Dental microwear in the orthodentine of the Xenarthra (Mammalia) and its use in reconstructing the palaeodiet of extinct taxa: the case study of Nothrotheriops shastensis (Xenarthra,Tardigrada, Nothrotheriidae)

The utility of orthodentine microwear analysis as a proxy for dietary reconstruction in xenarthrans (tree sloths, armadillos) was quantitatively and statistically accessed via low‐magnification stereomicroscopy. Features such as number of scratches and pits, as well as presence of gouges, hypercoarse scratches, > four large pits, > four cross scratches, and fine, mixed or coarse scratch texture were recorded in 255 teeth from 20 extant xenarthran species. Feature patterns are consistent with scar formation through abrasional (tooth–food) and attritional (tooth–tooth) contact. Number of scratches is the most dietary diagnostic microwear variable for xenarthrans, with herbivorous sloths characterized by > ten scratches and nonherbivorous armadillos by < ten scratches. Discriminant function analysis differentiated arboreal folivores (sloths) and frugivore‐folivores (sloths) both from each other and from fossorial carnivore‐omnivores (armadillos) and insectivores (armadillos). Microwear patterns in carnivore‐omnivores and insectivores are difficult to distinguish between; armadillo microwear may reflect a fossorial lifestyle (grit consumption) rather than primary diet. Cabassous centralis is anomalous in its microwear signal relative to all other insectivores. To test the utility of orthodentine microwear analysis as an indicator of palaeodiet in extinct xenarthrans, microwear in the ground sloth Nothrotheriops shastensis was quantitatively and statistically compared to microwear in extant taxa. Microwear patterns in N. shastensis are most comparable to extant folivores based on scratch number and hierarchical cluster analysis. This strongly supports an herbivorous diet for N. shastensis that is corroborated by multiple independent lines of evidence. Thus, orthodentine microwear analysis can be used to reconstruct diet in extinct xenarthrans. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 156 , 201–222.     

Behavioral changes in pottos (Perodicticus potto): Effects of naturalizing an exhibit

Observations of the potto (Perodicticus potto),a nocturnal prosimian primate,indicated a limited behavioral repertoire and prompted renovation of their exhibit at the Frankin Park Zoo (Boston, MA). We used the natural history of this species to direct the exhibit modifications, which used only nonsynthetic items. We added live plants, soil, bamboo, shelf fungi, grapevines, a hollow tree, and a log containing an insect dispenser to the exhibit at little expense. They provided new textures, odors, pathways, stimulation and cover for this secretive species. The changes produced a heightened aesthetic appeal to the nocturnal exhibit and improved its educational value by representing the animals’ habitat more accurately. The exhibit modifications also resulted in a significant increase in activity, an expansion of the pottos’ behavioral repertoire,the emergence of sexual behaviors, and an increased visibility to the public.     

Penile Morphology and Classification of Bush Babies (Subfamily Galagoninae)

The penile morphologies of nocturnal prosimians are complex and vary considerably between genera and species. Accordingly, comparative morphology can be useful in taxonomic studies, particularly when assessing the status of newly discovered species. I measured features of penile morphology—surface area of the glans penis; shape and size of the keratinized spines on the glans—for populations representing 14 species within the subfamily Galagoninae. Intraspecific variations in penile morphology were relatively minor. By contrast, there are significant differences in several morphological features among closely related, sympatric species, e.g., in the greater bush babies (Otolemur crassicaudatus and O. garnettii) and lesser bush babies (Galago senegalensis and Galago moholi). Assessment of glans area resulted in the recognition of a second needle-clawed form: Euoticus pallidus. Similar divisions exist in the dwarf and greater bush babies with respect to proportional spiny area and characteristics of spine size. I constructed a key based on the presence/absence of certain features—penile spines, dermal markings on the glans, penile lappets—as well as the shape of the baculum and possession of different spinal morphotypes. This key may be used to identify all 14 species of bush babies. Penile morphologies provide a useful guide to specific identity in the Galagoninae, which may be true also for other groups of nocturnal mammals.     

A Survey of Husbandry Practices for Lorisid Primates in North American Zoos and Related Facilities

Zoos and related facilities in North America currently manage five species in the primate family Lorisidae: the greater (Nycticebus coucang), Bengal (N. bengalensis) and pygmy (N. pygmaeus) slow lorises, red slender loris (Loris tardigradus), and potto (Perodicticus potto). We used an online survey to describe institutional housing and husbandry practices for these species and assess the extent to which practices are consistent with established guidelines. Our results show that most captive lorisids are housed solitarily or in pairs. Most individuals occupy a single exhibit space in a building dedicated to nocturnal animals. Facilities are commonly meeting recommendations for abiotic exhibit design and are providing animals with an enriched environment. However, pottos and slender lorises currently occupy exhibit spaces smaller than the recommended minimum, and the impact of cleaning protocols on olfactory communication should be critically evaluated. Few facilities are taking advantage of the benefits of positive reinforcement training for promoting animal welfare. Research is greatly needed on the effects of exhibit lighting on behavior, health, and reproduction; and to determine how best to manage the social needs of lorisids with naturally dispersed social structures. Although captive populations of slender lorises, pottos, and slow lorises are declining, we suggest that improved husbandry knowledge has the potential to positively influence population sustainability and to enhance future efforts to manage the growing pygmy loris population. Zoo Biol. 32:88‐100, 2013. © 2012 Wiley Periodicals, Inc.     

Mirror-Directed Social Behaviors of Garnett's Greater Bush Baby (Otolemur garnettii)

Many diurnal anthropoid species direct social behaviors toward their own mirror-image as though viewing a conspecific. To determine whether a nocturnal prosimian species would behave similarly, we videotaped social responses of 45 Garnett's greater bush babies (Otolemur garnettii) observing mirror-images for the first time, scored them for frequency and duration, and compared them with the same behaviors directed elsewhere in the test apparatus. Males scentmarked more than females did, principally with the hindfoot, and most when in immediate proximity to the mirror. Bush babies displayed bipedal posture and threat gestures when oriented directly toward a mirror from a near position. Orientation toward the mirror also increased the frequency of arched-back postures; however, this behavior was not contingent on proximity to the mirror or visibility of the mirror-image. The differential expression of specific behaviors toward mirror-images by male and female bush babies supports the view that this nocturnal prosimian, thought to be dependent on olfaction and audition for communication, is capable of specific recognition by visual cues alone.     

Behavioral and physiologic responses to environmental enrichment in the maned wolf (Chrysocyon brachyurus)

The ex situ population of maned wolves is not self‐sustaining due to poor reproduction, caused primarily by parental incompetence. Studies have shown that environmental enrichment can promote natural parental behaviors in zoo animals. The objective of this study was to determine the effects of environmental enrichment on behavioral and physiological responses of maned wolves. During an 8‐week experimental period, daily behavior observations and fecal sample collection were conducted on four adult wolves (2.2) individually housed in environments without enrichment. After 2 weeks, the wolves were chronologically provided with 2‐week intervals of hiding dead mice around the exhibit, no enrichment, and introduction of boomer balls. Responses of the wolves to enrichment were assessed based on activity levels and exploratory rates, as well as the level of corticoid metabolites in fecal samples collected daily throughout the study period. Providing wolves with environmental enrichment significantly increased exploratory behaviors (P<0.05), especially when mice were hidden in the enclosure. Fecal corticoid concentrations were increased during periods of enrichment in males (P<0.05), but not in females. Overall, there were no correlations between behavioral responses to enrichment and fecal corticoid levels. Behavioral results suggest that environmental enrichment elicits positive effects on the behavior of captive maned wolves. There is evidence suggesting that providing animals with ability to forage for food is a more effective enrichment strategy than introducing objects. There is need for a longer term study to determine the impact of environmental enrichment in this species. Zoo Biol 26:331–343, 2007. © 2007 Wiley‐Liss, Inc.     

A work‐for‐food enrichment program increases exploration and decreases stereotypies in four species of bears

Zoo‐housed bears are prone to exhibiting stereotypic behaviors, generally considered indicators of negative welfare. We explored the effects of a variable‐time feeding enrichment schedule on behavioral indicators of welfare in four bear species at Cleveland Metroparks Zoo. We distributed the diets of eight bears in one of five enrichment items, for two consecutive days each, and monitored behavior throughout the day. In Experiment 1, we compared variable‐time to fixed‐time presentation of enrichment over two, 10‐day periods. Overall, bears performed more exploratory behavior when enriched (p < 0.0001). Furthermore, variable‐time enrichment was associated with a greater increase in exploratory behavior than fixed‐time enrichment when compared to baseline (p < 0.001). Both fixed‐time (p_unadjusted <0.05, p_adjusted = 0.07) and variable‐schedule (p_unadjusted <0.05, p_adjusted = 0.09) enrichment were also associated with similar decreases in abnormal behavior compared to baseline. For Experiment 2, we tested habituation to enrichment over 30 days using multiple items and a semi‐variable presentation schedule. Again during the enrichment period, bears exhibited increased exploratory behavior (p < 0.0001) and decreased abnormal behaviors compared to baseline (p_unadjusted = 0.05, p_adjusted = 0.09). We observed no habituation during the 30‐day sustained enrichment period for these behaviors. Collectively, these results suggest that daily, variable‐schedule feeding enrichment, with intermittent presentation of unique enrichment items, increases behavioral indicators of positive welfare and decreases behavioral indicators of negative welfare.     

Longitudinal study of delayed reproductive success in a pair of white‐cheeked gibbons (Hylobates leucogenys)

Concern over a lack of breeding success in a pair of white‐cheeked gibbons (Hylobates leucogenys) prompted a four‐part study of gibbon behavior and physiology at the Lincoln Park Zoo. Data were collected to determine the female intermenstrual interval (IMI) and identify periods of peak receptivity. Subsequent behavioral data were gathered during both female menses and estrous periods to formulate a behavioral profile for each gibbon. The female experienced a species‐typical IMI of 21.6 days and exhibited heightened levels of behavioral receptivity toward the male during estrus. The male exhibited high levels of human‐directed behavior throughout the day. Closing the exhibit to visitors did not result in higher levels of social proximity or prosocial behavior between the pair, although it did eliminate the male's human‐directed behavior during the experimental condition only. The female exhibited higher levels of social grooming, solicitation of the male, and proximity to the male when the pair was locked indoors. Based on those findings, the pair was moved to an exclusively indoor exhibit. The female's visibility to the public decreased substantially in the alternate exhibit, but there were no other significant behavioral changes. Nearly one year after the exhibit change, the female gibbon was confirmed to be pregnant. Although the results of this study cannot be used to infer causal conditions that resulted in the pregnancy, they do support the notion that systematic documentation of animal behavior and physiology may be used as a tool for monitoring reproductive behavior and informing management decisions. Zoo Biol 21:413–434, 2002. © 2002 Wiley‐Liss, Inc.     

Unexpected Conservation of the X-Linked Color Vision Gene in Nocturnal Prosimians: Evidence from Two Bush Babies

Bush babies have had a long history of nocturnal life and it would be interesting to know whether their color vision genes have become degenerate. Therefore, we used PCR techniques to sequence the X-linked pigment gene of two of these nocturnal prosimians: Galago senegalensis and Otolemur garnettii. Southern hybridization of genomic DNA of G. senegalensis showed a single X-linked pigment gene. Interestingly, the deduced pigment sequences of the two bush babies are identical. By comparing the X-linked pigments of bush baby, human, squirrel monkey, and marmoset, 38 variable positions were identified. At those positions that may cause a spectral shift, the bush baby pigment has identical or biochemically similar residues to those of the marmoset cone pigment with a spectral peak of 543 nm. This result is consistent with the estimate of 544–545 nm for the spectral peak of the X-linked pigment of Otolemur crassicaudatus, which is closely related to Otolemur garnettii. The neighbor-joining tree of mammalian X-linked pigments showed a significantly shorter branch in the bush baby lineage than in other primate lineages. A relative rate test showed that the nonsynonymous substitution rate of the bush baby X-linked pigment gene is about three times slower than that of the human red pigment gene, though the synonymous substitution rates of the two genes are similar. The slower nonsynonymous rate in the bush baby lineage suggests that the bush baby X-linked pigment gene is under functional constraints, in spite of its nocturnal life. Two radical changes at positions in the intradiskal surface next to the sixth transmembrane domain were observed in the X-linked cone pigment of bush babies but not in other primates. They are changes from Ala to Ser and from Asn to His, which are similar in function to the corresponding residues in rhodopsins. These two changes may be of importance for dim light sensitivity, which is consistent with our proposal that the evolution of the bush baby X-linked pigment gene is under selective pressure. In addition, the 2.5% divergence in introns 2 and 5 of the X-linked pigment gene between the two bush babies supports their classification into two separate genera. Received: 30 November 1996 / Accepted: 17 June 1997     

Maracas for Macaca? Evaluation of three potential enrichment objects in two species of zoo‐housed macaques

One group each of Barbary macaques and stump‐tailed macaques, both zoo‐housed, received hard replica fruits in three experimental conditions: as empty (“unresponsive”) objects, as maracas that rattled when manipulated (“simple responsive”), and as objects from which food items could be extracted (“foraging devices”). Both groups manipulated the replica fruits most when they functioned as foraging devices, and responsiveness tended to decrease within sessions in all conditions. Thus, objects that increased the animals' sense of control in addition to providing food rewards appeared particularly suitable as enrichment devices, although novelty and indirect behavioral effects point to the need for thorough evaluation of enrichment interventions. Zoo Biol 19:181–191, 2000. © 2000 Wiley‐Liss, Inc.     

Husbandry of a pink fairy armadillo (Chlamyphorus truncatus): case study of a cryptic and little known species in captivity

Pink fairy armadillos, Chlamyphorus truncatus, are poorly known fossorial mammals that are endemic to central Argentina. These smallest of all extant armadillos are rarely observed in the field and extremely difficult to maintain under captive conditions. This case study describes the husbandry of a male pink fairy armadillo that was maintained in an artificial environment for 8 months. A stable, undisturbed environment consisting of abundant compact sand and hiding places on the surface was the key to its successful maintenance. The artificial diet consisted of a semiliquid mixture of ground cat food, insectivore diet, mashed banana, vitamins, and minerals. Any slight modification to its environment or diet triggered a stress response. Zoo Biol 30:225–231, 2011. © 2010 Wiley‐Liss, Inc.     

Dietary specialization and Eucalyptus species preferences in Queensland koalas (Phascolarctos cinereus)

Koalas specialize on Eucalyptus leaves, but also feed selectively. Food choice is not random, but depends on various factors that are not well understood, although most research has focused on the role of secondary plant compounds. We studied the feeding choices of four adult male koalas housed at the San Diego Zoo. All subjects had a choice of nine types of Eucalyptus leaves over the eight‐week study. The most preferred species was E. camuldulensis, but individual males exhibited different feeding preferences. We conclude that food selectivity among koalas is probably due to multiple factors, rather than only a consequence of secondary plant chemicals. A combination of intrinsic factors, such as developmental trajectory and reproductive state, as well as extrinsic factors, such as leaf chemical fingerprint and moisture, probably interact to shape koala foraging preferences. Koalas forage almost exclusively on Eucalyptus species, but have evolved an adaptive flexibility, enabling them to exploit various Eucalyptus species. Zoo Biol 30:52–58, 2011. © 2010 Wiley‐Liss, Inc.     

First experiences with free‐ranging giant day geckos (Phelsuma madagascariensis grandis,Gray 1870) in the masoala rainforest exhibit in Zurich Zoo,Switzerland

Sixty giant day geckos (Phelsuma madagascariensis grandis) have been introduced into the Masoala rainforest exhibit of Zurich Zoo. Eighteen geckos were monitored during a 3‐month study using the telemetry method. In general, the geckos were able to adapt well under these semi‐natural conditions of the exhibit. The geckos accessed to nearly all locations in the exhibit; some of the animals remained stationary, whereas others covered dozens of meters within a week. They preferred four species of plants as well as the artificial structures supporting the walls and roof of the exhibit, and displayed natural behaviors. Animals were observed feeding on all kind of arthropods and nectar substances, and also on food items dropped from feeding stations for other species. Deliberate feeding targeted at the geckos was finally reduced to a calcium‐rich squash along the visitor's main path. Reproduction was observed frequently within the exhibit. These findings suggest that the geckos will be able to build up a self‐sustaining population and contribute to a nearly‐authentic experience for zoo visitors. Zoo Biol 0:1–7, 2006. © 2006 Wiley‐Liss, Inc.     

Feeding enrichment by self‐operated food boxes for white‐fronted lemurs (Eulemur fulvus albifrons) in the Masoala exhibit of the Zurich Zoo

In the new Masoala exhibit of the Zurich Zoo four self‐operated food boxes were installed to encourage arboreal behavior and higher activity levels, and to increase the attractiveness to visitors of a group of three white‐fronted lemurs (Eulemur fulvus albifrons) and one Alaotran gentle lemur (Hapalemur griseus alaotrensis). Data obtained by direct observations with and without food boxes present were compared. In addition, visitors were surveyed to investigate attractiveness of the lemurs. Overall activity and locomotor behavior increased due to food box presentation. Furthermore, the visitor survey documented that the lemurs were spotted more often in trees when the food boxes were present. Because behavior patterns of the subjects approached natural levels with food boxes, the presentation of self‐operated food boxes seems a valuable tool to improve the captive environment of lemurs. Zoo Biol 0:1–10, 2005. © 2005 Wiley‐Liss, Inc.     

A molecular phylogeny of two extinct sloths

Xenarthra (Edentata) is an extremely diverse mammalian order whose modern representatives are the armadillos, anteaters, and sloths. The phylogeny of these groups is poorly resolved. This is particularly true for the sloths (phyllophagans), originally a large and diverse group now reduced to two genera in two different families. Both morphological analyses and molecular analyses of rDNA genes of living and extinct sloths have been used with limited success to elucidate their phylogeny. In an attempt to clarify relationships among the sloths, DNA was extracted and mitochondrial cytochrome b gene sequences were determined from representatives of two extinct groups of sloths (Mylodontidae and Megatheriidae), their two living relatives (two-toed sloths [Megalonychidae], three-toed sloths [Bradypodidae]), anteaters and armadillos. A consistent feature of the latter two species was the nuclear copies of cytochrome b gene sequences. Several methods of phylogenetic reconstruction were applied to the sequences determined, and the results were compared with 12S rDNA sequences obtained in previous studies. The cytochrome b gene exhibited a phylogenetic resolving power similar to that of the 12S rDNA sequences. When both data sets were combined, they tended to support the grouping of two-toed sloths with mylodontids and three-toed sloths with megatheriids. The results strengthen the view that the two families of living sloths adapted independently to an arboreal life-style.     

Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence

This study is undertaken in order to evaluate specific hypotheses of relationship among extant and extinct sloths (Mammalia, Xenarthra, Tardigrada). Questions of particular interest include the relationship among the three traditional family groupings of extinct ground sloths and the monophyletic or diphyletic origin of the two genera of extant tree sloths. A computer‐based cladistic investigation of the phylogenetic relationships among 33 sloth genera is performed based upon 286 osteological characteristics of the skull, lower jaw, dentition and hyoid arch. Characters are polarized via comparisons with the following successive outgroups, all members of the supraordinal grouping Edentata: the Vermilingua, or anteaters; the Cingulata, or armadillos and glyptodonts; the Palaeanodonta; and the Pholidota, or pangolins. The results of the analysis strongly corroborate the diphyly of living tree sloths, with the three‐toed sloth Bradypus positioned as the sister‐taxon to all other sloths, and the two‐toed sloth Choloepus allied with extinct members of the family Megalonychidae. These results imply that the split between the two extant sloth genera is ancient, dating back perhaps as much as 40 Myr, and that the similarities between the two taxa, including their suspensory locomotor habits, present one of the most dramatic examples of convergent evolution known among mammals. The monophyly of the three traditional ground sloth families Megatheriidae, Megalonychidae and Mylodontidae is confirmed in the present study, and the late Miocene–Pleistocene nothrotheres are shown to form a clade. It is suggested that this latter clade merits recognition as a distinct family‐level grouping, the family Nothrotheriidae. The monophyly of the Megatherioidea, a clade including members of the families Megatheriidae, Megalonychidae and Nothrotheriidae, is also supported. Within Megatherioidea, the families Nothrotheriidae and Megatheriidae form a monophyletic group called the Megatheria. The relationships within the families Megatheriidae and Mylodontidae are fully and consistently resolved, although the hypothesized scheme of relationships among the late Miocene to Pleistocene members of the mylodontid subfamily Mylodontinae differ strongly from any proposed by previous authors. Within the family Megalonychidae, Choloepus is allied to a monophyletic grouping of West Indian sloths, although the relationships within this clade are not fully resolved. © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society, 2004, 140 , 255–305.     

Intraspecific Variation in the Vocalizations and Hand Pad Morphology of Southern Lesser Bush Babies (Galago moholi): A Comparison with G. senegalensis

Previous studies have shown the taxonomic value of vocal repertoires and hand (volar) pad characteristics in the classification of cryptic nocturnal primates such as bush babies. However, no study included quantitative comparisons within the geographical range of any one species. We investigated levels of intraspecific variation in calls and hand pad characteristics of the southern lesser bush baby (Galago moholi), using the northern lesser bush baby (Galago senegalensis) for interspecific comparisons. Examination of calls recorded from different regions along a transect of 1500 km across southern Africa revealed low levels of intraspecific variation in Galago moholi, whereas comparisons with homologous call-types in G. senegalensis revealed them to be significantly different. Volar pad measurements across the ranges of both species also showed low levels of intraspecific variation and relatively high interspecific variation. These findings demonstrate that vocal and volar pad characteristics can be used as consistent measures of difference between species that look almost identical. These methods provide a practical means of distinguishing between cryptic species, whether in the field, in captivity, or, in the case of volar pads, of preserved specimens.     

Outbreak of Mycobacterium marinum infection among captive snakes and bullfrogs

Since 1985 mycobacterial infection has been observed occasionally among snakes and bullfrogs housed in the Wisconsin exhibit at the Milwaukee Zoo. Prospective screening of animals was initiated in September 1990, after two cases occurred in March and June 1990. Overall, of 47 animals that were housed in the exhibit from 1981 through its closure in 1995, 15 (31.9%) were diagnosed with mycobacterial infection. That includes 10 cases (of 24 animals; 40% prevalence) that occurred during the final 5 years, when all animals were actively being screened for infection. Infection was documented by culture for seven animals, histology for four animals, and both histology and culture for four animals. Species determination of nine of the 10 isolates revealed Mycobacterium marinum. Genetic fingerprinting of the eight available isolates using pulsed field gel electrophoresis (PFGE) showed that six animals (five snakes and one bullfrog) were infected with the same strain of M. marinum (strain A) and two snakes were infected with a second strain (strain B). Deaths of animals infected with strain A spanned 1992–1995, and for strain B 1990–1992. It is postulated that possible routes of transmission were inhalation of infected aerosols or ingestion of contaminated food, water, or fomites. These data suggest that in closed systems the presence of mycobacterial infection in one animal significantly increases the risk of infection for all animals. Moreover, individual pathogenic strains may persist for prolonged periods of time. Zoo Biol 21:233–241, 2002. © 2002 Wiley‐Liss, Inc.     

Note on optimizing environmental enrichment: a study of fennec fox and zoo guests

Environmental enrichment is widely used to stimulate animal time budgets that seem more natural and diverse than those of unenriched animals. Uncertainty of reward is a suggested means to maintain enrichment's efficacy. Foraging tasks are widely applied in zoo animal enrichment, yet few rely on the logic of optimal foraging theory to help maintain animal motivation. We applied a foraging strategy to zoo housed fennec foxes as enrichment. We varied only the probability of when and where food would occur in the animals' exhibit. Our methods increased behavioral diversity, animal activity, and stimulated guest interest in the exhibit.     

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.