A New Family of Large Omnivorous Bats (Mammalia, Chiroptera) from the Late Eocene of the Fayum Depression, Egypt, with Comments on Use of the Name “Eochiroptera”

Abstract

A new fossil from the Late Eocene BQ-2 locality in the Birket Qarun Formation in the Fayum Depression of northern Egypt (dated to ~37 mybp) does not fit within the diagnosis of any previously described family of bats from Africa or any other continent. Known from a partial maxilla, this taxon has dilambdodont tribosphenic molars with a well-developed, symmetrical, W-shaped ectoloph lacking a distinct mesostyle but with a strong parastyle and shallow U-shaped ectoflexus-all traits that are found in most archaic bat families and that are probably plesiomorphic for bats. However, this taxon also has an M2 with a large metaconule cusp and a large, bulbous hypocone set low on the posterolingual corner of the tooth, neither of which occur in any known bat family, living or extinct. Also notable is the size of the new BQ-2 bat, which appears to have been approximately the same size as the largest extant bats with dilambdodont dentitions, falling well within the size range of plant-eating megabats and carnivorous bats from several extant lineages. The combination of traits in the new BQ-2 bat suggests that it was omnivorous, probably including insects, small vertebrates, and plant material its diet. In this regard it represents an ecological niche previously unknown among archaic Eocene bats, which are otherwise thought to have been strictly animalivorous. Because extinct Eocene bat families exhibit considerable mosaic evolution in morphological traits, do not seem to have inhabited a uniform ecological niche, and do not form a monophyletic group, we argue against use of the name "Eochiroptera" to collectively refer to these taxa.

A new, large-bodied omnivorous bat (Noctilionoidea: Mystacinidae) reveals lost morphological and ecological diversity since the Miocene in New Zealand

“…In that speciose group, it appears to have evolved multiple times 43 , but it is otherwise uncommon (and particularly rare on M3) in bats with a dilambdodont dentition. Outside Noctilionoidea, a large bulbous hypocone also occurs in the late Eocene Egyptian bat Aegyptonycteris knightae Simmons, Seiffert & Gunnell, 2016 65 . The latter is known only from its dilambdodont M2-3 and is the only member of its family whose relationships to other bats are unknown 65 .…”

“…Outside Noctilionoidea, a large bulbous hypocone also occurs in the late Eocene Egyptian bat Aegyptonycteris knightae Simmons, Seiffert & Gunnell, 2016 65 . The latter is known only from its dilambdodont M2-3 and is the only member of its family whose relationships to other bats are unknown 65 . This large fossil bat differs significantly from Vulcanops in that its M2-3 also have a large conule at the base of the metacone and an ectostyle on the buccal margin, two features unknown in other bat families, living or extinct 65 .…”

“…The latter is known only from its dilambdodont M2-3 and is the only member of its family whose relationships to other bats are unknown 65 . This large fossil bat differs significantly from Vulcanops in that its M2-3 also have a large conule at the base of the metacone and an ectostyle on the buccal margin, two features unknown in other bat families, living or extinct 65 . Among mammals, a hypocone increases occlusal area, effectively doubling the tooth surface devoted to processing food 66 .…”

“…As body size increases in bats, species with dilambdodont molars often include small vertebrates in their diets 65 – 70 . The presence of a well-developed hypocone in the ~40 g Vulcanops , however, argues against a strictly carnivorous diet.…”

“…The latter’s dentition, and diet, was perhaps most similar to some phyllostomines that consume invertebrates, nectar, fruit, flowers, as well as small vertebrates (e.g. the large-bodied omnivorous Phyllostomus hastatus ; 65 ).…”