Fig 1.
Full suite of paratympanic sinuses and diverticula in a perinatal Alligator mississippiensis (OUVC 10606).
A. Rendered with skull and transparent skull. B. Left lateral view with brain endocast rendered in blue. C. Caudal view. D. Ventral view. E. Dorsal view. ARd, articular diverticulum; BOd, basioccipital diverticulum; BSd, basisphenoid diverticulum; IFd, infundibular diverticulum; ITd, intertympanic diverticulum; OTd, otoccipital diverticulum; PTd, pterygoid diverticulum; PTt, pharyngotympanic tube; Qd, quadrate diverticulum.
Fig 2.
Previous representations of the crocodilian middle-ear space shown as A) a lithographic rendering of a parasagittal cut through the skull of a crocodile, adapted from Owen, 1850; B) a schematic depiction of the communicating canals of the tympanic cavity in rostral oblique view, adapted from Miall, 1878; C) a schematic showing the development of the tympanic cavity in a late stage embryo of Crocodilus cataphractus in rostrocaudal aspect, adapted from Müller, 1967; D) A schematic of the development of the tympanic cavity in a late stage embryo of Alligator mississippiensis in dorsal view, adapted from Simonetta, 1956.
C. Tym., Tympanic cavity; D. Phar., Posterior pharyngeal diverticulum; D. Tym., Tympanic diverticulum; e’, bifurcation of the median Eustachian canal; eb, bifurcation of the basioccipital branch, eo, basioccipital branch of the Eustachian canal; es, basisphenoidal branch of the Eustachian canal; O.P., paratympanic organ; Phar., Pharynx; P. Hyp., Hypophyseal pedicle; R. Epit., epitubaric recess; R. Intert., intertympanic recess; R. Man., mandibular recess; Tub., Eustachian tube.
Table 1.
List of Alligator mississippiensis specimens used in current study.
Fig 3.
Skull measurements used to calculate Geometric Mean of skull size in Alligator mississippiensis, shown in A) left lateral, B) dorsal, C) caudal, and D) ventral views.
Linear measurements taken of the following: 1. Orbit length; 2. Orbit width; 3. Mandible height; 4. Mandibular fenestra height; 5. Mandibular fenestra length; 6. Post-orbital skull length; 7. Infratemporal fossa width; 8. Braincase length; 9. Retroarticular process length; 10. Rostrum length; 11. Dorsal skull length; 12. Interorbital width; 13. Palatal foramen width; 14. Infratemporal fossa width; 15. Supratemporal fossa maximum length; 16. Supratemporal fossa minimum width; 17. Supratemporal foramen length; 18. Supratemporal fenestra width; 19. Braincase width; 20. Skull width at quadrates; 21. Braincase height; 22. Foramen magnum width; 23. Pterygoid height; 24. Rostrum width at 2nd maxillary alveolus; 25. Rostrum width at 4th maxillary alveolus; 26. Rostrum width at anterior edge of palatine fenestra; 27. Palatal fossa length.
Fig 4.
Schematic showing ontogenetic trends in the pharyngotympanic sinus system (green) and the median pharyngeal sinus system (purple) in right lateral view.
Double ended arrows represent emergent confluences between diverticula and between the adjacent sinus systems. Ontogenetic stages are A. Day 0 (~30mm DSL), B. ~10 months (~50mm DSL), C. yearling to subadult (100–300mm DSL), and D. adult (>300mm DSL). ARd, articular diverticulum; BOd, basioccipital diverticulum; BSd, basisphenoid diverticulum; ETr, recessus epitubaricum; IFd, infundibular diverticulum; ITd, intertympanic diverticulum; MPs, median pharyngeal sinus; OTd, otoccipital diverticulum; PAd, parietal diverticulum; PRd, prootic diverticulum; PTd, pterygoid diverticulum; PTs, pharyngotympanic sinus; PTt, pharyngotympanic tube; QUd, quadrate diverticulum; Sph, siphonium; Tymp, tympanum.
Table 2.
Synonyms of paratympanic pneumatic structures used in this study and selected literature.
Fig 5.
Perinatal Alligator mississippiensis (OUVC 10606) demonstrating the median pharyngeal sinus system.
Rendered in A) ventral aspect with the basisphenoid in red. Isolated basisphenoid shown in B) ventral aspect and C) rendered transparent with the basisphenoidal diverticulum rendered in purple. Basisphenoid shown in D) dorsal aspect and E) rendered transparent. BSd, basisphenoid diverticulum; ca, carotid artery; cer, cerebral fossa; hpf, hypophyseal fossa; MPs, median pharyngeal sinus; MPso, ostium for median pharyngeal sinus; PTs, pharyngotympanic sinus.
Fig 6.
Perinatal Alligator mississippiensis (OUVC 10606) demonstrating the pharyngotympanic sinus.
Isolated braincase shown in A) left lateral view with B) the suspensorium rendered transparent and C) all bones rendered transparent. Also in D) ventral aspect with E) suspensorium rendered transparent and F) all bones rendered transparent. Pharyngotympanic sinus is rendered in green. ar, articular; bo, basioccipital; bs, basisphenoid; ls, laterosphenoid; MPso, ostium for median pharyngeal sinus; pa, parietal; PTs, pharyngotympanic sinus; qu, quadrate; Vgang, trigeminal ganglion.
Fig 7.
Perinatal Alligator mississippiensis (OUVC 10606) shown in A) ventral aspect with the basioccipital in red. Isolated basioocipital shown in B) ventral aspect and C) rendered transparent with the basisoccipital diverticulum rendered in green. And in D) dorsal aspect and E) rendered transparent with the basioccipital diverticulum rendered in green. bo, basioccipital; BOd, basioccipital diverticulum; bss, basisphenoidal suture; bt, basal tuber; occ, occipital condyle; ptsobo, communicating ostium between pharyngotympanic sinus and basioccipital diverticulum.
Fig 8.
Perinatal Alligator mississippiensis (OUVC 10606) shown in A) ventral aspect with the pterygoid in red. Isolated pterygoid shown in B) ventral aspect and C) rendered transparent with the pterygoid diverticulum (PTd) rendered in green. Pterygoid shown in D) dorsal aspect and E) rendered transparent. F) Left lateral transparent rendering of pterygoid. mPT, pterygoideus muscle; PTd, pterygoid diverticulum; ptsopt, communicating ostium between pharyngotympanic sinus and pterygoid diverticulum.
Fig 9.
Perinatal Alligator mississippiensis (OUVC 10606) shown in A) left lateral view with the braincase rendered in red and B) with the braincase isolated and the prootic rendered in red. Left lateral view of C) the isolated prootic, D) rendered transparent with endosseous labyrinth and G) with associated cranial nerves. Left prootic in E) medial aspect and F) rendered transparent with endosseous labyrinth. Labyrinth is rendered in pink, and the prootic diverticulum rendered in teal. cssc, caudal semicircular canal; lag, lagena; lssc, lateral semicircular canal; PRd, prootic diverticulum; PTsf, fossa for pharyngotympanic sinus; ptsopr, communicating ostium between pharyngotympanic sinus and prootic diverticulum; rssc, rostral semicircular canal; Vgang, trigeminal ganglion; Vtymp, tympanic ramus of trigeminal nerve; V1, ophthalmic ramus of trigeminal nerve; VII, facial nerve.
Fig 10.
Perinatal Alligator mississippiensis (OUVC 10606) shown in A) left lateral view with the braincase rendered in red and B) with the braincase isolated and the suspensorium rendered in red. Isolated suspensorium in C) left lateral view and D) rendered transparent. Suspensorium in E) medial aspect and F) rendered transparent. ar, articular; ARd, articular diverticulum; cty, crista tympanicum; fa, foramen aerum; IFd, infundibular diverticulum; poIFd, postinfundibular recess; prIFd, preinfundibular recess; ptsoifd, communicating ostium between pharyngotympanic sinus and infundibular diverticulum; ptsoqd, communicating ostium between pharyngotympanic sinus and quadrate diverticulum; ptsost, communicating ostium infundibular diverticulum and the subtympanic portion of the pharyngotympanic sinus; qbs, = basisphenoidal suture of quadrate; q, quadrate; Qd, quadrate diverticulum.
Fig 11.
Perinatal Alligator mississippiensis (OUVC 10606) shown in A) left lateral view with the braincase rendered in red and B) with the braincase isolated and the otoccipital rendered in red. Isolated otoccipital C) in left lateral view and D) rendered transparent. Both otoccipitals in E) caudal aspect with the left otoccipital rendered transparent and F) in anterior aspect with the left otoccipital rendered transparent. Labyrinth rendered in pink, otoccipital diverticulum rendered in blue. acar, carotid artery; cif, crista interfenestralis; cssc,caudal semicircular canal; fv, fenestra vestibularis; itdootd, communicating ostium between intertympanic diverticulum and otoccipital diverticulum; IX-XI, combined pathway for glossopharyngeal, vagus, and spinal accessory nerves; lag, lagena; ot, otoccipital; OTd, otoccipital diverticulum; pop, paroccipital process; ptsootd, communicating ostium between pharyngotympanic sinus and otoccipital diverticulum; rssc, rostral semicircular canal; scp, subcapsular process; XII, hypoglossal nerve.
Fig 12.
Perinatal Alligator mississippiensis (OUVC 10606) shown in A) left lateral view with the braincase rendered in red and B) with the braincase isolated and the prootic rendered in red and the supraoccipital rendered in green. Isolated prootic and supraoccipital with endosseous labyrinth C) in left lateral view and D) with the left prootic rendered transparent. Isolated prootic and supraoccipital E) in dorsal view and F) with the supraoccipital and left prootic rendered transparent. Labyrinth rendered in pink, intertympanic diverticulum rendered in blue. cssc,caudal semicircular canal; lag, lagena; lssc, lateral semicircular canal; padootd, communicating ostia between parietal diverticula and intertympanic diverticulum; pil, osseous pillar; pr, prootic; PTsf, fossa for pharyngotympanic sinus; ptsoitd, communicating ostium between pharyngotympanic sinus and intertympanic diverticulum; so, supraoccipital.
Fig 13.
Ontogenetic series of Alligator mississippiensis showing the skulls rendered transparent, the brain endocast in blue, and the middle ear sinuses and component diverticula in various other colors.
Columns pertain to different views of the same specimen. Specimens illustrated at unit scale to emphasize changing relative sizes of components. Rows: A) left lateral view; B) dorsal view; C) ventral view; D) caudal view. BSd, basisphenoid diverticulum; ITd, intertympanic diverticulum; OTd, otoccipital diverticulum; PAd, parietal diverticulum; PTd, pterygoid diverticulum; V, trigeminal nerve.
Fig 14.
Comparisons of reduced major axis (RMA) regressions for middle-ear volume regressed onto A) skull size, B) braincase volume, C) tympanum surface area.
BCv = braincase volume; Bv = brain volume; GMS = geometric mean of skull-size measurements; Mev = middle-ear volume; Tsa = tympanum surface area.
Table 3.
Comparisions of reduced major axis (RMA) regressions for middle-ear volume.
Fig 15.
Schematic showing calculated resonant frequencies for A) subtympanic foramen (pink oval) as candidate resonator opening along with plot showing calculated resonant frequencies for an ontogenetic series of alligators. B) tympanic membrane (green oval) as candidate resonator opening along with plot showing calculated resonant frequencies for an ontogenetic series of Alligator. C) Graph adapted from Higgs et al. (2008), showing frequencies of greatest cochlear sensitivity (blue) and juvenile vocalization intensity (red) with the results of the auditory performance analysis superimposed as pink and green bars. Superimposed resonance frequencies show correlation between resonance with the subtympanic foramen to greatest cochlear sensitivity and juvenile vocalization frequencies.