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Time-tree of xenarthrans analyzed in this work. It is based on the Maximum Clade Credibility DNA-only node-dated phylogeny including 4098 mammal species from Upham et al. (2019). The tree was subsequently adapted to the sample used in this study by pruning non-xenarthran mammals and adding taxa not included in Upham et al. (2019) (as detailed in Materials and Methods and Alfieri et al. 2021). The convergent evolution of slow arboreality in Choloepus spp., Bradypus spp., and Cyclopes are shown in light blue
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Identifying ecomorphological convergence examples is a central focus in evolutionary biology. In xenarthrans, slow arboreality independently arose at least three times, in the two genera of ‘tree sloths’, Bradypus and Choloepus, and the silky anteater, Cyclopes. This specialized locomotor ecology is expectedly reflected by distinctive morpho-functi...
Citations
... Recently developed methods for identifying and measuring convergence are often accompanied by statistical tests for comparing observed convergence to that which is expected by chance (Arbuckle et al., 2014;Castiglione et al., 2019;Ingram & Mahler, 2013;Mahler et al., 2013;Speed & Arbuckle, 2017;Stayton, 2015a). The increased accessibility of quantitative tests for phenotypic convergence has led to a flood of recent studies on that topic (e.g., Alfieri et al., 2022;Arbour & Zanno, 2020;Baliga & Mehta, 2018;Baumgart et al., 2021;Bennion et al., 2022;Button & Zanno, 2020;Canale et al., 2022;Da Silva et al., 2018;Friedman et al., 2016;Grossnickle et al., 2020;Huie et al., 2021;Law, 2022;Martinez et al., 2020;Rincon-Sandoval et al., 2020;Rovinsky et al., 2021;Serio et al., 2020;Spear & Williams, 2020;Tamagnini et al., 2021;Zelditch et al., 2017). ...
... The C1-C4 measures (hereafter, "C-measures") developed by Stayton (2015a) are a popular means of quantifying morphological convergence (e.g., Alfieri et al., 2022;Arbour & Zanno, 2020;Baliga & Mehta, 2018;Baumgart et al., 2021;Bennion et al., 2022;Button & Zanno, 2020;Canale et al., 2022;Da Silva et al., 2018;Friedman & et al., 2016;Grossnickle et al., 2020;Huie et al., 2021;Law, 2022;Martinez et al., 2020;Rincon-Sandoval et al., 2020;Rovinsky et al., 2021;Spear & Williams, 2020;Tamagnini et al., 2021;Zelditch et al., 2017). C-measures are calculated using geometric distances in phenotypic space between focal lineages, relying on ancestral reconstructions for morphologies at ancestral nodes. ...
Tests of phenotypic convergence can provide evidence of adaptive evolution, and the popularity of such studies has grown in recent years due to the development of novel, quantitative methods for identifying and measuring convergence. These methods include the commonly applied C1–C4 measures of Stayton (2015), which measure morphological distances between lineages, and Ornstein-Uhlenbeck (OU) model-fitting analyses, which test whether lineages converged on shared adaptive peaks. We test the performance of C-measures and other convergence measures under various evolutionary scenarios and reveal a critical issue with C-measures: they often misidentify divergent lineages as convergent. We address this issue by developing novel convergence measures— Ct1–Ct4-measures —that calculate distances between lineages at specific points in time, minimizing the possibility of misidentifying divergent taxa as convergent. Ct-measures are most appropriate when focal lineages are of the same or similar geologic ages (e.g., extant taxa), meaning that the lineages’ evolutionary histories include considerable overlap in time. Beyond C-measures, we find that all convergence measures are influenced by the position of focal taxa in phenotypic space, with morphological outliers often statistically more likely to be measured as strongly convergent. Further, we mimic scenarios in which researchers assess convergence using OU models with a priori regime assignments (e.g., classifying taxa by ecological traits) and find that multiple-regime OU models with phenotypically divergent lineages assigned to a shared selective regime often outperform simpler models. This highlights that model support for these multiple-regime OU models should not be assumed to always reflect convergence among focal lineages of a shared regime. Our new Ct1–Ct4-measures provide researchers with an improved comparative tool, but we emphasize that all available convergence measures are imperfect, and researchers should recognize the limitations of these methods and use multiple lines of evidence to test convergence hypotheses.
... In Xenarthrans, great strength is required for the extension and flexion movements of the elbow to perform several habits, such as arboreal, terrestrial, and even fossorial movements (Alfieri et al., 2022;White, 1993). In T. mexicana, there is a significant difference between the two muscle groups (elbow extensors and flexors), where extension of the elbow requires more force. ...
... In T. mexicana, there is a significant difference between the two muscle groups (elbow extensors and flexors), where extension of the elbow requires more force. This specialization of the elbow has been reported in Xenarthras and has occurred evolutionarily to generate more stable joints capable of adapting to the arboreal and digging habits of these species (Alfieri et al., 2022;Heredia-Díaz et al., 2022;Scheidt et al., 2022). Similarly, in the present study, it is evident that the muscles acting at the elbow have the highest proportion of the total mass of the thoracic limb muscles. ...
Tamandua mexicana is an anteater species native from Mexico to Peru. This species is of great evolutionary interest because it belongs to one of the oldest clades of placental mammals in the American continent. This study aimed to describe the origin, insertion, and arterial supply of the intrinsic shoulder and brachial muscles of T. mexicana. We also compared the masses of the functional groups. Gross dissections were performed on both thoracic limbs of 13 cadavers. ANOVA followed by Tukey's test was used for statistical analyses. The subscapularis muscle presents a hiatus to the common tendon of the caput breve of the biceps brachii and coracobrachialis muscles. A variant accessory muscle, the m. articularis humeri lateralis, was found on the lateral surface of the shoulder joint. M. deltoideus pars acromialis has two bellies. The teres major muscle is perforated by the aponeurotic origin of the m. tensor fasciae antebrachii. The triceps brachii has two capita longi. The caput mediale is fused with the m. anconeus medialis. The caput laterale can have an accessory belly as an anatomical variant. Among the functional groups, a significant difference was found between the elbow extensors and flexors, with the latter having the lowest mass. In conclusion, the intrinsic muscles of T. mexicana presented unique features for the species, as well as arrangements in mass distribution that evidence a possible evolutionary convergence among species of the Superorder Xenarthra.
... Diaphyseal and epiphyseal internal structure (crosssectional properties [CSP] and trabecular architectural properties, respectively) were quantified in the humeri and femora following part of the procedure in Alfieri et al. [77] ( Fig. 1 in orange, for raw data see Fig. 2). The two bones were oriented in anatomical standard position following Ruff [66] using VG Studio Max 3.3 (Volume Graphics, Heidelberg, Germany). ...
Background
Biological adaptation manifests itself at the interface of different biologically relevant ‘levels’, such as ecology, performance, and morphology. Integrated studies at this interface are scarce due to practical difficulties in study design. We present a multilevel analysis, in which we combine evidence from habitat utilization, leaping performance and limb bone morphology of four species of tamarins to elucidate correlations between these ‘levels’.
Results
We conducted studies of leaping behavior in the field and in a naturalistic park and found significant differences in support use and leaping performance. Leontocebus nigrifrons leaps primarily on vertical, inflexible supports, with vertical body postures, and covers greater leaping distances on average. In contrast, Saguinus midas and S. imperator use vertical and horizontal supports for leaping with a relatively similar frequency. S. mystax is similar to S. midas and S. imperator in the use of supports, but covers greater leaping distances on average, which are nevertheless shorter than those of L. nigrifrons .
We assumed these differences to be reflected in the locomotor morphology, too, and compared various morphological features of the long bones of the limbs. According to our performance and habitat utilization data, we expected the long bone morphology of L. nigrifrons to reflect the largest potential for joint torque generation and stress resistance, because we assume longer leaps on vertical supports to exert larger forces on the bones. For S. mystax , based on our performance data, we expected the potential for torque generation to be intermediate between L. nigrifrons and the other two Saguinus species. Surprisingly, we found S. midas and S. imperator having relatively more robust morphological structures as well as relatively larger muscle in-levers, and thus appearing better adapted to the stresses involved in leaping than the other two.
Conclusion
This study demonstrates the complex ways in which behavioral and morphological ‘levels’ map onto each other, cautioning against oversimplification of ecological profiles when using large interspecific eco-morphological studies to make adaptive evolutionary inferences.
... Both shape and structure exhibit numerous traits associated with ecological adaptations [23][24][25][26][27][28][29] , e.g., the short and robust limb bone shape of fossorial digging species 30,31 or the heterogeneously oriented trabecular struts within long bones of climbing species 28,29 . When one compares the two levels, though, shape is hypothesised to reflect ecology less directly than structure 32 . ...
... Both shape and structure exhibit numerous traits associated with ecological adaptations [23][24][25][26][27][28][29] , e.g., the short and robust limb bone shape of fossorial digging species 30,31 or the heterogeneously oriented trabecular struts within long bones of climbing species 28,29 . When one compares the two levels, though, shape is hypothesised to reflect ecology less directly than structure 32 . ...
... A small number of previous studies, all restricted taxonomically (i.e., xenarthrans 28 , mustelids 25,40 , squirrels 41 , squirrel-related rodents 17,[42][43][44] ) compared the ecological signal borne by bone shape and structure. Establishing the ecological signal of two bone anatomical levels might provide clues about their potential to evolve through adaptive phenotypic convergence and, in turn, about their evolvability (see above). ...
Eco-morphological convergence, i.e., similar phenotypes evolved in ecologically convergent taxa, naturally reproduces a common-garden experiment since it allows researchers to keep ecological factors constant, studying intrinsic evolutionary drivers. The latter may result in differential evolvability that, among individual anatomical parts, causes mosaic evolution. Reconstructing the evolutionary morphology of the humerus and femur of slow arboreal mammals, we addressed mosaicism at different bone anatomical spatial scales. We compared convergence strength, using it as indicator of evolvability, between bone external shape and inner structure, with the former expected to be less evolvable and less involved in convergent evolution, due to anatomical constraints. We identify several convergent inner structural traits, while external shape only loosely follows this trend, and we find confirmation for our assumption in measures of convergence magnitude. We suggest that future macroevolutionary reconstructions based on bone morphology should include structural traits to better detect ecological effects on vertebrate diversification.
... Numerous studies have shown a relationship among bone morphology, locomotor strategy, and ecological adaptations in a myriad of taxa (e.g., Alfieri et al., 2022;Amson et al., 2017;Amson & Kilbourne, 2019;Barak et al., 2011;Fajardo et al., 2007;Granatosky et al., 2018;Griffin et al., 2010;Hudson et al., 2010Hudson et al., , 2012Lieberman et al., 2003;Rafferty, 1998;Ragni, 2020;Ryan & Ketcham, 2002;Tsegai et al., 2013;Van Valkenburgh, 1987). However, none of them have specifically investigated internal bone morphology of felid species (family Felidae) that are closely related and occupy disparate geographical species. ...
A relationship exists between mechanical loading and bone morphology. Although studies show a relationship between trabecular bone morphology and locomotor strategy in mammals, none of them have studied trabecular bone morphology in felid species occupying disparate and overlapping habitats. We investigate trabecular bone volume fraction (BVF) in the femoral and humeral heads, and distal tibia of four felid species (mountain lions, jaguars, cheetahs, and leopards) to identify whether there is a relationship between BVF and locomotor behavior. This study's goals are to identify whether felid species with high daily travel distance or large home range size have greater BVF compared with those with small daily travel distance or home range size, and whether BVF is correlated among the three elements of the fore and hindlimb studied. We quantified BVF in micro‐ and peripheral computed tomography images and found no significant differences across species in the femoral and humeral head ( p > 0.05). However, in the distal tibia, results showed that leopards, mountain lions, and cheetahs have significantly greater ( p < 0.05) BVF than jaguars. Despite differences in home range size and daily travel distance, the proximal elements did not reflect differences in BVF; however, the distal‐most element did, suggesting decreased loading among jaguars. These findings suggest that the observed pattern of trabecular bone morphology is potentially due to the diversity in locomotor strategy of the forelimb. Additionally, these results imply that neither home range size nor daily travel distance are clear indicators of activity levels. A cautious approach is warranted in studying how loading influences trabecular morphology.
... This also comports with a study of Xenarthra by Toledo et al. (2021), finding the same pattern among terrestrial taxa with more robust ulna shafts and arboreal taxa with more gracile shafts (c.f. results from xenarthran upper limbs; Alfieri et al., 2022;Spear and Williams, 2021). ...
... Elbow joint morphology reflects function across mammalian groups, including carnivorans, xenarthrans, primates, and rodents (Elton, 2001(Elton, , 2006Samuels and Van Valkenburgh, 2008;Meloro et al., 2013;Elton et al., 2016;Meloro and de Oliveira, 2019;Spear and Williams, 2021;Toledo et al., 2021;Alfieri et al., 2022). Olecranon morphology and orientation in extant quadrupeds is useful for inferring locomotor postures in extinct taxa (Ciochon, 1993;Fujiwara, 2009;Fujiwara and Hutchinson, 2012;Lungmus and Angielczyk, 2021). ...
Because the ulna supports and transmits forces during movement, its morphology can signal aspects of functional adaptation. To test whether, like extant apes, some hominins habitually recruit the forelimb in locomotion, we separate the ulna shaft and ulna proximal complex for independent shape analyses via elliptical Fourier methods to identify functional signals. We examine the relative influence of locomotion, taxonomy, and body mass on ulna contours in Homo sapiens (n = 22), five species of extant apes (n = 33), two Miocene apes (Hispanopithecus and Danuvius), and 17 fossil hominin specimens including Sahelanthropus, Ardipithecus, Australopithecus, Paranthropus, and early Homo. Ulna proximal complex contours correlate with body mass but not locomotor patterns, while ulna shafts significantly correlate with locomotion. African apes' ulna shafts are more robust and curved than Asian apes and are unlike other terrestrial mammals (including other primates), curving ventrally rather than dorsally. Because this distinctive curvature is absent in orangutans and hylobatids, it is likely a function of powerful flexors engaged in wrist and hand stabilization during knuckle-walking, and not an adaptation to climbing or suspensory behavior. The OH 36 (purported Paranthropus boisei) and TM 266 (assigned to Sahelanthropus tchadensis) fossils differ from other hominins by falling within the knuckle-walking morphospace, and thus appear to show forelimb morphology consistent with terrestrial locomotion. Discriminant function analysis classifies both OH 36 and TM 266 with Pan and Gorilla with high posterior probability. Along with its associated femur, the TM 266 ulna shaft contours and its deep, keeled trochlear notch comprise a suite of traits signaling African ape-like quadrupedalism. While implications for the phylogenetic position and hominin status of S. tchadensis remain equivocal, this study supports the growing body of evidence indicating that S. tchadensis was not an obligate biped, but instead represents a late Miocene hominid with knuckle-walking adaptations.
... 3D GMMs have been proven extremely useful to characterize shape variation on such bones. They have been used to study the influence of locomotion and body mass in small carnivorans Fabre, Cornette, Argot et al., 2013;Fabre et al., 2015;Figueirido et al., 2015;Martín-Serra et al., 2014), rodents (Álvarez et al., 2013;Wölfer et al., 2019), xenarthrans (Alfieri et al., 2022) and primates (Botton-Divet & Nyakatura, 2021), as well as in heavier taxa like Suidae (e.g. Harbers et al., 2020). ...
During evolution, several vertebrate lineages have shown trends towards an increase in mass. Such a trend is associated with physiological and musculoskeletal changes necessary to carry and move an increasingly heavy body. Due to their prominent role in the support and movement of the body, limb long bones are highly affected by these shifts in body mass. Elephants are the heaviest living terrestrial mammals, displaying unique features allowing them to withstand their massive weight, such as the columnarity of their limbs, and as such are crucial to understand the evolution towards high body mass in land mammals. In this study, we investigate the shape variation of the six limb long bones among the modern elephants, Elephas maximus and Loxodonta africana, to understand the effect of body mass and habitat on the external anatomy of the bones. To do so, we use three-dimensional geometric morphometrics (GMMs) and qualitative comparisons to describe the shape variation, at both the intraspecific and interspecific levels. Our results reveal that the two species share similar negative ontogenetic allometric patterns (i.e. becoming stouter with increased length) in their humerus and femur, but not in the other bones: the proximal epiphyses of the stylopod bones develop considerably during growth, while the distal epiphyses, which are involved in load distribution in the elbow and knee joints, are already
massive in juveniles. We attribute this pattern to a weight-bearing
adaptation already present in young specimens. Among adults of the same species, bone robustness increases with body mass, so that heavier specimens display stouter bones allowing for a better mechanical load distribution. While this robustness variation is significant for the humerus only, all the other bones appear to follow the same pattern. This is particularly visible in the ulna and tibia, but less so in the femur, which suggests that the forelimb and hindlimb adapted differently to high body mass support. Robustness analyses, while significant for the humerus only, suggest more robust long bones in Asian elephants than in African savanna elephants. More specifically, GMMs and qualitative comparisons indicate that three bones are clearly distinct when comparing the two species: in E. maximus the humerus, the ulna and the tibia display enlarged areas of muscular insertions for muscles involved in joint and limb stabilization, as well as in limb rotation. These results suggest a higher limb compliance in Asian elephants,associated with a higher dexterity, which could be linked to their habitat and foraging
habits.
... Parsing the influence of body size, ecology, and phylogeny on trabecular bone is complicated. However, the effect of body size on TBA has been previously examined in birds, reptiles, mammals, rodents, primates, and humans, and many aspects of TBA scale allometrically (Alfieri, Botton-Divet, Nyakatura, & Amson, 2021;Amson & Bibi, 2021;Barak, Lieberman, & Hublin, 2013;Doube, Kłosowski, Wiktorowicz-Conroy, Hutchinson, & Shefelbine, 2011;Fajardo et al., 2013;Mielke et al., 2018;Plasse, Amson, Bardin, Grimal, & Germain, 2019;Ryan & Shaw, 2013;Saers, Ryan, & Stock, 2019;Swartz, Parker, & Huo, 1998;Wysocki & Tseng, 2018). Trabeculae have a minimum thickness of about 50 µm and a maximum of 460 µm, resulting from the mechanical limitations of osteoclasts and osteocytes respectively (Barak et al., 2013;Lozupone & Favia, 1990;Mullender & Huiskes, 1995;Ryan & Shaw, 2013), and trabecular thickness (Tb.Th) scales with negative allometry with body size (Barak et al., 2013;Ryan & Shaw, 2013). ...
... The presence of the xenarthrous process on the postdiaphragmatic vertebrae of xenarthrans has been examined using a wide variety of methods (Galliari, Carlini, & Sánchez-Villagra, 2010;Gaudin & Biewener, 1992;Hautier, Oliver, & Pierce, 2018;Miranda et al., 2022;Oliver, Jones, Hautier, Loughry, & Pierce, 2016;Oliver, Jones, Pierce, & Hautier, 2021). This extra articulation point for posterior thoracic and lumbar vertebrae stiffens the vertebral column, which is thought to facilitate digging behavior by stiffening the trunk while allowing the animal to use its forelimbs for digging (Gaudin & Biewener, 1992;Oliver et al., 2016 (Alfieri et al., 2021;Amson, Arnold, van Heteren, Canoville, & Nyakatura, 2017). Modern xenarthrans provide an opportunity to examine the details of scaling patterns across a more limited size range and phylogenetic scale than in mammal-wide datasets. ...
... The only metric with a significant correlation with body size for sloths is CSA, and most metrics have R-squared less than 0.05 (TABLE 3). It is unclear whether this is due to the small body size range or the suspensory ecology of extant sloths, which results in unique loading of the vertebral column in sloths (Alfieri et al., 2021;Nyakatura & Fischer, 2010;Olson, Glenn, Cliffe, & Butcher, 2018). ...
Synopsis
Trabecular bone is a spongy bone tissue that serves as a scaffolding-like support inside many skeletal elements. Previous research found allometric variation in some aspects of trabecular bone architecture (TBA) and bone microstructure, whereas others scale isometrically. However, most of these studies examined very wide size and phylogenetic ranges or focused exclusively on primates or lab mice. We examined the impact of body size on TBA across a smaller size range in the mammalian clade Xenarthra (sloths, armadillos, and anteaters). We µCT-scanned the last six presacral vertebrae of 23 xenarthran specimens (body mass 120 g–35 kg). We collected ten gross-morphology measurements and seven TBA metrics and analyzed them using phylogenetic and nonphylogenetic methods. Most metrics had similar allometries to previous work. However, because ecology and phylogeny align closely in Xenarthra, the phylogenetic methods likely removed some covariance due to ecology; clarifying the impact of ecology on TBA in xenarthrans requires further work. Regressions for Folivora had high P-values and low R-squared values, indicating that the extant sloth sample either is too limited to determine patterns or that the unique way sloths load their vertebral columns causes unusually high TBA variation. The southern three-banded armadillo sits far below the regression lines, which may be related to its ability to roll into a ball. Body size, phylogeny, and ecology impact xenarthran TBA, but parsing these effects is highly complex.
... Not only could the same diet habits lead to the convergent evolution of different species, but also the same living habits could lead to the eco-morphological convergence of different species. Previous studies found that there was eco-morphological convergence in slow arboreal xenarthrans through the analysis of multiple omics of the humeral and femoral internal structure [15]. Independently evolving species might lead to the convergent evolution of phenotypes in order to adapt to the same environment, but these convergent phenotypes do not necessarily result from convergent evolution at the molecular level. ...
The species living in the Qinghai-Tibet Plateau provide an excellent model system for studying the relationship between molecular convergent evolution and adaptation. Distant species experiencing the same selection pressure (i.e., hypoxia, low temperature and strong ultraviolet radiation) are likely to evolve similar genetic adaptations independently. Here, we performed comparative genomics studies on six independently evolved high-altitude species. The results also showed that the convergent evolution of the six species was mainly reflected at the level of rapidly evolving genes, and the functions of these rapidly evolving genes were mainly related to hypoxia response and DNA damage repair. In addition, we found that high-altitude species had more gene family changes than their low-altitude relatives, except for the order Lagomorpha. The results also show that the convergence of the gene family contraction of high-altitude species is much greater than that of expansion, revealing a possible pattern of species in adapting to high-altitude. Furthermore, we detected a positive selection signature in four genes related to hypoxia response and ultraviolet radiation damage in these six species (FYCO1, ERBIN, SCAMP1 and CXCL10). Our study reveals that hypoxia response might play an important role in the adaptation of independently evolved species to a high-altitude environment, providing a basic perspective for further exploring the high-altitude adaptation mechanism of different related species in the future.
... Our results add to increasing evidence that incomplete convergence is more common in the natural world than previously realized (Meloro et al. 2015;Grossnickle et al. 2020;Watanabe et al. 2021;Alfieri et al. 2022) and suggest that the textbook convergence in marine tetrapods may be superficial and likely restricted to general body shape (Motani 2002). When one focuses in on the details of craniodental architecture, strong ecomorphological convergence appears rare, especially when analyzing distant clades that colonized marine niches in widely distinct biosphere contexts, such as mosasaurids and early cetaceans. ...
... When one focuses in on the details of craniodental architecture, strong ecomorphological convergence appears rare, especially when analyzing distant clades that colonized marine niches in widely distinct biosphere contexts, such as mosasaurids and early cetaceans. Strong ecomorphological convergence has been theorized to occur when considering a specific, restricted niche with a single optimal morphology (Alfieri et al. 2022); this has been observed in short-necked plesiosaurs, which have an adaptive landscape defined by "peaks" of optimal morphology (Fischer et al. 2020). However, incomplete convergence may result in an adaptive landscape better described as a "slope," where groups show similar or parallel trajectories in ecomorphological evolution that are offset by their ancestral heritage (Grossnickle et al. 2020;Alfieri et al. 2022). ...
... Strong ecomorphological convergence has been theorized to occur when considering a specific, restricted niche with a single optimal morphology (Alfieri et al. 2022); this has been observed in short-necked plesiosaurs, which have an adaptive landscape defined by "peaks" of optimal morphology (Fischer et al. 2020). However, incomplete convergence may result in an adaptive landscape better described as a "slope," where groups show similar or parallel trajectories in ecomorphological evolution that are offset by their ancestral heritage (Grossnickle et al. 2020;Alfieri et al. 2022). Our results fit this pattern, with no clear optimal peaks of ecomorphology and trajectories that appear to be strongly influenced by intrinsic phylogenetic constraints. ...
The repeated return of tetrapods to aquatic life provides some of the best-known examples of convergent evolution. One comparison that has received relatively little focus is that of mosasaurids (a group of Late Cretaceous squamates) and archaic cetaceans (the ancestors of modern whales and dolphins), both of which show high levels of craniodental disparity, similar initial trends in locomotory evolution, and global distributions. Here we investigate convergence in skull ecomorphology during the initial aquatic radiations of these groups. A series of functionally informative ratios were calculated from 38 species, with ordination techniques used to reconstruct patterns of functional ecomorphospace occupation. The earliest fully aquatic members of each clade occupied different regions of ecomorphospace, with basilosaurids and early russellosaurines exhibiting marked differences in cranial functional morphology. Subsequent ecomorphological trajectories notably diverge: mosasaurids radiated across ecomorphospace with no clear pattern and numerous reversals, whereas cetaceans notably evolved toward shallower, more elongated snouts, perhaps as an adaptation for capturing smaller prey. Incomplete convergence between the two groups is present among megapredatory and longirostrine forms, suggesting stronger selection on cranial function in these two ecomorphologies. Our study highlights both the similarities and divergences in craniodental evolutionary trajectories between archaic cetaceans and mosasaurids, with convergences transcending their deeply divergent phylogenetic affinities.
