Macroscelidid afrotherians and canid carnivorans possess four premolar loci, the first of which is not replaced. Previous work suggests that the first premolar in macroscelidids is a retained deciduous tooth, but in Canis it is a successional tooth with no milk precursor. We tested this contrasting interpretation of first premolar homology with data from ontogenetic anatomy and with area predictions from the inhibitory cascade (IC) model. Our results based on anatomy support previous interpretations that the functional first premolar is a retained deciduous tooth (dp1) with no successor in macroscelidids, and a successional tooth (p1) with no precursor in Canis. Hyracoids are among the few placental mammals that show replacement at the first premolar locus and show less deviation than other taxa of actual from predicted areas across the deciduous and molar toothrow. However, predicted vs. actual tooth areas can depart substantially from one another. At least without a better means of representing tooth size, the inhibitory cascade does not help to distinguish the deciduous from successional first premolar. This observation does not rule out the possibility that factors such as a size-shift within the toothrow (e.g., carnivoran carnassials) help to explain deviations from the inhibitory cascade model.

Millions of people across the world have been exposed to the wildlife documentaries of David Attenborough and Bernhard Grzimek, who have thus greatly influenced the public’s views on nature and biodiversity. We investigated the way organisms’ biology is portrayed in these documentaries, quantifying different types of animal interactions shown. We evaluated 1498 (Attenborough) and 391 (Grzimek) interactions within- and between-species from documentaries covering a wide range of environments and animal taxa, first aired between 1956 and 2019. We tested whether the relative frequencies of different interactions were influenced by temporal trends as well as by the presenters and their production teams who likely reflect the given Zeitgeist in the UK compared to the European mainland. For our categorisation of animal interactions, we contrasted interspecific versus intraspecific interactions and antagonistic versus cooperative behaviour. While Grzimek’s documentaries put a stronger emphasis on cooperation and Attenborough’s on antagonistic behaviour, the trends were not statistically significant. Furthermore, these patterns show no significant change over time, contrasting with the changing view among biologists that cooperation is more predominant than considered in the traditional understanding of nature as ‘red in tooth and claw’.

The pattern of dental replacement in marsupial mammals has received much attention for its derived nature and potential relationship to the life history of the group. However, few species have been studied thoroughly, and little is known about the embryonic structures and their use in addressing issues of homology and dental evolution in general. We studied a developmental series of ten individuals of pouch young Caluromys philander to thoroughly document dental development with histological sections and 3D models of dental series. We report that the successor P3 arises from a lingual successional lamina from its predecessor dP3. The germs of vestigial, unerupted deciduous incisors and canines are present alongside their respective permanent successors. These discoveries demonstrate significant differences from the developmental patterns reported for Didelphis and Monodelphis and illustrate that an unsuspected diversity of dental ontogeny is not reflected in the adult pattern of mineralised, erupted or almost erupted teeth.