Jason A. Lillegraven

Survival in the first hours of the Cenozoic

For several hours following the Chicxulub impact, the entire Earth was bathed with intense infrared radiation from ballistically reentering ejecta. The global heat pulse would have killed unsheltered organisms directly and ignited fires at places where adequate fuel was available. Sheltering underground, within natural cavities, or in water would have been a necessary but not always sufficient condition for survival. Survival through sheltering from an initial thermal pulse is not adequately considered in literature about Cretaceous- Tertiary nonmarine extinctions. We compare predicted intense, short-term, thermal effects with what is known about the fossil record of nonmarine vertebrates and suggest that paleontological evidence of survival is compatible with theoretical results from bolide physics.

Vertebrate faunal changes through Lancian and Puercan time in southern Wyoming

We summarize faunal changes through the thickest and one of the most complete records of terrestrial vertebrates spanning Lancian (∼latest Cretaceous) and Puercan (∼earliest Paleocene) ages, the type Ferris Formation in the Hanna Basin, southern Wyoming. Observed faunal changes predate tectonic definition of local Laramide basins. Nonmammalian vertebrates exhibit no major changes in taxonomic composition below the Lancian-Puercan boundary; diversity of non-avian dinosaurs remains high within uppermost levels of the Lancian section. Nevertheless, dinosaurian extinction was not necessarily “catastrophic” within a biologically relevant interval. Primitive condylarths appear locally above the highest known dinosaurs, probably as immigrants. At least in this part of the North American western interior, the first evolutionary radiation of condylarths was subsequent to the last appearance of dinosaurs, not synchronous with or prior to it. Niche-partitioning among condylarths is first recorded near the boundary between Puercan Interval-zones Pu1 and Pu2 (early and middle Puercan time, respectively), by which time the first great mammalian diversification of the Cenozoic had begun. Major experimentations in dental morphology and increasing ranges of body sizes had developed within 400,000 years of the Lancian-Puercan boundary. We recognize no evidence suggesting that placental mammals were “recovering” from events that led to demise of the dinosaurs. The true diversity of marsupials and condylarths precisely at the Cretaceous-Tertiary boundary, throughout the western interior, remains unknown. We cannot, therefore, evaluate extensiveness of competition, if any, at that time among members of the two groups.

A new important record of earliest Cenozoic mammalian history Eutheria and paleogeographic/biostratigraphic summaries

We provide systematic description and discussion for each of 47 species of eutherian (“placental”) mammals from the type Ferris Formation of the western Hanna Basin, south-central Wyoming. All records are new for the basin, and for southern Wyoming in general. Although fossiliferous strata are both of Lancian (latest Cretaceous) and Puercan (earliest Paleocene) age, all but a few specimens (restricted to two genera) represent the Puercan. We describe five species of previously known genera as new, all of Puercan age. We also assign a previously described Puercan species to a new genus, to emphasize its distinctness. Ordinal categories are represented by Leptictida, Proteutheria, Condylarthra, and Cete. Except for fossils from lowest parts of the Puercan, the local early Paleocene fauna is biased taxonomically in favor of condylarths, animals of relatively large body size in early parts of the epoch. The taxonomic bias probably is due in part to fluvial size-sorting of specimens related to generally sandy, relatively high-energy depositional environments. The local Puercan mammalian fauna is of keen paleobiogeographic and biostratigraphic importance. Among the 59 species of Puercan mammals now known from the Hanna Basin (combining recently reported multituberculates and peradectians with eutherians considered here), at least 25 represent significant extensions of previously recognized geographic ranges (18 in northerly extent, 7 in southerly). Because many of those extended ranges involve major parts of the continent, confidence becomes greatly heightened in biostratigraphic utility of Puercan mammalian species for temporal correlations, even across vast distances of western North America. Composition of the Hanna Basin9s mammalian fauna confirms utility of most elements of the formalized interval-zones of Puercan time, established in the San Juan and Williston basins. We do, however, abandon use of Puercan Interval-zone Pu 0 as impractical, and use an expanded concept of Pu1 instead. Other than that adjustment, we strictly apply original faunal criteria for recognition of Puercan Interval-zones Pu1 through Pu3 to zonation of the type Ferris Formation. The unusually great thickness of Puercan parts of the formation, combined with our high density of sampled fossiliferous localities, has led to recognition of many extensions of temporal ranges beyond those known previously for individual species. The biostratigraphic importance of this section, therefore, becomes elevated for potential studies in: (1) long-distance temporal correlation of Puercan strata; and (2) many aspects of biological evolution across North America during earliest Cenozoic time. Basal parts of Interval-zone Pu2 in the Ferris Formation uniquely show persistence of some mammalian species known elsewhere only in Pu1. Faunal change within Interval-zone Pu2 greatly exceeds that observed between Pu2 and Pu3, although the evolutionary distinctiveness of Pu2 and Pu3 are confirmed in the present study. The newly discovered mammalian assemblages of Puercan age from southern Wyoming exhibit virtually no geographic endemism. Although they share species both from northern and southern fossil-bearing realms of the North American continent, composition of the Ferris assemblages clearly is more similar to southern than to northern faunas under comparison.

A new important record of earliest Cenozoic mammalian history :geologic setting, Multituberculata, and Peradectia

The type Ferris Formation of south-central Wyoming is thick, comparatively undeformed, and relatively fossiliferous. We documented more than 100 vertebrate-bearing, stratigraphically superposed fossil localities that span roughly 3,000 ft ( c. 900 m) of continental strata of Lancian (latest Cretaceous) and Puercan (earliest Paleocene) age. Fossil mammals were recovered from 39 of the localities, 32 or 33 of which represent Puercan time. The mammalian fossils allowed a detailed biostratigraphic zonation of the Puercan section, which is thicker, by nearly an order of magnitude, than any other known of that age. Preserved in a 1,763 ft- (537 m-) thick section are mammalian assemblages that represent all three Puercan Interval-zones ( i. e. , Pu1–Pu3), originally defined elsewhere from principally non-superposed strata. The local strata underwent only minor deformation, and that occurred late in the regional Laramide orogeny, not before the late Paleocene. On the basis of mammalian faunas, we place the Lancian-Puercan boundary at approximately 2,050 ft (625 m) above the base of the type Ferris Formation; remains of dinosaurs occur to just above that level, in absence of Puercan mammals. The lowest stratigraphic occurrence of Protungulatum donnae , a placental mammal diagnostic elsewhere of the earliest Puercan, exists at the 2,075 ft (632 m) level. Taxonomic composition of palynological samples is compatible with our placement of the Lancian-Puercan boundary. Previous workers assumed that advent of locally derived clasts in the Hanna Formation could be used to distinguish its outcrops from those of the underlying Ferris Formation. However, diverse pebbles from local sources also occur in the type Ferris Formation, even within its dinosaur-bearing parts. We have been unable to determine any combination of lithologic criteria that can be used reliably in the field to distinguish between outcrops of Ferris and Hanna Formations. We summarize important variations in depositional regime within Lancian-Puercan parts of the type Ferris Formation. We provide systematic description and discussion of multituberculate and peradectian components of the mammalian fauna. All reported taxa represent new records for the Hanna Basin and southern Wyoming in general, and the faunas help fill distributional gaps between species known to the north and south of central Wyoming. At least one species of multituberculate is recognized as new. Geographic range extensions include: (1) most southerly records of Cimolodon nitidus, Alphadon lulli, Mesodma ambigua, M. hensleighi, M. sp. cf. M. garfieldensis , and Catopsalis joyneri ; and (2) most northerly records of Ptilodus sp. cf. P. tsosiensis and Taeniolabis taoensis . Within the Hanna Basin, no genera of multituberculates or peradectians from the Ferris Formation have been documented in strata both of Lancian and Puercan age; several examples of pseudoextinction, however, may exist through taxonomic artifact. Temporal range extensions include first: (1) Puercan records of Mesodma hensleighi and Ectypodus spp.; (2) records within Puercan Interval-zone Pu3 of Ptilodus sp. cf. P. tsosiensis ; and (3) record in Puercan Interval-zone Pu2 of Catopsalis joyneri . In general, the Lancian multituberculate and peradectian faunas of the type Ferris Formation are similar to, although not nearly so diverse as, those from the type Lance Formation; the lower diversity almost certainly is an artifact of paucity of specimens available for study.

Amber from Upper Cretaceous through Paleocene strata of the Hanna Basin, Wyoming, with evidence for source and taphonomy of fossil resins

The Hanna Basin is a relatively small foreland basin in south-central Wyoming containing a combined thickness of roughly 38,000 ft (11.5 km) of Upper Cretaceous and Palecene strata. Amber occurs in the Hanna Basin in carbonaceous to lignitic strata, representing fluvial and paludal episodes bounded by incursions of epicontinental seas. Amber occurs, in decreasing age, in the Upper Cretaceous Allen Ridge, Medicine Bow, and Ferris formations (parts of the last straddle the Cretaceous–Tertiary boundary), as well as in the Paleocene Hanna Formation. Because of the extraordinary thickness, unequivocal stratigraphic superposition, and long-lived deposition of Upper Cretaceous and Paleocene amber-bearing strata in the Hanna Basin, a unique opportunity has been provided for integrated study of taxonomic sources, deposition, and taphonomic alteration of ancient resins. In all relevant Cretaceous and some Paleocene outcrops the amber is preserved mostly as small (4–8 mm diameter) droplets, often highly weathered and oxidized. One site in the Hanna Formation has yielded abundant, large pieces of transparent amber. Composition of samples analyzed by pyrolysis/gas chromatography-mass spectroscopy (PyGC-MS) indicates a common taxonomic source for amber from the Allen Ridge, Medicine Bow, and Hanna formations. The taxonomic source of amber from one part of the Ferris Formation, in contrast, is unique among the sites sampled; its chemical signature probably reflects a distinctive paleoenvironment and flora, originally recognized through palynomorphs. The characteristic PyGC-MS profile from that site is highly indicative of the Dipterocarpaceae, which would imply a rare but expected Mesozoic record of amber from a dicotyledonous tree. In the Hanna Basin a stratigraphic interval of more than 5 mi (> 8 km) and a time gap of approximately 20 million years separate the lowest and highest occurrences of amber. Such a range in one stratigraphic sequence is unprecedented among known deposits of amber. Of particular interest is that most of these samples apparently were formed by one or several closely related species of trees. The amber is chemically and physically mature, no doubt due to deep burial. Nevertheless, despite dramatic differences in age and depth of burial, only minor chemical changes from diagenetic causes were detected among the samples. Inclusions in well-preserved pieces of amber from the Hanna Formation are fairly abundant, but typically they are distorted or were partially destroyed by effects of compaction and/or microscopic-scale deformation. Sparse wood and plant fragments and spores/pollen grains are present, but only one insect (a thrips: Order Thysanoptera) has been recognized. Distinctive scales of conifer cones occur in the Allen Ridge Formation. The scales contain radiating vessels of resin, and they represent the taxonomically equivocal genus “ Dammara. ” PyGC-MS analysis of the vessel resin indicates that the same kind of tree that produced these cone scales also produced the amber in the Allen Ridge, Medicine Bow, and Hanna formations. Moreover, chemical composition of these samples closely matches that from vessels of “ Dammara ” cone scales from Upper Cretaceous (Turonian) strata in eastern North America. Circumstantial association of “ Dammara ” cone scales with several types of fossilized foliage suggests Taxodiaceae as the common source, although wood anatomy and amber chemistry also suggest Pinaceae. In spite of this taxonomic uncertainty, it is probable that 30 million years of amber production during the Late Cretaceous and Paleocene in northern North America, and probably much of Holarctica, was the result of a genus of tree that produced “ Dammara ” cone scales. These new data cast serious doubt upon recent proposals that all Cretaceous ambers were formed by members of the Araucariaceae. Wax residues were chemically discerned in one specimen of cone scale.

Evolutionary analysis of the middle and inner ear of Late Jurassic multituberculates

We describe three previously unreported specimens of petrosal bones of paulchoffatiid multituberculate mammals, collected from strata of Late Jurassic age in the Guimarota lignite mine of Leiria, west-central Portugal. The new fossils allow correction, supplementation, and confirmation of anatomical details, thus refining knowledge of general adaptation in the ear region among Jurassic multituberculates. Virtually all observed characters in the paulchoffatiid otic region are primitive relative to homologous features seen among Late Cretaceous and younger representatives of the Multituberculata; we recognize few unique otic specializations in paulchoffatiids that would preclude ancestry to later multituberculates. The plesiomorphic nature of paulchoffatiid ear regions provides no evidence in support of the hypothesis of a special, sister-group relationship between multituberculates and Late Cretaceous/Cenozoic marsupials plus placentals. Used in isolation, objective evidence derived from paulchoffatiid ear regions is consistent with interpretation of multituberculate divergence from other mammals predating the stem to living monotremes and postdating the stem to extinct morganucodontids. More broadly based comparative studies among Mesozoic mammals, however, suggest that independent acquisition of similarly advanced “mammalian” features was a pervasive theme among evolutionary histories of early mammals, probably including multituberculates. Although the phylogenetic position of multituberculates relative to other mammalian groups has yet to be unequivocally resolved, we suggest that a very early divergence of the group remains a distinct possibility.

Polarities in Mammalian Evolution Seen Through Homologs of the Inner Cell Mass

Embryogenetic pathways differ markedly among monotremes, marsupials, and placentals, and their analysis provides information of fundamental importance to recognition of mammalian evolutionary directions. The cap of cuboidal cells of the marsupial late unilaminar blastocyst, generally known as the “embryonic area,” probably is induced to form (prior to origin of Hensens node) by signals from earliest hypoblastic cells (“anterior visceral endoderm”). The thickened cap is a “medullary plate” of sauropsid terminology because it includes epiblastic cells presumptive to neurectoderm (including neural crest), Hensens node, primitive streak, and gut endoderm. The remainder of the definitive embryo (i.e., parts of epidermal origin, including ectodermal placodes) derives from squamous ectoderm (surrounding the medullary plate) of the blastocysts ill-named “trophoblastic area.” Amniotic ectoderm develops farther distally within the “trophoblastic area.” The autapomorphic inner cell mass (ICM) of placental mammals is homologous to medullary plate of the marsupial blastocyst plus morphologically undefined, proximal parts of surrounding ectoderm (of the “trophoblastic area”). Considerations of early cell lineages in marsupials are greatly affected by recognition that the boundary between future embryonic and extra-embryonic tissues does not match the margin of the medullary plate (i.e., “embryonic area”). Marsupials and monotremes largely conform to sauropsid early embryogenesis, but placentals express, at earliest developmental stages, innovations unique within Amniota that are linked to early establishment of the brain. Neonatal marsupials and hatchling monotremes are extremely altricial and closely comparable anatomically/physiologically; they share a temporal pattern in combining early morphogenesis of craniofacial features (related to suckling) with deferral of telencephalic completion into postnatal/posthatching life. Placentals contrast greatly in establishing the central nervous system prior to rudiments of the cranial skeleton and associated musculature, and they complete essentials of forebrain development before birth. Comparative evidence from transitory periderm suggests that primordial eutherians had extremely altricial hatchlings or newborns, whichever was the mode of early development. Details remain unknown about the origin of the unique specialization of ICM plus encapsulating trophoblast from the more generalized blastula of ancestral synapsids.

Repeatability of measurements of small mammalian fossils with an industrial measuring microscope

ABSTRACT Five small (<2.5 mm), morphologically complex mammalian teeth were measured repeatedly (10 measurers, 2 dimensions per tooth, 1 daily measuring session repeated over 10 days, to accuracy of 0.01 mm) using a “Shopscope” measuring microscope. The experiment was designed to show, within and among measurers: (1) the ranges of variation that may be expected; and (2) the primary components of observed variation. Variations in repeated measurements consistently were very low (for lumped samples, N = 100: 80% of time SEX was 0.002 mm or less; mean of SD = 0.019 mm), even though specimens were reoriented before each trial and several participants had no prior experience with the instrument. A randomized, complete block design (with repeated measures on blocks) analysis of variance showed that, in 8 of the 10 required length and width measurements, the component of intrameasurer variation explained a larger part of total variance than did the component of intermeasurer variation. Assuming that unambiguous ...

Stratigraphic placement of the Santonian-Campanian boundary (Upper Cretaceous) in the North American Gulf Coastal Plain and Western Interior, with implications to global geochronology

Recent micro- and macropaleontological research in the northern Aquitaine Basin of France, the stratotypic area for the Upper Cretaceous Santonian and Campanian Stages, was used to resolve a long-standing discrepancy in the stratigraphic position of the Santonian-Campanian boundary in east-central Texas as based upon zonations of planktonic foraminifers versus ammonites. On the basis of the presence in Texas of species of ammonites restricted to the lower reaches of the basal Campanian Placenticeras bidorsatum Zone of the Aquitaine Basin, the Santonian-Campanian boundary in Texas is significantly lower than has generally been considered by micropaleontologists. Specifically, it is within the foraminifer-based Globotruncana (= Marginotruncana ) concavata Zone ( sensu lato ). Such placement involves middle reaches of the type Austin Chalk, perhaps within the Dessau Chalk Member. An assumption that underlies the following conclusions is that the boundaries of the G. concavata Zone as recognized in European Tethys, the Atlantic and Caribbean basins, and North American Gulf Coast represent approximately synchronous stratigraphic levels. The following represent additional conclusions of pertinence to global chronology of the Cretaceous. (1) Rather than being younger than the Globotruncana concavata Zone, the Placenticeras bidorsatum Zone should be thought of as being contemporary with at least the younger half of the G. concavata (species total range) Zone. (2) Most of the Merchantville and Magothy Formations on the Atlantic seaboard of New Jersey and Delaware were deposited during early Campanian time, rather than principally during the Santonian. (3) The traditional placement of the Santonian-Campanian boundary in the Western Interior of North America slightly below the zone of Scaphites hippocrepis I is essentially correct. (4) The chronology of the Niobrara Formation of the North American Western Interior as based upon planktonic foraminifers is shown to be in serious error; specifically, it has been considered much too young. (5) Paleomagnetically sampled parts of the Niobrara Formation probably correlate with upper reaches of the “Cretaceous Long Normal Interval”, below magnetochron 33R. (6) Although the Santonian Stage surely represents a surprisingly brief interval of earth history, the Coniacian-Santonian boundary probably should be placed below the G. concavata Zone. (7) The Santonian-Campanian boundary slightly post-dates initiation of the last general Cretaceous regression of the North American Western Interior Seaway. (8) The beginning of the North American Aquilan Land Mammal “Age” represents earliest Campanian time. (9) Rather than representing an earliest Campanian geomagnetic event, the temporal span of global magnetochron 33R equates with approximately the second quarter of the total duration of the Campanian.

Primates from Later Eocene Rocks of Southern California

Newly discovered later Eocene (Uintan) primates (adapids, omomyids, and microsyopids) from San Diego Co., California are described and compared with those of other Eocene faunas in Ventura Co. (Sespe Formation) and the North American western interior. The 11 species of primates from San Diego Co. lived in coastal lowland riparian and deltaic environments; their remains are preserved in the Friars and Mission Valley formations (early Uintan, greater San Diego area) and Santiago Formation (later Uintan, northwestern San Diego Co.). Genera previously known from the western interior but recorded for the first time from the west coast include Pelycodus, Notharctus, Hemiacodon , and ? Macrotarsius ; to these is added Omomys , as I consider Stockia powayensis a species of Omomys . Range extensions into the early Uintan include Pelycodus, Notharctus , and Hemiacodon . The southerly climes of the Californian later Eocene coastal areas may have served as temporary havens for species that became extirpated earlier in the western interior. All nine primate species recorded from the early Uintan of the west coast had close relatives in the western interior, a faunal similarity shared by other vertebrates. Late in the Uintan, west coastal endemism increased as barriers to faunal interchange developed between the two areas.