A tiny Late Jurassic pre-rabbit: Henkelotherium

This earlier tracing and nesting
saw improvement with a higher resolution image.

Figure 1. Henkelotherium, a traditional pantothere, nests as a Late Jurassic pre-rabbit in the LRT.

Figure 1. Henkelotherium, a traditional pantothere, nests as a Late Jurassic pre-rabbit in the LRT. Image about 3.5x life size.

Henkelotherium guimarotae (Krebs 1991; Late Jurassic 150 mya; Figs. 1-3) was traditionally considered a pantothere or eupantothere. Here Henkelotherium nests with Nambaroo (Fig. 4) in the Plesiadapis + rabbits clade as a Late Jurassic member of the clade Glires. Like its sisters, the manus was small and the pes had long digits with sharp claws. The lumbar region was long and flexible. A tiny taxon, the image below (Fig. 2) is about twice natural size.

Figure 2. Henkelotherium reconstructed from DGS tracings in figure 1. Note the tiny manus and large pes, traits that continue into extant rabbits.

Figure 2. Henkelotherium reconstructed from DGS tracings in figure 1. Note the tiny manus and large pes, traits that continue into extant rabbits. Image about twice life size. What looks like an eye here is just a tracing of bone cracks, probably in the frontal. 

Wikipedia reports
“Eupantotheres are derived compared to symmetrodonts in having wider upper than lower teeth (although they still lack the protocone of tribosphenic forms.” The large reptile tree does not recover this clade. Rather the clade Lagomorpha should be extended to include the taxa found here (Fig. 3).

Figure 3. The Lagomorpha clade with the addition of Henkelotherium, Plesiadapis and Nambaroo.

Figure 3. The Lagomorpha clade with the addition of Henkelotherium, Plesiadapis and Nambaroo.

You might recall
that Nambaroo made news worldwide as ‘the grand-daddy of kangaroos‘, but the LRT nested it with rabbits as a kangaroo-mimic, more amazing than I thought.

Recently
I reconstructed the hind leg and foof of Nambaroo and was shocked to see the similarity to the kangaroo pes (Fig. 4). At first I thought I had made a mistake. The Nambaroo foot was exactly like that of a kangaroo… only different. As it turns out, Macropus, the kangaroo, enlarges pedal digit 3. Nambaroo enlarges pedal digit 4.

FIgure 4. Nambaroo hind limb reconstructed and compared to the Macropus kangaroo pes. Note: Nambaroo enlarges pedal digit 4, whereas Macropus enlarges digit 3. Remarkable convergence.

FIgure 4. Nambaroo hind limb reconstructed and compared to the Macropus kangaroo pes (boxed). Note: Nambaroo enlarges pedal digit 4, whereas Macropus enlarges digit 3. Remarkable convergence. The tibia was presented in proximal and distal parts. I’m not sure if they overlap or not, hence the ghosted version that does not overlap.

Nambaroo gillespieae (N. tarrinyeri Flannery & Rich 1986; Kear et al. 2007; Late Oligocene, 25 mya) was reported to be the “granddaddy of kangaroos” and to have had fangs, ‘probably for display,’ and mostly ate soft food such as fruit and fungi (Kear et al. 2007). It was found in Australia. In the large reptile tree Nambaroo nested far from kangaroos, with Henkelotherium and Plesiadapis + rabbits, close to the base of rodents + multituberculates. The first dentary premolar has the look of the same tooth in multituberculates. The short rostrum suggests a long soft trunk or nose.

Convergence is a wonderful thing.
It makes one taxon seem like another, but always betrays its true identity somehow. That’s what the LRT is for… testing a wide gamut of taxa so we don’t get fooled.

References
Flannery TF and Rich TH 1986. Macropodoids from the middle Miocene Namba Formatiion, South Australia, and the homology of some dental structures in kangaroos. Journal of Paleontology 60:418-447.
Kear BP, Cooke BN, Archer M and Flannery TF 2007. Implications of a new species of the Oligo-Miocene kangaroo (Marsupialia: Macropodoidea) Nambaroo, from the Riversleigh World Heritage Area, Queensland, Australia, in Journal of Paleontology 81:1147-1167.
Krebs B 1991. Skelett von Henkelotherium guimarotae gen. et sp. nov. (Eupantotheria, Mammalia) aus dem Oberen Jura von Portugal. Berl Geowiss Abh A.: 133:1–110.

wiki/Plesiadapis
wiki/Nambaroo
wiki/Henkelotherium

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