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 : 1526

Megalonychidae minus Hapalops

PP = 100, age = 18.21 Mya (16.90–19.84).

This clade is composed of the Santacrucian genera Hyperleptus , Megalonychotherium and Eucholoeops , along with the Megalonychinae . In all BI analyses and in par_IW, those three genera diverge successively, following the arrangement ( Hyperleptus , ( Megalonychotherium , ( Eucholoeops , Megalonychinae ))). In par_IW10 and par_IW5, they form a clade ( Megalonychotherium , ( Hyperleptus , Eucholoeops )), which is sister to Megalonychinae , and in par_EW, Megalonychotherium and Hyperleptus are in a polytomy with Eucholoeops and Megalonychinae .

The clade was supported by 18 synapomorphies (11 for both methods and seven exclusively for BI): Cf1 within size range of molariforms; presence of fossa on palatal surface of maxilla posterior to Cf1; maximum height of coronoid process shorter than its anteroposterior length (BI); snout elevated anteriorly; snout flared anteriorly, in dorsal view (BI); maximum length of nasal bones less than twice the width of both nasals; uniform nasal width in its anterior half, with lateral margins parallel (BI); well-developed buccinator fossa of maxilla, with a deep depression (BI); mediolateral width of premaxillary lateral rami greater than the anteroposterior length of incisive foramen; presence of a plate-like area anterior to incisive foramen; presence of pterygoid inflation (BI); elongate, triangular middle process of jugal (BI); dorsally situated infraorbital canal; deep zygomatic process, almost covers the entire squamosal exposure; pointed free end of zygomatic process; postorbital process of frontal roughly at the level of maxillary foramen; uniformly wide nuchal crest (BI); and medial expansion of entotympanic dorsal to basicranium.