Synopsis of Mesozoic Mammal Evolution

AFTER MAMMALS EMERGED FROM CYNODONTS, they coexisted with dinosaurs for about 150 million years during the Mesozoic. The Mesozoic radiation of mammals consisted largely of groups that became extinct by the end of that era, without direct descendants but some of them have been identified as structural, if not actual, stages in the evolution of the therian mammals prevalent today. Therefore a review of mammalian evolution during the Mesozoic will help to place Early Cenozoic mammals in...

Multituberculata

First Mammals Mesozoic

Multituberculates were the longest-lived order of mammals except for monotremes, recorded with certainty from Upper Jurassic through upper Eocene sediments, a time-span of more than 100 million years (from about 155 to 40 Ma). They have no living descendants. Isolated upper second molars from the Middle Jurassic (Bathonian) of England, assigned to the new genera Kermackodon and Hahnotherium, have recently been identified as multituberculate based on wear and inferred occlusal relationships...

Paleoceneeocene Climate And Flora

The world of the Paleocene and Eocene was very different from that of today. It was much warmer and more equable during most of that interval than at any other time during the Cenozoic Wing and Greenwood, 1993 . Temperatures varied little seasonally or latitudinally, mid-latitudes were largely frost-free, and there were no polar ice caps. Conditions were generally wet or humid. A paleotemperature curve reconstructed from deep-sea oxygen isotope records Zachos et al., 2001 shows that early...

European Land Mammal Ages

As mentioned earlier, standard ages are more widely used for biochronology of European faunas than are the European Land-Mammal Ages ELMAs , and are therefore used in this text. This preference for the former may have come about because the ELMAs are for the most part equivalent in time to the standard ages Dano-Montian Danian Cernaysian Selandian and Thanetian Neustrian most of the Ypresian Rhenanian the rest of the Ypre-sian through the Bartonian and Headonian Priabonian McKenna and Bell,...

Timing Of The Crowntherian Radiation

The question of when the therian radiation took place is a contentious issue, whose answer depends on the kind of data employed paleontological morphological or molecular. There are three principal models of the timing of origin and diversification of placental mammals Archibald and Deutschman, 2001 , which also apply generally to the therian radiation Fig. 1.2 1. The explosive model, in which mammalian orders both originated and diversified in a short period of about 10 million years after the...

Historical Background

Polyphyletic View

Not so long ago, Mesozoic mammals were assigned to a relatively small number of higher taxa, whose relationships seemed more or less understood. According to this Table 4.1. Synoptic classification of Mesozoic mammals excluding Metatheria and Eutheria fAdelobasileus, fHadrocodium1 fSinoconodontidae fKuehneotheriidae Order fMORGANUCODONTA fMorganucodontidae fMegazostrodontidae Order fDOCODONTA Order fSHUOTHERIDIA Order fEUTRICONODONTA fAmphilestidae fTriconodontidae fAustrotriconodontidae Order...

Mammalian Skeletal Structure and Adaptations

THE MAMMALIAN SKELETON HAS BEEN evolving for more than 200 million years, since it originated from that of nonmammalian cynodonts, resulting in variations as different in size and adaptation as those of bats, moles, horses, elephants, and whales. Therefore, to assume that there is a living species that displays the typical mammalian skeleton would be naive and misleading. Nevertheless, all mammalian skeletons represent variations on a fundamental theme, and in terms of the addition or loss of...

Symmetrodonts

Symmetrodonts were small shrew- to mouse-sized animals, known mainly from teeth and jaw fragments. They are considered to lie at or near the base of the therian radiation because they are the first mammals to show a nearly symmetrical triangular arrangement of the three main cusps on the upper and lower molariform teeth. The pattern varies from obtuse angled in primitive and some derived types to acute angled in the most derived. The resulting reversed triangles of the upper and lower molars...

Apatotheria

Apatotheria

This small but highly distinctive group is known from the Paleocene and Eocene of Europe and North America a single rare genus, Sinclairella, survived into the Oligocene in North America. The half-dozen known genera are all included in the family Apatemyidae. Based on dental morphology, their relationships have been variously considered to lie with proteutherians, Plesiadapiformes, or Cimolesta, but none of these proposals has been convincingly demonstrated. Apatemyids were small to...

Docodonta

Although unknown before the Middle Jurassic, and therefore not among the oldest known mammals, docodonts are considered to be one of the most archaic mammalian groups. Their remains were first discovered more than a century ago in the Late Jurassic Morrison Formation of Wyoming and Colorado, where they are found together with the bones of giant sauropod dinosaurs. They have subsequently been discovered at several sites in Europe and Asia. A purported docodont Reigitherium has been reported from...

Asian Land Mammal Ages

The Asian Land-Mammal Ages ALMAs are the most recently named and the most tentative. Several schemes have been proposed over the past two decades or so. The sequence used here follows that of McKenna and Bell 1997 , which stems principally from Li and Ting 1983 and Russell and Zhai 1987 , although a few of the ages were initially named by Romer 1966 . Important modifications were made by Tong et al. 1995 and Ting 1998 . A comparison of these reports reveals that there is still no consensus...

Phylogeny and Classification

Phylogenetic Tree Elephantidae

Phylogenetic inferences ideally should be based on all available evidence, but practical considerations restrict most analyses. The majority of studies have been based on either morphological traits or molecular sequences, and usually on only a subset of those data partitions. For example, analyses of fossil taxa are necessarily limited to the anatomy of the hard parts, because soft anatomy and molecular data are not available. In addition, the outcome of phylogenetic analysis may vary...

Eocene Oligocene Boundary

The Eocene Oligocene boundary in Europe was long equated with a major episode of faunal turnover called the Grande Coupure Stehlin, 1909 Savage and Russell, 1983 Russell and Tobien, 1986 Legendre, 1987 Legendre et al., 1991 . In North America the Eocene Oligocene boundary was believed to correspond to the boundary between the Duchesnean and Chadronian Land-Mammal Ages Wood et al., 1941 . With the advent of high-precision 40Ar 39Ar dating and the correlation of the Eocene Oligocene boundary in...

North American Land Mammal Ages

The sequence of NALMAs initially proposed by Wood et al. 1941 has been widely applied and provides a useful and well-documented biochronology for mammals of North America. Excellent summaries of the NALMAs and their mammal assemblages are found in the two volumes edited by Woodburne 1987, 2004 . The NALMAs of interest in Fig. 1.7. opposite Early Cenozoic mammalian geochronology and biochronology Chart shows the time period emphasized in this book Paleocene-Eocene , approximate age in millions...

Paleocene Eocene Boundary

The Paleocene Eocene boundary is situated in the lower part of polarity chron C24r, but its precise position and age have been contentious. Dates range from about 54.8 Berg-gren et al., 1995b to 55.8 million years ago Gradstein et al., 2004 in various reports over the past decade or so, most centering around 55.0 million years ago. The debate here, as for the Eocene Oligocene boundary, stems partly from the difficulty of correlating mammal-bearing continental beds with discontiguous marine...

The Early Cenozoic Mammalian Radiation

The fossil record documents an extensive and rapid often described as explosive adaptive radiation of mammals during the first third of the Cenozoic, characterized by a dramatic increase in diversity of therian mammals soon after the mass extinctions at the end of the Cretaceous e.g., McKenna and Bell, 1997 Alroy, 1999 Novacek, 1999 Archibald and Deutschman, 2001 . Nearly all of the modern mammal orders, as well as many extinct orders, first appear in the fossil record during this interval Rose...

Cheek Bones Skull Mammal

Alisphenoids Bird

The human skull consists of 28 bones including the three middle-ear ossicles , most of which are very tightly articulated or fused together. This constitutes a reduction of the cranial arrangement characteristic of primitive mammals e.g., several elements fuse to form the human temporal or occipital bones . Nevertheless, mammals as a rule have fewer skull bones than do reptiles. There are several excellent general accounts of the anatomy of the mammalian skull e.g., Romer and Parsons, 1977...

Monophyly and Paraphyly

Just as synapomorphic features indicate common ancestry monophyletic origin , the extent and distinctiveness of synapomorphies reflect proximity of relationship. The term monophyletic was long used to indicate descent from a common ancestor, but following Hennig 1966 , mono-phyly now usually connotes not just single origin but also inclusion of all descendants from that ancestor holophyly of Ashlock, 1971 . Monophyletic groups or taxa are called clades. Groups believed to have evolved from more...

Carnivora

Viverravidae

Carnivorans have been the principal group of predaceous mammals throughout much of the Cenozoic, although in the Early Cenozoic creodonts were equally or more successful. Many extant carnivorans remain primarily meat eaters, but some lineages have evolved away from that regimen toward omnivory, frugivory, myrmecophagy, piscivory, and other specialized diets. Carnivorans occupy arboreal, scan-sorial, cursorial, and fossorial niches on land and have also invaded both freshwater and marine...

Leptictida

Homo Erectus With Condyloid Process

Leptictida is an ordinal-level group that accommodates the Early Tertiary Leptictidae and the closely allied Late Cretaceous Gypsonictops Novacek, 1986a . McKenna and Bell 1997 included two additional families in their superorder Leptictida Kulbeckiidae now considered a junior synonym of Zalambdalestidae and Didymoconidae here tentatively included in Cimolesta . They also united Gypsonictops with a half-dozen other Cretaceous genera, including Proken- nalestes, Kennalestes, and Zhelestes, in...

Didelphodonta And Other Primitive Cimolesta

Hedgehog Dentition

The most plesiomorphic group of the Cimolesta, Didelphodonta as employed by McKenna and Bell, 1997 comprises the single family Cimolestidae, which is widely considered on dental criteria to include the ancestors or sister taxa of most or all of the other groups these authors assigned to Cimolesta. Didelphodonts also seem to be related to the early Tertiary families Palaeoryctidae and Wyolestidae, as well as to the origin of creodonts and carnivores. These inferred relationships are reflected by...

Metatheria

THE TERM METATHERIA IS USED to unite marsupials and their presumed extinct relatives, including the Deltatheroida and the Asiadelphia. Although generally overshadowed by placental mammals, marsupials persist today, and during the Cenozoic they underwent diverse radiations in South America and Australia, where they still predominate. The oldest known metatherians are from the Cretaceous. Deltatheroidans are a largely Asian clade restricted to the Cretaceous. They are generally considered to be...

South American Land Mammal Ages

The South American mammalian record is relatively incomplete, with discontinuities between all the Paleogene South American Land-Mammal Ages SALMAs . Nevertheless, a seemingly stable sequence of Cenozoic SALMAs of presumed age has been in use for decades. In the Paleogene, the following sequence has long been recognized Riochican late Paleocene , Casamayoran early Eocene , Mustersan middle Eocene , Divisaderan middle or late Eocene , and Deseadan early Oligocene Simpson, 1948 Patterson and...

Geochronology And Biochronology Of The Early Cenozoic

Superorden Afrotheria

The Paleocene and Eocene epochs make up the first 31 million years of the Tertiary Period of the Cenozoic Era from 65 Ma to 34 Ma Fig. 1.6 . The chronology of the Paleocene and Eocene used here Fig. 1.7 is based primarily on that of Berggren et al. 1995b and McKenna and Bell Table 1.2. Synoptic higher-level classification of Mammalia used in this book fAdelobasileus, fHadrocodium fSinoconodontidae fKuehneotheriidae Order fMORGANUCODONTA Order fDOCODONTA Order fSHUOTHERIDIA Order fEUTRICONODONTA...

Boreosphenida

Sinoconodon Fossil

Relationships of Mesozoic mammals. The current consensus places haramiyids including Haramiyavia and Multituberculata as sister taxa within Mammalia. Modified after Luo et al., 2002. Until these are found, Adelobasileus will remain a taxon of problematic relationships. Two other families that appeared in the Late Triassic Norian-Rhaetic , Haramiyidae and Theroteinidae, could be the oldest known mammals, but are also problematic. Both have been suggested to have possible affinities...

Wnn

Dentitions of South American Paleocene marsupials A Proto-didelphine Protodidelphis, right M1-4 B protodidelphine Guggenheimia, left PrM4 C didelphine Marmosopsis, right M1-2 D eobrasiliine Gaylordia, right P3-M4 E, F caenolestoid Carolopaulacoutoia, right upper and lower dentitions G, H microbiothere Mirandatherium, right upper and lower molars. A-D are didelphids. All scale bars 1 mm. From Marshall, 1987. zoic Paucituberculata and Sparassodonta. Both are believed to have originated...

Dentition

Marsupial Molar Nomenclature

Probably more than any other part of the skeleton, the dentition of fossil mammals plays a critical role in taxonomy, assessment of phylogenetic position, and interpretation of behavior primarily diet, but also such activities as grooming, gnawing, or even digging . In part, this reflects the durability of teeth enamel, the hard outer layer of most mammal teeth, is the hardest substance in the body , which accounts for why they are generally more common than other skeletal remains. But it is...

Didymoconidae

Didymoconids Fig. 7.5 are an enigmatic group of carnivorous Early Tertiary mammals probably endemic to Asia. The half dozen or so genera, most of which are known only from teeth and jaws, are characterized by loss of P1 and M3, and presence of simple premolars transverse tritubercular upper molars with connate paracone and metacone and a somewhat reduced stylar shelf, and usually lacking a hypo-cone or postcingulum and lower molars with tall trigonids and narrow talonids Gingerich, 1981b . The...

Mesozoic Mammals Of Uncertain Affinity

Pappotherium

A few Mesozoic mammals are so unusual that they cannot be placed with confidence in any of the established higher taxa, and their broader relationships remain uncertain. One Fig. 4.19. Tribothere teeth upper molars of A Pappotherium B Holocle-mensia. Left lower molars of C Pappotherium D Holoclemensia E Kermackia F Trinititherium. G Lower teeth of Slaughteria. C-G in crown and lingual views. From Butler, 1978. Fig. 4.19. Tribothere teeth upper molars of A Pappotherium B Holocle-mensia. Left...

Eutriconodonta

Multituberculates

Until recently, triconodonts were viewed as including three families Morganucodontidae then including Mega-zostrodontidae , Triconodontidae, and Amphilestidae Jenkins and Crompton, 1979 . A fourth family, Austrotricono-dontidae, was based on very fragmentary fossils from the Late Cretaceous of South America Bonaparte, 1994 . Two additional genera, Dinnetherium and Jeholodens, significant because of their excellent state of preservation, have proven difficult to accommodate within these four...

What Is A Mammal

Marsupial Pelvic Girdle

Living mammals are easily recognized by a suite of characteristics that distinguish them from all other vertebrates. Most obvious are an external covering of hair except in certain highly specialized types and nourishment of the young by milk produced in the mother's mammary glands. The heart has four chambers, allowing separation of blood flow to the lungs for reoxygenation from circulation to the rest of the body. There is a muscular diaphragm, related to increased oxygen consumption. Mammals...

Eutheria

Proposed relationships of the most primitive known eutherians. Simplified after Archibald et al., 2001, and Archibald, 2003. more primitive or more derived than others, permitting a first-order approximation of relationships among these primitive eutherians, which is shown in Figure 6.1. The terms Eutheria and Placentalia are sometimes used interchangeably, but there is a growing convention to restrict Placentalia to the last common ancestor of the extant orders and all its...

Paleogeographic Setting During The Beginning Of The Age Of Mammals

Paleogeographic Map Erectus

The evolution and dispersal of mammals during the early Cenozoic were strongly influenced by the positions of the continental plates, the connections among them, the amount and distribution of subaerial exposure, and the marine barriers separating or dividing continents. The salient aspects of paleogeography at that time summarized here are based primarily on McKenna 1972, 1975b, 1980a, 1983 and Smith et al. 1994 . At the end of the Cretaceous, a wide epicontinental sea extended between the...

E

Paranyctoides

Dentitions of primitive Cretaceous eutherians A Eomaia B Montanalestes C Daulestes D Kennalestes E Ukhaatherium. Key ap, angular process co, coronoid process dc, dentary condyle etd, entoconid hyd, hypoconid hyld, hypoconulid iof, infraorbital foramen med, metaconid mf, mandibular foramen mks, meckelian sulcus ms, masseteric fossa pad, paraconid prd, protoconid ptf, pterygoid fossa sym, symphysis. A from Ji et al., 2002 B from Cifelli, 1999 C from McKenna et al., 2000 D from...

Skeletal Adaptations

Hyracotherium

From small, probably terrestrial, carnivorous or insectivorous Mesozoic ancestors, mammals have diversified to occupy almost every major environment throughout the world. They have evolved a remarkable diversity of skeletal adaptations for life in the air, in trees, on land, under ground, and in water. Due in part to the versatile tribosphenic molar, mammalian dentitions have become modified for almost every conceivable diet, including leaves, grass, roots and tubers, seeds, fruits, sap,...

Pantolesta

This order includes several Paleogene families Pantolestidae, Pentacodontidae, Paroxyclaenidae, and Ptolemaiidae that appear to be related based on dental similarities Fig. 7.7 . Although the dentition in most forms retains the same generalized pattern seen in didelphodonts, most pantolestans are more derived in having lower-crowned molars with more rounded cusps uppers with a narrower stylar shelf and in pantolestids and pentaco-dontids a wide posterolingual cingulum, often bearing a distinct...

Postcranial Skeleton

Monotreme Skeleton

Although dental and cranial anatomy have generally received more attention in mammalian paleontology than has the postcranial skeleton, the skeleton is a critical source of information on body size, locomotion, habitat preference, and many other aspects of paleobiology. Postcranial characters are also playing an increasingly significant role in phy-logenetic analyses, as it becomes more accepted that these features are no more subject to homoplasy than are dental or cranial features...

Eutherian Mammals

EUTHERIA ARE DIFFERENTIATED FROM METATHERIA on the basis of reproductive anatomy and biology and the presence of a trophoblast during development an extra-embryonic layer that surrounds the inner cell mass of the embryo Novacek, 1986a Lillegraven et al., 1987 . Such a characterization, however, cannot be applied to fossils. Consequently, morphologists and paleontologists have sought reliable features of the hard tissues that can be used to recognize each group. As detailed in Chapter 5, there...

Tribosphenic Mammals

Tribosphenic Molar Mammal

Evolution of tribosphenic molars uppers with three principal cusps arranged in a triangle the trigon , the buc- cal paracone and metacone and a lingual protocone and lowers with a three-cusped triangular trigonid and a basined talonid for occlusion with the protocone see Fig. 2.2 was one of the most important anatomical innovations in mammalian history. It laid the stage for the great diversity in dentitions of therian mammals. Tribosphenic molars can grind as well as shear food. With this...

Primitive Marsupials

Pappotherium

From the late Early Cretaceous Albian, about 98 Ma of Utah comes another primitive metatherian, Kokopellia Fig. 5.6A , known from a well-preserved lower jaw Cifelli, 1993a Cifelli and Muizon, 1997 . It resembles marsupials in dental formula three premolars, four molars and various Fig. 5.5. Skeleton and right upper and lower postcanine dentition of the primitive metatherian Asiatherium. From Szalay and Trofimov, 1996. Fig. 5.5. Skeleton and right upper and lower postcanine dentition of the...

Tingamarra Tooth

Pictures Lateral Animal Skull View

Marshall 1980 suggested that caenolestoids evolved from didelphoid ancestors, which is consistent with the dentition of Carolopaulacoutoia Fig. 5.10E,F . Argyrolagids, best known from the Neogene, were highly specialized jerboa-like, bipedal marsupials with enormous orbits Simpson, 1970a . Were it not for possession of several diagnostic marsupial traits presence of four molars, a medially inflected mandibular angle, palatal vacuities, and an alisphenoid bulla...

Animal Skulls Identification

Auditory structure in carnivores. Elements forming the auditory bulla in left to right a bear arctoid , a dog cynoid , and a cat feloid . Top row shows ventral view of adult bulla, middle row shows ventral view of neonatal bulla. Bottom row shows isolated neonatal bulla in medial view, to reveal the rostral entotympanic, which is not exposed ventrally Key E, caudal entotympanic R, rostral entotympanic T, ectotympanic. From Hunt and Tedford, 1993. Fig. 8.9. Auditory structure in...

Pantodonta

Pantolambda Foot

The Pantodonta were a group of heavily built omnivorous and herbivorous mammals that were moderately common and diverse in the Northern Hemisphere during the Paleocene and Eocene. One genus is known from South America. About two dozen genera in 10 families are currently recognized McKenna and Bell, 1997 . Most of the families are restricted to the Paleocene and are known from either North America or Asia, but not both. Pantolambdo-dontidae and Coryphodontidae extended into the Eocene as well,...

Creodonta

Mustela Vison Mandible Anatomy

Also known as Pseudocreodi or archaic carnivores, creodonts are a group of extinct carnivorous mammals that thrived during the Eocene and Oligocene in North Fig. 8.1. A Relationships of creodonts and carnivorans. Alternatively, Amphicyonidae could be the most basal branch of Caniformia, and Pinnipedia could be the sister taxon of Musteloidea. Canidae constitute the Cynoidea. B Alternative view of basal carnivoran relationships. A based on Flynn and Wesley-Hunt, 2005 B modified from McKenna and...

The Evolutionary Transition To Mammals

Sinoconodon Skeletal Structure

The ancestors of mammals, Synapsida, diverged from basal amniotes protothyrid captorhinomorphs at least 300 million years ago, in the Pennsylvanian Period. As the oldest and most primitive amniotes, protothyrids were also ultimately ancestral to reptiles including lizards, snakes, and turtles and archosaurs crocodilians, dinosaurs, and birds . Synapsids include two successive radiations, the Pennsylvanian-Permian Pelycosauria, and the largely Permo-Triassic Therapsida see Carroll, 1988, for an...

Eupantotheres

Triconodont Tribosphenic

The eupantotheres Dryolestoidea and Peramura of McKenna and Bell, 1997 Figs. 4.15, 4.16 occupy a structural and phylogenetic position essentially between symmetro-donts, on the one hand, and aegialodonts therian mammals on the other. Among eupantotheres, dryolestoids dryolestids and paurodontids , amphitheriids, and pera-murans are successively more closely related to crown the-rians. This conclusion is founded on the anatomy of the teeth and jaws, which constitute almost all known fossils....

Taeniodonta

Taeniodont Hypsodont

The Taeniodonta from Greek roots meaning ribbon tooth, in allusion to the restricted band of enamel on the canines and cheek teeth of specialized forms constitute a small and peculiarly specialized order of mammals whose broader affinities appear to lie with Cimolesta. The bizarre morphology of specialized taeniodonts has long obscured their relationships, but the most primitive representatives are said to share tarsal and or dental traits with cimolestids and pantolestids Szalay, 1977 Schoch,...

Basal Metatherians

Pediomyidae

FHoloclemensia, f Sinodelphys Order fDELTATHEROIDA Order fASIADELPHIA Cohort MARSUPIALIA fKokopellia,1 flugomortiferum,1 fAnchistodelphys1 Magnorder AMERIDELPHIA Order DIDELPHIMORPHIA fPeradectidae2 Didelphidae fSparassocynidae Order DIDELPHIMORPHIA fPediomyidae2 fStagodontidae2 fProtodidelphinae Order PAUCITUBERCULATA Superfamily fCaroloameghinioidea fGlasbiidae fCaroloameghiniidae Superfamily Caenolestoidea fSternbergiidae Caenolestidae fPalaeothentidae fAbderitidae Superfamily...