The evolution of hyoid apparatus in Xenarthra (Mammalia: Eutheria)

The hyoid apparatus reflects aspects of the form and function of feeding in living and extinct organisms and, despite the availability of information about this structure for Xenarthra, it remains little explored from an evolutionary perspective. Here we compare the morphology of the hyoid apparatus in xenarthrans, describing its general morphology and variation in each major clade and score these variations as phylogenetic characters, which were submitted to ancestral states reconstructions. The general hyoid morphology of Xenarthra consists of a v-bone (basihyal fused with the thyrohyals) and three paired bones (stylohyal, epihyal and ceratohyal), which are unfused in the majority of taxa. The clade-specific morphology observed here, allowed us to obtain additional synapomorphies for all major clades of Xenarthra (Cingulata, Pilosa, Folivora and Vermilingua), for Glyptodontididae, and for Nothrotheriidae. The fusion of hyoid elements are convergentelly achieved among the diphyletic extant tree sloths, some extinct ground sloths and glyptodontids. Despite the heavy influence of adaptive evolution related to feeding habits, the morphology of the hyoid apparatus proved to be a valuable source of phylogenetic information.     

Aquatic feeding in a terrestrial turtle: a functional-morphological study of the feeding apparatus in the Indochinese box turtle Cuora galbinifrons (Testudines, Geoemydidae)

The Indochinese box turtle Cuora galbinifrons is regarded as a purely terrestrial species, but our results demonstrate that it can feed both on land and in water. The inverse relationship between the relative development of the hyoid apparatus and the tongue found in the most investigated chelonians is not valid in the Indochinese box turtle. Our morphological analysis of the feeding apparatus reveals that the palate shape and the design of the tongue are consistent with terrestrial feeders, but the construction of the hyoid complex is more characteristic of aquatic feeders. Previous studies have demonstrated that tongue enlargement negatively impacts the capacity of the turtles to suction feed. The present study focuses on the aquatic intraoral prey transport kinematic patterns. Our analysis is based on high-speed films with 250 fr/s and high-speed cineradiography with 50 fr/s. The aquatic intraoral food transport mechanisms differ depending on prey size: small items are transported predominantly by “inertial suction”, whereas larger items are moved by the tongue—normally a clear terrestrial strategy. As the genus Cuora is ancestrally aquatic, the use of lingual food transport in the aquatic environment is presumably an aberrant modus typical only for the most terrestrial among the Asian box turtles.     

Myology of the Feeding Apparatus of Myrmecophagid Anteaters (Xenarthra: Myrmecophagidae)

The musculoskeletal feeding apparatus of anteaters in the family Myrmecophagidae (Eutheria: Xenarthra) is described, compared among the three extant genera (Tamandua, Myrmecophaga, Cyclopes), and interpreted in a phylogenetic framework. Character polarities are assessed with reference to other xenarthrans, eutherians, and didelphid marsupials. Xenarthrans are widely regarded as basal eutherians, and this is reflected in the apparent retention of plesiomorphic character states in jaw and pharyngeal musculature. Jaw closing muscles are architecturally simple, the stylohyoideus is absent, the stylopharyngeus is robust and architecturally complex, and the superior pharyngeal constrictor is weak. At the same time, the highly specialized trophic ecology of myrmecophagids is reflected in derived features of the jaw, tongue, and palatal musculature. The sternomandibularis is present, the tongue is largely composed of a sternog-lossus with no attachments to the hyoid apparatus, other glossus muscles are modified and do not enter the tongue, and the mylohyoideus and stylopharyngeus contribute to the soft palate, while other palatal muscles vary among the myrmecophagid genera. Feeding apparatus mycology provides further support for myrmecophagid monophyly. Documentation of the morphological transformations that lead to the myrmecophagid condition is hampered by incomplete data on feeding apparatus structure in nonmyrmecophagid xenarthrans (sloths and armadillos) but a tentative character mapping onto an independently derived phylogeny is offered.     

The use of the tongue and hyoid apparatus during feeding in lizards (Ctenosaura similis and Tupinambis nigropunctatus)

The use of the tongue and hyoid is examined in cineradiographic and electromyographic investigations of feeding in two species of lizards, Ctenosaura similis (Iguanidae) and Tupinambis nigropunctatus (Teiidae). In both animals food is transported through the oral cavity by regular cycles of the tongue. Tongue movements correlate with jaw and hyoid movement. Similarities between the two animals in the use of the tongue in food transport, lapping, pharyngeal packing, and pharyngeal emptying are detailed. Mechanisms of tongue protrusion are examined and it is shown that the tongue in Tupinambis is relatively more protrusible than in Ctenosaura. This difference is complementary with data on the greater reliance of Tupinambis on the tongue as a sensory organ. Tupinambis further differs from Ctenosaura in possessing a greater mobility of the hyoid. In many features of tongue use in food transport, lizards resemble mammals, supporting postulations of a basic pattern of intra-oral food transport. However, whether this pattern can be attributed to convergence or a common, primitive neural pattern of control cannot be distinguished. Lizards lack two major characteristics of mammalian food transport: regular masticatory cycles and an internal swallowing mechanism.     

Comparative anatomy and histology of xenarthran osteoderms

Reconstruction of soft tissues in fossil vertebrates is an enduring challenge for paleontologists. Because inferences must be based on evidence from hard tissues (typically bones or teeth), even the most complete fossils provide only limited information about certain organ systems. Osteoderms ("dermal armor") are integumentary bones with high fossilization potential that hold information about the anatomy of the skin in many extant and fossil amniotes. Their importance for functional morphology and phylogenetic research has recently been recognized, but studies have focused largely upon reptiles, in which osteoderms are most common. Among mammals, osteoderms occur only in members of the clade Xenarthra, which includes armadillos and their extinct relatives: glyptodonts, pampatheres, and, more distantly, ground sloths. Here, I present new information on the comparative morphology and histology of osteoderms and their associated soft tissues in 11 extant and fossil xenarthrans. Extinct mylodontid sloths possessed simple, isolated ossicles, the presence of which is likely plesiomorphic for Xenarthra. More highly derived osteoderms of glyptodonts, pampatheres, and armadillos feature complex articulations and surface ornamentation. Osteoderms of modern armadillos are physically associated with a variety of soft tissues, including nerve, muscle, gland, and connective tissue. In some cases, similar osteological features may be caused by two or more different tissue types, rendering soft-tissue inferences for fossil osteoderms equivocal. Certain osteological structures, however, are consistently associated with specific soft-tissue complexes and therefore represent a relatively robust foundation upon which to base soft-tissue reconstructions of extinct xenarthrans.     

The mechanism of dewlap extension in Anolis carolinensis (Reptilia: Iguanidae) with histological analysis of the hyoid apparatus

Anolis carolinensis has two aggressive displays involving movements of the hyoid apparatus: erection of the throat and extension of the dewlap. Erection of the throat is an enlargement of the gular region and dewlap extension consists of a vertical erection of the gular flap. Cinefluoroscopy and high speed cinematography show that the dewlap is extended in three phases: 1) protraction of the entire hyoid apparatus; 2) forward pivoting movement of the ceratobranchials II; and 3) retraction of the ceratobranchials II and the entire hyoid apparatus. The cartilaginous elements of the hyoid apparatus are variably mineralized. The entoglossal process and the hypohyals are the most calcified elements. The mineralized portion of the hyoid body, to which the other elements articulate, presents a complex pattern. The calcification of entoglossal process and the hypohyals stop just where they are fused with the hyoid body. The hyoid body presents four mineralized masses, two central corresponding to the base of the ceratobranchials II and two lateral being the head of the ossified ceratobranchials I. The lateral masses articulate on the central masses by a synovial joint. Morphologically, the ceratobranchials II form the hyoid body and become separated at the mid length of the synovial articulation of the ceratobranchials I and the hyoid body. The calcified matrix of the ceratobranchials II gradually changes from a large calcified mass (within the hyoid body) to a semicircle, opened ventrally, which permits their bending during dewlap extension. The highly mineralized posterior tip of the entoglossal process and the hyoid body serve as a pivot to pivoting forward movement of the ceratobranchials II producing at the change of the pattern of mineralization. Forward movement of the ceratobranchials II is produced by electrical stimulation of the M. branchio hyoideus. The opposition of the throat skin to the movement of the ceratobranchials II produces the bending of those longest elements. Electrical stimulation of the hyoid muscles confirms the key role of M. branchiohyoideus during dewlap extension. Simultaneous contractions of all the hyoid and extrinsic tongue (retractor and protractor) muscles with the M. branchiohyoideus during dewlap extension may be a possible motor pattern for dewlap extension in Anolis lizards.     

Ants and xenarthrans involved in a Quaternary food web from Argentina as reflected by their fossil nests and palaeocaves

Genise, J.F. & Farina, J.L. 2011: Ants and xenarthrans involved in a Quaternary food web from Argentina as reflected by their fossil nests and palaeocaves. Lethaia, Vol. 45, pp. 411–422. Quaternary (Ensenadan stage‐age) deposits of the Miramar Formation from the Buenos Aires sea coast near Mar del Plata (Argentina) are well known for bearing long horizontal tunnels produced by xenarthrans, either ground sloths or armadillos. Little known is that, in some cases, these palaeocaves cross‐cut social insect nests. Nests of two studied palaeocaves can be attributed to ants based on the presence of abundant ant remains, filling of chambers and organic‐rich linings. Insect remains show part of a food web composed of army ants (Neivamyrmex) preying on leaf‐cutting ants (Acromyrmex), Pheidole and other soil invertebrates. The other main component of this web is represented by the xenarthrans feeding on these ants. The facultative foraging function of xenarthran palaeocaves is supported by the common record of these extended horizontal tunnel systems similar to other subterranean foraging mammals, the presence of insect nests cross‐cut by them and the extended myrmecophagy among xenarthrans. Xenarthran foraging burrows, despite their high‐energy cost, would have been favoured by abundance of underground ant nests during Quaternary times and harsh climate. This climate would have produced the scarcity of insects on surface and longest periods of underground activity by xenarthrans, involving the extension of shelter burrows for adult and possibly juvenile feeding. □Ant fossil nests, Argentina, Buenos Aires, food web, Quaternary, xenarthran palaeocaves.     

An Overview of the Presence of Osteoderms in Sloths: Implications for Osteoderms as a Plesiomorphic Character of the Xenarthra

The presence of osteoderms in the skin of some extinct sloths and in cingulates (armadillos, pampatheres, and glyptodonts) has often been considered a pleisomorphic character of the Xenarthra. While osteoderms are known from the earliest cingulates, they are absent in most sloths including the two extant taxa and only appear late in their fossil record. Osteoderms are currently only reported from five genera of mylodonts and two megatheres, out of the over 100 currently recognized genera of sloths. Consequently, rather than a plesiomorphic character of the Xenarthra, which has been secondarily lost in sloths, it is more likely that osteoderms in sloths are the result of parallel evolution to the cingulates that independently evolved in one, possibly two different sloth clades.     

Light microscopy and scanning electron microscopy studies on the reduction of the tongue microstructures in the white stork (Ciconia ciconia,Aves)

The structure of the tongue in the white stork (Ciconia ciconia) is observed macroscopically and under light and scanning electron microscopy. Our observations of the tongue reveal a rare terminal reduction of the size of the tongue and microstructures of the lingual mucosa among the investigations of birds published so far. The short, triangular tongue with a pointed tip is approximately 2.5 cm long in the adult and is situated in the caudal part of the oral cavity close to the laryngeal prominence. On the dorsal surface of the tongue, no typical mucosa microstructures like lingual papillae, median groove or lingual prominence are observed. The main structure of the tongue is composed of rostral part of hyoid apparatus, that is, entoglossal cartilage connects with basihyoid. Very thin mucosa is composed of fibrous connective tissue covered with orthokeratinized epithelium. No lingual glands and muscles are observed in the lamina propria of mucosa. Even though the triangular shape of the tongue in the white stork is typical for birds, the inner structure of the reduced organ is composed only of flat cartilagineous entoglossum of hyoid apparatus. During feeding behaviour of the white stork, the food transportation in oral cavity called cranio‐inertial transport is undoubtedly affected by structural reduction of the tongue.     

Kinematics of prey capture and chewing in the lizard Agama agama (squamata: Agamidae)

High speed video recordings (200 fields per second) of prey capture and food processing in Agama agama permit the identification of strikes, chews and transport movements. Ten variables from strike movements and seven variables from chewing sequences are digitized; transport movements are inspected only. Univariate and multivariate statistical analyses disclose significant interindividual differences for three variables (maximum gape distance, maximum head angle, and maximum throat distance); but neither these nor principal components analysis show differences between strikes and chews for any of the gape change and hyoid depression variables. However, strikes and chews obviously differ in tongue protrusion and body movements. Chewing may be divided into four stages, comparable to those of transport cycles of other lizards and the generalized tetrapod model. Transport differs from chewing by having a shorter power stroke and relatively more cranial and less jaw movement. The kinematics of feeding in Agama agama are compared with those of other lizards studied previously.     

Morphology and function of the tongue and hyoid apparatus in Varanus (Varanidae, Lacertilia)

The morphology and function of the tongue and hyoid apparatus in Varanus were examined by anatomical and experimental techniques. Morphological features unique to Varanus include a highly protrusible tongue that has lost a roughened dorsal surface, an exceptionally strong and mobile hyobranchial apparatus, a well-defined joint between the ceratohyal and anterior process, and a series of distinct muscles inserting at the anterior hyobranchial region. Varanus is also unusual among lizards in a number of feeding behaviors; it ingests prey entirely by inertial feeding, as the tongue does not participate in food transport. Further specializations include an increased reliance on hyobranchial movements in drinking and pharyngeal packing and compression. The long, narrow tongue is most likely related to the mechanics of tongue protrusion; the increased amount, strength, and complexity of hyobranchial movement is related to the fact that the hyobranchium in Varanus replaces the tongue in many functions. Previous hypotheses for the origin of these adaptations are discussed, and the difficulties of attributing these specializations to any specific scenario of adaptation or constraint are emphasized.     

Developmental patterns of the crocodilian and avian columella auris: reappraisal of interpretations of the derivation of the dorsal hyoid arch in archosaurian tetrapods

The morphogenesis of the crocodilian and avian columella auris is analysed, using Alligator and Struthio as models that are studied in detail, and Crocodylus, Gallus, and Coturnix as models for comparative purposes. This investigation was undertaken to address controversies emanating from previous studies concerning the identity of archosaurian hyal elements, and to clarify confounding nomenclature that has been used for both topographic and phylogenetic purposes. We found that confusion in the identification of the reptilian and avian hyoid arch derivatives is attributable to: (1) redundant and/or inconsistently applied topographical terminology; (2) mixing of topographical and phylogenetic terminology; (3) interpretation in a recapitulatory framework; and (4) failure to consider that developmental pathways of recent archosaurians (reptilians and birds) might be divergently modified. Our analysis identifies errors in previous interpretations, misinterpretations of prior work, and histological observations that have been idealized. The most controversial issues are addressed – the derivation of the supracolumellar process; the concept of the laterohyal component; and segmentation of the distal part of the reptilian and avian columella auris. Based on new data, we suggest that the osteichthyan infrapharyngohyal, suprapharyngohyal, epihyal, and ceratohyal are not applicable terms for reptilian and avian columellar components from a phylogenetic perspective, and should not be used as topographical terms either. We further propose that the original morphogenetic program of the hyoid arch has been overwritten in newly derived evolutionary pathways of crocodilians and birds, in which a new functional and morphological patterning of the hyoid arch, as a specific sound‐transmitting apparatus, have evolved. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 156 , 384–410.     

Development of the cranium ofNeoceratodus forsteri,with a discussion of the suspensorium and the opercular apparatus in Dipnoi

Summary The ontogeny of the cranium of Dipnoi is restudied. The investigation especially refers to the basic components of the dipnoan cranium and several functional and developmental aspects of the structure of the larval skull ofNeoceratodus. There are fundamental differences even in the early development and composition of the chondrocranium ofNeoceratodus and Lepidosirenidae. This result, and comparison with several osteichthyans and Tetrapoda, requires a reinterpretation of the components of the dipnoan skull base. The pterygoid processes are not reduced, but incorporated into the cranial base early in ontogeny. The characteristic elongate trabecular rods, which in Gnathostomata usually bridge the ethmoidal plate and the orbito-temporal base of the chondrocranium, are much delayed in development inNeoceratodus, or even seem absent inLepidosiren andProtopterus. Accordingly, in Dipnoi no typical basitrabecular junction is formed in early ontogeny. Instead, the pars quadrata is fused to the mesodermal basis cranii posteriorly. InNeoceratodus a mesially directed basal process of the palatoquadrate is recognizable, which topographically corresponds to the basal process of Urodela and the pseudobasal process of anuran larvae. The ethmosphenoid region of the dipnoan skull also develops quite differently. In Lepidosirenidae, the palatoquadrates are interconnected anteriorly by a distinct commissura palatoquadrati, whereas inNeoceratodus a continuous planum ethmoidale (trabecular plate) is formed. The primary embryonic quadrato-trabecular connection persists as a commissura quadratocranialis anterior below the foramen opticum, at the root of the ectethmoid process. The formation of the skull base in living Amphibia appears to provide the best model for comparison, though it is difficult to propose any undisputable shared derived character states of the cranium of Dipnoi and Tetrapoda beyond this similarity. A similar difficulty presents the phylogenetic interpretation of the hyoid arch. In contrast to the absence of any dorsal hyoid arch elements inLepidosiren, the small hyomandibula ofNeoceratodus is surprisingly complete. In larvae it consists of a laterohyale, an epihyal part, and a processus symplecticus. A stylohyal cartilage is present, which forms rather late in ontogeny. The major chondral components of the hyoid arch are thus comparable to those of living Actinopterygii, except that a distinct symplecticum is not separated off, the components are relatively smaller, and they do not ossify. In view of the early-immobilized palatoquadrate, the hyomandibula ofNeoceratodus has no suspensorial function, but represents part of an opercular hinge and opening mechanism. The hamuloquadrate knob at the posterior face of the quadrate body is comparable to the processus hyoideus in some Urodela. It provides a pivoting joint for the ceratohyale, and therefore functions in buccal expansion. The closed spiracular canals include mechanoreceptive lateral line organs, which probably represent proprioreceptive organs for adjustment of mandibular, hyoid, and opercular movements. It is concluded that considerable differences between the skull architecture of Dipnoi and other Osteognathostomata (Teleostomi) can be assigned to the fact that palatoquadrate and trabecular anlagen fail to separate, resulting in a dramatic and highly adaptive change of palatoquadrate development in early ontogeny. Though these differences include several characters that suggest a plagiostomate condition of the jaw apparatus, this can be explained as a secondary acquisition. The multitude of retained plesiomorphies observed in the cranium of Dipnoi do not exclude a sister group-relationship to Tetrapoda. However, the ancestral osteognathostome suspensorial pattern still presents a problem of interpretation, for we lack a detailed survey of the development and significance of different quadrato-neurocranial connections.     

Development of the muscles associated with the mandibular and hyoid arches in the Siberian sturgeon,Acipenser baerii (Acipenseriformes: Acipenseridae)

The skeleton of the jaws and neurocranium of sturgeons (Acipenseridae) are connected only through the hyoid arch. This arrangement allows considerable protrusion and retraction of the jaws and is highly specialized among ray‐finned fishes (Actinopterygii). To better understand the unique morphology and the evolution of the jaw apparatus in Acipenseridae, we investigated the development of the muscles of the mandibular and hyoid arches of the Siberian sturgeon, Acipenser baerii. We used a combination of antibody staining and formalin‐induced fluorescence of tissues imaged with confocal microscopy and subsequent three‐dimensional reconstruction. These data were analyzed to address the identity of previously controversial and newly discovered muscle portions. Our results indicate that the anlagen of the muscles in A. baerii develop similarly to those of other actinopterygians, although they differ by not differentiating into distinct muscles. This is exemplified by the subpartitioning of the m. adductor mandibulae as well as the massive m. protractor hyomandibulae, for which we found a previously undescribed portion in each. The importance of paedomorphosis for the evolution of Acipenseriformes has been discussed before and our results indicate that the muscles of the mandibular and the hyoid may be another example for heterochronic evolution.     

A 3D geometric morphometric analysis of digging ability in the extant and fossil cingulate humerus

Digging ability in armadillos has been shown to be closely related to the relative length of the olecranon process of the ulna. This study uses geometric morphometrics to examine the relationship between humeral shape, digging ability and size in a range of living and fossil cingulates. The extant species in the sample include representatives of 11 species of armadillo, while the fossil specimens include three species of fossil armadillos ( Peltephilus, Proeutatus and Eutatus ) and three Glyptodonts ( Propalaeohoplophorus, Glyptodon and Neosclerocalyptus ). The results show that in general, living species with good digging ability have larger sites for muscle attachment, particularly the proximal tubercles and the crests descending therefrom, and the epicondylar region at the distal end of the humerus. Some differences were found in the smallest armadillo ( Chlamyphorus truncatus ), which seems to have a different method of digging. The proportions of the olecranon process would indicate good digging ability in some glyptodonts, but humeral features do not fit with this interpretation and the differences may be related to large size. The relationship between cingulate phylogeny and humeral morphology is also examined, and it seems that while cingulates are to some extent constrained by their phylogeny, many of the humeral features are directly related to digging.     

Kinetics of tongue projection in Ambystoma tigrinum: Quantitative kinematics,muscle function,and evolutionary hypotheses

The projectile tongue of caudate amphibians has been studied from many perspectives, yet a quantitative kinetic model of tongue function has not yet been presented for generalized (nonplethodontid) terrestrial salamanders. The purposes of this paper are to describe quantitatively the kinnematics of the feeding mechanism and to present a kinetic model for the function of the tongue in the ambystomatid salamander Ambystoma tigrinum. Six kinematic variables were quantified from high-speed films of adult A. tigrinum feeding on land and in the water. Tongue protrusion reaches its maximum during peak gape, while peak tongue height is reached earlier, 15 ms after the mouth starts to open. Tongue kinematics change considerably during feeding in the water, and the tongue is not protruded past the plane of the gape. Electrical stimulation of the major tongue muscles showed that tongue projection in A. tigrinum is the combined result of activity in four muscles: the geniohyoideus, Subarcualis rectus 1, intermandibularis posterior, and interhyoideus. Stimulation of the Subarcualis rectus 1 alone does not cause tongue projection. The kinetic model produced from the kinematic and stimulation data involves both a dorsal vector (the resultant of the Subarcualis rectus 1, intermandibularis posterior, and interhyoideus) and a ventral vector (the geniohyoideus muscle), which sum to produce a resultant anterior vector that directs tongue motion out of the mouth and toward the prey. This model generates numerous testable predictions about tongue function and provides a mechanistic basis for the hypothesis that tongue projection in salamanders evolved from primitive intraoral manipulative action of the hyobranchial apparatus.     

Body mass estimation in xenarthra: A predictive equation suitable for all quadrupedal terrestrial placentals?

The Magnorder Xenarthra includes strange extinct groups, like glyptodonts, similar to large armadillos, and ground sloths, terrestrial relatives of the extant tree sloths. They have created considerable paleobiological interest in the last decades; however, the ecology of most of these species is still controversial or unknown. The body mass estimation of extinct species has great importance for paleobiological reconstructions. The commonest way to estimate body mass from fossils is through linear regression. However, if the studied species does not have similar extant relatives, the allometric pattern described by the regression could differ from those shown by the extinct group. That is the case for glyptodonts and ground sloths. Thus, stepwise multiple regression were developed including extant xenarthrans (their taxonomic relatives) and ungulates (their size and ecological relatives). Cases were weighted to maximize the taxonomic evenness. Twenty‐eight equations were obtained. The distribution of the percent of prediction error (%PE) was analyzed between taxonomic groups (Perissodactyla, Artiodactyla, and Xenarthra) and size groups (0–20 kg, 20–300 kg, and more than 300 kg). To assess the predictive power of the functions, equations were applied to species not included in the regression development [test set cross validation, (TSCV)]. Only five equations had a homogeneous %PE between the aforementioned groups. These were applied to five extinct species. A mean body mass of 80 kg was estimated for Propalaehoplophorus australis (Cingulata: Glyptodontidae), 594 kg for Scelidotherium leptocephalum (Phyllophaga: Mylodontidae), and 3,550.7 kg for Lestodon armatus (Phyllophaga: Mylodontidae). The high scatter of the body mass estimations obtained for Catonyx tarijensis (Phyllophaga: Mylodontidae) and Thalassocnus natans (Phyllophaga: Megatheriidae), probably due to different specializations, prevented us from predicting its body mass. Surprisingly, although obtained from ungulates and xenarthrans, these five selected equations were also able to predict the body mass of species from groups as different as rodents, carnivores, hyracoideans, or tubulidentates. This result suggests the presence of a complex common allometric pattern for all quadrupedal placentals. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

Ancient DNA from the extinct South American giant glyptodont Doedicurus sp. (Xenarthra: Glyptodontidae) reveals that glyptodonts evolved from Eocene armadillos

Glyptodonts were giant (some of them up to ~2400 kg), heavily armoured relatives of living armadillos, which became extinct during the Late Pleistocene/early Holocene alongside much of the South American megafauna. Although glyptodonts were an important component of Cenozoic South American faunas, their early evolution and phylogenetic affinities within the order Cingulata (armoured New World placental mammals) remain controversial. In this study, we used hybridization enrichment and high‐throughput sequencing to obtain a partial mitochondrial genome from Doedicurus sp., the largest (1.5 m tall, and 4 m long) and one of the last surviving glyptodonts. Our molecular phylogenetic analyses revealed that glyptodonts fall within the diversity of living armadillos. Reanalysis of morphological data using a molecular ‘backbone constraint’ revealed several morphological characters that supported a close relationship between glyptodonts and the tiny extant fairy armadillos (Chlamyphorinae). This is surprising as these taxa are among the most derived cingulates: glyptodonts were generally large‐bodied and heavily armoured, while the fairy armadillos are tiny (~9–17 cm) and adapted for burrowing. Calibration of our phylogeny with the first appearance of glyptodonts in the Eocene resulted in a more precise timeline for xenarthran evolution. The osteological novelties of glyptodonts and their specialization for grazing appear to have evolved rapidly during the Late Eocene to Early Miocene, coincident with global temperature decreases and a shift from wet closed forest towards drier open woodland and grassland across much of South America. This environmental change may have driven the evolution of glyptodonts, culminating in the bizarre giant forms of the Pleistocene.     

Movement of the hyoid in frogs during feeding.

Feeding, breathing, and vocalization sequences of Bufo marinus were recorded by cineradiography. Results of film analysis indicate that the hyoid moves during all three behaviors. Movement of the hyoid is critical in tongue protrusion of frogs, and a biomechanical model of this action is presented. The hyoid appears to represent a compromise morphological system for three functions, rather than an optimal system for any one. This may explain, in part, the retention of a relatively inefficient breathing mechanism in frogs.