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Is Inner Ear Morphology the Key to the Evolutionary Ecology of Bats?

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12 October 2026

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13 October 2026

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Abstract
1. The exceptional navigational ability of bats relies on specialised sensory organs; specifically, the inner ear is optimised to process high-frequency sounds in total darkness. 2. Despite its clear functional importance, inner ear morphology remains an underutilised source of evolutionary insight in Chiroptera, particularly the origins of echolocation and deep-time phylogenetic divergences. 3. Here, we review specialised anatomy of the chiropteran inner ear and contrast bat inner ear ecology with recent insights from echolocating whales 4. We address methodological challenges of studying minute features, demonstrate how non-destructive digital imagery advances overcome traditional barriers, and consider how confounding effects of phylogeny could be addressed in quantitative analyses. 5. We argue that known strong correlations between echolocation strategy and flight space point to excellent opportunities to use chiropteran inner ear morphology to infer the origins and evolution of chiropteran ecology and echolocation behaviour.
Keywords: 
Chiroptera
;  
sensory ecology
;  
audition
;  
echolocation
;  
mammalian inner ear
Subject: 
Biology and Life Sciences  -   Animal Science, Veterinary Science and Zoology

Introduction

With over 1500 species, bats (Order Chiroptera) constitute approximately 20% of living mammals (Burgin et al., 2018). Their dual adaptations of powered flight and echolocation allowed bats to colonise the night sky, resulting in a near-global distribution (King, 2024, Stevens et al., 2019, Ziegler et al., 2016) and unparalleled dietary diversity, ranging from insects, small vertebrates, fruit, nectar and even blood (Gual-Suárez and Medellín, 2021, Leiser-Miller and Santana, 2020, Potter et al., 2021, Rojas et al., 2011).
In all bats except pteropodids (flying foxes and old-world fruit bats), the high frequency biosonar system of echolocation has largely replaced the visual system for orientation, prey detection and localisation. These transitions coincided with extensive structural modifications, particularly in the inner ears (Davies et al., 2013; Sulser et al., 2022), which receive the ultrasonic signals (a high-frequency sound with a frequency above 20 kHz). Because the great diversity of echolocation types among bats is tightly associated with ecological traits such as diet and environmental surroundings, it is thus also expected that the inner ear of bats reflects a substantial amount of ecological information (Davies et al., 2013; Dickinson et al., 2023) through adaptations to particular echolocation types.
In this article, we review the specialised anatomy of the chiropteran inner ear. We trace the history of the discovery of bat echolocation and provide an overview of the known modifications of the chiropteran inner ear. We then contrast the relatively limited understanding of how bat inner ears reflect ecological traits with recent studies in the echolocating but distantly related odontocetes (whales). Lastly, we argue that the growing affordability and speed of tomography-based 3D digitisation offer an unprecedented opportunity to vastly expand understanding of chiropteran inner-ear morphology, its functional link to hearing ability, and its relationship to bat ecology.

Blinding Bats: The Historical Discovery of Echolocation

Bats' ability to navigate in complete darkness was a longstanding scientific mystery. In 1793, Italian scientist Lazzaro Spallanzani discovered that bats could fly and avoid obstacles with eyes covered or removed (Griffin, 2001, Dijkgraaf, 1960), and Spallanzani’s contemporary, Louis Jurine of Geneva, discovered that bats with their ears plugged became disoriented (Griffin, 2001). Neither researcher could explain how bats used their ears to navigate, and contemporary scientists dismissed the concept (Griffin, 2001). Over a century later, Walter Hahn (1908) replicated these earlier experiments and concluded that “…obstacles are perceived chiefly through sense organs in the inner ear”, but a mechanism eluded him because bats appeared to fly silently.
Hiram Maxim (1912) first suggested that bats might emit sounds to sense objects through reflected echoes, suspecting low-frequency echolocation; soon after, Hamilton Hartridge (1920) proposed that high-frequency sounds were more physically suitable (Griffin, 2001). In 1938, Hartridge’s proposal proved correct when Robert Galambos and Donald Griffin used an ultrasonic detector developed by William Pierce to show that bats were emitting ultrasonic sounds and receiving echoes (Griffin, 2001, Pierce and Griffin, 1938, Griffin and Galambos, 1941, Griffin, 1958). At the same time, Sven Dijkgraaf noted that bats made faint ticking noises and collided with objects when they flew with their mouths covered (Dijkgraaf, 1943, Dijkgraaf, 1946).

The Evolution and Systematic History of Chiroptera

After Galambos, Griffin, and Dijkgraaf’s discoveries established that bats navigate in the dark by sensing returning echoes of high-frequency sound emissions, researchers have identified several inner-ear adaptations for high-frequency hearing (Davies et al., 2013). However, these adaptations evolved in the context of echolocation's unusual evolutionary history, which remained confusing until recently. Until the early 2000s, chiropteran phylogenies divided bats into two suborders based primarily on echolocation: Megachiroptera (or megabats; the singular, non-echolocating family Pteropodidae) and Microchiroptera (or microbats; all echolocating families; Figure 1; Teeling et al., 2005). Megabats typically display greater body mass, larger eyes, simple pinnae lacking a tragus, and feed on plants (Almeida et al., 2025). Conversely, microbats are predominantly insectivores and possess complex pinnae with a tragus (Griffin, 1958; Lawrence and Simmons, 1982). These distinct differences drove early phylogeny mapping (Koopman, 1994) and even prompted suggestions that megabats were more closely related to primates than microbats (Pettigrew, 1989). Genomic analyses revealed that microbats were not a monophyletic clade and established the now broadly accepted subordinal division of Yinpterochiroptera and Yangochiroptera (Teeling et al., 2005; Simmons and Cirranello, 2026). Importantly, Yangochiroptera contains three echolocating superfamilies (Emballonuroidea, Noctilionoidea, and Vespertilionoidea), while Yinpterochiroptera comprises Pteropodidae and the echolocating superfamily Rhinolophoidea (Fig. 1; Teeling et al., 2005). As summarised in Fig. 1, this implies that laryngeal echolocation either evolved once and was subsequently lost in ancestral pteropodids (single origin hypothesis) or evolved convergently in the echolocating lineages (convergent origin hypothesis).

Diversification of species and echolocation across Chiroptera

Most major lineages within crown Chiroptera emerged by the Palaeocene (Santana et al., 2025, Morales et al., 2026). These did not diversify uniformly, so taxonomic diversity is more variable across bat families compared to most other mammalian orders (Jones et al., 2005). Vespertilionidae, Phyllostomidae, Rhinolophidae, Hipposideridae, and Pteropodidae are highly speciose and widely distributed, while most bat families are species-poor (Figure 1; Jones et al., 2005). These contrasting evolutionary trajectories suggest that taxonomic and morphological diversification are heavily influenced by the interplay between echolocation strategies and the various ecological niches they unlock.
Phyllostomids exhibit the greatest dietary range among bats, including insectivory, carnivory, sanguivory, frugivory, nectivory, and omnivory (Monteiro and Nogueira, 2011; Ochoa-Sanz et al., 2025; Riskin and Carter, 2023). This appears to have driven rapid adaptive radiation in skull morphologies (Arbour et al., 2019; Dumont et al., 2012; Giacomini et al., 2022), external sensory structures (nose leaf and pinnae) and craniodental characteristics (Leiser-Miller and Santana, 2020). For instance, the diversification of the predominantly frugivorous Stenodermatinae (New World fruit bats, tent-making bats) tracked that of angiosperms (Monteiro and Nogueira, 2011; Rojas et al., 2011), while the divergence of Desmodontinae coincided with the development of obligate sanguivory (Potter et al., 2021). Despite this high dietary and foraging diversity, many unrelated phyllostomids possess similar echolocation call structures, which seem shaped to navigate acoustically complex environments and secondarily adapted for specific foraging behaviours (Leiser-Miller and Santana, 2021). This possibly allows these bats to exploit a variety of resources and seasonal fluctuations in resource availability. However, nose-leaf morphology varies greatly among these bats and correlates with their foraging strategy (Leiser-Miller and Santana, 2020). Nose-leaves function as an acoustic modifier that shapes and directs vocalisations emitted from the nostrils (Anthwal et al., 2023). Therefore, even structurally similar calls are filtered into distinct acoustic beams that are optimise echolocation for specific foraging environments. Vespertilionidae is the most species-rich chiropteran family, with 545 almost exclusively insectivorous species distributed worldwide (Simmons and Cirranello, 2026). Vespertilionidae diversified much faster than Phyllostomidae and are morphologically highly conservative (Jones et al., 2005; Dool and Puechmaille, 2024). This may reflect limited shifts in niche utilisation, or rapid global radiation that drove swift reproductive isolation and outpaced phenotypic diversification in newly formed lineages (Stevens et al., 2019). However, unlike phyllostomids, vespertilionids exhibit highly diverse call structures (Fullard and Dawson, 1997; Eick et al., 2005) which appeare to have enabled the adoption of varied foraging strategies across various habitats (Siemers and Schnitzler, 2004). Like vespertilionids, the Old-World families Rhinolophidae and Hipposideridae are species-rich (118 and 94 species, respectively; Simmons and Cirranello, 2026) but show relatively low phenotypic variation (Foley et al., 2015). It is thought that the evolution of constant frequency (CF), high-duty cycle echolocation, facilitated their radiation into novel niches (Eick et al., 2005; Odendaal and Jacobs, 2011; Stoffberg et al., 2011). High-duty cycle echolocation exploits the Doppler shift to simultaneously emit calls and process returning echoes. This highly derived echolocation behaviour is specialised to detect and capture fluttering prey in densely vegetated environments. These CF calls are emitted nasally and require intricate nose-leaves to direct acoustic signals. The acoustic demands of high duty cycle echolocation likely imposed an evolutionary constraint that has limited cranial variation in rhinolophids and hipposiderids (Jacobs et al., 2014). Pteropodids (flying foxes or Old-World fruit bats) are behaviourally and morphologically distinct among Chiroptera. They are a highly speciose family widespread throughout the tropics and subtropics of Africa, Asia, and Australasia/Oceania (Ziegler et al., 2016). Pteropodids are the largest known bats, weighing up to 1 kg with wingspans reaching 2 m. These nocturnal frugivores and nectarivores do not echolocate, except for Rousettus, which uses tongue clicks for orientation (Springer et al., 2001). Instead, pteropodids rely heavily on visual and olfactory cues to locate food (Raghuram et al., 2009). Their high taxonomic diversity stems from adaptive radiation in isolated populations that followed their separation from the rest of yinpterochiropterans in the Early Eocene (Almeida et al., 2011).
Chiropteran diversification clearly resulted from an interplay of diverse ecological and environmental factors across widely different temporal and spatial scales. At the core of these spectacular divergences is the unique specialisation of the chiropteran inner ear from the ancestral mammalian condition, which we cover in the next section.
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Figure 2. Diagram of the mammalian peripheral auditory system.
Figure 2. Diagram of the mammalian peripheral auditory system.
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Structure, Function, and Comparative Visualisation of the Mammalian Inner Ear

Compared to non-mammalian vertebrates, mammalian auditory systems permit a broader range of frequency sensitivities (Manley 2017). Most mammals can process frequencies above >10 kHz, but certain lineages, specifically bats and toothed whales (Odontoceti), use biosonar to perceive ‘ultrasonic’ frequencies, spanning 20 kHz to over 200 kHz (Manley, 2017).
The mammalian outer ear (pinna and external auditory canal) funnels sound toward the tympanic membrane. The middle ear is an air-filled cavity positioned laterally to the basicranium and contains the three ear ossicles (incus, malleus, and stapes), which form a chain that transmits sound vibrations from the tympanic membrane to the inner ear via the articulation of the stapes footplate with the fenestra vestibuli (oval window). The bony labyrinth of the inner ear is situated in the petrous bone; it is a fluid-filled structure that includes the cochlea, vestibule, and semicircular canals. While the semicircular canals and vestibule control balance by sensing angular head motion and support movement and stable vision (Rabbitt, 2019), acoustic transduction occurs entirely in the cochlea (Anthwal and Thompson, 2016).
In therian mammals, the cochlea coils around the central modiolus and divides into three ducts: scala vestibuli, scala tympani, and scala media. The organ of Corti sits in the scala media atop the basilar membrane, which is tonotopically organised to perceive high frequencies at the base and low frequencies at the apex (Chittka and Brockmann, 2005). Hair cells within the organ of Corti act as sensory receptors (Manley 2017). Stapedial vibration sends waves through the scalae, displacing the basilar membrane and deflecting stereocilia to convert mechanical force into electrochemical signals. An osseous lamina projects from the modiolus to form a primary spiral lamina—a bony shelf anchoring the basilar membrane along most of the cochlea's length (Manley, 2018).

Adaptations for Ultrasonic Hearing in the Chiropteran Auditory System

The organisation of the chiropteran inner ear, particularly the cochlea, varies widely across the clade (Sulser et al., 2022). For example, laryngeally echolocating bats have more cochlear turns than pteropodids, with an average of 1.75 in pteropodids and 2.5 to 3.5 turns in echolocating lineages (Pye, 1966b, Pye, 1966a, Habersetzer and Storch, 1992). However, cochlear length does not necessarily indicate frequency-sensitivity range, nor is there a simple relationship between cochlear length and the number of turns (Del Rio et al., 2023, West, 1985, Ekdale, 2013, Manley, 2012). Because lower octaves normally require a disproportionately large area of the basilar membrane, the higher low-frequency threshold seen in bats plays a key evolutionary role (Kössl and Vater, 1985; Heffner et al., 2001; Vater et al., 1985; Manley, 2017). This loss of the lower octaves has expanded the area available for high-frequency octaves and could potentially lead to reduced cochlea coiling (Manley, 2017). This effect was used to explain the unusually short cochlea canal observed in the megadermatid Macroderma gigas (Australian ghost bat) compared to other echolocating bats (Davies et al., 2013). Moreover, the cochlea canal in some bats is characterised by an enlarged basal turn rather than a high number of cochlear turns. This is particularly prevalent in bats that use constant-frequency (CF; see below) echolocation because the cochlea needs to accommodate the auditory fovea (Russell et al., 2003, Schuller and Pollak, 1979).
A secondary osseous lamina projecting from the outer wall of the cochlea is prominent in species that use biosonar, including bats and toothed whales (Manley, 2018). This secondary lamina is believed to benefit animals with high-frequency hearing by increasing basilar membrane rigidity (Manley, 2018). The secondary osseous spiral lamina of some mammals corresponds to hearing frequency sensitivities above 10 kHz and is thought to increase basilar membrane rigidity in mammals (Manley, 2018). This explains its prominence in many bats (Bruns et al., 1989, Ramprashad et al., 1979, Küçük and Abe, 1992a), where it can extend between three-quarters to the entire cochlea length (Bruns, 1980, Dannhof and Bruns, 1991). Variation in the presence and extent of the osseous lamina relative to other echolocation-relevant anatomy is likely far more complex, and potentially ecologically informative, than currently understood. For example, Pye (1966b) found a secondary osseous lamina in species of Rhinolophus and Hipposideros but suggested that it was absent in other bat species, even though only two other species – Saccopteryx bilineata and Noctilio leporinus – were investigated. Thus, these early discrepancies highlight the need for broader comparative studies to reveal how subtle anatomical variation aligns with distinct echolocation strategies and ecological niches.

Echolocation, Foraging Mode, and Ecology Shape the Inner ears of Bats

Flight space and foraging modes are strongly linked to echolocation behaviour in bats (Denzinger and Schnitzler, 2013). However, determining how these factors co-vary and relate to morphological adaptations has been difficult as traditional classification schemes face challenges in faithfully capturing the combined dynamics of feeding mode, hunting strategies, and flight space use (such as proposed e.g. by Norberg and Rayner, 1987; McKenzie and Bullen, 2012). Static groupings can overlook behavioural plasticity as such megadermatids shifting foraging strategies across season and prey types (Schmidt et al., 2011; Gual-Suárez and Medellín, 2021). To provide a more adaptable model, Denzinger and Schnitzler (2013) developed the “foraging guild concept”. This comprehensive framework categorises bats by linking flight space use, foraging mode and morphology with specific echolocation adaptations. Under this concept, which we use here, bats fall into three groups based on how they navigate background clutter: open space, edge space and narrow space (Figure 3; Kalko et al., 2008; Denzinger and Schnitzler, 2013). Denzinger and Schnitzler’s (2013) framework is useful for tracing bat adaptations because they align behaviour and echolocation quite well. Open-space foragers typically use shallow frequency-modulated (FM) signals with long pulse intervals and high source levels (intensity of emitted call) to maximise long-range detection in unobstructed areas (Denzinger et al., 2018). Conversely, edge space foragers operating near vegetation, buildings or water surfaces use a variant of FM echolocation. These calls often include an additional acoustic component that either precedes or follows the standard FM sweep (a change in sound pitch/frequency over a short period). Narrow space foragers face the extreme challenge of distinguishing prey echoes from complex background clutter, making “flutter detection”, using long CF signals, advantageous. This allows bats to localise prey by detecting amplitude and frequency modulations in the returning echo of insect wing beats. Flutter detectors emit high duty cycle calls which result in by a temporal overlap of pulse and echo. To manage this overlap, flutter-detecting bats use Doppler shift compensation, a sophisticated vocalisation behaviour of adjusting emission frequency to compensate for Doppler shifts caused by flight speed relative to the target (Neuweiler, 1990). Other narrow space foragers “glean” by snatching stationary food items from surfaces. This strategy, used by both insectivorous and frugivorous species, can be either active, using short, broadband signals at a high frequency, or passive, relying on prey generated acoustic cues (leaf rustling) and even olfaction (Page and Ryan, 2008). Foraging guilds reflect an important mechanism of niche partitioning between differently specialised bat species, which often allows numerous species to share the same flight space and roost sites (Nicholls and Racey, 2006; Novella-Fernandez et al., 2020). A striking example of this behaviour is the coexistence of over 100 different species in certain regions of Brazil (Delgado-Jaramillo et al., 2020). Sustaining such high densities requires fine-scale niche partitioning (MacArthur and Levins, 1967; Schoener, 1974).
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Figure 3. Differential use of flight space by bats.
Figure 3. Differential use of flight space by bats.
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Ecological Signatures in the Inner Ear of Echolocating Mammals

The above shows that chiropteran inner-ear morphology clearly reflects echolocation behaviours, which in turn are deeply entwined with core ecological traits such as flight space and foraging strategies. These connections make bat inner-ear morphology, particularly cochlear morphology, an ideal source of information where ecologies cannot be directly observed. In addition, understanding how inner ear morphology reflects ecologies and echolocation behaviour has the potential to add crucial new data to existing debates about how echolocation has evolved.
An excellent precedent for relating ecology and inner ear morphology exists for another echolocating mammalian lineage, the toothed whales (Odontocetes). Despite mechanistic differences in echolocation function between air and water, chiropterans and odontocetes exhibit remarkable similarities in cochlea morphologies, call design and acoustic behaviour (Davies et al., 2013, Girdlestone et al., 2020, Park et al., 2019, Ketten et al., 2021). This includes a flattened cochlea with a wider basal turn than in other mammals (Vater and Kössl, 2011; Park et al., 2019), calls in the same frequency range, and call structures adjusted for different echolocation types (Moss et al., 2023; Madsen and Surlykke, 2013). In toothed whales, the cochleae reflect distinct acoustic habitats and frequency sensitivities (Park et al., 2023, Park et al., 2016, Costeur et al., 2018). For instance, cochlea width and length are indicative of habitat preference and modality, providing insights into dive depth limits and habitat boundaries (Gutstein et al., 2014, Park et al., 2023, Park et al., 2016, Viglino et al., 2021, Costeur et al., 2018). Convergent cochlea morphologies are also more pronounced in acoustically complex habitats. This suggests that strong acoustic demands impose evolutionary constraints, producing distinct morphological signatures for specific auditory specialisations (Park et al., 2019). These insights have broader implications for palaeoecological reconstructions of extinct echolocating mammals (Costeur et al., 2018, Madsen and Surlykke, 2013, Park et al., 2016, Park et al., 2019, Racicot, 2022).

Leveraging the digital revolution to expand studies of bat echolocation and ecology

We propose that the clear utility of morphological traits in predicting odontocete echolocation probably also exists in bats, warranting much deeper investigation than has been done. Cochlea morphology has already used to assess hearing sensitivity and echolocation capability in extinct bats (Novacek, 1987, Gunnell et al., 2003, Thewissen et al., 2009, Mennecart et al., 2022, Orliac and O’Leary, 2014, Hand et al., 2023), but detailed ecological and behavioural reconstructions are frequently hindered by the extremely fragile and flattened state of fossil petrosals (Gutstein et al., 2014, Park et al., 2023, Park et al., 2016, Viglino et al., 2021). However, several demonstrated or suspected connections between echolocation behaviour, foraging guild, and inner ear morphology have already been made in some clades. Table 1 summarises these, highlighting strong potential to link cochlear structure, habitat, and foraging behaviour (Dickinson et al., 2023). However, as Table 1 also shows, most of these very promising studies have narrow taxonomic coverage and small sample sizes, which limits the power of inference to other species.
Advances in non-destructive data acquisition through (micro-) Computed Tomography (CT) scanning and access to the resulting 3D data provide an excellent opportunity to explore the minute inner ears of bats at much greater scales than previously possible (Weisbecker et al., 2025). These virtual approaches have already yielded substantial new insights into the origins and evolution of hearing capabilities in extinct mammals, using auditory correlates from extant analogues (Da Cunha et al., 2023, Mennecart et al., 2022, Ruf et al., 2016). This comparative approach has been vital for tracing the transitional evolution of the inner ear (Luo et al., 2010), determining when key innovations, such as cochlea coiling, first arose (Graybeal et al., 1989; Hoffman et al., 2014), and inferring the ancestral hearing capabilities of modern lineages (Peacock et al., 2025; Coleman et al., 2010). Computer aided visualisation tools, such as Synchrotron-based tomography and microCT enable 3D reconstruction of these tiny, often inaccessible regions (for a full review see Cunningham et al., 2014; Racicot 2017). The rise of open-source platforms (i.e., 3D slicer (Fedorov et al ., 2021), ORS Dragonfly (Comet Technologies Canada Inc., 2025)) has made these methodological frameworks and digital reconstruction available to the broader scientific community; and well-established quantitative protocols, such as geometric morphometric analysis (Peacock and Thewissen, 2025), have made it easier than ever to undertake the large-scale comparative analyses required to confidently link auditory anatomy with echolocation and ecological traits in bats.
With these recent advances addressing sample-size issues, the main constraint on linking cochlear morphology to echolocation and foraging behaviour is the strong phylogenetic confounding of these traits across the chiropteran tree. For example, CF echolocation only exists in a monophyletic group (Rhinolophoidea) within the yinpterochiropterans, as well as in a small number of species of the yangochiropteran genus Pteronotus (Fig. 1); differences between CF and FM echolocation therefore need to be interpreted with caution because they could also be purely phylogenetic (Mitchell et al. 2026), and species representing both types may not be co-analysed meaningfully because their inner ears are substantially different. Similarly, foraging modes are often invariant within monophyletic radiations, again meaning it is impossible to determine whether differences reflect phylogenetic signal or functional meaning. Basing interpretations on first principles (e.g., physics) may therefore be the only statistically not very rigorous resort (Mitchell et al. 2024, 2026). However, this issue does not prevent the potential for important insights because many important variables – such as echolocation parameters, or foraging modes across the more variable FM bats – vary widely across species and can therefore be meaningfully analysed.

Conclusions

Bats exhibit remarkable diversity in morphology, ecology, and behaviour, reflected in diverse echolocation strategies associated with flight spaces and foraging strategies. The strong correlation between echolocation strategy and flight space we reviewed here suggests an adaptive complex between inner ear morphology, ecology, and echolocation behaviour ripe for analytical exploitation. Larger-scale, digitally powered studies can exploit this; ideal candidates are dimensions of the auditory fovea, overall cochlea shape and size, the basilar membrane, and a secondary osseous spiral lamina. Many questions can be answered with these data, including which inner ear traits can – or cannot – be used to trace the origin and evolution of echolocation in bats; how petrosa of extinct bats might reflect their echolocation mode or even foraging ecology; and how quickly behavioural modifications might be reflected in inner ear morphology in evolutionary time.

Funding

MCR was supported by an Australian Government Research Training Program (RTP) Scholarship. This research was conducted on the unceded lands of the Kaurna people.

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Figure 1. Cladogram depicting family-level relationships of crown Chiroptera based on Morales et al. (2026). The single-origin hypothesis states that echolocation evolved once in the common ancestor of all bats and was subsequently lost in Pteropodidae. In contrast, the independent-origin hypothesis refers to the idea that echolocation evolved twice; once in each of the laryngeal echolocating clades.
Figure 1. Cladogram depicting family-level relationships of crown Chiroptera based on Morales et al. (2026). The single-origin hypothesis states that echolocation evolved once in the common ancestor of all bats and was subsequently lost in Pteropodidae. In contrast, the independent-origin hypothesis refers to the idea that echolocation evolved twice; once in each of the laryngeal echolocating clades.
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Table 1. Summary of studies that measure morphological structures and adaptations in the inner ears of bats with associated behavioural and ecological importance.
Table 1. Summary of studies that measure morphological structures and adaptations in the inner ears of bats with associated behavioural and ecological importance.
Measured Source Ecological and/or behavioural importance
Auditory fovea Neuweiler (1990), Neuweiler et al. (1980)
  • An overrepresentation of hair cells dedicated to a narrow frequency range present in bats that use CF-FM echolocation. Important for detecting flutter information while foraging.
Basilar membrane Bruns (1976), Bruns et al. (1989), Davies et al. (2013), Henson (1978), Pye (1966b), Vater and Siefer (1995)
  • Relative basilar membrane length longer in echolocation bats compared to non-echolocating bats.
  • Basilar membrane stiffer and thicker at the base relative to the apex
  • High concentrations of hair cells located in the species-specific echolocation range.
Basal turn width Henson et al. (1984)
  • Wide basal turn that is particularly prevalent in CF echolocating bats to increase space for neural processing and fine frequency discrimination
Cochlea size Habersetzer and Storch (1992), Hsiao et al. (2015), Pye (1966a), Bruns et al. (1989)
  • Bats that use echolocation for prey detections typically have large cochlea relative to basicranial width. Among echolocating bats, CF-FM echolocators have the largest cochlea overall; an acoustic specialisation for doppler shift compensation and high-duty cycle echolocation.
  • Non-echolocating bats and echolocating bats that use passive cues to forage such as olfaction and vision (i.e., frugivores/nectivores), thermoregulation (i.e., sanguivorous) or prey generated sounds (i.e., passive gleaners) typically have smaller cochlea relative to bats that use echolocation for prey detection.
Cochlea spirality Dickinson et al. (2023), Hsiao et al. (2015)
  • Cochlea spirality is positively correlated with wing aspect ratio (habitat proxy), suggesting a link between hearing sensitivities and habitat type occupied.
  • CF-FM echolocating bats typically have more cochlea turns than FM echolocators and non-echolocating bats.
Secondary osseous spiral laminae Küçük and Abe (1992b), Pye (1966b)
  • Many Echolocating bats possess a secondary osseous spiral lamina that extends for most of the cochlea spiral that provides increased support and rigidity for the basilar membrane
Rosenthal’s canal Sulser et al. (2022)
  • Varied degrees of reduced ossification along the wall of Rosenthal’s canal, particularly prevalent in Yangochiroptera. Believed to increase neural connectivity between the basilar membrane and the cochlea nerve ganglion, allowing for increasingly diverse echolocation strategies.
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