Weasels and otters in the LRT

The weasel + otter clade
from temperate regions and aquatic niches is presented below (Figs 1, 2) along with a few arboreal outgroup taxa from tropical regions.

Figure 1. Weasels evolving into otters in the LRT to scale. ” data-image-caption=”

Figure 1. Weasels evolving into otters in the LRT to scale.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/weasels-otters2scale588.jpg?w=188″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/weasels-otters2scale588.jpg?w=584″ class=”size-full wp-image-91159″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/weasels-otters2scale588.jpg” alt=”Figure 1. Weasels evolving into otters in the LRT to scale.” width=”584″ height=”930″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/weasels-otters2scale588.jpg?w=584&h=930 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/weasels-otters2scale588.jpg?w=94&h=150 94w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/weasels-otters2scale588.jpg?w=188&h=300 188w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/weasels-otters2scale588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 1. Weasels evolving into otters in the LRT to scale.

One might logically view otters as seal (= pinniped) ancestors,
but that is not recovered in the LRT. Puijila and Neotherium (Figs 1, 2) were originally considered pinniped ancestors due to taxon exclusion and convergence. The large reptile tree (LRT, 2332) recovered previously overlooked pinniped ancestors, like Cynogale.

Figure 2. Weasel to otter skulls in the LRT to scale. ” data-image-caption=”

Figure 2. Weasel to otter skulls in the LRT to scale.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/weasels-otters2024-588.jpg?w=106″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/weasels-otters2024-588.jpg?w=363″ class=”size-full wp-image-91160″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/weasels-otters2024-588.jpg” alt=”Figure 2. Weasel to otter skulls in the LRT to scale. ” width=”584″ height=”1647″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/weasels-otters2024-588.jpg?w=584&h=1647 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/weasels-otters2024-588.jpg?w=53&h=150 53w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/weasels-otters2024-588.jpg?w=106&h=300 106w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/weasels-otters2024-588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 2. Weasel to otter skulls in the LRT to scale.

Neotherium is traditionally considered a basal pinniped.
So is Puijila. Here Neotherium is a sister to Puijila (Figs 1, 2), and both are otters, derived from minks and weasels.

Mustela lutreola
(Linneaus 1761; up to 43cm in length) is the extant European mink, a fast and agile animal related to weasels and polecats. Mustela lives in a burrow, but it also swims and dives skilfully. It is able to run along stream beds, and stay underwater for one to two minutes. Mustela is basal to otters.

Lontra canadensis
(von Schreber 1777, Gray 1843; 84cm in length) is the extant river otter, nesting between the mink and sea otter.

Enhydra lutris
(Fleming 1828, originally Mustela lutris Linneaus 1758) is the extant sea otter. Here it nests with Mustela and the river otter, Lontra. Uniquely it is often found floating on its back. The sea otter opens mollusc shells by hitting them with rocks held between their hands. Note the large flat feet with longer lateral toes.

Potamotherium valletoni
(Geoffroy 1833, Miocene, 1.5m long) is a traditional member of the otters and weasels, as it is in the LRT. Note the three premolars and two molars.

Puijila darwini
(Rybczynski, Dawson and Tedford 2009; Late Oligocene 23 mya;1m in length) was originally considered an extinct species of seal based chiefly on skull and tooth traits. Here it nests with sea otters not releated to seals. Note the elevation of the large orbits. Puijila lived in and near high Arctic lakes.

Neotherium mirum
(Kellogg 1931; Middle Miocene) was originally considered a small, tuskless walrus, but here nests with otters like Puijila. The molars are premolarized.

References
Kellogg AR 1931.Pelagic mammals of the Temblor Formation of the Kern River region, California. Proceedings of the California Academy of Science 19(12):217-397.
Kohno NL,Barnes G, and Hirota K 1995. Miocene Fossil Pinnipeds of the Genera Prototaria and Neotherium (Carnivora; Otariidae; Imagotariinae) in the North Pacific Ocean: Evolution, Relationships and Distribution. Island Arc 3: 285–308.
Linneaus C von 1761. Fauna Suecica sistens Animalia Sueciae Regni: Mammalia, Aves, Amphibia, Pisces, Insecta, Vermes. Distributa per Classes, Ordines, Genera, Species, cum Differentiis Specierum, Synonymis Auctorum, Nominibus Incolarum, Locis Natalium, Descriptionibus insectorum. Editio altera, auctior. Stockholmiae: L. Salvii, 48 + 578 pp.
Rybczynsk Ni, Dawson MR and Tedford RH 2009. A semi-aquatic Arctic mammalian carnivore from the Miocene epoch and origin of Pinnipedia. Nature Letter 458:1021–1023. doi:10.1038/nature0798.
Fleming J 1828. A history of British animals, exhibiting the descriptive characters and systematic arrangement of the genera and species of quadrupeds, birds, reptiles, fishes, Mollusca, and Radiata of the United Kingdom; including the indigenous, extirpated, and extinct kinds, together with periodical and occasional visitants. – pp. i-xxxii [= 1-23], 1-565, [1]. Edinburgh. (Bell & Bradfute).

wiki/Mustela
wiki/Sea_otter
wiki/North_American_river_otter
wiki/Lontra
wiki/Enhydriodon
wiki/Puijila
wiki/Potamotherium
wiki/Neotherium