Myrmecobiidae Waterhouse, 1841

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 : 220

Myrmecobiidae Waterhouse, 1841

CONTENTS: Myrmecobius (fig. 41).

STEM AGE: 20.2 Mya (95% HPD: 14.4–25.3 Mya).

CROWN AGE: N/A.

UNAMBIGUOUS CRANIODENTAL AUTAPOMORPHIES: Masseteric process present and projecting ventrally below plane of molar alveoli (char. 6: 0→1; ci = 0.125); jugal terminates in a ventrally expanded ectoglenoid crest (char. 22: 0→1; ci = 0.167); glenoid process of alisphenoid absent (char. 23: 1→ 0; ci = 0.125); scars of M. temporalis origin on braincase not fused middorsally to form sagittal crest in adults (char. 27: 1→0; ci = 0.059); maxillopalatine fenestrae consistently absent (char. 36: 1→0; ci = 0.111); posterolateral palatal foramina present, with complete posterior margins (char. 40: 1→0; ci = 0.200); palate extends posterior to presphenoid-basisphenoid suture (char. 42: 0→1; ci = 1.000); pterygoids separated from presphenoid by palatine-basisphenoid contact (char. 46: 0→1; ci = 0.111); pterygoids long, extending posteriorly to sheath the ventral margin of the carotid canal (char. 47: 0→1; ci = 0.333); masseteric fossa perforated by a distinct masseteric foramen (char. 99: 0→1; ci = 0.333); angular process weakly or not inflected (char. 102: 0→1; ci = 0.250); premolariform second upper premolar (P2) distinctly taller than premolariform P3 (char. 119: 2→0; ci = 0.118); i2 alveolus like those of i1 and i3 (char. 149: 0→1; ci = 0.250); paraconid well developed, but paracristid indistinct or absent on m1 (char. 159: 0→2; ci = 0.400); paraconid well developed, but paracristid indistinct or absent on m2 and m3 (char. 161: 0→2; ci = 0.667); cristid obliqua absent or indistinct (char. 167: 0→1; ci = 0.500); hypoconid small and indistinct (char. 172: 0→1; ci = 0.333); and entocristid indistinct or absent (char. 176: 0→1; ci = 0.077).

COMMENTS: Kealy and Beck (2017: table 1 ) defined Myrmecobiidae as the most inclusive clade including Myrmecobius fasciatus , but excluding Dasyurus viverrinus and Thylacinus cynocephalus . Under this definition, our dated total-evidence analysis ( fig. 33) indicates that the fossil dasyuromorphians † Barinya and † Mutpuracinus are myrmecobiids, as did the dated total-evidence analysis of Kealy and Beck (2017: fig.3). Given our estimate for the age of the split between the Myrmecobius lineage and Dasyuridae (median: 24.9 Mya; 95% HPD: 21.8–29.4 Mya) and those of other recent studies (e.g., Mitchell et al., 2014; Westerman et al., 2016; Kealy and Beck, 2017), we would expect stemmyrmecobiids in the fossil record from at least the early Miocene onward; the earliest of these would presumably have had a “typical,” unreduced dasyuromorphian dentition, in contrast to the secondarily simplified dentition of Myrmecobius . Thus, it is not implausible that † Barinya and † Mutpuracinus are indeed early myrmecobiids. However, the Myrmecobius + Barinya + Mutpuracinus clade receives only relatively weak support here (BPP = 0.67), and only one craniodental feature optimizes as an unambiguous synapomorphy, namely loss of the posterior cutting edge of P3 (char. 124: 1→2; ci = 0.667), which is clearly the case in † Barinya ( Wroe, 1999) , but which cannot be scored in † Mutpuracinus based on available material ( Murray and Megirian, 2000; Murray and Megirian, 2006a). We consider the evidence that Barinya and Mutpuracinus are stem myrmecobiids to be equivocal pending further studies, so we here restrict Myrmecobiidae to Myrmecobius .

Myrmecobius is characterized by a long list of craniodental apomorphies not seen in other dasyuromorphians: many of these are dental, but there are also a large number of unusual cranial features (see also Archer, 1976b, 1984c; Archer and Kirsch, 1977; Friend, 1989; Cooper, 2000). At least some of these apomorphies are likely related to myrmecophagy, including several relating to simplification of the molars (reflecting little or no occlusion between the upper and lower dentition; Charles et al., 2013).