A Dental Microwear Texture Analysis of the Early Pliocene African Ursid Agriotherium africanum (Mammalia, Carnivora, Ursidae)

Inter-microscope comparability of dental microwear texture data obtained from different optical profilometers: Part II Deriving instrument-specific correction equations for meta-analyses using published data

Dental microwear texture analysis (DMTA) has emerged as a valuable method for investigating the feeding ecology of vertebrates. Over the past decade, three-dimensional topographic data from microscopic regions of tooth surfaces have been collected, and surface texture parameters have been published for both extant and fossil species. However, different types of measurement instruments and surface processing used by respective laboratories conducting DMTA have limited the potential data comparison. In this study, we propose correction formulae for the DMTA data produced by different instruments to facilitate intercomparison. We used six confocal instruments from five laboratories to scan standard tooth samples with strictly defined scan areas. We found significant differences in DMTA parameter values among the different machines, despite scanning the exact same spots. The degree of discrepancy varied considerably, with instruments from the same manufacturer and similar models showing less variation. Some parameters exhibited high correlations between instruments, enabling the development of regression equations for correction formulae. Using these correction formulae, we adjusted published DMTA data and conducted a meta-analysis of extant herbivores to examine the effects of internal and external abrasives. Our findings indicate overall positive effects of internal and external abrasives on DMTA, with varying responses to the abrasives between ruminant and non-ruminant herbivores. The meta-analysis supports the hypothesis that ruminants effectively "wash ingesta" in their rumens, mitigating the impact of external abrasives and reducing overall dental wear.

Dietary ecology of the scimitar-toothed cat Homotherium serum

The scimitar-toothed cat Homotherium was one of the most cosmopolitan cats of the Pleistocene, present throughout Eurasia, Africa, and the Americas until at least ~28 thousand years ago.^1-3 Friesenhahn Cave (Bexar County, Texas) contains some of the best-preserved specimens of Homotherium serum alongside an abundance of juvenile mammoths, leading some to argue that H. serum preferentially hunted juvenile mammoths.^1,4 Dietary data of Homotherium are rare, with their ecology inferred from morphological, taphonomic, and genetic data.^1,3-10 Here, we use a multi-proxy approach to clarify the dietary ecology of H. serum as compared to extinct and extant cats and their relatives. Dental microwear texture analysis (DMTA) reveals that H. serum consumed soft and tough foods, similar to the extant cheetah, which actively avoids bone,^11,12 but in stark contrast to extant lions and hyenas, which are observed to engage in durophagy (i.e., bone processing).^11-14 DMTA data are consistent with taphonomic evidence of bone defleshing and the absence of bone-crunching behavior in H. serum. Stable carbon isotope values of H. serum indicate a clear preference for C₄ grazers including juvenile mammoths, in agreement with taphonomic evidence suggestive of a "Homotherium den"^1,4 and morphological data indicative of a relatively cursorial lifestyle.^6-8 Notably, the inferred diet of H. serum contrasts with the extinct dirk-tooth sabertooth cat Smilodon fatalis, which preferred forest/woodland prey and engaged in bone processing.^15-19Homotherium serum exhibited a novel combination of morphological adaptations for acquiring open-country prey, consuming their soft and tough flesh-including the tough flesh of juvenile mammoths. VIDEO ABSTRACT.

Eucyon khoikhoi sp. nov. (Carnivora: Canidae) from Langebaanweg ‘E’ Quarry (early Pliocene, South Africa): the most complete African canini from the Mio-Pliocene

A new medium-sized canid, Eucyon khoikhoi sp. nov., is described from the early Pliocene site of Langebaanweg ‘E’ Quarry (South Africa). It possesses a robust dentition with large upper- and lower-second molars, an m1 talonid without a transverse cristid between the entoconid and the hypoconid, and a well-developed hypoconulid shelf. Our cladistic analysis of the earliest better-known African canini, places E. khoikhoi as the most basal taxon of an African clade composed of E. wokari, ?Nyctereutes barryi, ?Schaeffia mohibi and Schaeffia adusta (living side-striped jackal). We suggest an alternative arrangement for the poorly known East African E. intrepidus from the Late Miocene and E. kuta from the Middle Pliocene. Eucyon intrepidus could belong to the same clade as E. khoikhoi, unlike E. kuta, whose dentition suggests a closer relation with the Lupulella group. Thus, these results support the paraphyly of Eucyon, demonstrating the need for an in-depth review of the genus. Eucyon khoikhoi has a body mass comparable to E. kuta and the European E. debonisi and E. monticinensis. We conclude that E. khoikhoi may have had a comparable role in the ecosystem to the extant hypocarnivorous S. adusta.

An eye for a tooth: Thylacosmilus was not a marsupial "saber-tooth predator"

Background

Saber-toothed mammals, now all extinct, were cats or “cat-like” forms with enlarged, blade-like upper canines, proposed as specialists in taking large prey. During the last 66 Ma, the saber-tooth ecomorph has evolved convergently at least in five different mammalian lineages across both marsupials and placentals. Indeed, Thylacosmilus atrox, the so-called “marsupial saber-tooth,” is often considered as a classic example of convergence with placental saber-tooth cats such as Smilodon fatalis. However, despite its superficial similarity to saber-toothed placentals, T. atrox lacks many of the critical anatomical features related to their inferred predatory behavior—that of employing their enlarged canines in a killing head strike.

Methods

Here we follow a multi-proxy approach using canonical correspondence analysis of discrete traits, biomechanical models of skull function using Finite Element Analysis, and 3D dental microwear texture analysis of upper and lower postcanine teeth, to investigate the degree of evolutionary convergence between T. atrox and placental saber-tooths, including S. fatalis.

Results

Correspondence analysis shows that the craniodental features of T. atrox are divergent from those of placental saber-tooths. Biomechanical analyses indicate a superior ability of T. atrox to placental saber-tooths in pulling back with the canines, with the unique lateral ridge of the canines adding strength to this function. The dental microwear of T. atrox indicates a soft diet, resembling that of the meat-specializing cheetah, but its blunted gross dental wear is not indicative of shearing meat.

Conclusions

Our results indicate that despite its impressive canines, the “marsupial saber-tooth” was not the ecological analogue of placental saber-tooths, and likely did not use its canines to dispatch its prey. This oft-cited example of convergence requires reconsideration, and T. atrox may have had a unique type of ecology among mammals.

New insights into the giant mustelids (Mammalia, Carnivora, Mustelidae) from Langebaanweg fossil site (West Coast Fossil Park, South Africa, early Pliocene)

Giant mustelids are a paraphyletic group of mustelids found in the Neogene of Eurasia, Africa and North America. Most are known largely from dental remains, with their postcranial skeleton mostly unknown. Here, we describe new craniodental and postcranial remains of the large lutrine Sivaonyx hendeyi and the leopard-size gulonine Plesiogulo aff. monspessulanus from the early Pliocene site Langebaanweg, South Africa. The new material of the endemic S. hendeyi, includes upper incisors and premolars, and fragmentary humerus, ulna and a complete astragalus. Its postcrania shares more traits with the living Aonyx capensis than the late Miocene Sivaonyx beyi from Chad. Sivaonyx hendeyi could therefore be tentatively interpreted as a relatively more aquatic taxon than the Chadian species, comparable to A. capensis. The new specimens of Plesiogulo comprise two edentulous maxillae, including one of a juvenile individual with incomplete decidual dentition, and a fragmentary forelimb of an adult individual. The new dental measurements point to this form being amongst the largest specimens of the genus. Both P3-4 differs from the very large species Plesiogulo botori from late Miocene of Kenya and Ethiopia. This confirms the existence of two distinct large species of Plesiogulo in Africa during the Mio/Pliocene, P. botori in the Late Miocene of Eastern Africa (6.1–5.5 Ma) and Plesiogulo aff. monspessulanus at the beginning of the Pliocene in southern Africa (5.2 Ma). Lastly, we report for the first time the presence of both Sivaonyx and Plesiogulo in MPPM and LQSM at Langebaanweg, suggesting that the differences observed from the locality may be produced by sedimentation or sampling biases instead of temporal replacement within the carnivoran guild.