Figure 1.
Anatomical structures of the testudine audiotory system in Trachemys scripta elegans.
A. Lateral view of head (1 cm scale bar). B: Horizontal MR image. (500 mm scale bar) C: Transverse MRI at the level of the tectum. Arrows indicates Eustachian tubes (500 mm scale bar). “Muscle” is the splenius capitus. D: Horizontal MR image, enlarged from box in B. The columella runs through the middle ear cavity to the inner ear. Arrow indicates the columella (500 mm scale bar).
Figure 2.
Examples of middle ear morphology of extant turtles and tortoises.
Middle ear cavities are in black with skulls in gray. Top row. Lateral view of the left side. Middle row: Dorsal view. Bottom row: Cross section CT images at the level of the middle ear cavity. Species in columns from left to right: Gopherus polyphemus, Chelus fimbriatus, Trachemys scripta elgans, Lepidochelys kempii. Scale bars = 1 cm. R = rostral. C = caudal. D = dorsal. V = ventral. Note that G. Polyphemus was scanned as only a skull.
Figure 3.
Allometry of middle ear cavities.
A: Scaling of middle ear cavity volume and head width across extant testudines B: Scaling of volume and head width in Trachemys scripta elegans. C: Scaling of middle ear cavity volume and head width across extant testudines divided by ecological niche. D: Scaling of middle ear cavity volume and head width across extant testudines divided by phylogenetic position.
Table 1.
Phylogenetic relationships of the species studied.
Figure 4.
Calculated best resonance underwater frequency of middle ear cavities of extant species, changing with head size.
Figure 5.
Examples of middle ear cavities of extinct testudines.
A-C: Connected ears of Galianemys emringeri. Connected middle ears are shown in dark gray; the skull is shown in light gray. The maximum space that the connected middle ears could possibly occupy is indicated by the dashed line. The dorsocaudal edge of the skull is outlined in orange. D-F: Separated ears of Nicholsemys baieri. Isolated middle ears are show in dark gray; skull is shown in light gray. A & D: Dorsal view. B & E: left lateral view. C & F: Transverse view from CT. Middle ear cavities are outlined in blue, and possible extent of middle ear cavity into pharynx is yellow. Asterisk indicates most caudal part of the middle ear cavity that can be seen intact before it opens into the pharynx. Scale bars = 1 cm. R = rostral. C = caudal. D = dorsal. V = ventral.
Table 2.
Published testudine in-air audiograms.
Figure 6.
Proposed middle ear structure across some extant vertebrate taxa.
Skulls are shown in black, tympanic ears in yellow, connections between the ears (Eustachian tubes or through the buccal cavity) in green. The dashed line on the avian diagram indicates trabeculated bone. The proposed diapsid ancestral condition is also shown. The dashed branch to testudines indicates their suggested phylogenetic position [33]–[35].