Fig 1.
Photographs of original Acanthostega gunnari specimens.
Dorsal views of the incomplete, articulated lower jaws (A) and posterior skull table (B) of MGUH-VP-8158 (“Rosie”). Lateral (C) and medial (D) views of the right side of MGUH-VP-8160 (“Grace”); lateral (E) and medial (F) views of the left side of MGUH-VP-8160; and posterior (G), dorsal (H) and ventral (I) views of both halves of MGUH-VP-8160. Dorsal view (J) of the large slab, containing MGUH 29019 (“Boris”, bottom center) and MGUH-VP-8161 (“Uncle Fred”, upper left). Close-up MGUH 29019 in dorsal view (K). All scale bars equal 10 mm except for the scale bar in K, which equals 50 mm.
Fig 2.
Segmentation of CT data of Acanthostega gunnari.
Isosurface (A) of (MGUH-VP-8160) with labeled sagittal (A), frontal (B) and transverse (C) planes. These slices are shown in insets, with shaded areas representing individual bones segmented from each other and the surrounding matrix.
Fig 3.
Surface models of Acanthostega gunnari prior to retrodeformation.
Lateral (A) and medial (B) views of the right side of MGUH-VP-8160. Dorsal (C) and ventral (D) views of the anterior ends of the lower jaws of MGUH-VP-8158. Dorsal (E) view of the skull roof of MGUH-VP-8158. Individual bones are shown in various colours. Anatomical abbreviations: ad, adsymphysial; an, angular; ar, articular; at, anterior tectal; bo, basioccipital; bs, basisphenoid; co1, coronoid 1; d, dentary; ect, ectopterygoid; f, frontal; j, jugal; l, lacrimal; mr, median rostral; mx, maxilla; n, nasal; p, parietal; pa, prearticular; pf, prefrontal; pl, palatine; pmx, premaxilla; po, postorbital; poc, preopercular; ps, parasphenoid; psp, postsplenial; pt, pterygoid; ptf, postfrontal; ptp, postparietal; q, quadrate; qj, quadratojugal; sa, surangular; sp, splenial; sq, squamosal; st, supratemporal; tab, tabular; v, vomer.
Fig 4.
3D reconstruction of the cranium of Acanthostega gunnari.
Lateral (A), dorsal (B) and ventral (C) views of the cranium. Individual bones are shown in various colours. Anatomical abbreviations: af, anterior fontanelle; apf, anterior palatal fossa; at, anterior tectal; bo, basioccipital; bs, basisphenoid; ch, choana; ect, ectopterygoid; en, external naris; f, frontal; iv, interpterygoid vacuity; j, jugal; l, lacrimal; mr, median rostral; mx, maxilla; n, nasal; o, orbit; p, parietal; pf, prefrontal; pl, palatine; pmx, premaxilla; po, postorbital; poc, preopercular; ps, parasphenoid; pt, pterygoid; ptf, postfrontal; ptp, postparietal; q, quadrate; qj, quadratojugal; sf, subtemporal fossa; sq, squamosal; st, supratemporal; tab, tabular; v, vomer. Dotted outline in C shows approximate outline of basioccipital.
Fig 5.
3D reconstruction of the lower jaw of Acanthostega gunnari.
Lateral (A), medial (B), ventral (C) and dorsal (D) views of the right lower jaw. Individual bones are shown in various colours. Anatomical abbreviations: ad, adsymphysial; an, angular; ar, articular; co1, coronoid 1; co2, coronoid 2; co3, coronoid 3; d, dentary; maf, mandibular adductor fossa; mf, Meckelian fenestra; pa, prearticular; psp, postsplenial; sa, surangular; sp, splenial.
Fig 6.
Symphysial morphology of Acanthostega gunnari.
Surface models of Acanthostega illustrating the morphology of the mandibular symphysis. Individual bones are shown in various colours. Medial views of the anterior right lower jaw of MGU-VP-8160 (A) and MGUH-VP-8158 (B), and anterior (C) and posterior (D) views of the articulated anterior lower jaws of MGUH-VP-8158. Green shading in A and B denotes contact surfaces at the symphysis; note the opening of the Meckelian canal enclosed between the adsymphysial, dentary and splenial. Right side bones are shown in darker shades in C and D; note that the anterior portion of the symphysis in MGUH-VP-8158 was sectioned. Anatomical abbreviations: ad, adsymphysial; co1, coronoid 1; d, dentary; lig, ligament pit of splenial; mc, anterior opening of the Meckelian canal; pa, prearticular; sp, splenial.
Fig 7.
Jaw joint morphology of Acanthostega gunnari.
Surface models of MGUH-VP-8160 illustrating the morphology of the right jaw joint. The quadrate (green bone) is shown in dorsal view (A) with all surrounding bones of the cranium removed and the lower jaw bones shown in gray. The posteroventral corner of the skull is shown in oblique lateral view (B) with the bones of the cranium transparent to reveal the underlying quadrate (green). The articular (yellow) is show in dorsal view (C) with facets that contact the quadrate shown in turquoise shading.
Fig 8.
3D reconstructon of the skull of Acanthostega gunnari.
Articulated cranium and lower jaws shown in oblique right lateral view (A). Right facial skeleton and skull roof shown in “exploded” view to illustrate the nature of sutural contacts (B); the left side of the cranium (braincase omitted) is shown in internal view (C). The right lower jaw in “exploded” view to illustrate sutural morphology. Individual bones shown in various colours.
Fig 9.
Suture maps of the upper and lower jaws of Acanthostega gunnari.
Suture maps of the left half of the cranium in dorsal (A) and ventral (B) views, the left half of the lower jaw in dorsal (C) and ventral (D) views, the cranium in lateral view (E), and the lower jaw in lateral (F) and medial (G) views. Solid lines indicate butt joints; medium shading indicates scarf joints and the direction of underlap (but not the extent of underlap); cross hatches indicate interdigitated sutures; dashed lines (C) indicate tongue-and-groove contacts; black shading indicates openings in the skull and jaw. Dotted lines indicate contacts for which sutural morphology is uncertain. The direction of underlap between the nasal and frontal bones is unclear; this is indicated by light shading (A and E). Dark shading in A indicates the unique, curved lapping joint between the tabular and squamosal. The articular is externally overlapped by all surrounding elements and is shown in light shading (C, D, and G).