Evolutionary adaptations in the flexor digitorum profundus muscle in Tamandua mexicana (Xenarthra, Myrmecophagidae)

Abstract

The northern tamandua (Tamandua mexicana) is a neotropical mammal of the order Pilosa, suborder Vermilingua, and family Myrmecophagidae. This species has anatomical and functional adaptations in its forelimb for semiarboreal quadrupedal locomotion. Several studies have reported that the medial head of the triceps brachii and flexor digitorum profundus muscles are fused in species belonging to the family Myrmecophagidae. However, there is no reference to the innervation in these. The triceps brachii muscle is commonly innervated by the radial nerve and the flexor digitorum profundus muscle by the ulnar and median nerves. This study aims to describe the gross anatomy of the flexor digitorum profundus muscle in Tamandua mexicana with respect to the shape, origin, insertion, innervation, and arterial supply. Both forelimbs of nine specimens were used, which were dissected from superficial to deep layers. The formalin‐fixed caudomedial forearm muscles were weighed, and the weight percentages of individual forearm muscle specimens were calculated. The flexor digitorum profundus had the highest weight among the forearm muscles and consisted of five heads (three humerals, one radial, and one ulnar). These heads were innervated by median and ulnar nerves; therefore, based on the innervation pattern, we concluded that the medial head of the triceps brachii muscle is not fused with the flexor digitorum profundus. Therefore, the flexor digitorum profundus muscle is highly developed in Tamandua and occupies the caudal part of the arm and forearm, which is an evolutionary adaptation that could have occurred during evolution from the common ancestor of Tamandua and Myrmecophaga.

Evolutionary and terminological analysis of the flexor digitorum superficialis, interflexorii and palmaris longus muscles in kinkajou (Potos flavus) and crab‐eating racoon (Procyon cancrivorus)

“…Thus, the aim of this study was to perform a detailed description of the FDS, IF and PL muscles of P. flavus and P. cancrivorus , reviewing their characteristics such as origin, insertion, innervation and arterial supply and to report differences that have not been described by several authors in P. flavus (Beswick‐Perrin, 1871; Julitz, 1909; Taverne et al., 2018; Böhmer et al., 2019, 2020) and P. cancrivorus (Windle, 1888; Lima et al., 2010; Santos, Bertassoli, Rosa, et al., 2010). This study also carried out a comparative study with those reported on other carnivores and primates to review the most appropriate terminology of these muscles according to their attachments, functionality and innervation, as recommended by several authors (Diogo & Abdala, 2010; Diogo & Wood, 2012; Kawashima et al., 2017; Vélez‐García et al., 2020). In carnivores, it is very common to find reports with several names for the same muscles; for example, the FDS is named as PL or the IF as FDS.…”

Evolutionary anatomical and functional characteristics of the intrinsic shoulder and brachial muscles in the northern anteater (Tamandua mexicana)

“…The m. anconeus medialis is similar in several species of Xenarthra (Galton, 1869;Humphry, 1869;Macalister, 1875b;Pereira et al, 2021;Rapp, 1852;Taylor, 1978;Vélez-García et al, 2021;Windle & Parsons, 1899). However, in B. variegatus, this muscle is a head of m. triceps brachii (accessory anconeus) (Olson et al, 2018).…”

“…Some anatomical studies in Xenarthrans present a functional analysis of the thoracic limb muscles (Amson & Nyakatura, 2018;Nyakatura & Fischer, 2011;Olson et al, 2016Olson et al, , 2018Polania-Guzm an & Vélez-García, 2019;Taylor, 1978;Toledo et al, 2013;Vélez-García et al, 2021). In order to perform such an analysis, it is necessary to take the muscle mass of the thoracic limbs into consideration (Polania-Guzm an & Vélez-García, 2019;Souza-Junior et al, 2021) that is a key variable for analyzing muscle strength by means of the physiologic cross-sectional area (Olson et al, 2018).…”

“…The species of the genus Tamandua perform fossorial and climbing activities (Amson & Nyakatura, 2018) and eat terrestrial and arboreal ants or termites with the help of the filiform papillae of their tongue (Naugher et al, 2004). The thoracic limb muscles of Tamandua are adapted to arboreal and terrestrial locomotion, providing it with the ability to obtain food and defend itself despite its small and toothless mouth (Polania‐Guzmán & Vélez‐García, 2019; Taylor, 1978; Vélez‐García et al, 2021). Therefore, the thoracic limb muscles are expected to be greatly developed in Tamandua to enable it to perform its normal daily activities (Vélez‐García et al, 2021).…”

“…The thoracic limb muscles of Tamandua are adapted to arboreal and terrestrial locomotion, providing it with the ability to obtain food and defend itself despite its small and toothless mouth (Polania‐Guzmán & Vélez‐García, 2019; Taylor, 1978; Vélez‐García et al, 2021). Therefore, the thoracic limb muscles are expected to be greatly developed in Tamandua to enable it to perform its normal daily activities (Vélez‐García et al, 2021).…”