T. macknessi lived during the Early Miocene.  Its fossils were found in north-western Queensland at the Riversleigh World Heritage area (Neville's Garden Site, Neville's Garden Local Fauna).  The oldest known member of the genus Thylacinus, its species name honors Brian Mackness, a long-time supporter of Australian vertebrate palaeontology.  The holotype specimen of T. macknessi is a nearly complete right dentary (lower jaw) in which all teeth are present except for the incisors.  When the species was first described, only the posterior section of the jaw (bearing the last three molars) was known.  Luckily, the anterior half of the holotype specimen was found two years later in a block of limestone from the same fossil site (Muirhead and Gillespie 1995).  In some respects, this species is more specialized than more recent members of its genus, which suggests that a common ancestor of all species of Thylacinus must have been older than T. macknessi.

    Thylacinus megiriani:

    Like T. potens, this species also lived during the Late Miocene, and was discovered at Alcoota (South Quarry, Ongeva Local Fauna), in the Northern Territory.
 

The remains of Thylacinus are very rare at Alcoota.  Although there were forests and a permanent water supply there during T. megiriani's time some 8 million years ago, palaeontologists have found many fossil bones at this site which are densely packed together from animals that died within a space of just a few years.  It is theorized that a period of very unpredictable climate occurred at Alcoota during the Late Miocene, and that there was little or no rain for several years in the area.

. A section of the cranium of Thylacinus megiriani, including several maxillary teeth.

    Badjcinus turnbulli:

    This Late Oligocene thylacine was found at the Riversleigh (White Hunter Site, White Hunter Local Fauna).  Its species name honors Bill Turnbull, who has contributed much to the study of fossil mammals.
 

. Some examples of Badjcinus turnbulli fossils (images not shown at relative size to each other).  Top - right dentary fragment containing P2-3 and M1-3.  Bottom - left portion of dentary containing P2, M1-4, and alveoli (sockets) for i(3), C, P1 and P3.  (Muirhead and Wroe 1998)

The genus was described on the basis of a partial skull and nearly complete upper and lower jaws.  B. turnbulli appears to be one of the oldest and most primitive types of thylacine yet known.  Muirhead and Wroe (1998) consider small thylacines such as Badjcinus to be approximately the same size as the larger living dasyurids (e.g. Dasyurus maculatus), and probably had similar ways of life, preying upon insects, reptiles and small mammals.

    Maximucinus muirheadae:

    M. muirheadae is from the Middle Miocene.  The holotype and only known specimen is a second upper molar (M2), found at Riversleigh (Ringtail Site, Ringtail Local Fauna).
 

Its species name honors Jeanette Muirhead for her work on fossil thylacinids.  It is the largest thylacine species known from Australia's Late Oligocene to Middle Miocene deposits, and is estimated by Wroe (2001) to have been about the same size as a small T. cynocephalus.  In its dental morphology, it appears to be less specialized than species of Thylacinus, Wabulacinus and Tyarrpecinus.

. The holotype specimen (an M2 tooth) of Maximucinus muirheadae.  A, occlusal view.  B, lateral view.  C, lingual view.  (Wroe 2001)

    Muribacinus gadiyuli:

    This is another thylacine species of Middle Miocene age from Riversleigh (System C localities - e.g. Gag and Henk's Hollow Sites, Dwornamor and Henk's Hollow Local Faunas). M. gadiyuli's specific name comes from an Waanyi Aboriginal word meaning "little", in reference to the fact that this species was considerably smaller than the modern thylacine.  M. gadiyuli is known from a well preserved right maxilla and section of the jugal bone (holotype), and a right dentary (paratype).  It is the most primitive member of the family Thylacinidae yet known, and was approximately the size of a fox-terrier dog.