Skeleton of an otter (Lutra lutra) with some regular and remarkable alterations

Abstract: On 24 April 2019 the remains of an otter (Lutra lutra) were found on the verge of a road on the island of Sula (Norway). About 95% of skeletal elements were collected. Inspection revealed several recently broken ribs and vertebrae, that may have led to the death of this individual. This paper describes the previously existing skeletal lesions, discusses the most probable cause of death, and attempts to estimate the age of the specimen. A comparison of skull measurements to those of otters from elsewhere in Europe (n=74) shows that this specimen is well within the 25th and 75th percentiles. Measurements of the baculum length / weight, shows that this otter was in the top 15% for European otters (n=65). Based on these comparisons, the specimen can be described as an adult male. Evidence of strong grinding of dentals and (pre)molars corroborates this estimation. The presence of a narrow strip of bone at the ventral part of the ischium increased the accuracy of the age estimation, which is set at four to five years. Besides a healed longitudinal fracture of the shaft of the left fibula, there were signs of severe arthrosis deformans on the femoral-tibia joints and erosion and enthesopathies were also noticed on the left tibia, all more extreme than on the right side. Three thoracal vertebrae showed erosion of the endplates and osteophytes to the stages of interlocking. The length of the osteophytes on each rim were quite regular. The breadth of the osteophytes, however, differed considerably. By describing these alterations, which can be described as ‘normal’ phenomena, this paper aims to contribute to increasing our knowledge of otters.