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Item Open Access Modification of vertebral regions explains heart position in arboreal colubrids (Serpentes: Colubridae)(Oxford University Press (OUP), 2024) Nash-Hahn, T.; Stepanova, N.; Davis Rabosky, A.R.; Sherratt, E.Recent research into the snake vertebral column has highlighted the importance of considering regionalization and its implications for the life history of snakes. Our research delves into the distinctions in vertebral column morphology and regionalization within the snake family Colubridae, comparing arboreal and terrestrial species. Our results provide significant support for dissociation between two pre-cloacal regions: the ‘pre-atrial’ (anterior to heart) and the ‘post-atrial’ (posterior to heart). Furthermore, the two ecological groups display distinct proportional compositions between the two pre-cloacal regions and the one post-cloacal region (caudal); arboreal species tend to possess a higher proportion of caudal vertebrae, whereas terrestrial species exhibit a higher proportion of post-atrial vertebrae. Our study reveals that the axial morphology of arboreal species is distinct from that of terrestrial species; however, this was not attributable to a convergent evolution process. By estimating the evolutionary history of vertebral number in each region between the ecological groups, we find each region has a unique pattern, further highlighting evolutionary disassociation between the regions. This study adds to the growing evidence on regionalization of the pre-cloacal snake vertebral column and underscores the importance in continuing to develop our understanding of snake evolution.Item Open Access Elucidating the morphology and ecology of Eoandromeda octobrachiata from the Ediacaran of South Australia(Wiley, 2023) Botha, T.; Sherratt, E.; Droser, M.; Gehling, J.; Garcia-Bellido, D.Eoandromeda octobrachiata is a poorly understood Ediacaran organism, with spiral- octoradial arms, found in South Australia and South China. The informal Nilpena member of the Rawnsley Quartzite, Flinders Ranges in South Australia preserves more than 200 specimens of Eoandromeda. Here we use the novel application of rotational geometric morphometrics together with palaeoenvironmental information to provide a better insight into their palaeobiology and ecology and to address conflicting hypotheses regarding mode of life and taxonomic affinity. We find that Eoandromeda likely had a radially symmetrical shape in life, was cone-shaped and had a high relief off the microbial mat. Analysis of the symmetric and asymmetric shape components revealed they deform strongly in the direction of palaeocurrent, therefore are thought to be made of a flexible material. Almost all specimens are compressed flat. Specimens that appear to have not fully collapsed support the idea that Eoandromeda was likely cone-shaped and further suggest that they possibly collapsed spirally. Our shape analysis along with observed morphological features support the benthic mode of life hypothesis rather than pelagic. Morphological and ecological inconsistencies such as a lack of biradial symmetry and a benthic mode of life do not support the hypothesis of a Ctenophora taxonomic affinity.Item Open Access Shape and size variation in elapid snake fangs, and the effects of phylogeny and diet(Springer Nature, 2023) Palci, A.; Lee, M.S.Y.; Crowe-Riddell, J.; Sherratt, E.Recent studies have found correlations between the shape of snake teeth/fangs and diet. These studies were done at a very broad phylogenetic scale, making it desirable to test if correlations are still detectable at a narrower evolutionary scale, specifically within the family Elapidae. To this end, we studied fang shape in a dense selection of elapids representing most genera worldwide (74%). We used three-dimensional geometric morphometrics to analyse fang diversity and evaluate possible correlations between fang shape, fang size, and diet. We detected only weak phylogenetic signal in our dataset for both shape and size, and no significant evolutionary allometry when correcting for phylogeny. Overall, the distribution of elapid fangs in morphospace was found to be surprisingly conservative, with only a few outliers. The only two dietary categories that were found to have a significant effect on fang shape are fish and snakes, while mammals have a significant effect on absolute but not relative fang size. Our results show that there are disparate patterns in fang-diet relationships at different evolutionary scales. Across all venomous snakes, previous work found that fangs are strongly influenced by diet, but within elapids our study shows these same associations are weaker and often non-significant. This could result from limitations in these types of studies, or could reflect the fact that elapids are a relatively young clade, where recent extensive divergences in diet have yet to be mirrored in fang shape, suggesting a lag between changes in ecology and dental morphology.Item Open Access Evolutionary transition from surface to subterranean living in Australian water beetles (Coleoptera, Dytiscidae) through adaptive and relaxed selection(Oxford University Press (OUP), 2024) Zhao, Y.; Guzik, M.; Humphreys, W.; Watts, C.; Cooper, S.; Sherratt, E.Over the last 5 million years, numerous species of Australian stygobiotic (subterranean and aquatic) beetles have evolved underground following independent colonisation of aquifers by surface ancestors, providing a set of repeated evolutionary transitions from surface to subterranean life. We used this system as an ‘evolutionary experiment’ to investigate whether relaxed selection has provided a source of variability for adaptive radiations into ecosystems containing open niches and whether this variability underpins phenotypic evolution in cave animals. Linear and landmark-based measurements were used to quantify the morphology of subterranean species from different aquifers, compared to interstitial and closely related aquatic surface species. Subterranean dytiscids were observed to be morphologically distinct, suggesting they have a different lifestyle compared to their surface relatives. However, the variation in the measured traits was much greater in the subterranean species, and unstructured, showing no evidence of clustering that would indicate adaptation to specific niches. Furthermore, a previously identified pattern of repeated non-overlapping size variation in beetles across aquifers was not correlated with repeated body shape evolution. The observed variability across body shape and limb traits provides support for the hypothesis that relaxed selection and neutral evolution underlie the phenotypic evolution in these species.Item Open Access Semicircular canal shape diversity among modern lepidosaurs: Life habit, size, allometry(BioMed Central, 2023) Latimer, A.; Sherratt, E.; Bonnet, T.; Scheyer, T.Background: The shape of the semicircular canals of the inner ear of living squamate reptiles has been used to infer phylogenetic relationships, body size, and life habits. Often these inferences are made without controlling for the effects of the other ones. Here we examine the semicircular canals of 94 species of extant limbed lepidosaurs using three-dimensional landmark-based geometric morphometrics, and analyze them in phylogenetic context to evaluate the relative contributions of life habit, size, and phylogeny on canal shape. Results: Life habit is not a strong predictor of semicircular canal shape across this broad sample. Instead, phylogeny plays a major role in predicting shape, with strong phylogenetic signal in shape as well as size. Allometry has a limited role in canal shape, but inner ear size and body mass are strongly correlated. Conclusions: Our wide sampling across limbed squamates suggests that semicircular canal shape and size are predominantly a factor of phylogenetic relatedness. Given the small proportion of variance in semicircular canal shape explained by life habit, it is unlikely that unknown life habit could be deduced from semicircular canal shape alone. Overall, semicircular canal size is a good estimator of body length and even better for body mass in limbed squamates. Semiaquatic taxa tend to be larger and heavier than non-aquatic taxa, but once body size and phylogeny are accounted for, they are hard to distinguish from their non-aquatic relatives based on bony labyrinth shape and morphology.Item Open Access A comparison of ecomorphology between introduced and native Australian dung beetles(CSIRO Publishing, 2022) Harvey, A.; Sherratt, E.; Deakin, J.Among the many catastrophic introductions of exotic species to Australia, the Australian Dung Beetle Project stands apart as a success story. From 1965 dung beetles (Coleoptera: Scarabaeinae) were introduced for biological control purposes, and 23 species survived to become integrated into the environment with apparently little-to-no competition with native species. To understand this, we investigated ecomorphological diversity in the Australian dung beetle fauna, examining variation in functional traits among rolling and tunnelling species that are native to Australia and introduced. We found that introduced species are on average larger than native species of the same nidification strategy, but the size ranges overlap. Native and introduced tunnellers are convergent in body shape, while introduced rollers have distinct body shape compared with native species. Rollers and tunnellers also have distinct allometric patterns, where shape variation predicted by size aligns along two diverging allometric trajectories between nidification strategies. Our results suggest that ecomorphological differences do not explain the apparent lack of competition between tunnellers, but this may be the factor for rollers. Also, these results indicate body size and associated allometric scaling is an important aspect of the ecomorphology of dung beetles that should be considered in future studies.Item Open Access Multilevel analysis of integration and disparity in the mammalian skull(Wiley, 2023) Sherratt, E.; Kraatz, B.Biological variation is often considered in a scalable hierarchy, e.g., within the individual, within the populations, above the species level. Morphological integration, the concept of covariation among constituent parts of an organism, is also hierarchical; the degree to which these ‘modules’ covary is a matter of the scale of the study as well as underlying processes driving the covariation. Multilevel analyses of trait covariation are a valuable tool to infer the origins and historical persistence of morphological diversity. Here we investigate concordance in patterns of integration and modularity across three biological levels of variation: within a species, within two genera-level radiations, and among species at the family level. We demonstrate this approach using the skull of mammalian family Leporidae (rabbits and hares), which is morphologically diverse and has a rare-among-mammals functional signal of locomotion adaptation. We tested three alternative hypotheses of modularity; from the most supported we investigated disparity and integration of each module to infer which is most responsible for patterns of cranial variation across these levels, and whether variation is partitioned consistently across levels. We found a common pattern of modularity underlies leporid cranial diversity, though there is inconsistency across levels in each module’s disparity and integration. The face module contributes the most to disparity at all levels, which we propose is facilitating evolutionary diversity in this clade. Therefore, the distinctive facial tilt of leporids is an adaptation to locomotory behavior facilitated by a modular system that allows lineages to respond differently to selection pressures.Item Metadata only Island tiger snakes (Notechis scutatus) gain a ‘head start’ in life: how both adaptation and evolution underlie skull shape differences(Springer Nature, 2023) Ammresh,; Sherratt, E.; Thomson, V.A.; Lee, M.S.Y.; Dunstan, N.; Allen, L.; Abraham, J.; Palci, A.Repeated island colonisation by Australian tiger snakes (Notechis scutatus) has become a model system demonstrating how prey size on islands infuences a snake’s body and jaw size. Tiger snakes on islands with large prey have relatively longer jaws compared to their mainland counterparts, due to diet-induced phenotypic plasticity followed by assimilation of favourable traits. We present the frst examination of the efects of diet on all skull elements that are involved in feeding, by analysing shape and size diferences using CT imaging and a combination of linear measurements and three dimensional geometric morphometrics. We compared two populations of tiger snakes, one from Carnac Island, where the snakes were frst introduced approximately 100 years ago, and another from Herdsman Lake on the mainland (a putative source population). Each population was divided into two groups, one was fed small prey and the other large prey. While snakes from the island exhibited relatively longer trophic bones at birth, they also had slightly slower growth rates for these elements regardless of diet. The island forms showed diet-induced plasticity within specifc trophic elements, the mandible and palatopterygoid, which grew longer when the snakes were fed larger prey. Importantly, skull plasticity was expressed only after prolonged dietary stress, and was not clearly observable until the snakes approached adulthood. We hypothesize that this plastic response resulting in increased gape may be adaptive, allowing ingestion of large prey items available to adult tiger snakes on Carnac Island. In contrast, no plastic response was observed in the mainland population.Item Metadata only In the Year of the Rabbit, spare a thought for all these wonderful endangered bunny species(The Conversation, 2023) Sherratt, E.Item Metadata only On a tiny Australian island, snakes feasting on seabirds evolved huge jaws in a surprisingly short time(The Conversation, 2023) Palci, A.; Sherratt, E.; Lee, M.S.Y.Item Open Access Macroevolution in axial morphospace: innovations accompanying the transition to marine environments in elapid snakes(The Royal Society, 2022) Sherratt, E.; Nash-Hahn, T.; Nankivell, J.; Rasmussen, A.R.; Hampton, P.M.; Sanders, K.Sea snakes in the Hydrophis-Microcephalophis clade (Elapidae) show exceptional body shape variation along a continuum from similar forebody and hindbody girths, to dramatically reduced girths of the forebody relative to hindbody. The latter is associated with specializations on burrowing prey. This variation underpins high sympatric diversity and species richness and is not shared by other marine (or terrestrial) snakes. Here, we examined a hypothesis that macroevolutionary changes in axial development contribute to the propensity, at clade level, for body shape change. We quantified variation in the number and size of vertebrae in two body regions (pre- and post-apex of the heart) for approximately 94 terrestrial and marine elapids. We found Hydrophis-Microcephalophis exhibit increased rates of vertebral evolution in the pre- versus postapex regions compared to all other Australasian elapids. Unlike other marine and terrestrial elapids, axial elongation in Hydrophis-Microcephalophis occurs via the preferential addition of vertebrae pre-heart apex, which is the region that undergoes concomitant shifts in vertebral number and size during transitions along the relative fore- to hindbody girth axis. We suggest that this macroevolutionary developmental change has potentially acted as a key innovation in Hydrophis-Microcephalophis by facilitating novel (especially burrowing) prey specializations that are not shared with other marine snakes.Item Open Access Anatomical correlates of cursoriality are compromised by body size and propensity to burrow in a group of small mammals (Lagomorpha)(Springer Nature, 2022) Martin, E.; Young, J.; Fellman, C.; Kraatz, B.; Sherratt, E.Highly cursorial animals are specialised for fast, sustained running via specific morphological adaptations, notably including changes in limb segment length and mechanical advantage. Members of the order Lagomorpha (hares, rabbits and pikas) vary in cursorial ability; hares are generally highly cursorial, rabbits more frequently saltate, and pikas predominantly trot. Previous investigations of lagomorphs have identified anatomical trends correlated with this ‘cursoriality gradient’, however, the phylogenetic sampling of such investigations has been limited to three American species, namely the American pika (Ochotona princeps), brush rabbit (Sylvilagus bachmani), and black-tailed jackrabbit (Lepus californicus). Here, we expand the phylogenetic sample and body size range by including novel data from Australian samples of the European rabbit (Oryctolagus cuniculus) and European hare (L. europaeus), alongside unpublished data on the Eastern cottontail (S. floridanus). X-ray Computed Tomography and digital landmarking were used to capture proportions within the appendicular skeleton of ~ 40 specimens of each European species. In doubling the number of species studied, we find the previously-identified morphological gradients associated with cursorial behaviour are complicated when evaluated in the larger sample. The relative length and joint velocity of limbs was found to be lower than predicted in European rabbits and hares. Furthermore, we present a novel assessment of morphological integration in the lagomorph appendicular skeleton, finding between-limb covariation patterns that are generally similar to those of other mammals. Broadly, these results suggest cursoriality is only one of many selective forces driving lagomorph skeletal evolution, with variations in body size and fossoriality potentially having measurable impacts.Item Open Access Down a rabbit hole: Burrowing behaviour and larger home ranges are related to larger brains in Leporids(Springer, 2022) Todorov, O.; Hird, C.; Kraatz, B.; Sherratt, E.; Hill, N.; de Sousa, A.; Blomberg, S.; Weisbecker, V.Studies on the evolution of brain size variation usually focus on large clades encompassing broad phylogenetic groups. This risks the introduction of ‘noise’ in the results, often obscuring effects that might be detected in less inclusive clades. In the current study we focus on a sample of 18 species of leporids from 60 individuals, and test five different hypotheses related to brain size (approximating it from endocranial volume) evolution in mammals. This includes the evolution of the whole brain, as well as the olfactory bulb. We also address a pervasive issue in comparative phylogenetic studies by dealing with missing data via multiple phylogenetic imputations as to conserve the full sample size for all subsequent analyses. Using leporids as a sample allows for the coverage of good body size diversity while avoiding the issue of too wide taxonomic sampling. Our analyses show that home range and burrowing behaviour are the only predictors of leporid brain size variation in this clade. Additionally, the evolutionary increase in litter size (often found as a constraint in brain size evolution) is related to increased temperature seasonality therefore tentatively masking the constraining effect of litter size on brain size in leporids. Unreasonable estimations of phylogenetic signal (Pagel’s lamba) additionally warrant caution when using small sample sizes in comparative studies.Item Open Access Cranial shape variation in domestication: a pilot study on the case of rabbits(Wiley, 2022) Geiger, M.; Sánchez-Villagra, M.; Sherratt, E.Domestication leads to phenotypic characteristics that have been described to be similar across species. However, this ‘domestication syndrome’ has been subject to debate, related to a lack of evidence for certain characteristics in many species. Here, we review diverse literature and provide new data on cranial shape changes due to domestication in the European rabbit (Oryctolagus cuniculus) as a preliminary case study, thus contributing novel evidence to the debate. We quantified cranial shape of 30 wild and domestic rabbits using micro CT-scans and 3D geometric morphometrics. The goal was to test (1) if the domesticates exhibit shorter and broader snouts, smaller teeth, and smaller braincases than their wild counterparts; (2) to what extent allometric scaling is responsible for cranial shape variation in wild and domestic rabbits; (3) if there is evidence for more variation in the neural crest-derived parts of the cranium compared to those derived of the mesoderm, in accordance with the ‘neural crest hypothesis’. Our own data is consistent with older literature records, suggesting that while there is evidence for some cranial characteristics of the ‘domestication syndrome’ being present in domestic rabbits – e.g., concerning a diminution of braincase size –, facial length is not reduced. In accordance with the ‘neural crest hypothesis’, we found more shape variation in neural crest vs. mesoderm derived parts of the cranium. Within the domestic group, allometric scaling relationships of the snout, the braincase, and the teeth shed new light on ubiquitous patterns among related taxa. This study – albeit preliminary due to the limited sample size – adds to the growing evidence concerning non-uniform patterns associated with domestication.Item Metadata only Redescription, taxonomy and phylogenetic relationships of Boavus Marsh, 1871 (Serpentes: Booidea) from the early–middle Eocene of the USA(Informa UK Limited, 2021) Onary, S.; Hsiou, A.S.; Lee, M.S.Y.; Palci, A.The extinct fossil snake Boavus occurs in early–middle Eocene localities in the United States. Four species are currently recognized, but until now, no formal phylogenetic analyses have been conducted to test its relationships within snakes. Here, we provide an osteological redescription and systematic revision of the genus, accompanied by phylogenetic analyses using multiple methods. Based on new morphological information obtained through first-hand observation and published descriptions, differences between Boavus occidentalis, B. agilis and B. affinis can be ascribed to normal intracolumnar vertebral variation, making the latter two junior synonyms of the first species. Our phylogenetic analyses retrieved Boavus within crown-Booidea as an early booid but outside of Boidae. A morphological and molecular analysis of booids, with dense taxon sampling including fossil and living forms, results in a new booid phylogeny. Boavus, along with other fossil booids from Europe (Eoconstrictor, Messelophis, Rieppelophis, Rageryx), suggests that crown-Booidea likely diverged earlier than estimated by some molecular studies (-45.4Ma).Item Open Access Welfare Assessment Tools in Zoos: From Theory to Practice(MDPI, 2022) Jones, N.; Sherwen, S.; Robbins, R.; McLelland, D.; Whittaker, A.Zoos are increasingly implementing formalized animal welfare assessment programs to allow monitoring of welfare over time, as well as to aid in resource prioritization. These programs tend to rely on assessment tools that incorporate resource-based and observational animal-focused measures. A narrative review of the literature was conducted to bring together recent studies examining welfare assessment methods in zoo animals. A summary of these methods is provided, with advantages and limitations of the approaches presented. We then highlight practical considerations with respect to implementation of these tools into practice, for example scoring schemes, weighting of criteria, and innate animal factors for consideration. It is concluded that there would be value in standardizing guidelines for development of welfare assessment tools since zoo accreditation bodies rarely prescribe these. There is also a need to develop taxon or species-specific assessment tools to complement more generic processes and more directly inform welfare management.Item Metadata only Diversity, distribution, and natural history of the marine snakes of Sri Lanka(Springer Science and Business Media LLC, 2022) Ukuwela, K.D.B.; de Silva, A.; Sivaruban, A.; Sanders, K.L.Marine snakes comprise 90% of all marine reptiles, yet they are the least known of all marine reptiles. Among the marine snakes, very little is known about the marine snakes of the Indian Ocean (IO) compared to the marine snake fauna of the Indo-West Pacific (IWP). Hence, there is a dearth of information about the diversity, systematics, distribution, abundance, natural history, and conservation of IO marine snakes. Therefore, to gain insights to the IO marine snake fauna, we conducted a systematic survey on the marine snakes in the island of Sri Lanka, a central tropical location in the IO. Eight sites around the islandwere sampled for fisheries by-catch from 2010 to the end of 2012. The study documented 14 species (Acrochordidae 1, Homalopsidae 2, Elapidae (Hydrophiinae) 11) of marine snakes from Sri Lankan waters. Our by-catch data indicates that Acrochordus granulatus, Hydrophis curtus, Hydrophis cyanocinctus, Hydrophis schistosus, Hydrophis spiralis, and Hydrophis viperinus are highly abundant (n>20). Further, data demonstrates that the most widely distributed species in Sri Lankan waters are H. spiralis and H. curtus. However, high volumes of marine snakes in fisheries by-catch indicate that fishing-related mortality is a major threat to marine snakes of Sri Lanka. Given the distinct evolutionary history of these snakes in the IO and the unique conservation value, the IO marine snake fauna (inclusive of Sri Lankan marine snakes) should be considered a separate conservation management unit.Item Open Access [PLEASE UPDATE Auth Aff] Ontogenetic allometry underlies trophic diversity in sea turtles (Chelonioidea)(Springer, 2022) Chatterji, R.; Sherratt, E.; Hipsley, C.; Hutchinson, M.; Jones, M.Despite only comprising seven species, extant sea turtles (Cheloniidae and Dermochelyidae) display great ecological diversity, with most species inhabiting a unique dietary niche as adults. This adult diversity is remarkable given that all species share the same dietary niche as juveniles. These ontogenetic shifts in diet, as well as a dramatic increase in body size, make sea turtles an excellent group to examine how morphological diversity arises by allometric processes and life habit specialisation. Using three-dimensional geometric morphometrics, we characterise ontogenetic allometry in the skulls of all seven species and evaluate variation in the context of phylogenetic history and diet. Among the sample, the olive ridley (Lepidochelys olivacea) has a seemingly average sea turtle skull shape and generalised diet, whereas the green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) show diferent extremes of snout shape associated with their modes of food gathering (grazing vs. grasping, respectively). Our ontogenetic fndings corroborate previous suggestions that the skull of the leatherback (Dermochelys coriacea) is paedomorphic, having similar skull proportions to hatchlings of other sea turtle species and retaining a hatchlinglike diet of relatively soft bodied organisms. The fatback sea turtle (Natator depressus) shows a similar but less extreme pattern. By contrast, the loggerhead sea turtle (Caretta caretta) shows a peramorphic signal associated with increased jaw muscle volumes that allow predation on hard shelled prey. The Kemp’s ridley (Lepidochelys kempii) has a peramorphic skull shape compared to its sister species the olive ridley, and a diet that includes harder prey items such as crabs. We suggest that diet may be a significant factor in driving skull shape differences among species. Although the small number of species limits statistical power, differences among skull shape, size, and diet are consistent with the hypothesis that shifts in allometric trajectory facilitated diversification in skull shape as observed in an increasing number of vertebrate groups.Item Open Access Ontogenetic shift in diet of a large elapid snake is facilitated by allometric change in skull morphology(Springer, 2022) Patterson, M.; Wolfe, A.; Fleming, P.; Bateman, P.W.; Sherratt, E.; Warburton, N.As snakes are limbless, gape-limited predators, their skull is the main feeding structure involved in prey handling, manipulation and feeding. Ontogenetic changes in prey type and size are likely to be associated with distinct morphological changes in the skull during growth. We investigated ontogenetic variation in diet from stomach contents of 161 Dugite specimens (Pseudonaja affinis, Elapidae) representing the full range of body size for the species, and skull morphology of 46 specimens (range 0.25–1.64 m snout-vent-length; SVL). We hypothesised that changes in prey type throughout postnatal ontogeny would coincide with distinct changes in skull shape. Dugites demonstrate a distinct size-related shift in diet: the smallest individuals ate autotomised reptile tails and reptiles, medium-sized individuals predominantly ate mammals, and the largest individuals had the most diverse diet, including large reptiles. Morphometric analysis revealed that ~40% of the variation in skull shape was associated with body size (SVL). Through ontogeny, skulls changed from a smooth, bulbous cranium with relatively small trophic bones (upper and lower jaws and their attachments), to more rugose bones (as a likely reflection of muscle attachment) and relatively longer trophic bones that would extend gape. Individual shape variation in trophic bone dimensions was greater in larger adults and this likely reflects natural plasticity of individuals feeding on different prey sizes/types. Rather than a distinct morphological shift with diet, the ontogenetic changes were gradual, but positive allometry of individual trophic bones resulted in disproportionate growth of the skull, reflected in increased gape size and mobility of jaw bones in adults to aid the ingestion of larger prey and improve manipulation and processing ability. These results indicate that allometric scaling is an important mechanism by which snakes can change their dietary niche.Item Metadata only Scaling at different ontogenetic stages: gastrointestinal tract contents of a marsupial foregut fermenter, the western grey kangaroo Macropus fuliginosus melanops(Elsevier, 2021) Munn, A.J.; Snelling, E.P.; Taggart, D.A.; Clauss, M.Prominent ontogenetic changes of the gastrointestinal tract (GIT) should occur in mammals whose neonatal diet of milk differs from that of adults, and especially in herbivores (as vegetation is particularly distinct from milk), and even more so in foregut fermenters, whose forestomach only becomes functionally relevant with vegetation intake. Due to the protracted lactation in marsupials, ontogenetic differences can be particularly well investigated in this group. Here, we report body mass (BM) scaling relationships of wet GIT content mass in 28 in-pouch young (50 g to 3 kg) and 15 adult (16-70 kg) western grey kangaroos Macropus fuliginosus melanops. Apart from the small intestinal contents, in-pouch young and adults did not differ in the scaling exponents ('slope' in log-log plots) but did differ in the scaling factor ('intercept'), with an implied substantial increase in wet GIT content mass during the out-of-pouch juvenile period. In contrast to forestomach contents, caecum contents were elevated in juveniles still in the pouch, suggestive of fermentative digestion of milk and intestinal secretion residues, particularly in the caecum. The substantial increase in GIT contents (from less than 1 to 10-20% of BM) was associated mainly with the increase in forestomach contents (from 25 to 80% of total GIT contents) and a concomitant decrease in small intestine contents (from 50 to 8%), emphasizing the shifting relevance of auto-enzymatic and allo-enzymatic (microbial) digestion. There was a concomitant increase in the contents-to-tissue ratio of the fermentation chambers (forestomach and caecum), but this ratio generally did not change for the small intestine. Our study not only documents significant ontogenetic changes in digestive morpho-physiology, but also exemplifies the usefulness of intraspecific allometric analyses for quantifying these changes.