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The narrow-bridged mud turtle, Kinosternon angustipons, is a rare and poorly studied species of mud turtle endemic to the Caribbean versant of the Central American countries of Panama, Nicaragua, and Costa Rica. The known range of K. angustipons runs from the mouth of the San Juan River near the Costa Rican-Nicaraguan border to Bocas del Toros province in northern Panama.1 K. angustipons was described in 1965 from 15 individuals.1 Further research on the species has been limited by the difficulty of locating specimens. The closest extant relative of K. angustipons is Dunn's mud turtle (K. dunni), a species endemic to western Colombia that is also poorly researched.2
The largest known male specimen of K. angustipons measured 112mm in carapace length and the largest female 119mm. Due to the arrest in growth normally seen in adult turtles upon reaching a certain size, it is likely that the average size achieved by K. angustipons is near these values. K. angustipons has an oval-shaped, flattened and smooth carapace that is generally drab in color.3 The plastron is hinged in both the front and back; it is reduced and cannot be used to completely close off the shell as in some other mud turtles, such as the closely related white-lipped mud turtle (K. leucostomum). The bridge is characteristically narrow, making up no more than 20 percent of the length of the carapace.3 The head is unmarked and the beak is unremarkable, having a smooth profile for both the upper and lower aspects.3 The tail is also unremarkable. In males the tail extends beyond the carapace. In females it extends at most to the posterior edge of the carapace.3 Male specimens have patches of rough scales, referred to as clasping organs, on the inner surface of the posterior limbs.3 In older specimens the anal notch and interlaminal seams of the plastron may fill with soft tissue.3
Information regarding the preferred habitat of K. angustipons is sparse, based of off a mere 14 specimens trapped during the research leading to the species description. Most of the trapped specimens were captured in areas of permanent shallow swamp with no discernible current and poor water clarity. These areas featured muddy to hard bottoms with surface vegetation consisting of grasses and buttressed trees, and subsurface vegetation was nonexistent.1 Two specimens of K. angustipons, recently captured in Alajuela Province, Costa Rica, were located in similar shallow swampy areas, although both specimens were taken on land by hand rather than by trapping.4 Recent findings suggest that the sister species of K. angustipons, K. dunni, may prefer environments featuring small, rapidly moving bodies of water (John Iverson, personal communication, March 2014).
Information regarding the dietary habits of K. angustipons is limited to the stomach contents of two individuals, the analysis of which suggests that K. angustipons has a primarily herbivorous diet, but will opportunistically feed on other sources such as insects. Captured specimens were of K. angustipons regularly consumed hamburger.1
Life History and Behavior
The behavior, life cycle, and life expectancy of K. angustipons remain completely unknown due to the cryptic nature of the species. From the data available from only two adult female specimens, Legler states, “... it can be hypothesized that K. angustipons lays as many as four eggs, that they may be laid singly, and that more than one clutch of eggs per year can be produced.”1
Molecular Biology and Genetics
Recent phylogenetic analysis using both mitochondrial and nuclear markers, a more thorough approach than in previous attempts, suggests that K. angustipons is evolutionarily part of a distinct genus within the family Kinosternidae. Iverson et al. suggest the reclassification of this newly identified genus as Cryptochelys. The proposed genus would include the species K. leucostomum, K. angustipons, K. dunni, K. Herrerai, K. Creaseri and K. acutum. It is proposed that this new genus breaks from the remaining species of the present genus Kinosternon and the genus Sternotherus which, taken together, would represent the actual sister taxa of the suggested genus Cryptochelys.5
At present K. angustipons is defined as a vulnerable species by the IUCN.7 No management efforts exist that directly pertain to K. angustipons. Humans generally have no direct interaction with K. angustipons as either a resource or a pest and, as noted by Legler, K. angustipons is practically unknown even to local inhabitants of its range.1 This general lack of awareness suggests that there are no direct human threats to K. angustipons, although indirect threats to its habitat may exist.