Cimar Round Ray vs Common Fat-tailed Mouse Opossum

Urotrygon cimar compared with Thylamys pusillus

Key Differences

• Cimar Round Ray is Near Threatened while Common Fat-tailed Mouse Opossum is Least Concern.

Taxonomic Classification

Rank	Cimar Round Ray	Common Fat-tailed Mouse Opossum
Kingdom same	Animalia (Animals)	Animalia (Animals)
Phylum same	Chordata (Chordates)	Chordata (Chordates)
Class	Elasmobranchii	Mammalia (Mammals)
Order	Myliobatiformes (Myliobatiformes)	Didelphimorphia (Didelphimorphia)
Family	Urotrygonidae	Didelphidae
Genus	Urotrygon	Thylamys
Species	Urotrygon cimar	Thylamys pusillus

Evolutionary Relationship

Cimar Round Ray and Common Fat-tailed Mouse Opossum share a common ancestor at the Phylum level: Chordata. (Chordates)

Conservation Status

Cimar Round Ray

NT — Near Threatened

Common Fat-tailed Mouse Opossum

LC — Least Concern

Physical Characteristics

Attribute	Cimar Round Ray	Common Fat-tailed Mouse Opossum
Diet	—	—
Average Lifespan	—	—
Average Length	—	—
Average Weight	—	—

Habitat & Geographic Range

Cimar Round Ray

Common Fat-tailed Mouse Opossum

Habitat

Typically found in diverse terrestrial and aquatic ecosystems.

Cimar Round Ray

The Cimar round ray (Urotrygon cimar) is a small stingray in the family Urotrygonidae, found in the eastern Pacific Ocean along the coasts of Central America and northern South America, including the waters of Costa Rica, Panama, Colombia, and Ecuador. It inhabits shallow coastal and estuarine waters over sandy and muddy bottoms, typically at depths of less than 50 meters, where it feeds on small benthic invertebrates and fish. Like other round rays in the genus Urotrygon, it has a nearly circular disc outline, a relatively slender tail, and a venomous caudal spine used defensively against predators. The species is classified as Near Threatened by the IUCN, reflecting its restricted range, vulnerability to coastal habitat degradation, and incidental capture in artisanal and commercial fisheries throughout its range. Bycatch in shrimp trawls and gill nets represents a significant ongoing threat to Urotrygon species throughout the eastern Pacific. Shallow coastal habitats in Central America and Colombia face continued pressure from development, mangrove loss, and pollution. The species' reproductive biology, like that of most Urotrygon rays, involves ovoviviparity, with females giving birth to live young after internal development. Population assessments for this species remain limited, and more data on abundance and mortality rates are needed.

Common Fat-tailed Mouse Opossum

The Common Fat-tailed Mouse Opossum (<em>Thylamys pusillus</em>) is a small marsupial belonging to the genus Thylamys within the family Didelphidae. Like other members of its genus, this species typically stores fat in its tail, which becomes swollen during periods of food abundance and is metabolised during leaner times, a physiological adaptation that provides energy reserves. <em>Thylamys pusillus</em> is generally found in diverse terrestrial and aquatic ecosystems, often in dry woodlands, scrublands, and grassland habitats of South America. The species is assessed as Least Concern on the IUCN Red List, indicating it is not currently considered at risk of extinction. Detailed geographic range data are not available in the current record, but members of this genus are typically distributed across parts of Argentina, Bolivia, Paraguay, and Uruguay. Biological traits including average lifespan, body dimensions, and specific dietary composition remain poorly documented in the scientific literature, though Thylamys species are generally considered omnivorous, often consuming insects, small vertebrates, and plant material.