

A new early Miocene octodontoid rodent (Hystricognathi, Caviomorpha) from Patagonia (Argentina) and a reassessment of the early evolution of Octodontoidea

ABSTRACT A new caviomorph rodent, Dudumus ruigomezi, gen. et sp. nov., is described from the Sarmiento Formation, Trelew Member (early Miocene), of the Argentinian Patagonia. This new taxon is represented by upper and lower cheek teeth, mandible, and maxillary remains. It is characterized by retention of deciduous premolar, and low-crowned and terraced lower and upper cheek teeth with well-differentiated cusps, as in Caviocricetus lucasi; upper molariforms with the mesolophule and metacone fused with the posterior-most crest, as in C. lucasi; lower molars with lingual cusp enlarged and metalophulid II longer in m2 than in m1and m3, as in Prospaniomys priscus; and dp4 with metalophulid I separated from the metaconid and a spur projecting posterolingually from the posterior wall of metalophulid I, between the protoconid and anteroconid. The incisor enamel microstructure is derived, with the interprismatic matrix perpendicular (at a right angle) to the prisms, as in other octodontoids. A cladistic analysis corroborates that D. ruigomezi represents an octodontoid rodent with unusual tooth morphology. This analysis demonstrates that the early evolutionary history of Octodontoidea was characterized by the differentiation of successive lineages that survived until the early or middle Miocene, with no direct relationships with modern Octodontidae and Echimyidae. This analysis also suggests that fossil taxa previously classified as octodontoids are instead more closely related to the other caviomorph rodents. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at http://www.tandfonline.com/UJVP.

Zegdoumyidae (Rodentia, Mammalia), stem anomaluroid rodents from the Early to Middle Eocene of Algeria (Gour Lazib, Western Sahara): new dental evidence

The Palaeogene fossil record of rodents in Africa is very poor compared to that of North America or Eurasia. Despite this, Africa has long appeared to be a centre of adaptive radiation for two distinct groups of Rodentia: Hystricognathi and Anomaluroidea. The >45-million-year-old enigmatic Zegdoumyidae is the oldest and only rodent family known of this age from Africa (Algeria and Tunisia). Zegdoumyids have been tentatively regarded as a possible early African stem group for Anomaluridae, a link that has never been clearly established because of the highly fragmentary nature of zegdoumyid fossils, as well as the major temporal and morphological gaps between zegdoumyids and the first true anomaluroids from the Late Eocene. About 200 rodent teeth have been sorted after acid treatment of indurated sediments from several new localities in the Gour Lazib of western Algeria dating from the late Early or early Middle Eocene. These new fossils allow us to better describe the morphology of the Zegdoumyidae (especially Glibia and Zegdoumys) and to identify a new taxon, Lazibemys zegdouensis gen. et sp. nov. With this material, we investigated the phylogenetic position of the Zegdoumyidae in a high-level rodent phylogeny with cladistic assessment of the dental evidence. Our analyses have yielded six equally most-parsimonious trees in which zegdoumyids represent the earliest offshoots (pectinately arranged) of a large clade that embraces Eocene anomaluroids plus stem and crown Anomaluridae. This phylogenetic assumption underscores the great antiquity of the Anomaluroidea clade in Africa, as expected given the high morphological divergence of the Late Eocene African anomaluroids. Zegdoumyids exhibit a variety of dental morphologies and provide some suggestions on evolutionary trends within the Anomaluroidea (early stages of pentalophodonty, incisor enamel microstructure transitional from the pauciserial to the uniserial condition). The source of Zegdoumyidae is still unclear inasmuch as there is no well-identified sister group among early Palaeogene rodents. Zegdoumyids seem to share a common ancestry with both stem Myodonta and North American Sciuravidae. Given the high degree of dental specialization of zegdoumyids, we cannot exclude the possibility that zegdoumyids are rooted in a more primitive, as yet unknown, African rodent lineage older than the Early-Middle Eocene.

Incisor Enamel Microstructure and the Concept of Sciuravida

Incisor enamel microstructure analysis does not support a rodent suborder Sciuravida (most recent common ancestor of Ivanantoniidae, Sciuravidae, Chapattimyidae, Cylindrodontidae, Ctenodactylidae and all its descendants) as proposed by McKenna and Bell (1997). Early to middle Eocene Ivanantonia, Sciuravidae, and Prolapsus have the plesiomorphic rodent schmelzmuster with pauciserial Hunter-Schreger bands (HSB). Within the Cylindrodontidae a schmelzmuster with uniserial HSB evolved: early Eocene Dawsonomys and middle Eocene Jaywilsonomyinae possess a schmelzmuster with pauciserial HSB, and middle to late Eocene Cylindrodontinae have more derived schmelzmuster with uniserial HSB. Chapattimyidae and Ctenodactylidae represent a clade with the potential to evolve multiserial schmelzmuster. Early Eocene Chapattimyinae, Yuomyinae, and Cocomyinae have plesiomorphic schmelzmuster with pauciserial HSB, whereas middle Eocene Cocomyinae, Yuomyinae, late Eocene Protophiomys, early Miocene Baluchimyinae, and the Ctenodactylidae possess derived schmelzmuster with multiserial HSB. Uniserial and multiserial HSB are derived but represent different pathways of evolution. Schmelzmuster distribution supports the hypothesis of a basal dichotomy of Rodentia suggested by Luckett and Hartenberger (1985) characterized by an ischyromyoid clade with the potential to evolve schmelzmuster with uniserial HSB and a ctenodactyloid plus hystricognath clade with the potential to evolve schmelzmuster with multiserial HSB.

Adaptive diversity of incisor enamel microstructure in South American burrowing rodents (family Ctenomyidae, Caviomorpha)

The aim of this study was to analyse the morphofunctional and adaptive significance of variation in the upper incisor enamel microstructure of South American burrowing ctenomyids and other octodontoid taxa. We studied the specialized subterranean tooth-digger daggerEucelophorus chapalmalensis (Pliocene - Middle Pleistocene), and compared it with other fossil and living ctenomyids with disparate digging adaptations, two fossorial octodontids and one arboreal echimyid. Morphofunctionally significant enamel traits were quite similar among the species studied despite their marked differences in habits, digging behaviour and substrates occupied, suggesting a possible phylogenetic constraint for the Octodontoidea. In this context of relative similarity, the inclination of Hunter-Schreger bands, relative thickness of external index (EI) and prismless enamel zone were highest in daggerEucelophorus, in agreement with its outstanding craniomandibular tooth-digging specialization. Higher inclination of Hunter-Schreger bands reinforces enamel to withstand high tension forces, while high external index provides greater resistance to wear. Results suggest increased frequency of incisor use for digging in daggerEucelophorus, which could be related to a more extreme tooth-digging strategy and/or occupancy of hard soils. Higher external index values as recurring patterns in distant clades of tooth-digging rodents support an adaptive significance of this enamel trait.

Incisor enamel microstructure and its implications to higher-level systematics of Eurasian Oligocene and Early Miocene hamsters (Rodentia)

Incisor enamel microstructure and its implications to higher-level systematics of Eurasian Oligocene and Early Miocene hamsters (Rodentia)

Incisor Schmelzmuster Diversity in South America's Oldest Rodent Fauna and Early Caviomorph History

Investigation of the enamel microstructure of 20 isolated rodent incisors from the ?Eocene Santa Rosa local fauna (Peru) yielded exclusively schmelzmuster with multiserial Hunter–Schreger bands (HSB). All three subtypes of multiserialHSB with parallel, acute angular, and rectangular interprismatic matrix (IPM) that were previously reported for caviomorph rodents are present. Two lower incisors with rectangular IPM can be attributed to the Octodontoidea, a caviomorph superfamily exhibiting this highly derived enamel type. The plesiomorphic pauciserial condition that characterizes early Paleogene rodents such as North American Ischyromyoidea (including “Franimorpha”) has not been detected. It is therefore probable that the founder populations of South American Caviomorpha already possessed a derived incisor schmelzmuster with multiserial HSB that is shared with African Thryonomyoidea. Because on the North American continent a possible stem-lineage representative of Caviomorpha with multiserial HSB has never been detected, incisor enamel microstructure supports the hypothesis of an African origin of Caviomorpha from a common ancestor shared with Thryonomyoidea.

High-level phylogeny of early Tertiary rodents: dental evidence

Major crown-groups of rodents were well established in the early Tertiary, and fossils provide an invaluable window into their evolutionary history. The main focus of this project was to perform a cladistic assessment of the dental evidence for early Tertiary rodent cladogenesis - the masticatory apparatus and teeth are the most frequently preserved anatomical features in the fossil record. We focused on groups that existed in a period corresponding to their early history, combining fossils belonging to extinct lineages and to stem-groups leading to modern lineages. While the monophyly of some groups is not systematically explored, our results have important implications for high-level rodent relationships and systematics. These results are consistent with those of recent molecular phylogenies and reliably congruent with the stratigraphic record, thus enhancing the pertinence of dental characters for phylogenetic inference. Our approach provides evidence of a fundamental dichotomy in early rodent history. Two major clades have been identified: (1) the earliest ‘ctenodactyloid’ (Ctenodactylidae, Chapattimyidae, Yuomyidae, Diatomyidae) and hystricognathous (Tsaganomyidae, Baluchimyinae, ‘phiomorphs’, ‘caviomorphs’) rodents, and (2) the earliest ‘ischyromyoid’ rodents with their closest relatives (Muroidea + Dipodoidea + Geomyoidea + Anomaluroidea + Castoroidea + Sciuravidae + Gliroidea, and Sciuroidea + Aplodontoidea + Theridomorpha). This topology has led us to endorse Ctenohystrica as the first clade and propose a new taxon, Ischyromyiformes, for the second. Although minimized in our working hypothesis, the homoplasy in dental characters remains significant. However, a number of homoplasic characters reveal structuring in their internal distribution, allowing us to discern evolutionary morphological patterns, notably the pentalophodonty of molars, zygomasseteric complex and incisor enamel microstructure.

On the systematic position ofChaetomys subspinosus (Rodentia: Caviomorpha) based on evidence from the incisor enamel microstructure

We have studied the incisor enamel microstructure ofChaetomys subspinosus and other possibly closely related caviomorph rodents.Chaetomys subspinosus lacks the important synapomorphy of the Octodontoidea, reactangular plate-like interprismatic matrix (IPM) in the portio interna (PI) of the incisor Schmelzmuster. Therefore its transfer from the Erethizontidae to the Echimyidae, as proposed by Patterson and Wood (Bull. Mus. Comp. Zool. 149, 371–543, 1982) based on retention of dP4, is contested. The parallel to acute angular IPM in the PI ofChaetomys and the Erethizontidae is a symplesiomorphy and does not indicate close relationship. Contrary to previous claims, a posterior carotid foramen is also retained inChaetomys. Chaetomys is characterized by an unusual thin enamel which is considered primitive after outgroup comparison. Therefore, it is proposed to leaveChaetomys in the monospecific erethizontid subfamily Chaetomyinae, until additional information on the species is available.

African origin of caviomorph rodents is indicated by incisor enamel microstructure

The same three subtypes of derived multiserial Hunter-Schreger bands are found in the incisor enamel of African phiomorph rodents from the late Eocene-early Oligocene and the oldest South American Caviomorpha from the Deseadan (late Oligocene). The synapomorphies contained therein, especially arrangement and orientation of interprismatic matrix, make an African origin of the Caviomorpha very probable. A North American origin of the Caviomorpha is thus rejected, as only primitive pauciserial Hunter-Schreger bands have been observed in possible ischyromyoid caviomorph ancestors. A multiserial Schmelzmuster apparently never evolved in the North American rodent fauna.

Early rodent incisor enamel evolution: Phylogenetic implications

Incisor enamel microstructure proved to be a very effective tool for assessment of phylogenetic relationships among the Rodentia. Pauciserial and multiserial Schmelzmuster are clearly distinct by structural characters such as orientation of interprismatic matrix, presence or absence of transition zones between Hunter-Schreger bands (HSB), inclination of HSB, enamel thickness, and others. Pauciserial HSB are structurally very close to the earliest known mammalian HSB found in Paleocene arctocyonids. Biomechanical arguments and outgroup comparison with mixodontians indicate that the pauciserial Schmelzmuster is a symplesiomorphy of the Rodentia. Transitional stages from pauciserial to multiserial Schmelzmuster were observed in middle Eocene ctenodactyloids and from pauciserial to uniserial in middle to late Eocene anomalurids. The multiserial Schmelzmuster is considered a synapomorphy of the Hystricognathi, ctenodactylids, and pedetids. Schmelzmuster evolution reflects the early dichotomy of the Rodentia: In the Asian ctenodactyloid lineage a multiserial Schmelzmuster evolved once and in the North American/European ischyromyoid lineage a uniserial Schmelzmuster developed several times convergently. The pauci- to uniserial Schmelzmuster of the anomalurids excludes a close relationship to the phiomyids, because the ctenodactyloid-phiomyid lineage is characterized by the development of a multiserial Schmelzmuster.