Shale and the Dakota Group of Kansas contain fossils of several conifers. Jelinite contains succinic acid (Buddhue, 1938), which further suggests a conifer origin, as well as several types of conifer pollen (personal observations). The amber was originally described as being associated with "Auracaria" [sic] wood (Langenheim et al., 1965). Almost all Cretaceous ambers from North America are thought to have come from members of the Araucariaceae (Langenheim, 1969).
Small flakes of this amber were mounted in glycerol and examined for the presence of microfossils. As reported in the original description (Buddhue, 1938), many dark brown to yellow-orange microscopic inclusions were present, generally oriented in parallel along the direction of resin flow, giving the amber its cloudy texture. Most of these are obviously bubbles; many contain organic material and look somewhat like microorganisms. Only a few are identifiable with any certainty as fossils.
References and keys for taxonomy are Buchanan and Gibbons (1975) for the bacteria and Bovee (1985a, 1985b) for the protists.
Genus cf. Leptothrix Kützing, 1843
Figures 3, 4
Material: UCMP type 39885. Numerous filaments.
Description: Fossil filaments in a felted mass, no septa, some tips slightly swollen, all surrounded by a light brown, translucent hyaline tubular sheath with attached particles, 7 mm total diameter. Several of the sheaths have a refringent, transparent central lumen and appear empty.
The sheath precludes identification with the actinomycetes. The fossil is quite similar to modern sheathed bacteria; nearly identical forms have been isolated by the author from moss on the University of California-Berkeley campus. In living forms, and presumably in the fossils, Fe(OH)2 is responsible for the light brown color of the sheath and its associated granules. The presence of empty sheaths as well as overall morphology, color, and size suggest placement in the modern genus Leptothrix. In the absence of culturing or biochemical and molecular analysis, this identification must remain tentative.
Remarks: Although bacteria have been reported from amber several times (Blunck, 1929; Katinas, 1983; Poinar, 1992; Waggoner, 1993), it has been suggested that some of these are more recent contaminants (Larsson, 1978). The presence of some isolated fragments of sheathed filaments, completely encased in the amber, shows that these fossils are not contaminants. It is also difficult to see how sheathed bacteria of this sort could grow in liquid or solid resin. in liquid or solid resin.
The "sheathed bacteria" group is probably artificial. Aside from cyanobacteria, various sheathed, filamentous prokaryotes are known from several Precambrian localities (reviewed in Schopf, 1992); in fact, Leptothrix-like bacteria nearly identical to those described here were among the first Precambrian microfossils ever found, in the Biwabik chert of Minnesota (Gruner, 1922, pl. 8A). Sheathed iron bacteria are known from several Paleozoic sites (reviewed in Knoll, 1977) and sheaths referable to Leptothrix are known from Permian and Triassic salt deposits (Müller and Schwartz, 1953) and Triassic amber (Poinar et al., 1993a).
Genus cf. "Pontigulasia" Rhumbler, 1895
Figures 2c, 7
Material: UCMP type 39886. One test.
Description: Brown, pyriform test, 86 mm long, surface irregular. Neck joins body in indistinct V-shaped wedge; body has rounded lateral convex protuberances, but suture between neck and body is not well marked. Optical sectioning shows ovoid cross-section; dark internal bar indicates internal diaphragm, but details of diaphragm apertures are not visible. Pseudostome somewhat constricted.
The lateral protuberances, flattening, test construction, and V-shaped suture between neck and body are very characteristic of Pontigulasia (Loeblich and Tappan, 1964; Ogden and Hedley, 1980; Pls. 70, 71). The outline generally distinguishes it from Lagenodifflugia, which has a narrower body (Bovee, 1985a). However, without details of the internal diaphragm, this test could represent either Pontigulasia or Zivkovicia (Ogden, 1987). In overall shape and proportions it resembles modern Z.
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