Ulnar articular surface 3-D landmarks and ecomorphology of small mammals: a case study of two early Miocene typotheres (Notoungulata) from Patagonia

Abstract

Articular surfaces reflect the relative movements between adjacent bones, and the ones involved in the elbow joint provide information about forelimb movements and may be useful for making inferences about the substrate use. The proximal articular surface of the ulna was examined through 3-D geometric morphometrics, in order to assess its usefulness as a proxy for paleoecological interpretations; particularly for two small mammals from the early Miocene of Patagonia. The sample was composed of 22 extant small mammals (rodents, carnivorans and primates) and two extinct typotheres: Hegetotherium mirabile (Hegetotheriidae) and Interatherium robustum (Interatheriidae). Forty-five landmarks were taken and principal component analysis (PCA) was used to explore the morphospace structure. The results of PCA for the whole surface were inconclusive; therefore, successive analyses were made, subdividing the surface into sub-units. The PCA for the proximal part of the trochlear notch was the most informative, allowing the recognition of morphospaces with functional value: one for digging rodents and another for most climbers. Neither typothere would have had a specialisation for climbing or digging in the features analysed. This study allows morphological patterns on different parts of a joint to be detected; interpreted, at least partially, as differential responses to different kinds of mechanical stress.

The tarsal‐metatarsal complex of caviomorph rodents: Anatomy and functional‐adaptive analysis

“…Similarly, fossorial octodontoids, belonging to three different families (Echimyidae, Ctenomyidae and Octodontidae) have short and robust metatarsals. So, as noted in other mammals (e.g., Muñoz, Cassini, Candela, & Vizcaíno, 2017;Samuels et al, 2013), within and between different superfamilies of caviomorphs, species with similar locomotor habits display similar tarsal-metatarsal features as a result of convergent evolution, despite their distinct evolutionary histories.…”

Notoungulata and Astrapotheria (Mammalia, Meridiungulata) of the Santa Cruz Formation (Early-Middle Miocene) Along the Río Santa Cruz, Argentine Patagonia

“…The paleoecological interpretations and comparisons were made at a genus level following most of the inferences in the studies performed with the coastal materials both in the taxa analysed here and in other clades (e.g., Cassini et al, 2012;Cassini, 2013;Toledo et al, 2013Toledo et al, , 2015Muñoz et al, 2017).…”

Functional morphology of the forelimb of Early Miocene caviomorph rodents from Patagonia

“…The proximal facet, formed by the trochlear and radial notch, provides valuable information on the relationship of the ulna to the humerus and radius (Muñoz et al . ). A mediolaterally broad medial coronoid process, when compared with the radial notch, can perform a greater function of weight support of the body, releasing the radius from loads, a remarkable feature in the Erethizontidae compared to the rest of the Hystricognathi (Candela & Picasso ).…”

“…Steiromys has the most lateralized radial notch among the analysed taxa (Fig. 4E), which would give more freedom of movement to the radius (but see Muñoz et al 2017).…”