To follow is an account of genera and species which have been described at various times since Owen (1859), and more recently by Archer and Dawson (1982), that have defined the position of some of these taxa.

    Plectodon Krefft, 1870: A brief description was published by Krefft (1870a) of material which included some badly damaged mandibular incisors said to come from an animal "allied to Thylacoleo" which he named Plectodon.  No type specimen was named and no details regarding its locality of discovery were mentioned.  A specimen was sent to Owen but no species name was ever recorded, despite the fact that Krefft made further references to Plectodon in later publications (1870b, 1882) and provided an illustration of the incisor (1882). Plectodon is considered by Archer and Dawson (1982) as a junior synonym of Thylacoleo Gervais.

   Mylodon? australis Krefft, 1870: Krefft found a large, hooded ungual phalanx amongst some of the material collected from the Wellington Caves.  It rather resembled that of a South American ground sloth, Mylodon.  He assigned the specimen to the genus Mylodon? and made it the type of Mylodon? australis.  A short description was published (Krefft, 1870a), however, it was Owen (1871, 1877) who first illustrated the specimen from a series of photographs of two variously shaped types of phalanges which had been sent to him by Krefft.  Owen produced figures of both types of phalanges and, by excluding all other marsupials known to have existed in the discovery locality at that time as being of the improper size, he expressed that Thylacoleo must have been the possessor of the curved ungual phalanges.  He rejected the possibility that Mylodon had ever existed in Australia.  Etheridge (1918) examined the confusing situation which had developed out of Owen's referral of two distinct types of phalanges to Thylacoleo and the listing by Lydekker (1887) of a cast of a third form of phalanx as also being ascribed as that of a thylacoleonid.  Krefft's hooded, ungual bone was likely referable to Thylacoleo.  Of the two unhooded phalanges, the highly arched and compressed type was morphologically most similar to that of the great flying phalanger while the more elongate, less compressed claws were more like those of the koala.  In a study (1982), Archer and Dawson demonstrated that Thylacoleo carnifex is a senior synonym of Mylodon australis.

    Thylacoleo oweni McCoy, 1876: The innate difficulties in having to base the taxonomy of fossil species upon a few incomplete specimens are highlighted by the studies of McCoy (1876).  In 1875, he had been given a fragmentary skull and mandible collected by Adeney from the same locality at Lake Colongulac as the specimens that had been sent to him thirty years earlier.  The skull appeared to be lacking part of Owen's specimen and bore all precarnassial teeth in situ.  McCoy made a thorough comparison between the Victorian material (including the newly obtained mandible) and that from darling Downs and the Wellington Caves (Owen 1859, 1866, 1871) which led him to differentiate the New South Wales Thylacoleo as a distinct species, T. oweni.

    The basis provided by McCoy for the new species was as follows:

    Thylacoleo robustus Krefft, 1872: The name of Thylacoleo robustus was given by Krefft (1872a) to a right maxillary canine found at the Wellington Caves.  His only reason for assigning it to a distinct species was because the homologous tooth of T. carnifex was said to be reasonably smaller than that of the new species.  T. robustus is now considered a junior synonym of T. carnifex (Archer & Dawson, 1982).

   Thylacopardus australis Owen 1888: An array of fossil specimens from a newly found cave in Wellington valley, New South Wales, gave Owen a skull lacking a mandible, and that was smaller than his previous specimens of Thylacoleo.  He called it Thylacopardus australis, the name first being published in Nature (1888).  Owen presented his complete description of the specimen to the Royal Society of London in 1888, however, the paper itself was only published by title (1889 or 1888).  Two characteristics were used to make a distinction between this new genus and Thylacoleo, its small size and its possession of a small molar or "molariform prominence" on the posterior margin of the palate behind M¹.

    Owen wrote in his yet to be published manuscript (quoted by C. Anderson in 1929) that "the dentinal structure" of the molariform prominence has been shown, thus exhibiting the existence of a second maxillary molar.  The manuscript and type specimen (which was then in the collection of the Geological and Mining Museum, Sydney) was examined by Anderson and he came to the determination (1929) that the "M²" was merely the broken edge of the post-palatine bar and showed no evidence of dentine material.  He held that the animal was in fact Thylacoleo carnifex, but could only have been a young individual on account of its small size and the fact that it had unworn teeth.  Anderson pointed out that even though Owen's measurements of the skull bones of Thylacopardus and Thylacoleo displayed a reasonable degree of difference in size, the lengths of the maxillary carnassials were virtually the same.  Therefore, it is unlikely that Thylacopardus represents a valid genus and species.  It is considered as a junior synonym of T. carnifex by Archer and Dawson (1982).

   Thylacoleo crassidentatus Bartholomai, 1962: Included in the material from the Darling Downs area kept at the Queensland Museum in Brisbane is a collection which comes from Chinchilla, northwestern Darling Downs.  These specimens were thought by Woods (1956) to be significantly different enough to warrant continuing study, and proposed that they were of Pliocene age.  All known Thylacoleo carnifex material is considered to be of Pleistocene age.  Acquiring a partial right mandibular ramus from Chinchilla gave Bartholomai (1962) the necessary material for the classification of a new species, T. crassidentatus.  Bartholomai lists the basic distinguishing characteristics of this species as compared to T. carnifex as:

    Further material which can be referred to T. crassidentatus has been described from the Allingham Formation (Lower Pliocene) of Northern Queensland (Archer & Wade, 1976) and at Bow in New South Wales (Archer & Dawson 1982).

    Balladonia specimens: Glauert (1912) and Merrilees (1968) both refer to Thylacoleo material from caves near Balladonia, Western Australia.  Merrilees makes note that Glauert failed to differentiate between the various caves around Balladonia but Merillees himself mentions Wonberna Cave as being the source of Thylacoleo "probably not carnifex".  This animal was significantly smaller than T. carnifex and may be a distinct species (Finch & Freedman, 1982).  The age of the deposit from which the material came is not known.

   Thylacoleo hilli Pledge, 1977: An isolated left P³ of Thylacoleo found in 1956 in a cave at Curramulka, South Australia has been described by Pledge (1977).  The fossil is of unknown age, but is thought to be Late Miocene or Early Pliocene.  It is quite peculiar due to its small size (Finch & Freedman, 1982), being roughly half the length of the P³ of T. carnifex.  Because of this, it has been designated a new species, Thylacoleo hilli.  A discovery of new material referable to this species at Bow, New South Wales, has been reported by Archer and Dawson (1982).

   Wakaleo: From the Miocene deposits of South Australia and the Northern Territory have come thylacoleonids which are considered by Clemens and Plane (1974) to be a genus which bears notable dissimilarities from Thylacoleo.  These animals had a different dentition, as they had retained three mandibular molars, had a comparatively shorter carnassial tooth, and bore only one precarnassial premolar.  The latter is a characteristic not evident in Thylacoleo species.  Such dissimilarities, they gathered, was a sufficient basis for constituting a new genus, Wakaleo.

    The species name, W. oldfieldi, was given to the South Australian specimen from lake Ngapakaldi consisting of a left dentary which includes the incisor, P3 and M1.  Also present are alveoli for P1 (or P2), M2 and M3.  Because of wear facets formed on an isolated M2, it was presumed that there were two maxillary molars which were positioned posterior to, and not lingual to, the carnassial.

    The fossil from Bullock Creek, Northern Territory was a fragment of mandible bearing a single molar, M1, alveoli for M2 and M3, and a partial alveolus for I1.  The dentary was somewhat larger than that of W. oldfieldi, and when one takes into consideration the spatial separation as well as a possible time difference between the two specimens, Clemens and Plane (1974) felt well-founded in designating a second species, W. vanderleuri.

    A third species of this genus, W. alcootaensis, from the Miocene Alcoota local fauna of the Northern Territory (Archer & Rich 1982), would appear to be the largest member of the genus yet found.  This specimen, a fragment of a skull, retained tribosphenic molars, a characteristic which implies secondary modification of the ancestral quadritubercular molars for a life of carnivory.

    Mention is made by Clemens and Plane (1974) of an edentulous (missing its teeth) skull fragment from the mid-Miocene Ngapakaldi Fauna.  Possibly, it was a thylacoleonid, as it displays alveoli for an enlarged P³ and four molars.