Chaeropodidae Gill, 1872

Beck, Robin M. D., Voss, Robert S. & Jansa, Sharon A., 2022, Craniodental Morphology And Phylogeny Of Marsupials, Bulletin of the American Museum of Natural History 2022 (457), pp. 1-353 : 211-213

Chaeropodidae Gill, 1872

CONTENTS: Chaeropus (fig. 37).

STEM AGE: 20.0 Mya (95% HPD: 15.3–24.5 Mya).

CROWN AGE: N/A.

UNAMBIGUOUS CRANIODENTAL AUTAPOMORPHIES: Accessory palatal fenestrae present (char. 35: 0→1; ci = 0.250); auditory bulla large, contacting rostral tympanic process of petrosal (char. 55: 1→2; ci = 0.300); upper canine with distinct anterior cusp only (char. 112: 0→3; ci = 0.375); paracone and metacone subequal (char. 137: 2→1; ci = 0.400); M1 preparacrista present (char. 138: 1→0; ci = 0.333); second lower premolar (p2) distinctly taller than p3 (char. 156: 1→0; ci = 0.118); cristid obliqua on m1 contacts metaconid (char. 169: 1→0; ci = 0.250); and anterior terminus of cristid obliqua of m2–4 bypasses metacristid to terminate at entoconid or entocristid (char. 170: 0→1; ci = 0.500).

COMMENTS: Chaeropus , the sole known representative of the family Chaeropodidae , is recovered in our molecular (figs. 27–29) and total-evidence (figs. 32, 33) analyses as sister to the remaining perameloids (crown-clade peramelemorphians) as also found in several other recent molecular and total-evidence analyses ( Westerman et al., 2012; Kear et al., 2016; Travouillon and Phillips, 2018). However, as already noted (see Perameloidea above), the dated totalevidence analysis of Travouillon and Phillips (2018: figs. 1E, 2) placed Chaeropus sister to Macrotis , the dated total-evidence analyses of Travouillon et al. (2021) placed Chaeropus sister to Peramelidae , and the molecular phylogenetic analyses of Travouillon et al. (2019) placed Chaeropus as either sister to Isoodon + Perameles + Peroryctes (in an undated maximum likelihood analysis; Travouillon et al., 2019: fig. 15) or sister to Isoodon (in an Bayesian node-dating analysis; Travouillon et al., 2019: fig. 16). The underlying cause(s) of these topological differences warrants further investigation.

Most of the unambiguous cranidodental autapomorphies of Chaeropodidae listed above are homoplastic within Peramelemorphia . However, the paracone and metacone of the upper molars are subequal in height in Chaeropus (see Wright et al., 1991: plate 1A), whereas the metacone is distinctly taller in all other known peramelemorphians. The morphology of the m2–4 cristid obliqua is also unusual in Chaeropus in that it terminates at the entocristid rather than the metacristid (a morphology also seen in some Isoodon specimens). These two dental features may be connected with the predominantly grazing diet of Chaeropus by facilitating greater transverse shear ( Wright et al., 1991; Travouillon, 2016).

Besides the two Recent species— Chaeropus ecadautus and the recently described C. yirratji (see Travouillon et al., 2019)—only one other chaeropodid is currently known: Chaeropus † baynesi from the latest Pliocene or earliest Pleistocene (2.47–2.92 Mya) Fisherman’s Cliff Local Fauna in New South Wales ( Travouillon, 2016; Travouillon et al., 2017). Thus, Chaeropodidae is currently characterized by a lengthy ghost lineage; based on the divergence dates estimated here and in other recent studies ( Westerman et al., 2012; Kear et al., 2016; Travouillon and Phillips, 2018), fossil chaeropodids should be expected in fossil Australian deposits from the early-to-middle Miocene onward.