The locomotion of Babakotia radofilai inferred from epiphyseal and diaphyseal morphology of the humerus and femur

Abstract

Palaeopropithecids, or "sloth lemurs," are a diverse clade of large-bodied Malagasy subfossil primates characterized by their inferred suspensory positional behavior. The most recently discovered genus of the palaeopropithecids is Babakotia, and it has been described as more arboreal than Mesopropithecus, but less than Palaeopropithecus. In this article, the within-bone and between-bones articular and cross-sectional diaphyseal proportions of the humerus and femur of Babakotia were compared to extant lemurs, Mesopropithecus and Palaeopropithecus in order to further understand its arboreal adaptations. Additionally, a sample of apes and sloths (Choloepus and Bradypus) are included as functional outgroups composed of suspensory adapted primates and non-primates. Results show that Babakotia and Mesopropithecus both have high humeral/femoral shaft strength proportions, similar to extant great apes and sloths and indicative of forelimb suspensory behavior, with Babakotia more extreme in this regard. All three subfossil taxa have relatively large femoral heads, also associated with suspension in modern taxa. However, Babakotia and Mesopropithecus (but not Palaeopropithecus) have relatively small femoral head surface area to shaft strength proportions suggesting that hind-limb positioning in these taxa during climbing and other behaviors was different than in extant great apes, involving less mobility. Knee and humeral articular dimensions relative to shaft strengths are small in Babakotia and Mesopropithecus, similar to those found in modern sloths and divergent from those in extant great apes and lemurs, suggesting more sloth-like use of these joints during locomotion. Mesopropithecus and Babakotia are more similar to Choloepus in humerofemoral head and length proportions while Palaeopropithecus is more similar to Bradypus. These results provide further evidence of the suspensory adaptations of Babakotia and further highlight similarities to both extant suspensory primates and non-primate slow arboreal climbers and hangers. J. Morphol. 277:1199-1218, 2016. © 2016 Wiley Periodicals, Inc.

Ontogenetic and morphological variation in primate long bones reflects signals of size and behavior

“…Previous studies interested in cross‐sectional strength and rigidity have controlled for muscle attachment sites like the deltoid tuberosity; typically by evaluating cross sections distal to the humeral‐midshaft (Alba et al, 2011; Marchi et al, 2016; Ruff, 2002). Analyses of mid‐humeral cross‐sectional shape ratios in a sample of humans, chimpanzees, and gorillas identified significant differences between the 50 and 40% locations among humans, but not among chimpanzees or gorillas (Mongle et al, 2015).…”

Postcranial elements of small mammals as indicators of locomotion and habitat

“…Studies of other mammalian orders (excluding here larger mammals such as ungulates and large diprotodontid marsupials) include smaller marsupials ( Lemelin, 1999 ; Argot, 2001 , 2002 ; Szalay & Sargis, 2001 ; Weisbecker & Warton, 2006 ; Bassavora, Janis & Archer, 2009 ; Flores & Díaz, 2009 ; Warburton et al, 2011 ; Den Boer, Campione & Kear, 2019 ); scandentians ( Sargis, 2002a , 2002b ); lagomorphs ( Reese, Lanier & Sargis, 2013 ); and xenarthrans ( Toledo, Bargo & Vizcaíno, 2013 ; Amson & Nyakatura, 2018 ; De Oliveira & Santos, 2018 ). A few such comparative studies have included a diversity of mammalian orders within each study ( MacLeod & Rose, 1993 ; Shockey, Croft & Anaya, 2007 ; Salton & Sargis, 2008 ; Croft & Anderson, 2008 ; Seckel & Janis, 2008 ; Kelly & Sears, 2011 ; Ercoli, Prevosti & Álvarez, 2012 ; Álvarez, Ercoli & Prevosti, 2013 ; Gould, 2014 ; Chen & Wilson, 2015 ; Figueirido, Martín-Serra & Janis, 2016 : Marchi et al, 2016 ; DeBay & Wilson, 2017 ; Muñoz et al, 2017 ).…”

Leg Muscle Architecture in Primates and Its Correlation with Locomotion Patterns

“…Though primates' primary locomotor pattern is quadrupedalism, locomotor specializations are present within the order depending on the taxon, diet, body size, and general ecology of a species (Fleagle, 2013). Functional morphologists have already generated a large body of work devoted to understanding the relationship between morphology, substrate use, and locomotion in primates (Ward and Sussman, 1979;Glassman, 1983;Schaffler et al, 1985;Fleagle and Meldrum, 1988;Ruff, 1988;Burr et al, 1989;Meldrum, 1991;Demes and Jungers, 1993;Rose, 1993;Gebo and Sargis, 1994;Nakatsukasa, 1996;Runestad, 1997;Strasser et al, 1998;Kimura, 2002;Ruff, 2002;Marchi, 2005;Wright, 2007;DeSilva, 2009;Kikuchi and Hamada, 2009;Marchi et al, 2016;Orr, 2017;Leischner et al, 2018). The majority of these studies focus on the bony morphology of the hands and feet-the parts of the body in direct contact with the substrate during locomotion-and the humerus and femur-the skeletal components that bear the greatest load in locomotion.…”