Richard C. Fox

Osseous inner ear structures and hearing in early marsupials and placentals

Based on the internal anatomy of petrosal bones as shown in radiographs and scanning electron microscopy, the inner ear structures of Late Cretaceous marsupials and placentals (about 65 Myr ago) from the Bug Creek Anthills locality of Montana, USA, are described. The inner ears of Late Cretaceous marsupials and placentals are similar to each other in having the following tribosphenic therian synapomorphies: a fully coiled cochlea, primary and secondary osseous spiral laminae, the perilymphatic recess merging with the scala tympani of the cochlea, an aqueductus cochleae, a true fenestra cochleae, a radial pattern of the cochlear nerve and an elongate basilar membrane extending to the region between the fenestra vestibuli and fenestra cochleae. The inner ear structures of living therians differ from those of their Late Cretaceous relatives mainly in having a greater number of spiral turns of the cochlea and a longer basilar membrane. Functionally, a coiled cochlea not only permits the development of an elongate basilar membrane within a restricted space in the skull but also allows a centralized nerve system to innervate the elongate basilar membrane. Qualitative and quantitative analyses show that, with a typical therian inner ear, Late Cretaceous marsupials and placentals were probably capable of high-frequency hearing.

New primitive carnivorans (Mammalia) from the Paleocene of western Canada, and their bearing on relationships of the order

ABSTRACT The earliest Carnivora are known from two families, the Miacidae, which retain M3/m3 and occur first in latest Paleocene (Clarkforkian) rocks, and the Viverravidae, which have lost M3/m3, but are known first in the middle Paleocene (Torrejonian). This paper describes two new genera and species of carnivorans, one (Pristinictis connata) a viverravid and the other (Ravenictis krausei) of uncertain familial affinities, from the early Tiffanian of Alberta and early Puercan of Saskatchewan, respectively; both have a molar structure more primitive than previously known for the order. The new carnivorans allow a reassessment of character state polarities in the early evolution of the Carnivora, thereby providing the opportunity for reexamination of the relationships of carnivorans to other eutherian orders. As a consequence of this study, it appears that carnivorans and creodonts share no uniquely derived character states of the dentition that might indicate they are sister-groups, and that carnivorans ...

New specimens of Elphidotarsius russelli (Mammalia, ?Primates, Carpolestidae) and a revision of Plesiadapoid relationships

Abstract Significant new material of the plesiadapiform Elphidotarsius russelli is described from Montana and Alberta. Previously the most poorly documented carpolestid, this species is now known from numerous isolated teeth and many jaw fragments. New material from the Crazy Mountains Basin, Montana substantially extends its known geographic range and shows that E. russelli is the most derived species of Elphidotarsius, with many features that foreshadow characteristics of Carpodaptes; consequently, emending the diagnosis of Elphidotarsius has been necessary. A phylogenetic analysis based on 73 characters scored for all species of Elphidotarsius, Pronothodectes, and Saxonella, as well as Purgatorius unio, Purgatorius janisae, Pandemonium dis, Chronolestes simul, and Carpodaptes hazelae, indicates that Elphidotarsius is a paraphyletic stem taxon at the base of Carpolestidae. Numerous crossing synapomorphies among these taxa show that a single anagenetic lineage can no longer represent the evolution of early carpolestids. This analysis also clarifies basal plesiadapoid relationships. Carpolestidae is the sister taxon to Plesiadapidae, and Saxonellidae is sister group to the carpolestid/plesiadapid clade. Contrary to previous hypotheses, Chronolestes and Pandemonium are found to lie outside of a clade including the other members of Carpolestidae, Saxonellidae, and Plesiadapidae, implying that they are basal plesiadapoids that diverged before the evolution of the common ancestor to the three main plesiadapoid families.

Therian Petrosals From the Oldman and Milk River Formations (Late Cretaceous), Alberta, Canada

ABSTRACT Therian petrosals from the Milk River and Oldman formations of Alberta are described. The Milk River specimen is the earliest known ear structure of a therian from North America and has a cochlea with one and a quarter turns. Two of the Oldman specimens are from marsupials, probably Eodelphis. These specimens provide significant new evidence about the earliest known otic structures in marsupials, including: absence of the promontory and stapedial grooves on the promontorium, presence of a prominent rostral tympanic process of the petrosal, achievement of a fully coiled cochlear canal, and development of the radial innervation system of the cochlea. Implications of the new findings are: 1) absence of the stapedial artery is consistently distributed in marsupials; 2) the rostral tympanic process of the petrosal has evolved more than once in marsupials; 3) a fully coiled cochlear canal had evolved in the therian ear by the Late Cretaceous; 4) a radial innervation complex of the cochlea evolved along...

A new spalacotheriid symmetrodont from the Early Cretaceous of northeastern China

Abstract Symmetrodonts are Mesozoic mammals having lower molars with nearly symmetrical trigonids but lacking talonids. They appear to be stem members of the mammalian clade that led to extant tribosphenic mammals, but the fossil record of symmetrodonts is poor. Here we report a new genus and species of an acute-angled spalacotheriid symmetrodont, Heishanlestes changi, n.gen. and n.sp., represented by well-preserved lower jaws with teeth from the Early Cretaceous of northeastern China. The new mammal has four tightly spaced premolars and three morphological groups of lower molars, in which the first molar has an obtuse trigonid angle and the last two molars have a large neomorphic cusp in the center of the trigonid, a feature not seen in other mammals. Heishanlestes appears to be a specialized member of the spalacotheriid subfamily, Spalacolestinae, which is otherwise only known from North America. The animal probably used the premolars to crush its prey before shearing it with the molars.

WINDOWS ON THE EVOLUTION OF PICRODUS (PLESIADAPIFORMES: PRIMATES): MORPHOLOGY AND RELATIONSHIPS OF A SPECIES COMPLEX FROM THE PALEOCENE OF ALBERTA

Abstract Since 1908, the peculiar North American primate Picrodus Douglass, 1908 (Picrodontidae; Plesiadapiformes) has been thought to contain only a single species, P. silberlingi Douglass, 1908, of late Paleocene age. However, new collections from the Paskapoo Formation, Alberta, Canada, reveal that instead a rich complex of Picrodus species lived during the Paleocene. Three of these, Picrodus calgariensis, P. canpacius, and P. lepidus, are described herein as new. Others, represented by more fragmentary specimens from Canada and the United States, are included in this paper, but are not named. P. calgariensis, from Who Nose? (late Torrejonian), Calgary, is the most primitive known species of Picrodus, having molars with little crenulation of the enamel. P. canpacius, from Cochrane 2 (earliest Tiffanian), northwest of Calgary, most resembles P. silberlingi sensu stricto, but differs in P4 structure, denser enamel crenulation, and weaker molar cusps. P. lepidus, from DW-2 (middle Tiffanian), near Red Deer, is the most advanced, having, for example, a two-rooted P4, tiny p3, and single-rooted p4. At least two of these species also occur in the United States, documented by fossils referred to P. silberlingi by previous workers. Dental evolution within Picrodus seems marked by several trends, including increase in size of i1, simplification of P4, reduction of molar cusps and crests, enlargement of the horizontal occlusal surfaces of the molars, and greater crenulation of enamel. From present knowledge, Zanycteris paleocenus Matthew, 1917 is dentally more primitive than Picrodus, Draconodus Tomida, 1982 is a valid genus, and picrodontids probably originated from “purgatoriid-grade” plesiadapiforms in earliest Paleocene time.

Saxonella (Plesiadapiformes: ?Primates) in North America: S. naylori, sp. nov., from the late Paleocene of Alberta, Canada

ABSTRACT Saxonella Russell is a small plesiadapiform described in 1964 from incomplete dental and jaw remains occurring in Paleocene fissure fills at Walbeck, Germany. The first North American discovery of Saxonella was reported in 1984, based on an incomplete dentary with teeth from the late Paleocene Paskapoo Formation, Alberta, nearly 10,000 km from the Walbeck site; since then, several additional Paskapoo specimens have been collected. The Canadian fossils represent a new species evidently more primitive than the Walbeck S. crepaturae. In the new species, both p3 and p4 are bladelike teeth (p3 is the larger), in contrast with S. crepaturae, in which p4 is smaller relative to p3 and its crown rounded. The new fossils include three incomplete maxillaries that together preserve P2–4, M1–3; these are the only articulated upper dentitions of Saxonella now known. A long diastema separates P2, which is small and peg-like, from the next more anterior tooth, which is undiscovered. P3 is the largest cheek-tooth...

New craniodental material of Pronothodectes gaoi Fox (Mammalia, “Plesiadapiformes”) and relationships among members of Plesiadapidae

Plesiadapidae are a family of Paleogene mammals thought to have phylogenetic affinities with modern Primates. We describe previously unpublished dentitions and the first skull and isolated petrosals of the plesiadapid Pronothodectes gaoi, collected from middle Tiffanian localities of the Paskapoo Formation in Alberta. Other species of Pronothodectes, traditionally considered the most basal members of the Plesiadapidae, occur at earlier, Torrejonian horizons in Montana, Wyoming, and Alberta. Classification of P. gaoi as a species of Pronothodectes has proved controversial; accordingly, we use the newly available samples and the more extensively preserved specimens to re-evaluate the generic affinities of this species. Included in our study are comparisons with craniodental material known for other plesiadapids and plesiadapiforms. Cladistic analysis of craniodental characters is used to assess the hypothesis that P. gaoi and other species in this genus are basal members of the Plesiadapidae. The new dental evidence confirms that P. gaoi lacks derived character states of other plesiadapids except for a variably present fissuring of the m3 hypoconulid. Moreover, several aspects of the cranium seem to be more primitive in P. gaoi (i.e., more like nonplesiadapid plesiadapiforms) than in later occurring plesiadapids, such as Plesiadapis tricuspidens and Plesiadapis cookei. Cladistic analysis of craniodental morphology supports a basal position of P. gaoi among species of Plesiadapidae, with the exception of other species of Pronothodectes. The basicranium of P. gaoi preserves a laterally placed bony canal for the internal carotid neurovascular system, suggesting that this was the ancestral condition for the family.

The primitive dental formula of the Carpolestidae (Plesiadapiformes, Mammalia) and its phylogenetic implications

ABSTRACT New evidence from Elphidotarsius and Carpodaptes indicates that the primitive dental formula for Carpolestidae is I3/3, Cl/1, P4/3, M3/3, not I2/2, Cl/1, P3/3, M3/3, the formula long thought to be primitive for carpolestids and all other plesiadapiforms except Purgatorius; the revised formula differs from that of primitive Tertiary eutherians generally only in the loss of p1. Hence, if Carpolestidae and Plesiadapidae are sister groups, as has traditionally been believed, primitive carpolestids are more primitive than known plesiadapids in the number of incisors and retention of two upper teeth (C and P1) between I3 and P2. Nothing of the dentition or other known parts of the anatomy supports the recent suggestion that carpolestids are dermopterans.

THE DENTITION AND RELATIONSHIPS OF CARPODAPTES CYGNEUS (RUSSELL) (CARPOLESTIDAE, PLESIADAPIFORMES, MAMMALIA), FROM THE LATE PALEOCENE OF ALBERTA, CANADA

Abstract Re-examination of the dentitions of carpolestid plesiadapiform mammals from the late Paleocene Swan Hills locality, northern Alberta, and correlative localities in the vicinity of Roche Percée, southeastern Saskatchewan, Canada, indicates that Carpodaptes cygneus (Russell) as known from these sites is polyphyletic: the name C. cygneus is here restricted to the Swan Hills carpolestid, while the Roche Percée form represents a new, more derived species, Carpodaptes stonleyi. Other purported records of C. cygneus are reconsidered as well: C. cygneus from DW-1, central Alberta, is more appropriately dubbed C. cf. cygneus; C. cygneus at Canyon Ski Quarry, central Alberta, is best identified as C. cf. stonleyi, while C. cf. cygneus from Police Point, southeastern Alberta, has closest affinities to C. hazelae Simpson. Carpolestids from the Tongue River Formation, North Dakota, are referred to Carpodaptes cf. hobackensis Dorr and C. cf. hazelae. After a review of the available evidence, the recent hypothesis that C. cygneus and other North American carpolestids are congeneric with Carpocristes oriens Beard and Wang from the Paleocene or Eocene of China, is rejected.