Morphology of the tongue of Vermilingua (Xenarthra: Pilosa) and evolutionary considerations

Abstract

The tongue of anteaters (Xenarthra, Pilosa, Vermilingua) is a highly specialized for myrmecophagy. Here, we describe the topography and histology of the tongue, and compare it to that of other xenarthrans and other myrmecophagous eutherian mammals. The tongue of Vermilingua is long and slender, with an apical protuberance, which differs between Myrmecophagidae and Cyclopes didactylus. In the former, the rostral region is conical, and in the latter, it is dorsoventrally compressed, as observed in sloths. The tongue of Vermilingua has filiform and circumvallate papillae on the surface; foliate and fungiform papillae are absent. The filiform papillae of Myrmecophaga tridactyla are simple all over the tongue, differing from Tamandua tetradactyla and Cyclopes didactylus, which present composed filiform papillae in the rostral and middle regions. Histologically, the tongue has a peculiar organization of muscular and neurovascular tissues, differing from the usual mammalian pattern. However, the tongue structure is less divergent in Cyclopes. The presence of two circumvallate papillae is common to the three major clades of Xenarthra (Cingulata, Folivora and Vermilingua). In each group, the tongue may reflect functional features related to myrmecophagous (anteaters and some armadillos), omnivorous (remaining armadillos) and folivorous (sloths) feeding habits. The similarities between the tongues of Vermiligua and other non-xenarthran eutherian myrmecophagous mammals are somewhat general and, under close inspection, superficial, being an example of different lineages achieving the same morphofunctional adaptations through distinct evolutionary pathways.

Computed tomography and cross‐sectional anatomy of the head in the giant anteater (Myrmecophaga tridactyla)

“…The giant anteater uses the tongue to capture prey and transfer it to the oesophagus, and the oral cavity provides the space where this tongue is left when not being used (Endo et al., 2007). Casali et al., (2017) claimed that the morphology of the tongue may reflect functional features related to myrmecophagous feeding habits. At the level of the last cervical vertebrae, it was possible to identify the sternoglossus muscle.…”

“…At the root of the tongue, the sternoglossus muscle joins with the genioglossus muscle to form the free part of the tongue, although the sternoglossus muscle is the main muscle that forms the giant anteater tongue (Reiss, 1997). The sternoglossus muscle resulting from the fusion of sternohyoideus and hyoglossus muscles and is the main extrinsic muscle that contributes to the tongue in suborder Vermilingua (Casali et al, 2017).…”

“…There are several studies associating computed tomography and anatomical sections describing the nasal, oral, pharyngeal and cranial cavities in the mammals such as in one-humped camel (Blanco et al, 2014), donkey (El-Gendy et al, 2014), Egyptian sheep (Awaad et al, 2019) and red fox (Mahdy & Zayed, 2020). The anatomy of the head and neck regions in the giant anteater been studied in some aspects, such as, for example, the anatomy of the masticatory system (Reiss, 1997;Naples, 1999;Endo et al, 2007), the shape and relationships of the hyoid apparatus (Borges et al, 2017), and morphology of the tongue (Casali et al, 2017). However, to our knowledge, there are no descriptions of the head in the giant anteater using CT.…”

Exploring the Ecomorphology of Two Cretaceous Enantiornithines With Unique Pedal Morphology

“…trivirgata, access into the hard wood substrate is achieved through a pair of specialized rostromedially placed incisors, similar to rodents, paired with robust jaw muscles (Morris et al, 2018). Similarly, although not feeding within a wood-substrate, members of the families Myrmecophagidae (ant-eaters) and Orycteropodidae (aardvarks) remove hard substrates (arthropod mounds) with their robust forelimbs in order to access their prey with specialized elongated tongues (Sesoko et al, 2015;Casali et al, 2017;Legendre and Botha-Brink, 2018). In extant avian wood-probers, picids have evolved dense skulls and a suite of other features including reinforced cervical vertebrae that aid in the hammering and subsequent removal of woody matter (Lovette and Fitzpatrick, 2016), whereas the honeycreeper H. munroi has evolved a stocky, dense, lower bill that allows it to hammer into wood.…”

Pathology in the appendicular bones of southern tamandua, Tamandua tetradactyla (Xenarthra, Pilosa): injuries to the locomotor system and first case report of osteomyelitis in anteaters

“…Anteaters have peculiar anatomical features that distinguish them from all other mammals such as an elongated rostrum with a posteriorly displaced palate, incomplete zygomatic arch, a worm-like tongue attached in the xiphoid process of the sternum, absence of teeth and forelimbs with strong muscles adapted for the increase of force during the movement (e.g. The Teres major with its origin enlargement on the scapula and more distally inserted on the humerus) [3, 4]. Vermilingua are endemic to the Neotropics and widely distributed in South and Central America, including Trinidad [2].…”