J. Howard Hutchison

Eocene lower vertebrates from Ellesmere Island, Canadian Arctic Archipelago

Lower vertebrates from the Early Eocene Eureka Sound Formation, Ellesmere Island, Canadian Arctic Archipelago, form a mixed aquatic—riparian—terrestrial assemblage similar to that of many North American Late Cretaceous and Paleogene continental deposits. Taxa include the bony fishes Amia and Lepisosteus, the salamander Piceoerpeton, anguid and varanid lizards and a boid snake. Turtles include two emylids, the tortoise Geochelone, and anosteirine, Trionyx s.s. and an unidentified turtle adapted for durophagy. The durophagous alligator Allognathosuchus is also present. The varanid, tortoise and alligator indicate an equable climate with winters that rarely suffered freezing temperatures. These animals (especially the varanid) have high temperature optima today. Such optima are more likely to have occurred seasonally, under present obliquity of the earths axis, than with the low obliquity model that has been suggested by paleobotanical data. If so, these animals must have undergone periods of winter dormancy, unlike their living relatives. Zoogeographic affinities of the lower vertebrates are generally with North America although some of the taxa also occur in Palaeogene Europe; only the anosteirine turtle shows Asian affinities. Two of the taxa appear to have been endemic to the Arctic region, and the assemblages as a whole may have been part of a pan-Arctic fauna rather than resembling that of any northern continent in particular.

Diversity of turtles across the cretaceous/tertiary boundary in Northeastern Montana

Abstract The abundant chelonian faunas of the Hell Creek and Tullock formations of McCone and Garfield counties, Montana, span the Cretaceous/Tertiary boundary and provide a basis for assessing extinction and changes in diversity. Over three thousand specimens were counted on a modified minimum number basis from 510 localities. The Lancian (Maastrichtian) part of the Hell Creek Formation contains at least 19 genera and subgenera of turtles and probably a greater but undetermined number of species and comprises the most diverse fossil turtle fauna known from a single rock unit. At least 15 generic level taxa survive into the Puercan (early Paleocene) part of the overlying Tullock Formation and only one new genus appears. The magnitude of the change in diversity across the Cretaceous/Tertiary boundary is less than or compaable to examples within the Tertiary and is readily explained by moderate ecological changes.

Paleogene terrestrial vertebrates: northernmost occurrence, ellesmere island, Canada.

Recently discovered Paleogene land vertebrates from the Eureka Sound Formation at about latitude 78� north in Arctic Canada include fish, turtles, an alligatorid, and several taxa of mammals. The assemblage, which is probably early or middle Eocene in age, adds to previously known paleobotanical evidence in suggesting temperate to warm-temperate climatic conditions.

A new eucryptodiran turtle from the Late Cretaceous of North America (Dinosaur Provincial Park, Alberta, Canada)

Abstract The holotype of Judithemys sukhanovi gen et. sp. nov. from the Late Cretaceous (Campanian) Dinosaur Park Formation of Alberta, Canada, has been included in four cladistic analyses. New material allows for a more complete description of this taxon. Judithemys sukhanovi is represented by 65 specimens (most very fragmentary) including one virtually complete skeleton (the holotype) and several partial shells. It differs from all other “macrobaenids” in the combination of wide vertebral scales, absence of central plastral fontanelles, and lack of strongly upturned peripherals. The morphology of Judithemys reiterates a suite of characters (large size, well-differentiated neurals reduced to eight, and greater overlap of the twelfth marginal scales onto the second suprapygal) common to Late Cretaceous–Paleocene “macrobaenids” and distinct from Early Cretaceous members. Judithemys and “Clemmys” backmani are close in morphology, geography, and stratigraphic position and are possibly closely related phylogenetically. A preliminary phylogenetic analysis supports the hypothesis that Judithemys is not part of the crown group.

First report of snakes (Serpentes) from the Late Middle Eocene Pondaung Formation, Myanmar

Department of Anthropology, University of Iowa, Iowa City, IA 52242, USAThe reptile fauna of the Eocene Pondaung Formation of central My-anmar (Fig. 1) has received little attention compared to its well-knownmammalian fauna (e.g., Colbert, 1938; Tsubamoto et al., 2000). In priorreports, Buffetaut (1978) described indeterminate crocodylians and dy-rosaurids. Hutchison et al. (in press) described carettochelyid, trionychid,testudinoid, and pelomedusoid turtles from the formation. They addi-tionally noted the presence of agamid lizards, a pristichampsine croco-dilian, and snakes. The snakes are described here.The occurrence of snakes in the Pondaung Formation is significantbecause the fossil history of Paleogene South Asian snakes has histori-cally been under studied relative to the North American and Europeanrecords (e.g., Rage, 1984; Szyndlar, 1984; Holman, 2000), despite hypoth-eses predicting the region as the origin of extant clades (e.g., Underwoodand Stimson, 1990; Rage et al., 1992). The South Asian record consistsprimarily of marine palaeophiid taxa as well as terrestrial/terrigenousspecimens referred to Boidae (Boinae + Erycinae, Table 1). The onlyderived snakes from the South Asian Paleogene are six colubrid verte-brae from the late Eocene Krabi Basin of Thailand (Rage et al., 1992)and a single vertebra referred to Colubroidea (possibly Colubridae) fromthe early Eocene of India (Rage et al., 2003). The absence of coevalcolubroids elsewhere (Rage, 1988), combined with the occurrence of theKrabi Basin record, led Rage et al. (1992) to conclude that Asia repre-sents the center of origin for Colubridae, the most speciose and diverseextant snake clade.The Pondaung snake record consists of two specimens derived fromterrestrial sediments occurring in the upper 100+ meters of the otherwisemarine Pondaung Formation as it crops out to the west and northwest ofMogaung village, Myaing Township, central Myanmar (Fig. 1). Thesnake localities are interpreted as swale-fills and/or paleosols depositedin an ancient floodplain (Soe et al., 2002; see also Ciochon and Gunnell,2002, and Gunnell et al., 2002 for more detailed discussions of the lithol-ogy and stratigraphy of these localities). Traditionally, the age of thePondaung fauna was considered to be late Eocene (e.g., Pilgrim, 1928;Bender, 1983); however, Holroyd and Ciochon (1994) concluded that thePondaung fauna is latest middle Eocene (Bartonian) in age and broadlycontemporaneous with Asian faunas assigned to the SharamurunianLand Mammal Age, a finding confirmed by fission-track dates of 37.2 ±1.3 Ma (Tsubamoto et al., 2002). These findings indicate that thePondaung fauna is slightly older than the Krabi Basin record, which hasbeen dated between 33.54 and 34.65 Ma in age based on paleomagneticcorrelations (Benammi et al., 2001).Here we describe the Pondaung snakes and discuss their relativeimplications for paleoecology, divergence timings, and biogeographichistories. We refrain from erecting new taxa for the Pondaung speci-mens because the record is limited to just the two elements and neitheris complete. Additional material will be necessary to determine wheth-er or not the Pondaung record represents new, distinct taxa, or indi-vidual or intracolumnar variants of previously known South Asiansnakes.

MIOCENE VERTEBRATES FROM THE SIWALIK GROUP, WESTERN NEPAL

At least 33 vertebrate taxa from the lower and middle Siwalik Group (middle and late Miocene) of southern and western Nepal compare well with assemblages from the lower and middle Siwaliks of Pakistan and India. Localities low in the Nepal section contain the suid Conohyus, the hominoid Sivapithecus, the rhinocerotid Brachypotherium, and typical lower Siwalik artiodactyls, car- nivorans, and proboscideans. Several stratigraphically higher localities yield Hipparion, as well as artiodactyls characteristic of the middle Siwaliks. The Nepal fossils were found in rocks deposited under apparently relatively moist climatic conditions, primarily marl, siltstone and fine sandstone without prominent multistoried channel sandstone se- quences. Abundant remains of fish, chelonians, and crocodilians in the Nepal fauna corroborate this sedimentological interpretation. The structural development of the Himalaya had an effect on the paleoclimate of South Asia. A pattern of increasing dryness westward along the mountain front probably had developed by the Miocene. The mountains and the Tibetan Plateau to the north, however, did not achieve their present great elevations until the Pliocene and Pleistocene.

Nonmarine extinction across the Cenomanian-Turonian boundary, southwestern Utah, with a comparison to the Cretaceous-Tertiary extinction event

There is a marked, possibly stepwise, extinction of marine taxa across the Cenomanian-Turonian boundary. Across the boundary in southwestern Utah, there is only minor species-level extinction of brackish-water taxa, and an actual increase in diversity of fully terrestrial organisms; significant family-level extinctions are restricted to aquatic taxa such as fishes and turtles. It is not possible in the nonmarine setting to determine if this is a gradual, stepwise, or instantaneous extinction, or to what degree it correlates to marine extinction events. Nonmarine faunas underwent no major change during the transgressive phase of the Greenhorn cycle, and the loss of aquatic taxa along with displacement (but not extinction) of brackish-water vertebrates and some marsupial mammals is first apparent in rocks deposited during regression in the Turonian. The loss of flood-plain habitat at maximum transgression may have caused the extinction of some of the aquatic taxa. The absence but not extinction of certain taxa on flood plains during the Greenhorn regression suggests that there may be some significant difference in transgressive and regressive flood plains. Drawdown increases the gradients of rivers and results in incision along coastal margins. This restricts the extent of brackish-water environments and may have had an impact on faunal compositions of riverine systems and contributed to extinction within aquatic communities. This pattern is quite different from that at the Cretaceous-Tertiary (K-T) boundary. Aquatic taxa underwent relatively minor losses at that boundary, whereas terrestrial organisms underwent major extinction. It appears that much of the Late Cretaceous aquatic community was restructured (mostly by exclusion of many taxa rather than extinction) and reduced in diversity during large-scale regression in the middle of the Maastrichtian before the end of the Cretaceous. This aquatic community was living in a rapidly expanding environment (overall regression of marine waters) at the K-T boundary. The extinction of terrestrial taxa at the boundary is unlike the pattern observed at the Cenomanian-Turonian boundary and suggests that some mechanism other than eustatic change played a significant role in the extinction.

Early Kinosterninae (Reptilia: Testudines) and their phylogenetic significance

ABSTRACT Two genera of kinosternids in the Eocene of North America exhibit specializations of the Kinosteminae such as the presence of incised musk ducts, loss of one suprapygal, and a generally derived neural pattern. The shell of Baltemys staurogastros, gen., et sp. no v., from the Wasatchian (early Eocene) of Wyoming shows striking phenetic resemblance to that of Staurotypus but these are judged as primitive features on the basis of out-group analysis. Xenochelys lostcabinensis, sp. nov., from the Wasatchian and X. bridgerensis, sp. nov., from the Bridgerian of Wyoming exhibit additional derived features of the extant kinosternines such as the reduction in musk duct length, development of an intergular scale, and expansion of the plastron. Baltemys and Xenochelys lack plastral kinesis. The morphology of the fossil forms bridges much of the morphological gap between the extant Kinosterninae and Staurotypinae. The wealth of derived morphological features that the two subfamilies share indicate that they ...

Arctic plant diversity in the Early Eocene greenhouse

For the majority of the Early Caenozoic, a remarkable expanse of humid, mesothermal to temperate forests spread across Northern Polar regions that now contain specialized plant and animal communities adapted to life in extreme environments. Little is known on the taxonomic diversity of Arctic floras during greenhouse periods of the Caenozoic. We show for the first time that plant richness in the globally warm Early Eocene (approx. 55–52 Myr) in the Canadian High Arctic (76° N) is comparable with that approximately 3500 km further south at mid-latitudes in the US western interior (44–47° N). Arctic Eocene pollen floras are most comparable in richness with todays forests in the southeastern United States, some 5000 km further south of the Arctic. Nearly half of the Eocene, Arctic plant taxa are endemic and the richness of pollen floras implies significant patchiness to the vegetation type and clear regional richness of angiosperms. The reduced latitudinal diversity gradient in Early Eocene North American plant species demonstrates that extreme photoperiod in the Arctic did not limit taxonomic diversity of plants.

Determinate growth in the Baenidae (Testudines): taxonomic, ecologic, and stratigraphic significance

ABSTRACT Members of the family Baenidae cease significant growth and co-ossify the shell as adults. Recognition of adults allows size to be effectively used as a means of taxon discrimination in taxonomic, stratigraphie, and ecologie studies. The feature is used to discriminate the Eocene genera Baena and Chisternon and trace their increase in size through time.