Megalonychidae, Ameghino, 1889

Casali, Daniel M, Boscaini, Alberto, Gaudin, Timothy J & Perini, Fernando A, 2022, Reassessing the phylogeny and divergence times of sloths (Mammalia: Pilosa: Folivora), exploring alternative morphological partitioning and dating models, Zoological Journal of the Linnean Society 196 (4), pp. 1505-1551 : 1525-1526

Megalonychidae plus Megatheriidae

PP = 100, age = 22.14 Mya (19.08–25.29).

The clade, which includes all megatherioids excepting the genera Pelecyodon and Schismotherium , was recovered in all Bayesian analyses using H models, and in par_EW and par_IW100, although in these MP analyses, Hapalops was not recovered closely associated with megalonychids, but as sister to the clade uniting all other megalonychids and megatheriids. In par_IW10 and par_IW5, a distinct arrangement was obtained, with a clade ( Hapalops , ( Pelecyodon , Schismotherium )) recovered as sister to Megatheriidae . In trees from analyses with UN and A models, in which Megatherioidea was recovered as paraphyletic, the clade uniting Megalonychidae and Megatheriidae is also absent.

The clade was supported by 16 synapomorphies (11 for both methods and five exclusively for BI): Cf1 and cf1 slightly depressed ventrally relative to molariforms; presence of a well-developed diastema between Cf1/cf1 and molariforms; ovate mediolaterally to rectangular Mf1 cross-section (B1); mandibular symphysis longer than molariform toothrow; horizontal orientation of spout, in lateral view; external opening of mandibular canal opens anterolaterally, on ascending ramus (B1); tip of zygomatic process anterior to frontoparietal suture; nuchal crest splits dorsally into anterior and posterior crests, with a raised triangular area in the dorsal surface of the skull roof (B1); nuchal crest overhangs occiput posteriorly; presence of a distinct neck at the base of occipital condyles (B1); rugose ectotympanic external surface; presence of an ectotympanic medial expansion; presence of pterygoid lateral groove for m. tensor veli palatini; medial extent of trochlear notch of ulna equal to or less than that of the olecranon (B1); straight posterior margin of ulnar diaphysis in lateral view; and lateroproximal process of tuber calcis more distal than medioproximal process.