Fig 1.
A, ventral, B, dorsal, C, posterior, and E, anterior views. Osseous labyrinth within the basicranium in E, anterior and F, left lateral views. Legend: bt, basal tubera, fm, foramen magnum, oc, occipital condyle.
Fig 2.
A, ventral view, B, dorsal view, C, posterior view, D, medial view with the osseous labyrinth, E, posterior view with the osseous labyrinth. Legend: bt, basal tubera, oc, occipital condyle.
Fig 3.
A, ventral view, B, dorsal view, C, posterior view, D, anterior view. Osseous labyrinth within the basicranium in E, ventral view, F, anterior view. Legend: bt, basal tubera, fm, foramen magnum, oc, occipital condyle, pp, paroccipital process.
Fig 4.
Virtual thin section through the osseous labyrinth of MTA/ACL001 specimen.
Orthogonal virtual thin sections in A, horizontal plane, B, coronal plane, C, sagittal plane through the right osseous labyrinth of MTA/ACL001 specimen. D, three-dimensional rendering of the right osseous labyrinth with semi-transparent outline of the whole specimen in anterolaterodorsal view. Scale bar: 10 mm.
Fig 5.
Virtual thin section through the osseous labyrinth of MTA/ACL002 specimen.
Orthogonal virtual thin sections in A, horizontal plane, B, coronal plane, C, sagittal plane through the right osseous labyrinth of MTA/ACL002 specimen. D, three-dimensional rendering of the right osseous labyrinth with semi-transparent outline of the whole specimen in anterolaterodorsal view. Scale bar: 10 mm.
Fig 6.
Virtual thin section through the osseous labyrinth of MTA/ACL003 specimen.
Orthogonal virtual thin sections in A, horizontal plane, B, coronal plane, C, sagittal plane through the left osseous labyrinth of MTA/ACL003 specimen. D, three-dimensional rendering of the left osseous labyrinth with semi-transparent outline of the whole specimen in posterolaterodorsal view. Scale bar: 10 mm.
Fig 7.
Diagrammatic scheme of the linear measurements performed.
Osseous labyrinth in A, posterior view. B, lateral view. C, anterior view. D, dorsal view. Abbreviations: APHSC, angle between the posterior and horizontal semicircular canal, AAHSC, angle between the anterior and horizontal semicircular canal, AAPSC, angle between the anterior and posterior semicircular canal. LDASC, lumen diameter of the anterior semicircular canal. LDPSC, lumen diameter of the posterior semicircular canal. LDHSC, lumen diameter of the anterior semicircular canal. AMaSCD, anterior major axis of the semicircular canal diameter. AMiSCD, anterior minor axis of the semicircular canal diameter. PMaSCD, posterior major axis of the semicircular canal diameter. PMiSCD, posterior minor axis of the semicircular canal diameter. HMaSCD, horizontal major axis of the semicircular canal diameter. HMiSCD, horizontal minor axis of the semicircular canal diameter.
Table 1.
Vertical semicircular canal elliptical eccentricity measurements for the mammalian sampled taxa, the Endothiodon specimens and Niassodon.
Abbreviations: AMiSCD, anterior semicircular canal minor axis diameter, AMaSCD, anterior semicircular canal major axis diameter, PMiSCD, posterior semicircular canal minor axis diameter, PMaSCD, posterior semicircular canal major axis diameter, HMiSCD, horizontal semicircular canal minor axis diameter, HMaSCD, horizontal semicircular canal major axis diameter, LogBM, log10 body mass, asterisk refers to estimated body mass calculated using the linear regression model. See also S3 Table.
Table 2.
Linear measurements for each Endothiodon cf. bathystoma specimen.
Each variable for the three specimens was measured at five different loci of each SC. Abbreviations: SE, standard error, σ, variance, conf. int. confidence interval, LDASC Lumen diameter of the anterior semicircular canal, LDPSC Lumen diameter of the posterior semicircular canal, LDHSC Lumen diameter of the horizontal semicircular canal.
Table 3.
Angular measurements and respective descriptive circular statistics for each Endothiodon cf. bathystoma specimen.
Five repeated measurements of the angle between the three SCs was measured for the three sampled specimens. Abbreviations: conf. int., confidence interval, AAHSC, Angle between the anterior and horizontal semicircular canal, APHSC, Angle between the posterior and horizontal semicircular canal, AAPSC, Angle between the anterior and posterior semicircular canal.
Fig 8.
A, anterior view. B, lateral view. C, dorsal view. D, anterior view. E, ventral view. F, medial view. Abbreviations: ASC, Anterior semicircular canal. PSC, Posterior semicircular canal. HSC, horizontal semicircular canal. ve, vestibulus. cc, crus communis. aASC, Ampulla of the anterior semicircular canal. aPSC, Ampulla of the posterior semicircular canal, “*”, estimates based on the average radius of the semicircular canal. See also S1 Fig.
Fig 9.
A, dorsal view. B, anterior view. C, ventral view. D, lateral view. E, posterior view. F, medial view. Abbreviations: ASCC, Anterior semicircular canal. PSCC, Posterior semicircular canal. HSCC horizontal semicircular canal. ve. vestibulus. cc. crus communis. aASCC, Ampulla of the anterior semicircular canal. aPSCC, Ampulla of the posterior semicircular canal. jc. jugular canal. See also S1 Fig.
Fig 10.
A, dorsal view. B, posterior view. C, ventral view. D, lateral view. E, anterior view. F, medial view. Abbreviations: ASCC, Anterior semicircular canal. PSCC, Posterior semicircular canal. HSCC, Horizontal semicircular canal. ve, vestibulus. cc, crus communis. aPSCC, Ampulla of the posterior semicircular canal. See also S3 Fig.
Fig 11.
Comparative charts between the various semicircular canals among the different Endothiodon cf. bathystoma specimens.
A, angle between the semicircular canals. B, lumen diameter of the various semicircular canals. Notice that all the semicircular canals are nearly orthogonal, but the AAHSC is consistently greater than 90°, and the AAPSC is consistently lower than 90°. Also, the horizontal and the anterior semicircular canals have consistently similar lumen diameters and the posterior semicircular canal is consistently the thinnest.
Fig 12.
Comparison between the three Endothiodon cf. bathystoma specimens. Images are not at scale to facilitate comparisons.
A, MTA-ACL001 in anterior view. B, MTA-ACL002 in anterior view (reversed). C, MTA-ACL003 in anterior view (reversed). D, MTA-ACL001 in dorsal view. E, MTA-ACL002 in dorsal view (reversed). F, MTA-ACL003 in dorsal view (reversed). Variation of semicircular canal lumen diameter for: G, MTA-ACL001 in lateral view, H, MTA-ACL002 in lateral view (reversed), I, MTA-ACL003 in lateral view (reversed).
Fig 13.
Niassodon mfumukasi (ML 1620) right inner ear.
A, dorsal view. B, posterior view. C, lateral view. D, anterior view. Abbreviations: ASC, Anterior semicircular canal. PSC, Posterior semicircular canal. LSC, horizontal semicircular canal. aPSC, ampulla posterior semicircular canal. aASC, ampulla anterior semicircular canal. cc, crus communis.
Fig 14.
Linear regression of the log10 average semicircular canal radius to estimate the log10 body mass.
The estimates for the Endothiodon cf. bathystoma specimens range from ~116 to 182 kg. The correlation coefficient between the two variables is 0.787. The extant mammal measurements can be found in S3 Table and from [15].
Fig 15.
Simplified cladogram of published dicynodont bony labyrinths.
Phylogeny based on the most recent analysis [51]. Patranomodon, Eodicynodon, Pristerodon and Lystrosaurus from [27]; Diictodon from [29]; Brachyprosopus from [38]; Emydops from [34]; Cistecephalus from [33]; Kawingasaurus from [35] and Placerias from [31]. Asterisks indicate bony labyrinths that did not result from computed tomography renderings.