Among marsupials, the evolutionary relationship between thylacines and dasyurids such as the Tasmanian devil, quolls and phascogales is no closer than that of the wolf to its placental relations within the order Carnivora - bears, pandas and raccoons.  Man's primate ancestors are thought to have diverged from monkeys only about 15 million years ago.     Dr. Mike Westerman, molecular geneticist at La Trobe University, believes that the wide genetic gap between the thylacine and modern dasyurids will be the most significant obstacle to cloning a thylacine.

. The skull of Borhyaena, a carnivous marupial from the Miocene Santa Cruz Formation of Patagonia, Argentina.

    Genetically speaking, the bridge may possibly be too far to cross.  Westerman has been working with Dr. Carey Krejewski, of the University of Illinois, and Dr. Mark Springer, of the University of California, Riverside, in comparing the DNA of the world's major groups of marsupials in order to construct a detailed family tree.

    Westerman took small samples of tissue from infant thylacines which are preserved in alcohol at the Museum of Victoria (Melbourne), and obtained full DNA sequences from two genes - one from the main genetic repository within the cell nucleus, and another from the cell's mitochondria, the tiny, intracellular structures that synthesize biochemical fuel for cells.

    Mitochondria possess their own compact, specialized genome, separate from the executive genetic program contained in the cell nucleus.  The nucleus and mitochondria maintain a continuous, biochemical correspondence with each other in which vital proteins and enzymes are exchanged.

    Krejewski has decoded a second mitochondrial gene from DNA obtained from a thylacine pelt in the collection of the Smithsonian Institution in Washington DC, where he formerly was employed.
 

. This is "Site D" at Riversleigh.  The boulders sitting atop the hill are weathered remnants of the Carl Creek Limestone, from which have come a significant amount of Miocene vertebrate fossils.  The rocks of Riversliegh have provided a unique glimpse into the life of the Australian rainforests which existed here 12-25 million years ago, a very imporant time time period in the evolution of Australia's marsupial fauna.

Westerman and colleague Dr. Steve Wroe have made a comparison of the DNA sequences from the nuclear and mitochondrial genes from thylacines and discovered that they were "terribly divergent" from analogous genes in dasyurids such as the Tasmanian devil, quolls, marsupial "mice" and planigales.      "Our estimate is a minimum of 25 million years" says Westerman.  "And that's supported by the presence of fossils of relatives of thylacines, devils and native cats (quolls) at Riversleigh.  Given what we know about the relatively rapid mutation rates in mitochondrial genes, the chances of getting the nuclear genes of thylacines to talk to the mitochondrial genes of a devil or a quoll must be very slim."

    The difficulty arises, says Westerman, from the discovery that when the original nucleus is removed from an oocyte (egg cell), the mitochondria remain behind.  So when an isolated thylacine nucleus, lacking its own mitochondria, is fused with an emptied oocyte from a devil or quoll, it will need to communicate closely with the host cell's original mitochondria before the oocyte will start dividing to create a new thylacine embryo.  This is a seemingly unlikely possibility.

    Improbable, perhaps, but not impossible, according to Professor Roger Short of Melbourne's Royal Women's Hospital.

    In 1998 in Dubai, Short, one of Australia's premier reproduction physiologists, participated in the 20th century's most amazing hybridization experiment, one that spanned an ocean and at least 11 million years in time: a successful crossing between a guanaco (Lama guanicoe) (the small, South American progenitor of both the domesticated llama and alpaca), and an Arabian dromedary camel (Camelus dromedarius).

    The scientists artificially inseminated a number of female camels with guanaco sperm; they also inseminated female guanacos with camel sperm.  Two of the female camels became pregnant, but both aborted in late pregnancy.  Six of the guanacos conceived, but two resorbed their embryos in early pregnancy, and three others produced stillborn, late-term fetuses.  Short believes that a communication problem between the sperm genes and the eggs' mitochondrial genes are the reason for the failures.

    However, on 14 January 1998, one of the guanacos gave birth to the world's first camel-guanaco hybrid after a 328-day pregnancy - the usual gestation period for a guanaco.  "It's doing fantastically well," says Short.