The exceptionally well preserved skull and mandible of the Miocene thylacinid
Nimbacinus dicksoni is described. Phylogenetic analysis
supports the contention that, within the family, the dentition of
N. dicksoni is unspecialised, less derived than the
recent Thylacinus cynocephalus for at least 12 features.
However, relatively few cranial specialisations evident in
T. cynocephalus clearly distinguish it from
N. dicksoni. These two taxa share at least three derived
cranial features not present in the most generalised thylacinid known from
significant cranial material, the late Oligocene
Badjcinus turnbulli. On the other hand, where comparison
is possible, even the most specialised thylacinid,
T. cynocephalus, is plesiomorphic for at least 10
cranial features common to modern dasyurids and five present in the Miocene
dasyurid, Barinya wangala. Two character states found in
thylacinids are more derived than in B. wangala.
Relative to the remaining dasyuromorphian family, Myrmecobiidae, represented
by the monotypic Myrmecobius fasciatus, thylacinids are
derived for five cranial features and plesiomorphic for five. It appears that
despite considerable anatomical diversity among the dentitia of thylacinids
and the presence of many highly specialised dental features in some species,
the crania of thylacinids have remained remarkably conservative. Even with
respect to dentitia, in terms of overall similarity, the Miocene
Thylacinus macknessiand late Oligocene material referred
to Thylacinus does not differ greatly from the recently
extinct T. cynocephalus. It now also seems probable that
T. macknessi was also very similar to
T. cynocephalus with respect to cranial anatomy.
Numerical parsimony analysis incorporating this new material produced moderate
bootstrap and Bremer support for a monophyletic Thylacinidae. In this same
treatment strict consensus placed Myrmecobius fasciatus
as the sister taxon to Thylacinidae–Dasyuridae, but bootstrap and Bremer
support was lacking. Both of these results are contra
those of the most recent attempt to resolve dasyuromorphian relationships
using numerical parsimony and anatomical data. In the present analysis, the
early Eocene Australian taxon, Djarthia murgonensis,
fell outside a clade inclusive of all other Australian taxa and was
monophyletic with the borhyaeniod, Mayulestes ferox.
This latter relationship is based on limited material, poorly supported and
considered highly unlikely, but it does strengthen the argument that formal
placement of D. murgonensis beyond the level of
Marsupialia incertae sedisis unwarranted at present.
Mouthpart homologies and life habits of Mesozoic long-proboscid scorpionflies