Geochronology And Biochronology Of The Early Cenozoic

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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

Class MAMMALIA

fAdelobasileus, fHadrocodium fSinoconodontidae fKuehneotheriidae Order fMORGANUCODONTA Order fDOCODONTA Order fSHUOTHERIDIA Order fEUTRICONODONTA Order fGONDWANATHERIA Subclass AUSTRALOSPHENIDA

Order fAUSKTRIBOSPHENIDA Order MONOTREMATA1

Subclass fALLOTHERIA

Order fHARAMIYIDA Order fMULTITUBERCULATA Subclass TRECHNOTHERIA2

Superorder fSYMMETRODONTA Superorder fDRYOLESTOIDEA

Order fDRYOLESTIDA Order fAMPHITHERIIDA Superorder ZATHERIA

Order fPERAMURA Subclass BOREOSPHENIDA3

Order fAEGIALODONTIA Infraclass METATHERIA

Order fDELTATHEROIDA Order fASIADELPHIA Cohort MARSUPIALIA

Magnorder AMERIDELPHIA (American marsupials)

Order DIDELPHIMORPHA (opossums)

Order PAUCITUBERCULATA (rat opossums, polydolopids, argyrolagids, and kin) Order fSPARASSODONTA (borhyaenids) Magnorder AUSTRALIDELPHIA (Australian marsupials) Superorder MICROBIOTHERIA Superorder EOMETATHERIA

Order NOTORYCTEMORPHIA (marsupial moles) Grandorder DASYUROMORPHIA (marsupial mice and cats, numbats, Tasmanian wolf, Tasmanian devil) Grandorder SYNDACTYLI

Order PERAMELIA (bandicoots)

Order DIPROTODONTIA (kangaroos, phalangers, wombats, koalas, sugar gliders)

Infraclass EUTHERIA

fEomaia, fMontanalestes, fProkennalestes, fMurtoilestes Order fASIORYCTITHERIA Cohort PLACENTALIA (placental mammals) Order fBIBYMALAGASIA

Order XENARTHRA (edentates: armadillos, sloths, anteaters) Superorder INSECTIVORA

Order fLEPTICTIDA

Order LIPOTYPHLA (moles, shrews, hedgehogs, tenrecs, golden moles) Superorder fANAGALIDA4

fZalambdalestidae5 fAnagalidae fPseudictopidae Order MACROSCELIDEA (elephant shrews) Grandorder GLIRES

Mirorder DUPLICIDENTATA Order fMIMOTONIDA Order LAGOMORPHA (rabbits, hares, pikas) Mirorder SIMPLICIDENTATA fSinomylus Order fMIXODONTIA

Order RODENTIA (squirrels, beavers, rats, mice, gophers, porcupines, gerbils, guinea pigs, chinchillas, capybaras, etc.) Superorder FERAE4

Order fCREODONTA

Order CARNIVORA (carnivores: cats, dogs, bears, raccoons, hyenas, weasels, otters, badgers, civets, mongooses, seals, walruses)

continued

Table 1.2. Continued

Mirorder fCIMOLESTA6 fDidymoconidae fWyolestidae Order fDIDELPHODONTA Order fAPATOTHERIA (apatemyids) Order fTAENIODONTA Order fTILLODONTIA Order fPANTODONTA Order fPANTOLESTA

Order PHOLIDOTA (pangolins or scaly-anteaters) Superorder ARCHONTA

Order CHIROPTERA7 (bats) Grandorder EUARCHONTA

Order DERMOPTERA ("flying lemurs" or colugos) Order SCANDENTIA (tree shrews)

Order PRIMATES (plesiadapiforms, lemurs, lorises, tarsiers, monkeys, apes, humans) Superorder UNGULATOMORPHA8 fZhelestidae9

Grandorder UNGULATA8 (ungulates: hoofed mammals) Order fCONDYLARTHRA8 Order TUBULIDENTATA (aardvarks) Order fDINOCERATA (uintatheres) Order fARCTOSTYLOPIDA

Order ARTIODACTYLA (even-toed ungulates: pigs, hippos, camels, deer, giraffes, antelope, gazelles, sheep, goats, cattle, etc.) Mirorder CETE

Order fMESONYCHIA Order CETACEA10 (whales, dolphins) Mirorder fMERIDIUNGULATA8 (endemic South American ungulates) Order fLITOPTERNA Order fNOTOUNGULATA Order fASTRAPOTHERIA Order fXENUNGULATA Order fPYROTHERIA Mirorder ALTUNGULATA

Order PERISSODACTYLA (horses, tapirs, rhinos, fchalicotheres, ftitanotheres) Order PAENUNGULATA

Suborder HYRACOIDEA (hyraxes) Suborder TETHYTHERIA

Infraorder fEMBRITHOPODA Infraorder SIRENIA (sea cows, dugongs) Infraorder PROBOSCIDEA (elephants)

Notes: Classification is modified mainly after McKenna and Bell (1997) and Kielan-Jaworowska et al. (2004). This table and all others presented in this book represent a compromise between traditional and cladistic classifications and are an attempt to provide a consensus view. Ordinal-level and higher taxa are shown in upper case; unassigned taxa immediately below a higher taxon are either plesiomorphic or of uncertain phylogenetic position within that taxon. Many taxa are probably paraphyletic, but no attempt is made in the tables to differentiate them from those believed to be monophyletic; instead these distinctions are discussed in the text. The dagger (f) denotes extinct taxa.

1McKenna and Bell (1997) assigned monotremes to the subclass Prototheria and recognized two orders, Platypoda (platypuses) and Tachyglossa (echidnas).

2Trechnotheria is essentially equivalent to the concept of Holotheria.

3Essentially equivalent to Tribosphenida.

4Several taxa considered grandorders by McKenna and Bell (1997) are considered superorders here.

5 May be basal eutherians.

6 Monophyly of Cimolesta and interrelationships of its constituents are very uncertain.

7Relationship of Chiroptera to other archontans is in dispute.

8 Monophyly questionable.

9 Monophyly of Zhelestidae and their relationship to ungulates are controversial.

10 May be nested in Artiodactyla.

(1997), with modifications as indicated in the following discussion. Geologic periods and epochs may be subdivided into successive stages/ages (chronostratigraphic and geo-chronologic units) and, in the case of the Cenozoic epochs, land-mammal ages (a biochronologic unit). Land-mammal ages "describe the age and succession of events in mammalian evolution" based on characteristic mammal assem blages, lineage segments, or in some cases first or last appearances (Woodburne, 2004: xiv; see also Walsh, 1998, for an insightful discussion of the definition of land-mammal ages). Although absolute dates have been placed on many of these units using a combination of magnetostratigraphy and radiometric methods, such as high-precision 40Ar/39Ar dating (Berggren et al., 1995b; Gradstein et al., 1995, 2004),

Mammal Phylogeny Novacek
Fig. 1.4. Relationships of higher taxa of mammals based on morphology Thicker lines indicate documented geologic ranges. (From Wible et al., 2005, based on Novacek, 1999.)

precise dating of some intervals remains tenuous and in some cases controversial.

Geologic time applies worldwide, whereas land-mammal ages are specific to each continent and are relatively well constrained geochronologically only in North America and Europe. Nevertheless, their sequence is reasonably well understood, as is the correlation between North American Land-Mammal Ages (NALMAs) and standard stages/ages (more widely used in Europe than land-mammal ages). For this reason, land-mammal ages and their subdivisions (or stages/ages, particularly in Europe) provide a useful framework for placing fossil mammals in relative chronologic context, and they are employed throughout this volume. As we shall see, the precise age and the correlation of Asian and South American Land-Mammal Ages with those of North America and Europe are more controversial.

Hundreds of radiometric dates are now available for the Mesozoic, permitting a relatively accurate estimate of the age of the oldest known mammals (Gradstein et al., 1995, 2004). Based on these data, mammals first appeared at least 205-210 million years ago, and perhaps as much as 225 million years ago (see Chapter 4). They survived alongside dinosaurs for the first 145 million years of their history, up to the K/T boundary at about 65 million years ago, when the last

Fig. 1.5. Relationships of higher taxa of mammals based on molecular data. Most higher taxa in these studies are based on only one to five species. Interrelationships among taxa within Afrotheria are particularly unstable. (Modified after Murphy et al., 2001, and Springer et al., 2005.)

Superorden Afrotheria

Fig. 1.5. Relationships of higher taxa of mammals based on molecular data. Most higher taxa in these studies are based on only one to five species. Interrelationships among taxa within Afrotheria are particularly unstable. (Modified after Murphy et al., 2001, and Springer et al., 2005.)

nonavian dinosaurs became extinct. The K/T boundary and thus the base of the Paleocene, is situated near the top of geomagnetic polarity chron C29r and has been dated at 65.0 million years ago (Swisher et al., 1992, 1993; Gradstein et al., 1995) or, most recently, 65.5 million years ago (Gradstein et al., 2004).

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