DOI: 10.15468/5k3v6s
title: Early Eocene Bat from Wyoming

description: This dataset contains the digitized treatments in Plazi based on the original journal article Jepsen, Glenn L. (1966): Early Eocene Bat from Wyoming. Science (New York, N. Y.) 154 (3754): 1333-1339, DOI: 10.1126/science.154.3754.1333, URL: http://dx.doi.org/10.1126/science.154.3754.1333Abstract. A fossil skeleton of an early Eocene bat, the oldest known flying mammal, was found in southwest Wyoming. The bat is assigned to the new species Icaronycteris index of the suborder Microchiroptera. It was apparently of a young male whose body was buried in varved marls of the Green River Formation, on the bottom of Fossil Lake, about 50 million years ago. The bones, some as slender as a human hair, show a few " primitive " characteristics such as a clawed index finger and a complete phalangeal formula, but the bat was fully developed -an anatomically precocious contemporary of the dog-sized polydactylous horse.Remarkably complete and beautifully preserved, the skeleton of an early Eocene bat (see cover) from southwest Wyoming represents the -oldestknown genus and species, here named Icaronycteris index, within the order Chiroptera. Found about 33 years ago (1) in the fossil-fish marlstones of the Green River Formation, the specimen is one of the most extraordinary vertebrate fossils in both the superb completeness of the bony skeleton and the rare preservation of remnants of structures such as wing membranes, abdominothoracic diaphragm, and cartilages of the ribs and throat-even of fragmentary residues of ingested food.I now report for the first time some of its unique characteristics. Living bats are so numerous, in contrast with the rarity of fossil bats, and have such diversified variations in functional adaptations (2) that every bone in this specimen, especially the carpus, may give information about the origin and evolution of bats.Dorsal (Fig. 1) and ventral (Fig. 2) aspects of the specimen show some of the extensive cracking and crushing that attended postdepositional compaction of the investing sediments. The film-thin top of the skull is so shattered and flattened that the relative development (size) of the midbrain colliculione of the most significant and diagnostic traits of microchiropteranscannot be determined. The right lower jaw has been pressed into and through the skull so far that some tips of the cusps of the lower teeth have pierced the. palate and the skull roof; this penetration was favorable in that the crowns of the lower teeth could be further exposed in the laboratory without much additional destruction of skull bone.Fortunate also was the movement of the left dentary from a vertical to a horizontal position: as a result, the entire external side of this jaw, and its teeth, could be exposed when the matrix was removed from the ventral side of the head (Fig. 2). Figure 2 also shows several delicate and minute skeletal structures (hyoid bones, No. 76; baculum?, No. 88) that are not frequently preserved in fossil vertebrates.Extreme fragility and delicacy and the smallness of parts of the bat make study difficult: A flat area of the left,scapula, now free of matrix on both sides, is translucently thin; and the gracile bony bar lateral to the vertebroarterial canal of the second cervical vertebra is only 0.07 mm thick. Excavation was tedious, and such sharp points were needed for removing the matrix that the steel digging needles had to be sharpened under the microscope (3).