Rhizosmilodon
Name:
Rhizosmilodon
(Root Smilodon).
Phonetic: Rhy-zo-smy-lo-don.
Named By: Steven C. Wallace & Richard
C. Hulbert Jr - 2013.
Classification: Chordata, Mammalia, Carvnivora,
Felidae, Machairodontinae, Smilodontini.
Species: R. fiteae (type).
Diet: Carnivore.
Size: Uncertain due to lack of remains, but
analysis of fore limbs leads to an estimated weight of between
55.7-58.3 kg for one individual, and 76.6-85 kg for another.
Known locations: USA, Florida - Upper Bone
Valley Formation.
Time period: Early Pliocene.
Fossil representation: Partial mandible (lower
jaw) with teeth, as well as a complete left tibia and proximal
right tibia, left humerus and distal end of the right humerus.
Remains are of at least two individuals.
Though
only named from a jaw and associated fore limb bones, the 2013
description of Rhizosmilodon meant excitement for
anyone interested in
the machairodonts,
better known as the sabre-toothed cats. As of
2013, Rhizosmilodon is considered to be the
oldest known member of
the Smilodontini, the type genus of which is the world famous
Smilodon.
Not surprisingly Rhizosmilodon is considered to
have been
more primitive that the earliest known Smilodon
genus, S.
gracilis, but Rhizosmilodon is also
considered to have been more
primitive than Megantereon.
Limb
bones attributed to Rhizosmilodon have led to size
estimates for the
genus ranging between just under fifty-six and eighty-five kilograms in
weight. The describers of Rhizosmilodon noted
that the extant
(still alive) big cats Puma concolor (a.k.a.
cougar/mountain
lion) and Panthera onca (Jaguar) would have
been roughly
equivalent to Rhizosmilodon in terms of weight.
However, if this
was as large as Rhizosmilodon got, then the genus
would have actually
been quite small when compared to most later machairodonts.
Because
of the early appearance and primitive features, Rhizosmilodon
may
have been an ancestral genus to later machairodonts, particularly
smilodonts that appeared in North America later in the Pliocene and
subsequent Pleistocene. It really is still early days to guess at the
full temporal range of Rhizosmilodon, but it may
have lived alongside
other machairodonts such as Megantereon hesperus
and Smilodon gracilis
before disappearing from Pliocene North America.
The
name Rhizosmilodon was named by the describers to
mean ‘Root
Smilodon’, and was intended to be a reference to
the earlier
appearance and possible ancestry of Rhizosmilodon
to the Smilodon
genus, as the ‘root’ of the latter genus. The name Smilodon
actually means ‘knife tooth’ and is a reference to the enlarged
sabre’like canines of the upper jaw. The type species name of
Rhizosmilodon, R. fiteae,
is in honour of Barbara Fite who
donated the Rhizosmilodon paratype specimen.
Further reading
- A New Machairodont from the Palmetto Fauna (Early Pliocene) of
Florida, with Comments on the Origin of the Smilodontini
(Mammalia, Carnivora, Felidae) - Steven C. Wallace
& Richard C. Hulbert Jr - 2013.
- Body size of Smilodon (Mammalia: Felidae). - P.
Christian & M. Harris (2005).
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