Lutreolina crassicaudata (Desmarest 1804, length 21 to 45 cm + tail) is the extant big lutrine (= otter like) opossum native to grasslands of South America close to water. A pouch is present. It has a long, weasel-like morphology with short legs. This carnivore can climb, walk and swim.

Chironectes minimus (von Zimmermann 1780, 30 cm snout to rump, 36cm tail) is the extant water opossum. This sole aquatic marsupial has a water-proof pouch with a unique sphincter for access. And it nests in the LRT as the proximal outgroup taxa to the Eutheria, although the aquatic niche and webbed feet are autapomorphies not retained in descendant taxa among the placental mammals. These traits have had the entire Cretaceous and Cenozoic to develop after that phylogenetic split. Both males and females have a pouch.

Gobiohyus orientalis (Matthew and Granger 1925, Coombs and Coombs 1977) was considered a member of the Helohyidae and Artiodactyla. Here it nests with Palaeosinopa.

Chriacus pelvidens (Cope 1884). Bridgerian (Palaeocene) ~48 mya is known from too few parts to accurately nest. Here it nests best with the extant water opossum, Chironectes. With three molars and fewer than four incisors.

The anterior teeth of Chriacus angled anteriorly. Chriacus was considered an omnivore, eating insects, fruit, meat. The cervicals were smaller with high neural spines. The limbs were all longer and the torso shorter. The wrist and ankle were highly mobile, permitting hind foot reversal as in squirrels and bats.

Van Valen (1971) nested Chriacus close to the base of the artiodactyls, or hooved mammals, because the two taxa share a similar tooth pattern. Rose (1987) considered Chriacus to be arboreal. This appears to be a novel hypothesis of interrelationships.

Carroll, RL 1988. Vertebrate Paleontology and Evolution. WH Freeman and Company.

Coombs MC and Coombs WP Jr. 1977. Dentition of Gobiohyus and a Reevaluation of the Helohyidae (Artiodactyla). Journal of Mammalogy58(3): 291-308.

Cope ED 1884. Second addition to the knowledge of the Puerco Epoch. Proceedings of the American Philosophical Society. 21, 309–324.

Desmarest AG 1804. Tabl. Méth. Hist. Nat., in Nouv. Dict. Hist. Nat. 24:19.

Matthew WD 1937. Paleocene faunas of the San Juan basin, New Mexico. Transactions of the American Philosophical Society, new series 30: 1-510.

Matthew WD and Granger W 1925. New mammals from the Irdin Manha Eocene of Mongolia. American Museum Novitates 198:1-10.

Rose KD 1987. Climbing adaptations in the early Eocene mammal Chriacus and the origin of Artiodactyla. Science 236:314-316.

Rose KD and von Koenigswald W 2005. An exceptionally complete skeleton of Palaeosinopa (Mammalia, Cimolesta, Pantolestidae) from the Green River Formation, and other postcranial elements of the Pantolestidae from the Eocene of Wyoming (USA): Palaeontographica Abteilung A 273: 55–96.

Van Valen LM 1971 Toward the origin of artiodactyls. Evolution 25: 523-529.


Wittich E 1898 1902. ein Raubtier aus dem Mitteleozän von Messel. Notizblatt des Vereins für. Erdkunde zu Darmstadt (5)14: 81-88.

Zimmerman EAWv 1780. Geographische Geschichte der Menschen, und der algemein verbreiteten Vierfüssigen Thiere. Zweiter Band. Leipzig: Wenganschen Buchhandlung 2:6.

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