What is Fruitafossor? A basal echidna from Colorado

Updated March 23, 2021
with revised scoring that moved Fruitafossor, an edentate-mimic, to a basal relationship with Cifelliodon (Early Cretaceous) and Tachyglossus (extant), two echidnas. Luo and Wible 2005 tested Tachyglossus, but did not know about Cifelliodon, published in 2018.

Fruitafossor
was a Late Jurassic fossorial digger with universally acknowledged xenarthran (edentate) traits including a long lumbar area that included xenarthran (interlocked) vertebrae. For reasons unknown Luo and Wible 2005 did not test Fruitafossor against another fossorial xenarthran, Peltephilus. Rather the authors compared their digger to an arboreal sloth, Bradypus, among several other taxa, including distinctly different anteaters and armadillos.

Figure 1. Scapula of Fruitafossor compared to several candidate sisters. Luo and Wible made things a bit more difficult by presenting left and right scapulae. Here they are all left scapulae for ready comparison. There is no doubt that the Fruitafossor scapula looks more like that of Ornithorhynchus.

ºªº Figure 1. Scapula of Fruitafossor compared to several candidate sisters. Luo and Wible made things a bit more difficult by presenting left and right scapulae. In frame 2 they are all left scapulae for ready comparison. There is no doubt that the Fruitafossor scapula was illustrated to look more like that of Ornithorhynchus. Unfortunately the photo data (Fig. 2) does not clearly support that shape. That shape is so important, it needed to be better documented.

Luo and Wible 2005
brought us a small, mostly articulated, rather crushed and incomplete Late Jurassic mammal with simple blunt teeth and digging forelimbs. Fruitafossor windscheffeli (Figs. 1–6) is best represented by a CT scan (Figs. 2–4) and original drawings (Figs. 5, 6) created by Luo and Wible.

Figure 2. Fruitafossor in situ from Digimorph.org and used with permission and here colorized to an uncertain extent.

Figure 2. Fruitafossor in situ from Digimorph.org and used with permission and here colorized to an uncertain extent. All those little white dots could be scattered osteoderms.

The original analysis
nested Fruitafossor between extremely tiny Hadrocodium + Shuotherium and the pre-mammal, Gobiconodon, in a tree topology that does not resemble the topology of the large reptile tree (LRT, 1048 taxa then, 1818+ taxa now). The authors noted Fruitafossor is “not a eutherian, let alone a xenarthran” despite noting Fruitafossor had tubular molars and xenarthran intervertebral articulations, traits otherwise found only in xenarthrans.

Earlier
the LRT nested Fruitafossor with the horned, armored digging ‘armadillo’ more closely related to BradypusPeltephilus. Reconsideration of several traits now nests Fruitafossor with the echindas Cifelliodon and Tachyglossus.

Luo and Wible compared
Fruitafossor to the arboreal and extant Bradypus, but not to the fossorial and extinct Peltephilius.

Figure 5. Several drawings from Zhou and Wible that one must trust for accuracy. The verification data is too fuzzy to validate.

Figure 3. Several drawings from Luo and Wible that one must trust for accuracy. The verification data is too fuzzy to validate. As in other xenarthrans, the ilia actually form a pair of horizontal plates on either side of the long fused and eroded sacrals. Four fingers is a trait shared with Peltephilus. Imagine that rib cage wider and not so deep.

The retention of the coracoid
in Fruitafossor is a trait found in pre-Therian mammals. Comparisons to echidnas were previously overlooked, but are presently more parsimonious, down to the sprawling limbs. Early Cretaceous Cifelliodon retains derived tubular teeth, precursors to the toothless condition found in extant Tachyglossus. Loss of manual digit 5 in Fruitafossor could be due to taphonomy since the skeleton is somewhat scattered (Fig. 2).

Figure 1. Early Cretaceous Cifelliodon is ancestral to the living echidna, Tachyglossus according to the LRT. The lack of teeth here led to toothlessness in living echidnas. The skull of Tachyglossus is largely fused together, lacks teeth and retains only a tiny lateral temporal fenestra (because the jaws don't move much in this anteater. Compared to Cifelliodon the braincase is greatly expanded, the lateral arches are expanded and the two elements fuse, unlike most mammals.

Figure 4. Early Cretaceous Cifelliodon is ancestral to the living echidna, Tachyglossus according to the LRT. The lack of teeth here led to toothlessness in living echidnas. The skull of Tachyglossus is largely fused together, lacks teeth and retains only a tiny lateral temporal fenestra (because the jaws don’t move much in this anteater. Compared to Cifelliodon the braincase is greatly expanded, the lateral arches are expanded and the two elements fuse, unlike most mammals.

Figure 3. Tachyglossus skeleton, manus and x-rays. Note the perforated pelvis.

Figure 5. Tachyglossus skeleton, manus and x-rays. Note the perforated pelvis.

Fruitafossor windscheffeli
(Luo and Wible 2005; Late Jurassic) was originally considered a digging basal mammal based on the shape of the scapula and sprawling forelimbs. Here Fruitafossor nests as a basal echidna from Colorado, prior to tooth loss. The teeth are blunt, as in xenarthrans, and the four fingers (perhaps five originally) have broad, digging claws with short phalanges. The torso was wider than deep with a long lumbar area that included xenarthran (interlocked) vertebrae. The skeleton was µCT scanned (see above).


References
Luo Z-X and Wible JR 2005. A late Jurassic digging mammal and early mammal diversification. Science 308:103–107.

wiki/Fruitafossor

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