Fig 1.
Map of western Japan showing position of the type locality.
Areas marked by hashed lines indicate outcrops of the Tetori Group in this region.
Fig 2.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, holotype block.
A, digital photograph showing surface view of the specimen after manual preparation; B, rendered view of the surface from μCT data showing identifications of exposed elements. Abbreviations: Br, braincase elements; Fr, frontal; L.La, left lacrimal; L.Mx, left maxilla; L.N, left nasal; L.Pa, left parietal; LPf, left prefrontal; L.Sm, left septomaxilla; L.Sq, left squamosal; R.La, right lacrimal; R.Pa, right parietal; R.Pf, right prefrontal; R.Sq, right squamosal;?, unidentified element. Scale bars = 5 mm.
Fig 3.
Shirerpeton isajii gen. et sp. nov., skull reconstruction.
A-D, Model construction. 3-D models constructed using printouts of the individually segmented elements from the μCT data (mirrored as needed: nasal, parietal, possible supratemporal) and fitted into modelling clay. A, dorsal; B, right lateral; C, left lateral; D, left anterolateral showing the relations of the nasal, lacrimal, and maxilla in the narial margin. The tip of the rostrum is roughly reconstructed in modelling clay. E, outline reconstruction of the skull in dorsal view, based on the 3-D model in A-D. Note that the suspensorial elements are omitted as their positions are uncertain. Abbreviations: Fr, frontal; J, jugal; La, lacrimal; Mx, maxilla; N, nasal; Pa, parietal; Pf, prefrontal; S.O, supraoccipital;? St, possible supratemporal.
Fig 4.
Shirerpeton isajii gen. et sp. nov., referred right dentaries.
A-D, SBEI 2405, in A, labial view as preserved, digital photograph; B-C, specimen as segmented from μCT slice data in B, labial, and C, lingual views; D, lingual view, interpretative drawing. E, SBEI 2462, labial view as preserved, digital photograph. Abbreviations:? an, possible angular facet; mk.f, Meckelian fossa; pra, facet for prearticular; sds, subdental shelf; sym, symphyseal prongs. Scale bars = 1 mm.
Fig 5.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, holotype block in dorsal view showing elements segmented from μCT slice data.
Abbreviations: Ept, epipterygoid; Ex.O, exoccipital plate; Fr, frontal; L.J, left jugal; L.La, left lacrimal; Lm.B, limb element; L.Mx, left maxilla; L.N, left nasal; L.Pa, left parietal; LPf, left prefrontal; L.Q, left quadrate; L.Sm, left septomaxilla; L.Sq, left squamosal;? Opis, possible opisthotic;? Ot, otic associated element;? Pal, possible palatal element;? Pro, possible prootic; R.J, right jugal; R.La, right lacrimal; R.Mx, right maxilla; R.Pa, right parietal; R.Pf, right prefrontal; R.Q, right quadrate; R.Sq, right squamosal; Sph, sphenoid;? St, possible supratemporal;?, unidentified elements. Scale bar = 1 mm. Note that the vertebrae are not labelled in this figure but are described and figured later in the text.
Fig 6.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, holotype block in ventral view showing elements segmented from μCT slice data.
Abbreviations: Ex.O, exoccipital plate; Fr, frontal; L.J, left jugal; L.La, left lacrimal; Lm.B, limb element; L.Mx, left maxilla; L.N, left nasal; L.Pa, left parietal; L.Pf, left prefrontal; L.Q, left quadrate; L.Sm, left septomaxilla; L.Sq, left squamosal;? St, possible left supratemporal;? Opis, possible opisthotic;? Ot, otic associated element;? Pal, possible palatal element;? Pro, possible prootic; R.J, right jugal; R.La, right lacrimal; R.Mx, right maxilla; R.Pa, right parietal; R.Q, right quadrate; R.Sq, right squamosal; S.O, supraoccipital;?Sk1, unidentified skull element; Sph, sphenoid;? St, possible supratemporal;?, unidentified elements. Scale bar = 1 mm. Note that the vertebrae are not labelled in this figure but are described and figured later in the text.
Fig 7.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, holotype block.
Lateral view of skull elements as segmented from μCT slice data. Abbreviations: Ex.O, exoccipital plate; Fr, frontal; L.La, left lacrimal; Lm.B, limb element; L.Mx, left maxilla; L.N, left nasal; L.Pa, left parietal; LPf, left prefrontal; Q, quadrates; L.Sm, left septomaxilla;? Opis, possible opisthotic;? Ot, otic associated element;? Pal, possible palatine;? Pro, possible prootic; R.La, right lacrimal; R.Pa, right parietal; R.Pf, right prefrontal; R.Sq, right squamosal; S.O, supraoccipital; Sph+ Ept, sphenoid and epipterygoid;? St, possible supratemporal;?, unidentified elements. Scale bar = 1 mm. Note that the vertebrae are not labelled in this figure but are described and figured later in the text.
Fig 8.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, nasal.
Left nasal as segmented from μCT slice data in A, dorsal; B, ventral; C, medial; D, lateral; and E, anterior views. Abbreviations: Fr.ft, frontal facet; La.ft, lacrimal facet; N.bd, narial border; Pf.ft, prefrontal facet; Pm.ft, anterodorsal facet for nasal process of premaxilla;? Pm.ft, possible anteroventral facet for the premaxilla. Scale bar = 1 mm.
Fig 9.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, septomaxilla.
Left septomaxilla as segmented from μCT slice data in A, dorsal; B, ventral; C, posterior; D, anterior; E, lateral; and F, medial views. Scale bar = 0.5 mm.
Fig 10.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, frontal.
Frontal as segmented from μCT slice data in A, dorsal; B, ventral; C, right lateral; D, left lateral; and E, posterior views. Abbreviations: alp, anterolateral process; inp, internasal process; N.ft, nasal facet; Pa.ft, parietal facet; Pf.ft, prefrontal facet; vlc, ventrolateral crest; vmc, ventromedian crest. Scale bar = 1 mm.
Fig 11.
Shirerpeton isajii gen. et sp. nov, SBEI 2459, digital photograph showing details of skull roofing elements.
A, frontal and left parietal; B, right parietal. Abbreviations: Fr, frontal; Fr,ft, frontal facet; L.La, left lacrimal; L.Mx, left maxilla; L.Pa, left parietal; L.Pf, left prefrontal; plp, posterolateral process; pmp, posteromedial process; PoW, postorbital wing; R.Pf, right prefrontal;? St, possible supratemporal; V, vertebra. Scale bars = 1 mm.
Fig 12.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, right parietal.
Right parietal as segmented from μCT slice data in A, dorsal; B, ventral; C, oblique anteroventral; D, anterior views. Abbreviations: al.re, anterolateral recess; ap.c, anteroposterior crest; Fr.ft, frontal facet; l.re, lateral recess; Occ.s, occipital shelf; plp, posterolateral process; pmp, posteromedial process; PoW, postorbital wing; SO.ft, supraoccipital facet; tr.c, transverse crest; Scale bar = 1 mm.
Fig 13.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, left parietal.
Left parietal as segmented from μCT slice data in A, dorsal; B, ventral; C, anteroventral; D, ventromedial; and E, anterior views. Abbreviations: al.re, anterolateral recess; ap.c, anteroposterior crest; br.ed, broken edge; Fr.ft, frontal facet; occ.s, occipital shelf; pmp, posteromedial process; PoW, postorbital wing; So.ft, supraoccipital facet; tr.c, transverse crest. Scale bar = 1 mm.
Fig 14.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, maxilla.
A-G, left maxilla as segmented from μCT slice data, in A, lingual; B, labial; C, dorsal; D, ventral; E, oblique anterior; F, oblique posterior; G, anterior views. H, right maxilla in lingual view. Abbreviations: a.ft, anterior facet; fa.p, facial process; J.ft, jugal facet; J.p, jugal process; La.ft, lacrimal facet; m.e, medial emargination; Mx.s, maxillary shelf; n.m, narial margin; p.ft, posterior facet; Pm.p, premaxillary process;? Sm/Pm, bone fragment, part of premaxilla or septomaxilla; v.fl, ventral flange; Scale bar = 1 mm.
Fig 15.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, prefrontal.
Left prefrontal as segmented from μCT slice data in A, dorsal; B, ventral; C, lateral; and D, medial views. Abbreviations: Fr.ft, frontal facet; La.ft, lacrimal facet; N.ft, nasal facet. Scale bar = 1 mm.
Fig 16.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, lacrimal.
Left lacrimal as segmented from μCT slice data in A, medial; B, lateral; C, anterodorsomedial; D, anterior; E, posterior; F, dorsal; and G, ventral views. Abbreviations: J.ft, jugal facet; La.f, lacrimal duct foramen; l.lm, lateral lamina; m.lm, medial lamina; Mx.ft, maxillary facet; N.bd, narial border; N.ft, nasal facet; Or.bd, orbital border; Pf.ft, prefrontal facet; Scale bar = 1 mm.
Fig 17.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, jugal.
Left jugal as segmented from μCT slice data in A, lateral; B, medial; C, dorsal; and D, ventral views. Abbreviations: La.ft, lacrimal facet; Mx.ft, maxillary facet. Scale bar = 1 mm.
Fig 18.
Celtedens ibericus, Lower Cretaceous (Barremian), Las Hoyas, Spain.
digital photograph of specimen (Museo de las Ciencias de Castilla-La-Mancha, MCCM-LH-5710), skull of A, part and B, counterpart. Abbreviations: At, atlas; Ax, axis element; D, dentary; Ex.O, exoccipital; Fr, frontal; J, jugal; Ot.c, otic capsule; Pa, parietal; Pf, prefrontal; Pm, premaxilla; Sph, sphenoid; Sq, squamosal. Scale bars = 1 mm.
Fig 19.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, squamosal.
Right squamosal as segmented from μCT slice data in A, anterodorsal; B, posteroventral; C, lateral; D, anteromedial; E, posteromedial; and F, ventral views. Abbreviations: Q.ft, quadrate facet. Scale bar = 1mm.
Fig 20.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, quadrate.
Left quadrate as segmented from μCT slice data in A, anterodorsal; B, posteroventral; C, posterolateral; D, medial; E, lateral; and F, ventral views. Abbreviations: cd, condyle; l.co, lateral concavity; l.lp, lateral lip; m.b, medial boss; pt, pit; Pt.ft, pterygoid facet; Sq.ft, squamosal facet. Scale bar = 1 mm.
Fig 21.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, skull element.
Possible left supratemporal element as segmented from μCT slice data in A, ventral; B, dorsal; C, lateral; D, medial; and E, anterior. Abbreviations:? ex.s,? exposed surface;? Pa.ft,? parietal facet. Scale bar = 1 mm.
Fig 22.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, possible palatal element.
Element as segmented from μCT slice data in A,? dorsal; B,? ventral; C,? lateral; and D,? medial views. Abbreviations: em, emargination; ft1, facet 1; ft2, facet 2 (as described in the text). Scale bar = 1 mm.
Fig 23.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, skull element.
Unidentified skull element as segmented from μCT slice data in five views (anatomical orientation uncertain). Abbreviations: em, emargination; ft1, facet 1; ft2, facet 2 (see text). Scale bar = 0.5 mm.
Fig 24.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, endocranium.
A, Braincase elements as segmented from the μCT data; B, braincase elements as they appear at the surface of the matrix block, showing where erosion of the edges has occurred (note that the views in A and B are rotated in relation to one another, with B in the same orientation as in Fig 5). Abbreviations: Ept, epipterygoid; Ex.O, exoccipital plate;? Opis, possible opisthotic; Ph, parts of a digit;? Pro, possible prootic; S.O, supraoccipital; Sph, sphenoid;?, unidentified element. Scale bars = 1 mm.
Fig 25.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, exoccipital plate.
Conjoined exoccipitals as segmented from μCT slice data in A, dorsal; B, ventral; C, oblique left dorsolateral; D, posterior; E, anterior; F, oblique left ventrolateral; G, left lateral; and H, right lateral views. Abbreviations:? a.s, possible articular surface; l.cr, lateral crest; l.s, lateral surface; l.w, lateral wing; m.cr, medial crest; m.s, medial surface; occ.co, occipital condyles. Scale bar = 1 mm.
Fig 26.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, sphenoid.
Sphenoid as segmented from μCT slice data in A, posterodorsal; B, anteroventral; C, dorsal; D, posteroventral; E, left lateral; F, right lateral; G, posterior; and H, anterior views. Abbreviations: an.lm, antotic lamina; f, small foramina; ft, facet;? f.5, possible trigeminal foramen; hy.fs, hypophyseal fossa; l.pr, lateral process; m.f, median foramen; o.s, oval surface. Scale bar = 1 mm.
Fig 27.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, sphenoid and epipterygoids.
Sphenoid (blue/purple) in association with epipterygoids (darker blue) as segmented from μCT slice data in A, dorsal; B, ventral; C, right lateral; D, posteroventral; and E, anteroventral views. Note that the apparent opening in the hypophyseal region is an artefact of segmentation, this image having been rendered from the slice data of the higher resolution scan. Scale bar = 1 mm.
Fig 28.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, supraoccipital.
Supraoccipital as segmented from μCT slice data in A, dorsal; B, ventral; C, right lateral; D, posterior; and E, left lateral views. Abbreviations: de, ventral depression; ExO.ft, exoccipital facet; f.mg, foramen magnum; ft, separate part of exoccipital facet, possibly for part of otic capsule;? ft, possible otic capsule facet; Pa.ft, parietal facet. Scale bar = 1 mm.
Fig 29.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, otic capsule.
Possible left opisthotic as segmented from μCT slice data in A, dorsolateral; B, medial; C, posterolateral; and D, ventrolateral views. Abbreviations: adc, anterodorsal cleft;? f, curved edge of possible foramen;? f.v, possible position of fenestra vestibuli;? ft, surface depression that may represent a facet for a roofing element; lsc, groove or prominence for lateral semicircular canal; psc, groove or prominence for posterior semicircular canal. The apparent anterodorsal cleft is due to damage. Scale bar = 1 mm.
Fig 30.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, otic capsule.
Possible right prootic as segmented from μCT slice data in A, anterolateral; B, lateral; and C, posteromedial views. Abbreviations: asc, groove or prominence for the anterior semicircular canal;? c.m, possible crista muscularis;? f.v, possible edge of fenestra vestibuli; lsc, groove or prominence for lateral semicircular canal. Scale bar = 1 mm.
Fig 31.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, ossicle.
A-F, Otic associated element as segmented from μCT slice data in six views (anatomical orientation uncertain). G is a partial view of the segmented braincase showing the position of this small element (arrowed) in relation to the exoccipital plate (but note that this view is rotated relative to the entire block in Fig 6). Scale bars A-F = 0.5 mm; G = 1 mm.
Fig 32.
Shirerpeton isajii gen. et sp. nov., SBEI 2462, a right dentary, as segmented from μCT slice data.
A, labial view; B, lingual view; C, ventral view; D, occlusal view; E, anterolingual view. Abbreviations: an, angular facet; co, concavity in dorsal jaw margin; cv, convexity in dorsal jaw margin; mk. f, Meckelian fossa; n.f, nutrient foramina; pra, prearticular facet; rr, rugose ridge; sds, subdental shelf; sym, symphyseal region with prongs; Scale bar = 1 mm.
Fig 33.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, vertebrae.
Associated vertebrae as segmented from μCT slice data. The numbers relate to the text description. Abbreviations:? rb, rib-like elements illustrated in Fig 34. Scale bar = 1 mm. Note that this figure is rotated relative to the scans of the entire specimen in Figs 5 and 6.
Fig 34.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, rib-like elements.
Rib-like elements adjacent to vertebrae as segmented from μCT slice data in five views (original orientation uncertain). The dark grey elements are probably ribs or hyoid elements. The pale grey element is unidentified. Scale bar = 0.5 mm.
Fig 35.
Shirerpeton isajii gen. et sp. nov., SBEI 2459, limb element.
Limb element as segmented from μCT slice data in six views (original orientation uncertain). Scale bar = 1 mm.
Fig 36.
Lateral profiles of maxillae in albanerpetontids (not to scale).
A, Anoualerpeton priscum (Middle Jurassic, UK); B, An. unicum (Early Cretaceous, Morocco); C, Shirerpeton isajii (Early Cretaceous, Japan); D, Wesserpeton evansae (Early Cretaceous, UK); E, Albanerpeton arthridion (Early Cretaceous, North America); F, Albanerpeton gracile (Late Cretaceous, North America); G, Albanerpeton nexuosum (Late Cretaceous, North America); H, Albanerpeton galaktion (Late Cretaceous, North America); I, Albanerpeton inexpectatum (Miocene, France); J, Albanerpeton pannonicum (Pliocene, Hungary). Outlines redrawn or reconstructed from: A-B [20]; C, original, SBEI 2459; D [34]; E [26]; F-H [29]; I [72]; J [16]. Images C-H have been "mirror-imaged" for ease of comparison.
Fig 37.
Comparison of frontal shape in albanerpetontids, scaled so that posterior widths are roughly equal.
A, Anoualerpeton unicum (Early Cretaceous, Morocco); B, Celtedens ibericus (Early Cretaceous, Spain), based on [28]; C, cf. Celtedens ibericus (Early Cretaceous, Spain); D, Wesserpeton evansae (Early Cretaceous, UK); E, Shirerpeton isajii (Early Cretaceous, Japan); F, Albanerpeton arthridion (Early Cretaceous, North America); G, Albanerpeton gracile (Late Cretaceous, North America); H, Albanerpeton pannonicum (Pliocene, Hungary); I, Albanerpeton inexpectatum (Miocene, France). Figures redrawn from: A [20]; B [28]; C, original, MCCM-LH-15710; D [34]; E, original, SBEI 2459; F [26]; G [29]; H [16]; I [72].
Fig 38.
Strict consensus of 19 MPT’s from an analysis of the full matrix (NT search in TNT with Ratchet followed by a Traditional search of the resulting trees in RAM).
Of the 19 MPT’s, 11% placed Shirerpeton as the sister taxon to a monophyletic Albanerpeton; 42% placed it as the sister taxon to A. arthridion; and 47% placed it crownward of A. arthridion (see Fig 39). An analysis with the limited matrix and without Hypothetical Ancestor yields trees with the same topology for the in-group taxa.
Fig 39.
The three configurations recovered within the individual trees of the different analyses described in the text.
In (C) the position of Shirerpeton is unstable with respect to individual Albanerpeton sp. The ‘A. inexpectatum clade’ consistently comprises A. inexpectatum, A. pannonicum and the Paskapoo taxon, with the variable addition of A. nexuosum.
Fig 40.
Bootstrap analysis (1000 replicates) using TNT (NT search + Ratchet [20 iterations]) of the full matrix, with the hypothetical ancestor as outgroup.
The same analysis run using the limited matrix yielded the same topology, with minor differences in the Bootstrap values.
Fig 41.
Skull roofing bones in albanerpetontids (not to scale).
A, Shirerpeton isajii; B, Celtedens ibericus; C, Albanerpeton inexpectatum; D, Albanerpeton pannonicum. B-D, redrawn from [16], but with B based on [8].
Fig 42.
Parietal morphology in albanerpetontids (not to scale).
A, Anoualerpeton priscum (Middle Jurassic, UK); B, c.f. Wesserpeton evansae (Early Cretaceous, UK); C, Celtedens ibericus (Early Cretaceous, Spain); D, Shirerpeton isajii, Early Cretaceous, Japan); E, Albanerpeton inexpectatum, Miocene, France). In each case, the small asterisk marks the lateral limit of the frontal facet, lateral to which is the postorbital wing. Abbreviations: Occ.s, occipital shelf; PoW, postorbital wing. Figures redrawn from: A [23] (mirror-imaged for comparison); B, original, NHMUK PV R 36956; C [6]; D, original, SBEI 2459; E [3].
Fig 43.
Celtedens ibericus, Las Hoyas specimen, Museo de las Ciencias de Castilla-La-Mancha, MCCM-LH-15710, digital photograph of skull of part and counterpart.
A,B MCCM-LH-15710b, with A, whole skull and B, enlargement of braincase region; C,D, MCCM-LH-15710a, with C, whole skull and D, enlargement of braincase region. In B and D, blue outlined element is the exoccipital plate, and red outlined element is the sphenoid. Scale bar = 1 mm.