Stylar Cusps Research Articles

The Order of Cusp Calcification on the Upper First Molar of the Gray Short-tailed Opossum (Monodelphis domestica: Marsupialia)

During the course of a study into the tooth development of marsupials, an interesting feature concerning cusp development was revealed by micro-focus computed tomography analysis and alizarin red S staining of the dentition from 9 to 25 days after birth (as a pouch-young specimen) of the gray short-tailed opossum (Monodelphis domestica). The metacone was the first cusp to calcify on the upper first molar, which commenced calcification 13 days after birth. The paracone and protocone were the second and the third cusps to calcify respectively, followed by the external stylar cusps. This order of cusp calcification differed from the order on the upper deciduous molar and permanent molars of Didelphis virginiana belonging to the same family, in which the stylar cusps calcified earlier than the protocone.

A new Early Oligocene peradectine marsupial (Mammalia)from the Burqin region of Xinjiang, China

Tertiary marsupial records are very scarce in Asia. A new peradectine marsupial, Junggaroperadectes burqinensis gen. et sp. nov., is reported from the Early Oligocene Keziletuogayi Formation in the Burqin region, Xinjiang, China. This new species is based on a single right upper M2. The tooth possesses a straight centrocrista, a characteristic of peradectines. Its main cusps lean buccally, with the paracone being smaller and lower than the metacone. The conules and stylar cusps are weakly developed. These characters distinguish J. burqinensis from Euro-American Tertiary peradectines, but they also imply a close phylogenetic relationship to Siamoperadectes and Sinoperadectes, two Asian Early Miocene peradectines.

Description of new material for Propalorchestes novaculacephalus (Marsupialia: Palorchestidae) from the mid Miocene of Riversleigh, northwestern Queensland

Additional material referable to Propalorchestes novaculacephalus from System B and System C deposits from the Riversleigh World Heritage Area, northwestern Queensland, is described. One of these specimens, a juvenile maxilla, represents the most complete and least worn dentition currently known for the species, and includes a dP3 and P3. It supports Murray's (1990) hypothesis that Propalorchestes molars are transitional between the fully bilophodont Palorchestes and the subselenodont/ semilophodont wynyardiid molar morphologies. The paracone and stylar cusp C and the metacone and stylar cusp D are clearly differentiated on the protoloph and metaloph, respectively of P. novaculacephalus. Other, new material tentatively assigned to P. novaculacephalus extends the temporal range for the species from early to middle Miocene.

Arikareean (Oligocene Miocene) Herpetotherium (Marsupialia, Didelphidae) from Nebraska and Florida

North American Herpetotherium (Marsupialia, Didelphidae) is a small mouse-sized (<80g) opossum that ranged from the middle Eocene into the early Miocene (Uintan-Hemingfordian) of the Great Plains, Pacific Northwest, and Atlantic Southeast. New Arikareean (30-18.8Ma) Herpetotherium samples are described from the lower Arikaree Group of Nebraska (Dw-121 or Ridgeview Local Fauna, a locality south of Chadron, from localities of the Wildcat Ridge region, and the McCann Canyon Local Fauna) as well as from 4 localities in Florida (I-75, Brooksville 2, SB-1A, and White Springs). The samples from Dw-121 and Brooksville 2 are the first large (>25) populations of Herpetotherium described from the Arikareean age. Three species are recognized in the Arikareean: H. fugax, H. youngi, and H. merriami. Most early Arikareean samples are referred to H. fugax and are slightly smaller on average than older H. fugax. Later Arikareean Herpetotherium samples are referable to H. youngi on the basis of possessing a single central stylar cusp. A large species, H. merriami, from the early Arikareean John Day Formation in Oregon is similar to Herpetotherium molars described from the early Arikareean or late Whitneyan Florida I-75 locality. Taxonomy of Herpetotherium has previously been based on tooth size and upper molar stylar cusp morphology. H. fugax exhibits several configurations of stylar cusp morphology, separate to fused central stylar cusps, and a wide range of dental size variation. These ranges of variation are similar to those exhibited by the Chadronian species, H. valens.

The deciduous premolars of Mammut americanum (Mammalia, Proboscidea)

ABSTRACT Deciduous premolars of Mammut americanum have received relatively little study, and previous work was based on small sample sizes. We present morphologic descriptions and quantitative data for a sample of over 135 deciduous premolars of M. americanum from Florida. Most second and third deciduous premolars are bilophodont, although a few anomalous teeth deviate from this pattern to a varying degree. Although the premolars are morphologically similar to the adult molars in many respects, differences in development of cingula, orientation of lophs and lophids, and relative strengths of enamel crests are observed. Distal cingula and stylar cusps are the most variable portions of the crown. Crown length increases distally along the tooth row, with no observed overlap in length between adjacent teeth.

Chapter 5: Marsupial Mammals from the Albian–Cenomanian (Early–Late Cretaceous) Boundary, Utah

The Mussentuchit local fauna, upper Cedar Mountain Formation (Cretaceous: Albian–Cenomanian), Utah, includes the geologically oldest marsupials: Kokopellia juddi, described previously, and three new taxa named herein. Adelodelphys muizoni, new genus and species, and Sinbadelphys schmidti, new genus and species, both unassignable to family, are among the smallest of Cretaceous marsupials; Pariadens mckennai, new species, tentatively assigned to Stagodontidae, is among the largest. The three are morphologically similar: they bear certain dental specializations of Marsupialia (e.g., presence of labial postcingulid and “twinning” of hypoconulid and entoconid on lower molars), but are plesiomorphic with respect to most or all Late Cretaceous marsupials in other features (e.g., relatively lingual position of conules, lack of stylar cusps C or D on upper molars). Compared to Late Cretaceous (Cenomanian– Maastrichtian) assemblages of North America, the marsupials of the Mussentuchit local fauna are rare and low in morphologic and taxonomic diversity. Biogeographic origin of Marsupialia and their antiquity in North America remain unknown. However, patterns of diversification and differentiation suggest that the taxa from the Cedar Mountain Formation lie near the base of North America's Cretaceous marsupial radiation.

The affinities of Roberthoffstetteria nationalgeographica (Marsupialia) and the origin of the polydolopine molar pattern

ABSTRACT A reanalysis of the upper and lower molar morphology of the early Paleocene marsupial Roberthoffstetteria nationalgeographica led to an interpretation of the molar homologies of the Polydolopinae (Polydolopimorphia). Several derived features support the attribution of Roberthoffstetteria to the Polydolopimorphia: thick dentary, molars with thick enamel, upper molars with reduced preparacrista that points to stylar cusp A, open centrocrista (that is, postparacrista not connected to the premetacrista), and metaconule large to very large, forming a “hypocone.” Other derived features support the monophyly of Roberthoffstetteria + polydolopines: alignment of paraconule, protocone, and metaconule in a lingual row; well-expanded anterior and posterior cingula, which are level with the trigon basin; variable occurrence of accessory cuspules at the labial face of the upper molars; and the labially placed paraconid with respect to the metaconid in the lower molars. Both Roberthoffstetteria and the polydolopines are plesiomorphic in having stylar cusp E, which is absent in most other South American marsupials. Several character complexes may be involved in the evolution of the polydolopine molar pattern.

Monotremes as Pretribosphenic Mammals

An abundance of evidence points to the conclusion that monotremes are phyletically allied with pretribosphenic, rather than with tribosphenic, mammals. Monotremes do not have a tribosphenic dentition. Character analyses that apply tribosphenic cusp terminology to monotreme dentitions are implicitly limited thereby. A review of the molar dentition of living and fossil monotremes suggests that upper molars are composed of a strongly developed pretribosphenic paracone and metacone and a series of stylar cusps attached to them in a bicrescentic, or dilambdodont, fashion. The lower molars are composed of a trigonid, with a pretribosphenic protoconid, paraconid, and metaconid, and distal metacristid. The paraconid of m1 is reduced or lost. The talonid is composed of the pretribosphenic hypoconid, hypoconulid, and cristid obliqua. There is no evidence for a tribosphenic entoconid, nor for a talonid basin. There was no tribosphenic protocone. Monotremes are not related to other taxa included in Australosphenida. The dentition of Cretaceous taxa, such as Teinolophos and Steropodon, apparently still functioned by orthal mechanisms, whereas by the “medial” Paleocene (Monotrematum) and later (Obdurodon), monotremes appear to have accommodated a diet of soft-bodied organisms that left little trace of a mastication regime that had changed to apical wear via propalinal motion. Monotremes appear to be modern representatives of a Mesozoic radiation of pretribosphenic mammals centered largely in Gondwana, where they still reside today.

New stem-lineage representatives of Zatheria (Mammalia) from the Late Jurassic of Portugal

ABSTRACT Nanolestes drescherae, new genus and species, a stem-lineage representative of Zatheria, is represented by 48 isolated teeth, a dentary with p2 only, and an anterior dentary fragment with p3–p5 from the Kimmeridgian of the Guimarota coal mine, Portugal. Lower molars of N. drescherae have an enlarged, unicuspid talonid and a small additional cuspule on the cristid obliqua not referable to any of the standard talonid cusps. No trace of an incipient talonid basin is present. Tooth formula is I?/4, C?/1, P?/5, M?/5; all lower teeth except for incisors and m5 are double-rooted. The dentary has a well developed angular process, an internal groove extending beyond m3, and a mandibular foramen in an anterior position. Upper molars have a comparatively large stylocone; cusp “C” is present, stylar cusps are well developed, and additional cusps on the paracrista are present. The former attribution of these specimens to the peramurids cannot be corroborated. The “Porto Pinheiro Molar” from the latest Jurassic/earliest Cretaceous of Porto Pinheiro (or Dinheiro) is referred to Nanolestes as N. krusati, new species. There are no autapomorphies for Arguimuridae Dashzeveg, 1994. The teeth preserved in the holotype of Arguitherium cromptoni Daszheveg, 1994 are p3–p5 and not p4–m1 as assumed in the original description. The teeth described as upper molars of the symmetrodont Thereuodon Sigogneau-Russell, 1989 are posterior upper deciduous premolars (DP?3–5) of holotherians (probably zatherians).

A new basal “didelphoid” (Marsupialia, Mammalia) from the Early Paleocene of Tiupampa (Bolivia)

ABSTRACT Szalinia gracilis, gen. et sp. nov. is a new “didelphoid” marsupial from the early Paleocene beds of the Santa Lucía Formation at Tiupampa (Bolivia). It is characterized by a short rostrum and a strong anteroposterior compression of the molars. Stylar cusp C is small and stylar cusp A is very large, strongly projecting anteriorly. Like most of the other marsupial genera from Tiupampa, S. gracilis presents greater similarities with other South American “didelphoids” (e.g., lncadelphys, Tiulordia, Marmosopsis, Derorhynchus, Carolopaulacoutoia) than with any of the North American basal marsupials (Kokopellia, Aenigmadelphys, Anchistodelphys, Iqualadelphys, and the Alphadon group). Szalinia is, in many respects, more plesiomorphic than the “didelphoids” from Itaboraí (late Paleocene) and is part of a basal stock for the South American “didelphoids.” Szalinia appears to be morphologically intermediate between basal North American taxa (e.g., Kokopellia, Aenigmadelphys, Anchistodelphys, Iqualadelphys) and the later “didelphoids” of South America. This is consistent with a North American origin of the South American “didelphoids.” Limited available data on Late Cretaceous and early Paleocene South American tribosphenic mammals suggests that their dispersal from North America was complex and may have involved several distinct events. The fact that Szalinia and structurally similar taxa from Tiupampa form a diverse assemblage that already possesses some apomorphies of South American “didelphoids” suggests that they arrived before the “condylarths” and pantodonts also present at Tiupampa.

DURUDAWIRINES, A NEW GROUP OF PHALANGEROID MARSUPIALS FROM THE MIOCENE OF RIVERSLEIGH, NORTHWESTERN QUEENSLAND

Abstract The early Miocene Durudawiri inusitatus new genus and species (Marsupialia: Phalangeroidea) is described from the Riversleigh World Heritage Property in northwestern Queensland. It appears to represent the plesiomorphic sister group of the late Oligocene species of Miralina from South Australia. Its molar morphology is not as complex as that of species of Miralina or ektopodontids, but it is more complex than that of phalangerids. The degree of morphological difference between species of Durudawiri and Miralina suggests subfamilial distinction for the two groups. Strange cusps on the upper molars could be interpreted as either large neometaconules and paraconules, or lingually-displaced metacones and paracones with very large stylar cusps on the buccal shelf.

Durudawirines, a new group of phalangeroid marsupials from the Miocene of Riversleigh, northwestern Queensland

The early Miocene Durudawiri inusitatus new genus and species (Marsupialia: Phalangeroidea) is described from the Riversleigh World Heritage Property in northwestern Queensland. It appears to represent the plesiomorphic sister group of the late Oligocene species of Miralina from South Australia. Its molar morphology is not as complex as that of species of Miralina or ektopodontids, but it is more complex than that of phalangerids. The degree of morphological difference between species of Durudawiri and Miralina suggests subfamilial distinction for the two groups. Strange cusps on the upper molars could be interpreted as either large neometaconules and paraconules, or lingually-displaced metacones and paracones with very large stylar cusps on the buccal shelf.

A new genus and species of dasyurid from the Pliocene Chinchilla Local Fauna of south-eastern Queensland

A new genus and species of dasyurid is described on the basis of P3, M1–M3 and M2–3 collected from the middle Pliocene Chinchilla Local Fauna of south-eastern Queensland. Character analysis supports the placement of this new taxon within the dasyurid subfamily Dasyurinae. Derived dasyuromorphian features common to A. chinchillaensis and most dasyurines include: reduction of P3, reduction of stylar cusp B on M1; reduction of metaconids; approximation of stylar cusp B and the metacone on M1; alignment of the postmetacrista on M1 with the long axis of the maxilla and an oblique orientation of the hypocristids with respect to the long axis of the teeth. However in most instances, A. chinchillaensis is less specialised than other members of the subfamily for characters considered. One derived dental feature, reduction of the entoconid, may indicate a special relationship with ‘parantechinines’, Dasyuroides and/or Dasycercus. Additionally, the presence of this feature is suggestive of an open woodland/seasonal habitat. Autapomorphic P3 morphology compounds difficulties with the phylogenetic placement of this taxon.

Dentition and Jaw of Kokopellia juddi , a Primitive Marsupial or Near-Marsupial from the Medial Cretaceous of Utah

We add to the knowledge of the dentition and lower jaw of the primitive marsupial or near marsupial, Kokopellia juddi, based on newly collected materials from the medial Cretaceous (Albian–Cenomanian) of central Utah. The dental formula, i4 c1 p3 m4, is primitive for (or with respect to) Marsupialia, as are a number of features of the dentary and dentition: presence of a labial mandibular foramen, ?an inflected angle, ?and a trace of the meckelian groove; lack of “staggering” of the lower incisor series; lack of “twinning” between entoconid and hypoconulid on lower molars; incompletely lingual position of lower molar paraconid; upper molar protocone relatively small and mesiodistally narrow; and conules placed about halfway between the protocone and the paracone–metacone. Other than the stylocone, cusps are lacking from the stylar shelf; we argue that this represents the primitive marsupial condition based on the economy of character change and the stratigraphic record of marsupials in the Cretaceous of North America. Recent discoveries of early marsupials, eutherians, and therians of metatherian–eutherian grade provide data indicating that some derived features of the dentary and dentition (e.g., loss of coronoid, meckelian groove, and labial mandibular foramen; acquisition of strong, “winged” conules, double rank postvallum/prevallid shearing, and stylar cusp D) probably arose independently, in some cases more than once, among the major groups of tribosphenic mammals. In turn, this suggests that a common ancestor for marsupials and placentals was more primitive than has generally been appreciated.

A Reexamination of Proposed Morphology-Based Synapomorphies for the Families of Dasyuromorphia (Marsupialia). I. Dasyuridae

The validity of eight morphological features previously advanced as synapomorphic for Dasyuridae is investigated in the light of new fossil and molecular data. Results indicate that one of these features (alisphenoid–periotic enclosure of the foramen ovale) is common to outgroups for Dasyuromorphia. Another feature (loss of intestinal cecum) is a likely synapomorphy for Dasyuromorphia. Two features (development of a hypoconulid notch, enlargement of stylar cusp D) may represent shared–derived characters within Dasyuromorphia but not at the family level for Dasyuridae (i.e., probably unite Dasyuridae–Thylacinidae). Another two features (loss of posterolateral palatine foramina, reduction of P3) are also apomorphic within Dasyuromorphia but unite specialized clades within Dasyuridae. Only two previously treated features are probable synapomorphies for the family (enlargement of the alisphenoid tympanic wing and development of a distinct periotic hypotympanic sinus). An additional feature is identified as a dasyurid synapomorphy (presence of a distinct tubal foramen). Of all putative synapomorphies proposed to date, only the presence of a periotic hypotympanic sinus and tubal foramen are unique for Dasyuridae among dasyuromorphians. Results suggest considerable homoplasy for basicranial features within Dasyuromorphia. Independent acquisition for alisphenoid enclosure of the foramen ovale, development of secondary foramina ovale and loss of posterolateral palatal foramina has occurred in derived thylacinid and dasyurid clades. Convergence is also indicated for hypertrophy of the alisphenoid tympanic wing shown for dasyurids and myrmecobiids, and the development of a squamosal epitympanic sinus in Thylacinidae, Dasyuridae, and Myrmecobiidae. The finding of plesiomorphy for alisphenoid–periotic enclosure of the foramen ovale within Dasyuromorphia undermines the strongest morphology-based synapomorphy uniting a monophyletic Dasyuridae–Myrmecobiidae. Phylogenetic placement for some plesiomorphic fossil dasyuromorphians, known only from dental material, within Dasyuridae is currently untenable, with no dental synapomorphies uniting the family. The value of identifying morphoclines within clades known from robust phylogenetic data for consideration in character analysis is stressed, as is the importance of form–function and ontogenetic data.

The marsupials of the Lac Pelletier lower fauna, Middle Eocene (Duchesnean) of Saskatchewan

ABSTRACT Four species of marsupials occur in the Lac Pelletier Lower Fauna (Duchesnean), Cypress Hills Formation, Saskatchewan. Herpetotherium sp., cf. H. marsupium from Lac Pelletier is intermediate in size and stylar cusp morphology between Uintan H. marsupium and Chadronian H. valens. Herpetotherium sp., cf. H. knighti from this assemblage shows smaller and less transverse upper molars than in H. knighti from the Uintan. Copedelphys sp., cf. C. innominata from Lac Pelletier is smaller than in Uintan samples, and is also smaller, with a smaller stylar cusp D, than Copedelphys titanelix of the Chadronian. Peradectes californicus is the only peradectid recognized in the Lac Pelletier Lower Fauna. The marsupial assemblage from the Lac Pelletier Lower Fauna is transitional in nature between Uintan and Chadronian faunas. Evidence from this fauna indicates that the genera Herpetotherium and Copedelphys, previously recognized from Chadronian and later assemblages, include Duchesnean and earlier species.

New marsupial from the Fort Union Formation, Swain Quarry, Wyoming

Previously described upper and lower molars from the Fort Union Formation (Swain Quarry, Wyoming) are referred to Swaindelphys cifellii new genus and species. This taxon is assigned to the subfamily Herpetotheriinae, family Didelphidae. These molars were originally referred to a new, unnamed species of Peradectes (subfamily Peradectinae), with similarities to P. pusillus (now Thylacodon pusillus) and P. elegans. However, upper molars differ from these taxa in being dilambdodont, in possessing more strongly developed stylar cusps, especially on M2 and M3, and in having a protocone that is shifted anteriorly. These characters suggest similarity to taxa such as Peratherium (subfamily Herpetotheriinae, family Didelphidae), rather than Peradectes. The assignment of the lower molars from Swain Quarry is more problematic: these molars are similar to the holotype Thylacodon pusillus in that the entoconid and hypoconulid separated by a strong notch; however, the Swain Quarry lower molars differ in being smaller overall and possessing an anteroposteriorly shorter talonid. These lower molars are similar to didelphid lower molars in having a hypoconulid that is lower than the entoconid (these are subequal in height on lower molars of Peradectes), but differ from didelphid lower molars in that the hypoconulid does not form a low, posteriorly projecting shelf. Nevertheless, the upper and lower molars from Swain Quarry are considered to belong to a single taxon, and with the assignment of the Swain Quarry materials to the subfamily Herpetotheriinae, the geological range of this subfamily is extended from the early Eocene back into the middle Paleocene (Torrejonian, or To3).

Herpetotherium valens(Lambe), a didelphid marsupial from the Calf Creek local fauna (Chadronian), Saskatchewan

ABSTRACT Herpetotherium valens (Lambe, 1908) is the only species of Herpetotherium represented in the Calf Creek local fauna (Chadronian), Cypress Hills Formation of Saskatchewan. The species is unusually variable in size and morphology; on M1-2, stylar cusps A and C disappear with wear. On M3 stylar cusp C is present but not cusp D. Stylar cusp E is seen only as a ridge on some M3s. Previous speculations that two species of Herpetotherium might be present in the Calf Creek sample are unfounded: dental measurements are normally distributed, and morphological characters show continuous distribution. Other Calf Creek marsupials are much smaller forms, with a few specimens representing the didelphid Copedelphys titanelix and the peradectid Didelphidectes pumilus.

Early Cretaceous mammal from North America and the evolution of marsupial dental characters.

A mammal from the Early Cretaceous of the western United States, represented by a lower jaw exceptional in its completeness, presents unambiguous evidence of postcanine dental formula in an Early Cretaceous marsupial-like mammal, and prompts a reconsideration of the early evolution of marsupial dental characters. A marsupial postcanine dental formula (three premolars and four molars) and several marsupial-like features of the lower molars are present in the new taxon, but a hallmark specialization of marsupials (twinning of the hypoconulid and entoconid on lower molars) is lacking. This, coupled with recent evidence from the Late Cretaceous of the western United States, suggests that the distinctive marsupial dental formula evolved prior to the most characteristic specialization of lower molars and that apomorphies presumed to be diagnostic of the upper molars (such as auxiliary stylar cusps) were relatively more recent developments in marsupial history. Dental evidence supports the monophyly of higher (tribosphenic) mammals and suggests that the predominantly Old World Deltatheroida, recently proposed as a sister taxon to marsupials, represents a primitive and unrelated group of higher mammals; by this interpretation, early marsupials and their presumed close relatives are restricted to North America. This, together with the hypothesized relationships of South American/Australian marsupials (in the context of the North American Cretaceous radiation) and evidence from the fossil record of South America, in turn supports a North American origin for the group.

Therian mammals from the Cenomanian (Upper Cretaceous) Dakota Formation, southwestern Utah

ABSTRACT A diverse therian fauna is present in the Dakota Formation of Cenomanian age. Two pediomyid-like taxa are described on the basis of upper molars, but may be deciduous molars of nonpediomyid taxa. A new genus and species of marsupial-like tribothere is described and named (Dakotadens morrowi). A new family of marsupials (Alphadontidae) is established for Alphadon-like genera. The range of Alphadon is extended back into the Cenomanian, two new species are named (A. clemensi, A. lillegraveni), and a possible third new species is described. The range of Protalphadon is also extended back into the Cenomanian. Possible upper molars of Pariadens kirklandi are described and the diagnosis of the genus is revised based on unsheared lower molars; placement of this taxon in the Stagodontidae remains problematic. Upper molars of all therians recovered from the Dakota Formation have relatively broad stylar shelves; collectively, they include a wide range of stylar cusp configurations, although a cusp or cusps ...