M. archibaldi was discovered in the Middle Miocene deposits at Bullock Creek (Blast Site, Bullock Creek Local Fauna) in the Northern Territory, and named in honor of Ian Archibald for his contributions to the natural history of the Northern Territory.  The holotype specimen is a left maxilla containing P2-3 and M1-4.
 

. A close-up occlusal view of molars M2-3 in the holotype maxilla of M. archibaldi.  (Murray and Megirian 2000)

Other known fossils of the species include a premaxilla with alveoli (sockets) for four incisors, and a dentary fragment bearing M3-4.  Of the ancient thylacinids yet discovered, M. archibaldi is the smallest, and was about the same size as a modern quoll (Dasyurus sp.).  Mutpuracinus is also a plesiomorphic taxon, considered to be only somewhat more derived in its dental characteristics than Muribacinus gadiyuli.  M. archibaldi was found in the same deposit as the larger Nimbacinus richi, with which it was contemporary.

    Ngamalacinus timmulvaneyi:

    This Early Miocene species was found at Riversleigh (Inabeyance Site, Inabeyance Local Fauna; also Camel Sputum Local Fauna).  Its species name honors Tim Mulvaney.  This species is more plesiomorphic than Wabulacinus or Thylacinus, but more derived than Nimbacinus or Muribacinus.  Overall, it most closely resembles Wabulacinus, but is the sister group to a combined Wabulacinus/Thylacinus clade.  Like Wabulacinus, Ngamalacinus was a small, dog-sized thylacine that was contemporary with at least two other small thylacinid species.  It is assumed that each type was independently specialized to pursue certain prey in the Early Miocene rainforest of Queensland.

    Nimbacinus dicksoni:

    N. dicksoni is from the Late Oligocene to ?Middle Miocene, and like many of the other known thylacinids of Tertiary age, was recently found in the rocks of Riversleigh. 
 

. A life reconstruction of Nimbacinus dicksoni (based upon an illustration by Anne Musser).  Nimbacinus was only about the size of a fox - considerably smaller than the modern thylacine.  As is the case with the palaeontological reconstructions of Thylacinus potens shown on page 1 of the Tertiary subsection, the coat pattern depicted here is conjectural.

The species was originally described on the basis of just upper and lower jaws that were found at Riversleigh Site D, but at Riversleigh Site AL90, a nearly complete skeleton with a perfect skull has since been discovered. Nimbacinus lacks many of the specializations found in other thylacines, and more closely resembles dasyurids than other thylacinids.

A fox-sized hunter of the rainforest floor, it lived contemporarily with several other species of thylacines also known from Riversleigh.   At right are shown palatal (above) and dorsal (below) views of the skull of Nimbacinus dicksoni, which I photographed during a visit to the University of Sydney in 2002 to discuss fossil marsupials with Dr. Stephen Wroe.  Other thylacinid genera that have been found at Riversleigh include Badjicinus, Maximucinus, Muribacinus, Ngamalacinus, and Wabulacinus.  Although the thylacinid family was once known only from the modern species, T. cynocephalus, the discoveries that have been made at Riversleigh, especially in recent years, have greatly expanded our understanding of the evolutionary history of this and other Australian marsupial groups.  Along with the Naracoorte Caves of South Australia, Riversleigh was designated a World Heritage Site in 1994.  Places such as these are integral to our understanding of the history of life, and must be preserved and protected.

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