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3 - Shoulder joint and inner ear of Tachypteron franzeni, an emballonurid bat from the Middle Eocene of Messel
- Edited by Gregg F. Gunnell, Duke University, North Carolina, Nancy B. Simmons, American Museum of Natural History, New York
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- Book:
- Evolutionary History of Bats
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- 05 June 2012
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- 29 March 2012, pp 67-104
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Summary
Introduction
Over 600 Middle Eocene bat specimens have been excavated from the Messel pit (Grube Messel, near Darmstadt, Germany), and seven species have been described thus far. Many of the fossils are preserved as complete skeletons, often with soft body outlines and gut contents. Six of the bat species represent three extinct families, whereas Tachypteron franzeni can be assigned to the extant family Emballonuridae (Storch et al., 2002). T. franzeni is known only from two specimens; however, these are extraordinarily well preserved, including the shoulder joints and inner ears, so this had already been recognized in the original description of T. franzeni, and these close resemblances to extant emballonurids led to the conclusion that T. franzeni had already evolved similar bioacoustic specializations and a similar flight style to modern taxa.
The shoulder joints of bats are sophisticated structures showing remarkable morphological variation. Miller's (1907) investigations on the differentiations of the shoulder within the Microchiroptera were continued by the studies of other authors (Vaughan, 1970; Strickler, 1978; Hermanson and Altenbach, 1983).
Three different types of shoulder joint can be distinguished within the Chiroptera: the primitive morphology of the shoulder joint with a globular humeral head and corresponding glenoid cavity, as seen in Megachiroptera and Rhinopomatidae; a derived shoulder joint with an oblong humeral head and a single trough-like articular surface on the scapula, found in members of the superfamilies Emballonuroidea, Rhinolophoidea and Noctilionoidea; a derived shoulder joint with a secondary articulation between the tuberculum majus and a secondary articular facet on the dorsal side of the scapula, as seen in the remaining families. Their distribution within the order gives evidence of parallel evolution of the derived types (Schlosser-Sturm and Schliemann, 1995). The morphological modifications of the derived joints are interpreted as a functional response to a biomechanical demand connected with flight (Norberg, 2002), i.e., to limit pronation of the humerus during the downstroke of the wing beat cycle, realized in two different mechanical ways (Schlosser-Sturm, 1982; Altenbach, 1987; Schliemann and Schlosser-Sturm, 1999). Because movement restriction was described for the primitive type as well (Bergemann, 2003), functional interpretations are still a matter of controversy.
2 - Systematics and paleobiogeography of early bats
- Edited by Gregg F. Gunnell, Duke University, North Carolina, Nancy B. Simmons, American Museum of Natural History, New York
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- Book:
- Evolutionary History of Bats
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- 05 June 2012
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- 29 March 2012, pp 23-66
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Summary
Introduction
The phylogenetic and geographic origins of most extant mammalian orders are still poorly documented. Many first appear in the fossil record during the Paleocene-Eocene Thermal Maximum (PETM) at the beginning of the Eocene epoch about 55.5 million years ago (Smith et al., 2006). However, three prominent orders are exceptions to this pattern. Rodents first appeared in North America about 0.5–1.0 million years before the PETM, but probably had an Asian origin like other Glires (Meng et al., 2003). Bats and whales are not known with any certainty before Middle Ypresian, about 54 mya.
The earliest known bats are small, insectivorous forms that are preserved in both terrestrial and lacustrine fossil faunas. Their phylogenetic and geographic origins are still unknown, although the absence of clear transitional forms in the fossil record suggests that bat origins are potentially either quite ancient or their evolution from non-volant mammals was quite rapid. Although morphological evidence has generally supported an origin from within Euarchontoglires, sequence data from multiple genes strongly supports an origin of bats from within Laurasiatheria (Springer et al., 2003; Gunnell and Simmons, 2005).
The oldest known fossil bats are early-middle Early Eocene taxa, and the first members of modern bat families and superfamilies seem to appear in the fossil record in the Middle Eocene (Gunnell and Simmons, 2005). We thus here restrict the term “early bats” to the species known from the Early and early-middle Middle Eocene (Ypresian and Lutetian, and global equivalents, encompassing European mammalian reference levels MP7 through MP13). These early bats mainly include “eochiropterans” (Eochiroptera Van Valen 1979 is a controversial paraphyletic group composed of primitive taxa; see Simmons and Geisler, 1998 for an overview) and a few taxa belonging to the first members of modern families.
16 - Early evolution of body size in bats
- Edited by Gregg F. Gunnell, Duke University, North Carolina, Nancy B. Simmons, American Museum of Natural History, New York
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- Book:
- Evolutionary History of Bats
- Published online:
- 05 June 2012
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- 29 March 2012, pp 530-555
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Summary
Introduction
Size is the single most important factor affecting physiology, locomotion, ecology and behavior of mammals (MacNab, 2007 and citations therein). Understanding evolution of size is important in all organisms, but especially so in cases like bats which exhibit many energetically expensive behaviors (e.g., powered flight, echolocation, long-distance migration), as well as characteristics that represent extreme energy-saving mechanisms (e.g., torpor and hibernation). Most bat species are small: from data in Smith et al. (2004), the central tendency in size in extant bats, as estimated by the median value, is around 14 g (Figure 16.1). However, size in bats as a group spans three orders of magnitude, ranging from 2–3 g (e.g., Craseonycteris, Thyroptera, Furipterus, some vespertilionids; Smith et al., 2004) to a few species exceeding 1 kg (e.g., Acerodon jubatus, Pteropus vampyrus; Kunz and Pierson, 1994). This variation in size scales a number of fundamental traits in bats, including physiological features (e.g., basal metabolic rate; McNab and Bonaccorso, 2001; MacNab, 2003, Speakman and Thomas, 2003); aerodynamic performance (Norberg, 1986, 1990; Rayner, 1986; Watts et al., 2001); dimensions of limb bones and their biomechanical properties (Swartz, 1997, 1998; Swartz and Middleton, 2008); behaviors (e.g., extreme dietary habits like carnivory; Norberg and Fenton, 1988); echolocation call parameters (Jones, 1999); and most life-history traits (e.g., litter mass; Hayssen and Kunz, 1996). These traits likely have an important phylogenetic component of variation, as has been shown, for instance, for the relationship of basal metabolic rate to body mass (Cruz-Neto et al., 2001; cf. MacNab, 2007). Besides the many dependent variables responding to body mass in various ways, size is a fundamental trait that should be understood by itself as an evolving character in bat lineages.