49
abdomen of Proplebia dominicana preserved in 25–40 million year old amber from
the Dominican Republic. Cano and Borucki (1995) claim to have cultured a strain
of Bacillus schadericus from P. dominicana in Dominican amber. These studies corroborate an earlier work by Galippe (1920) who claimed to have revived bacteria
(some of which appear to be Bacillus spp.) from 40 to 50 million years ago Baltic
amber, although none were fully characterized or named. However, more recently,
Hamamoto and Horikoshi (1994) reported that they isolated, cultured and characterized a bacterium from Baltic amber that had a 99.6% homology with that of B. subtilis. And if Dombrowski’s report (1963) on reviving Permian Bacillus circulans
from the Kali and Zechstein salt deposits in Germany can be verified, it would show
the environmental persistence of Bacillus spores. While such an extended period of
dormancy for bacterial spores appears incredulous, Hornek et al. (1994) documented bacterial spore survival for long periods in outer space, adding credence to
their ability to survive in the ground encased in amber for millions of years.
2.4 Protozoan Fossils
Protozoa, a group of single-celled eukaryotic organisms formely assigned to the
Kingdom Protista, are an ancient group with a fossil record extending back to the
Archean Eon, some 2 billion years ago (Baker 1965). Protozoa probably originated
in the sea where they formed associations with various organisms. One of their first
habitats with marine invertebrates and vertebrates probably was in the alimentary
tract. Freshwater and terrestrial habitats would have been explored soon afterwards.
Some protozoa became permanent residents with their “hosts” and established
mutualistic and parasitic associations. Eventually, life cycles were established that
involved the transfer of protozoa between hematophagous arthropods and vertebrates. Fossil examples of a range of associations between parasitic protozoa and
animals are presented below.
2.4.1 Direct Evidence of Fossil Protozoan Parasites
2.4.1.1 Fossil Trypanosome Parasites
One of the earliest fossil records of a protozoan parasite was in the gut lumen of a
phlebotomine sand fly entrapped in mid-Cretaceous Myanmar amber (Fig. 2.28)
(Poinar 2004). In the midgut lumen of the sand fly, Palaeomyia burmitis, were various stages of the leishmanial parasite, Paleoleishmania proterus (Poinar and Poinar
2004a, b) (Fig. 2.29). Aside from normal promastigotes, elongate nectomonad promastigotes (Fig. 2.30) and short procyclic promastigotes (Fig. 2.31) were also present. Vertebrate infective amastigotes occurred in the proboscis of the fossil sand fly
(Fig. 2.32) and a view into the thoracic lumen of the fossil sand fly revealed nucleated vertebrate blood cells. Based on morphological characteristics of the blood
2 Fossil Record of Viruses, Parasitic Bacteria and Parasitic Protozoa
abdomen of Proplebia dominicana preserved in 25–40 million year old amber from
the Dominican Republic. Cano and Borucki (1995) claim to have cultured a strain
of Bacillus schadericus from P. dominicana in Dominican amber. These studies corroborate an earlier work by Galippe (1920) who claimed to have revived bacteria
(some of which appear to be Bacillus spp.) from 40 to 50 million years ago Baltic
amber, although none were fully characterized or named. However, more recently,
Hamamoto and Horikoshi (1994) reported that they isolated, cultured and characterized a bacterium from Baltic amber that had a 99.6% homology with that of B. subtilis. And if Dombrowski’s report (1963) on reviving Permian Bacillus circulans
from the Kali and Zechstein salt deposits in Germany can be verified, it would show
the environmental persistence of Bacillus spores. While such an extended period of
dormancy for bacterial spores appears incredulous, Hornek et al. (1994) documented bacterial spore survival for long periods in outer space, adding credence to
their ability to survive in the ground encased in amber for millions of years.
2.4 Protozoan Fossils
Protozoa, a group of single-celled eukaryotic organisms formely assigned to the
Kingdom Protista, are an ancient group with a fossil record extending back to the
Archean Eon, some 2 billion years ago (Baker 1965). Protozoa probably originated
in the sea where they formed associations with various organisms. One of their first
habitats with marine invertebrates and vertebrates probably was in the alimentary
tract. Freshwater and terrestrial habitats would have been explored soon afterwards.
Some protozoa became permanent residents with their “hosts” and established
mutualistic and parasitic associations. Eventually, life cycles were established that
involved the transfer of protozoa between hematophagous arthropods and vertebrates. Fossil examples of a range of associations between parasitic protozoa and
animals are presented below.
2.4.1 Direct Evidence of Fossil Protozoan Parasites
2.4.1.1 Fossil Trypanosome Parasites
One of the earliest fossil records of a protozoan parasite was in the gut lumen of a
phlebotomine sand fly entrapped in mid-Cretaceous Myanmar amber (Fig. 2.28)
(Poinar 2004). In the midgut lumen of the sand fly, Palaeomyia burmitis, were various stages of the leishmanial parasite, Paleoleishmania proterus (Poinar and Poinar
2004a, b) (Fig. 2.29). Aside from normal promastigotes, elongate nectomonad promastigotes (Fig. 2.30) and short procyclic promastigotes (Fig. 2.31) were also present. Vertebrate infective amastigotes occurred in the proboscis of the fossil sand fly
(Fig. 2.32) and a view into the thoracic lumen of the fossil sand fly revealed nucleated vertebrate blood cells. Based on morphological characteristics of the blood
2 Fossil Record of Viruses, Parasitic Bacteria and Parasitic Protozoa