Megalonychinae, Trouessart, 1904

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 : 1526-1527

Megalonychinae

PP = 100, age = 10.82 Mya (8.60–13.21).

This clade is composed of the genera Megalonyx (Megalonychini) and Pliometanastes , plus a clade uniting Pliomorphus, Antillean megalonychines and Choloepus (Choloepodini) and a clade of intertropical megalonychids (Ahytheriini). Alternative arrangements were observed for the relationships among Megalonyx , Pliometanastes and the other megalonychines: as successive sister taxa, diverging earlier than all other megalonychines— Megalonyx earliest (H models EW and IW100, par_EW and par_ IW100), Pliometanastes earliest (UN and A models, especially those including ACRV); Megalonyx and Pliometanastes as sister taxa to each other, and this clade sister to all other megalonychines (A models with equal rates, excepting A1_e); or as sister to Ahytheriini (H models IW10 and IW5, par_IW10 and par_IW5).

Megalonychinae was supported by 59 synapomorphies (24 for both methods and 35 exclusively for BI): Cf1 and cf1 strongly depressed relative to molariforms; Cf1 smaller than smallest molariform (BI); long axis of molariforms oblique to toothrow along its entire length; trapezoidal Mf2 and Mf3 cross-section; trapezoidal mf2 cross-section; trigonal Mf4 cross-section; mandibular horizontal ramus length less than two times its depth (BI); ascending ramus of mandible completely covers the posterior teeth in lateral view (BI); three processes of ascending mandibular ramus equidistant (BI); absence of a medial ridge running along anterior edge of coronoid process (BI); maximum height of coronoid process shorter than its anteroposterior length (BI); intermediate development of angular process; symphysial spout much shorter than the length of molariform toothrow (BI); posterior external opening of mandibular canal opens laterally on horizontal ramus (BI); low and broad braincase (BI); reflexed basicranial/basifacial axis; nuchal crest continuous with dorsal edge of zygomatic process of squamosal (BI); premolariform portion of palate roughly equal to, or longer than molariform toothrow (BI); presence of fossa at the anterior edge of maxilla, lateral to external nares (BI); presence of ventral extension in maxilla for dental alveoli (BI); ventral extension in maxilla for dental alveoli only posteriorly (BI); jugal does not participate in rim of maxillary foramen (BI); absence of dorsal process of premaxilla; presence of a crest at median suture of palatine (BI); presence of alisphenoid-parietal contact (BI); anteroventrally inclined zygomatic process of squamosal; absence of a marked postorbital constriction (BI); postorbital process well anterior to maxillary foramen; semicircular occiput, in posterior view (BI); hypoglossal foramen smaller than jugular foramen (BI); basioccipital narrow and convex mediolaterally (BI); median fusion of posterior alae of vomer; ectotympanic fused dorsally; carotid foramen fully exposed in ventral view (BI); anteroposteriorly oriented entotympanic (BI); dorsal edge of entotympanic with a strong concave curvature in lateral view, with dorsal projection at anterior end (BI); lateral process of entotympanic extending above anterior portion of tympanic, forming a portion of the roof of tympanic cavity (BI); bulbous, mediolaterally expanded paroccipital process; absence of paroccipital process foramen (BI); nuchal and exoccipital crests diverge proximally and converge distally (BI); posteroventrolateral stylomastoid canal; entotympanic, ectotympanic and pterygoid composing eustachian tube opening (BI); hypoglossal foramen recessed dorsally, lies at same level as jugular foramen; presence of a groove connecting the internal opening of the posterior lacerate foramen to foramen magnum; glenoid fossa ventral to superficies meatus; mediolaterally widened glenoid fossa (BI); smooth posterior surface of glenoid; glenoid fossa wellseparated from porus acusticus (BI); laterally directed root of zygoma; deltoid crest faces anteriorly, reaching the medial side of the humerus in anterior view (BI); strongly marked brachiocephalicus crest of humerus (BI); quadrangular laterodistal corner of scaphoid, in dorsal view (BI); fusion of trapezium and metacarpal I, forming the carpal-metacarpal complex; absence of a strong concavity between greater trochanter and the head of femur (BI); moderately developed lesser trochanter of femur, with a laminar projection; femoral patellar trochlea isolated or only abuts the condylar surfaces; medial trochlear ridge protruded anteriorly to lateral trochlear ridge (BI); distal epiphyses of femur twisted with respect to the main axis; and an obtuse (around 120°) angle formed by facets for cuboid and metatarsal IV, in metatarsal V.