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Figure 4. Permo-Triassic dicynodont bone histology. A in Do extraordinarily high growth rates in Permo-Triassic dicynodonts (Therapsida, Anomodontia) explain their success before and after the end-Permian extinction?

Figure 4. Permo-Triassic dicynodont bone histology. A, juvenile Dicynodon humerus SAM-PK-K5576d; B, subadult Dicynodon humerus NMQR3633a; C, subadult Lystrosaurus maccaigi ulna NMQR3663b; D, juvenile Lystrosaurus declivis tibia NMQR735b; D, E, adult Lystrosaurus humerus (possibly Lystrosaurus declivis) NMQR3678; F, late subadult Kannemeyeria femur NMQR2674b. Arrows indicate enlarged channels in all genera. Scale bars: D, E = 500 mm; A, B, C, F = 413 mm.

Figure 6. Permo-Triassic eutherapsid bone histology. A in Do extraordinarily high growth rates in Permo-Triassic dicynodonts (Therapsida, Anomodontia) explain their success before and after the end-Permian extinction?

Figure 6. Permo-Triassic eutherapsid bone histology. A, subadult gorgonopsian Scylacops femur SAM-PK-10188; B, adult therocephalian Pristerognathus femur SAM-PK-11557; C, late subadult nonmammalian cynodont Cynognathus femur SAM-PK-K6235a; D, early subadult nonmammalian cynodont Diademodon ulna SAM-PK-K8971c. Enlarged channels are absent from these taxa. Arrows indicate growth rings. Scale bars: B, D = 500 mm; A, C = 413 mm.

Figure 3. Permo-Triassic dicynodont bone histology. A, subadult Cistecephalus ulna NMQR1465b in Do extraordinarily high growth rates in Permo-Triassic dicynodonts (Therapsida, Anomodontia) explain their success before and after the end-Permian extinction?

Figure 3. Permo-Triassic dicynodont bone histology. A, subadult Cistecephalus ulna NMQR1465b; B, early subadult Dicynodontoides tibia NMQR479a; C, adult Rhachiocephalus ulna SAM-PK-3714a; D, subadult Tropidostoma tibia SAM-PK-K9960c; E, adult Oudenodon femur SAM-PK-K4807a; F, adult Aulacephalodon femur NMQR3016. Arrows indicate enlarged midcortical channels in Rhachiocephalus and Aulacephalodon. Scale bars: A, D, E = 500 mm; B, C, F = 413 mm.

Figure 5 in X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny

Figure 5. The lateral wall of the braincase of Pristerodon mackayi (BP/1/2642): right prootic (blue) in (A) anterior, (B) lateral, (C) posterior, (D) ventral and (E) medial views; and left opisthotic (golden) in (F) anterior, (G) lateral and (H) posterior views. afac, articulation facet concavity; ascc, attachment of the anterior semicircular canal; boa, basioccipital sutural area; bsa, parabasisphenoid sutural area; CNV, passage of the cranial nerve five (V); eoa, exoccipital sutural area; fa, facial foramen; flo, floccular fossa; fo, fenestra ovalis; jf, jugular foramen; lscc, attachment of the lateral semicircular area; lvb, opisthotic lateral vertical buttress; osu, opisthotic posterior vertical sulcus; ovmp, opisthotic ventromedial process; pa, pila antotica; pab, prootic anterior bulge; pad, pila antotica anterior depression; pdp, prootic dorsal process; prd, prootic lateral depression; pscc, attachment of the posterior semicircular canal; ptf, posttemporal fenestra; spa, supraoccipital sutural area; vea, vestibular area; ve, vestibule. The horizontal line pattern on the prootic in (B) represents the prootic depression. The diagonal square pattern in (F) represents the articular surface of the prootic. Scale bars equal 5 mm. The upper scale bar serves for (A-E) and the lower for (F-H).

Figure 11 in X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny

Figure 11. Illustration of a cistecephalid species and its inferred palaeobiology. Skin texture is inspired by the naked mole-rat and the foraging behaviour typical of a fossorial taxon feeding on insects. Reconstruction credits: copyright Luzia Soares (2021).

Figure 10 in X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny

Figure 10. The lateral and occipital portions of the braincase of Kaaeingasaurus fossilis (GPIT-PV-117032): epipterygoid (light pink) in (A) anterior and (B) right lateral views; exoccipital (pink) in (C) anterior view; supraoccipital (dark green) in (D) anterior, (E) posterior, (F) left lateral and (G) medial views; prootic (blue) in (H) anterior, (I) lateral, (J), medial and (K) posterior views; opisthotic (golden) in (L) anterior, (M) medial and (M) posterior views. ascc, attachment of the anterior semicircular canal; cc, attachment of the crus communis; eo, exoccipital; eoc, exoccipital condyle; eocr, exoccipital descending crest; eodc, exoccipital dorsal component; epap, anteromedial angular process of the epipterygoid; epar, ascending ramus of the epipterygoid; epft, epipterygoid footplate; fa, facial foramen; flo, floccular fossa; fo, fenestra ovalis; fm, foramen magnum; ihb, impressions of the hindbrain; jf, jugular foramen; lscc, attachment of the lateral semicircular canal; nc, nuchal crest; oae, opisthotic anterior depression; od, opisthotic posterior depression; opc, opisthotic posterior crests; pa, pila antotica; pabt, prootic anterior buttress; pade, pila antotica ellipsoidal depression; pard, pila antotica anterodorsally directed ridges; pbg, prootic anterior bulge; pg, prootic anterior groove; plbt, prootic lateral vertical buttress; pmbt, prootic medial vertical buttress; prs?, prootic sinus; pscc, attachment of the posterior semicircular canal; ptf, posttemporal fenestra; pvfo, prootic vertical fossa; sacr, crests of the supraoccipital ala; saex, medial excavation of the supraoccipital lateral ala; sfo, supraoccipital posterior fossa; sap, supraoccipital anterior process of the median lobe; slr, supraoccipital lateral recess; sor, supraoccipital anterior oblique ridges; spp, supraoccipital posterior process; su, supraoccipital; tgn, passage of the cranial nerve (V); ve, vestibular area. Scale bars equal 1 mm. The first scale serves for (A-B), the second for (C-G) and the third for (H-N).

Figure 4 in X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny

Figure 4. The ventral and posterior walls of the braincase of Pristerodon mackayi (BP/1/2642): basioccipital (lime green) in (A) posterior, (B) dorsal, (C) ventral and (D) right lateral views; exoccipital (pink) in (E) anterior and (F) posterior views; and supraoccipital (dark green) in (G) anterior, (H) internal, (I) right lateral and (J) anterolateral views. ascc, attachment of the anterior semicircular canal; boc, basioccipital condyle; bocc, basioccipital condyle dorsal concavities; bocex, basioccipital collar-like excavation; bocf, basioccipital condyle foramina; bocr, basioccipital condyle median ridge; bomr, basioccipital median ridge; bosr, basioccipital lateral ridges; bovtr, basioccipital ventral trough; bt, basioccipital tubera; cca, attachment of the crus communis; eo, exoccipital; eoat, exoccipital anterior tuberosity; eobg, exoccipital posterior bulge; eobt, exoccipital subvertical buttress; eoc, exoccipital condyle; eodc, exoccipital dorsal component; flo, floccular fossa; fm, foramen magnum; fo, fenestra ovalis; ite, intertuberal eminence; jf, jugular foramen; ms, M-like suture between the basioccipital and exoccipital; pa, pila antotica; pbs, parabasisphenoid; pr, prootic; ptf, posttemporal fenestra; sap, supraoccipital anteriorly projected crest; sar, supraoccipital anterior recess; slr, supraoccipital lateral recess; sor, supraoccipital anterior horizontal ridges; spp, supraoccipital posterior process; su, supraoccipital; ve, vestibule. Note that the articular surface of the parabasisphenoid is black squared pattern in C. Scale bars equal 5 mm. The first scale serves for (A-D), the second for (E-F) and the third for (G-J).

Figure 2 in X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny

Figure 2. Comparisons of the braincase between Pristerodon and emydopoids. Pristerodon mackayi (BP/1/2642) in (A) anterior, (B) left lateral, (C) posterior and (D) ventral views. Myosaurus gracilis (BP/1/2690) in (E) anterior, (F) left lateral, (G) posterior and (H) ventral views. The Malawian cistecephalid (DMMM-PK-16-1) in (I) anterior, (J) left lateral, (K) posterior and (L) ventral views. Kaaeingasaurus fossilis (GPIT-PV-117032) in (M) anterior, (N) left lateral, (O) posterior and (P) ventral views. Dark green – supraoccipital; Purple – orbitosphenoid; Dark orange – opisthotic; Light orange – pterygoid; Green – basioccipital; Magenta – exoccipital; Cyan blue – parasphenoid rostrum; Navy blue – prootic; Aqua blue – basisphenoid; Light Rose – epipterygoid. Same color code scheme is used in the following figures.

Figure 1 in X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny

Figure 1. Illustration of the braincase region within the entire skull. Pristerodon mackayi (BP/1/2642) in (A) right lateral, (B) posterior and (C) ventral views. Myosaurus gracilis (BP/1/2690) in (D) right lateral, (E) posterior and (F) ventral views. The Malawian cistecephalid (DMMM-PK-16-1) in (G) left lateral and (H) posterior views. Kaaeingasaurus fossilis (GPIT-PV-117032) in (I) right lateral, (J) posterior and (K) ventral views. Note that the Malawian cistecephalid specimen is completely covered by matrix, such that a good contrast to enable the visibility of the skull was not obtained. Dark green – supraoccipital; Purple – orbitosphenoid; Dark orange – opisthotic; Light orange – pterygoid; Green – basioccipital; Magenta – exoccipital; Cyan blue – parasphenoid rostrum; Navy blue – prootic; Aqua blue – basisphenoid; Light Rose – epipterygoid.

Figure 7 in X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny

Figure 7. The posteroventral braincase wall of Myosaurus gracilis (BP/1/2690 and BP/1/2701a): basioccipital (lime green) in (A) posterior, (B) dorsal, (C) ventral and (D) right lateral views; the exoccipital (pink) in (E) anterior, (F) posterior, (G) dorsal and (H) ventromedial views; supraoccipital (dark green) in (I) anterior, (J) posterior, (K) ventral and (L) dorsal views; prootic (blue) in (M) anterior, (N) left lateral, (O) medial, (P) dorsal and (Q) posterior views; (R) the complete braincase of BP/1/2690 in left lateral view; opisthotic (golden) of BP/1/2690 in (S) anterior and (T) posterior views; right opisthotic of BP/1/2701a in (U) posterior view; the braincase of BP/1/2690 in (V) ventral view. ap, alar process of the prootic; ascc, attachment of the anterior semicircular canal; bo, basioccipital; boc, basioccipital condyly; bocc, basioccipital condyle concavities; bod, basioccipital ventral depression; bocdr, basioccipital condyle dorsal ridge; bomr, basioccipital median ridge; bonf, basioccipital nutritive foramina; bosr, basioccipital lateral ridges; bt, basioccipital tubera; CNV, passage of the cranial nerve five (V); eo, exoccipital; eoat, exoccipital anterior tuberosity; eoc, exoccipital condyle; eodc, exoccipital dorsal component; eopsu, exoccipital posterior sulcus; fa, facial foramen; flo, floccular fossa; fm, foramen magnum; fo, fenestra ovalis; gp, gap between the prootic and the clinoid process; hf, hypoglossal foramen; jf, jugular foramen; lscc, attachment of the lateral semicircular area; lvb, opisthotic lateral vertical buttress; ob, opisthotic body; obu, opisthotic bulges; occp, occipital pit; olc, opisthotic lateral crest; omc, opisthotic medial crest; op, opisthotic; opmb, opisthotic posteromedial buttress; osu, opisthotic posterior vertical sulcus; ovmp, opisthotic ventromedial process; pa, pila antotica; pabt, prootic anterior buttress; pbs, parabasisphenoid; ppex, prootic posterior excavation; pr, prootic; prac, pila antotica anterior crests; prmc, prootic medial crest; prpb, prootic posterior bulge; pscc, attachment of the posterior semicircular canal; pt, pterygoid; ptf, posttemporal fenestra; sac, supraoccipital semicircular crests; sap, supraoccipital anteriorly projected crest; slr, supraoccipital lateral recess; smb, supraoccipital subvertical buttress; spi, supraoccipital posterior pit; su, supraoccipital; svd, supraoccipital posterior vertical depressions; ve, vestibular area. The horizontal square pattern in (O) represents the sutural area between the prootic and supraoccipital; the horizontal line pattern in (O, Q) represents the articular surface between the prootic and the opisthotic and the oblique pattern in (O) represents the articular surface between the prootic and the parabasisphenoid. Finally, the vertical pattern in (S), represents the articular surface for the prootic on the opisthotic. Scale bars equal 5 mm. The first scale serves for (A-H), the second for (I-L), the third for (M-Q, S, T, V), the fourth for (R) and the fifth for (U).

Figure 3 in X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny

Figure 3. The complete and separated braincase elements of Pristerodon mackayi (BP/1/2642): orbitosphenoid in (A) anterior, (B) dorsal and (C) left lateral views; complete braincase in (D) anterior, (E) dorsal, (F) ventral, (G) occipital and (H) left lateral views; parabasisphenoid in (I) dorsal, (J) right lateral and (K) ventral views. aptr, anterior (palatal) ramus of the pterygoid; bo, basioccipital; bpdc, basisphenoidal dorsal subvertical concavity; bpt, basisphenoidal tubera; bpvsu, basisphenoidal ventral sulcus; clp, clinoid process; co, crista oesophagea; ds, dorsum sellae; eo, exoccipital; eobg, exoccipital posterior bulge; eobt, exoccipital subvertical buttress; epi, epipterygoid; fu, pterygoid anteroposterior furrow; hpl, horizontal plate; ic, internal carotid foramina; lvb, opisthotic lateral vertical buttress; mpw, mesethmoid posterior wall; obdn, the orbitosphenoid dorsal notch; obvp, orbitosphenoid medial vertical process; obw, orbitosphenoid wings; ofc, olfactory cavity; op, opisthotic; osu, opisthotic posterior vertical sulcus; ovmp, opisthotic ventromedial process; pab, prootic anterior bulge; pad, pila antotica anterior depression; pbs, parabasisphenoid; pdp, prootic dorsal process; pr, prootic; ps, parasphenoid rostrum; psgr, parasphenoid rostrum dorsal groove; pt, pterygoid; pt amp, anteromedial process of the pterygoid; pt dsu, ptergoid dorsal sulcus; ptll, pterygoid lateral lamina; ptlp, pterygoid lateral process; ptmp, pterygoid median plate; pt nt, pterygoid anteroposterior notch; ptqr, pterygoid quadrate ramus; ptvt, pterygoid ventral trench; sap, supraoccipital anteriorly projected crest; sar, supraoccipital anterior recess; slr, supraoccipital lateral recess; sor, supraoccipital anterior horizontal ridges; spp, supraoccipital posterior process; su, supraoccipital; stu, sella turcica; tse, tuberculum sellae. Scale bars equal 5 mm. The first scale serves for (A-C), the second for (D-H) and the third for (I-K).

Figure 12 in X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny

Figure 12. Phylogenetic results simplified to highlight Emydopoidea intra- and interrelationships. Numbers at nodes represent: Symmetric Resampling values/CG values above nodes; Bremer Support values/Relative Bremer Support values below nodes. See the Supporting Information (Figs S1–S3) for the complete tree.

Figure 9 in X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny

Figure 9. The anterior and ventral portions of the braincase of Kaaeingasaurus fossilis (GPIT-PV-117032): orbitosphenoid (purple) in (A) anterior, (B) dorsal and (C) left lateral views; basioccipital (lime green), parabasisphenoid (light blue) and pterygoid (yellow) in (D) dorsal, (E) left lateral and (F) ventral views; parabasisphenoid in (G) ventral view; and basioccipital in (H) posterior view. Horizontal CT-image through the parabasisphenoid and basioccipital (I). aptr, anterior (palatal) ramus of the pterygoid; bo, basioccipital; boc, basioccipital condyle; bocf, basioccipital longitudinal furrow; bolp, basioccipital lateral process; bovr, basioccipital median ridge; bovs, basioccipital vestibular space; bpt, basisphenoidal tubera; bt, basioccipital tubera; bvex, basioccipitalbasisphenoidal ventral excavation; clp, clinoid process; ds, dorsum sellae; dsu, orbitosphenoid dorsal sulcus; ic, internal carotid foramina; jf, jugular foramen; obasu, orbitosphenoid lateral sulci; obgu, orbitosphenoid dorsal gutter; obno, lateral notch; obpl, orbitosphenoid dorsal plate; obvp, orbitosphenoid medial vertical process; obw, orbitosphenoid wings; ofc, olfactory cavity; pbs, parabasisphenoid; psgr, parasphenoidal groove; pt, pterygoid; ptqr, posterior (quadrate) ramus of the pterygoid; stu, sella turcica; tra, trabecular spaces; ve, vestibule. Note that the articular surface of the exoccipital is represented by the horizontal square pattern in (D). The upper scale bar equals 5 mm and 1 mm in the lower. The upper scale serves for (A-C) and the lower for (D-H).

Figure 6 in X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny

Figure 6. The anterior, ventral and lateral walls of the braincase of Myosaurus gracilis (BP/1/2690 and BP/1/2701a): orbitosphenoid (purple) of BP/1/2690 in (A) anterior, (B) dorsal and (C) right lateral views; the pterygoid (yellow) of BP/1/2690 in (D) dorsal, (E) right lateral and (F) ventral views; ventral braincase floor of BP/1/2701a in (G) dorsal and (H) right lateral views; epipterygoid (pink) of BP/1/2701a in (I) anterior, (J) right lateral and (K) medial views; and the parabasisphenoid (turquoise) of BP/1/2690 in (L) dorsal, (M) left lateral and (N) ventral views. apf, pterygoid anteroposterior furrow; aptr, anterior (palatal) ramus of the pterygoid; bpt, basisphenoidal tubera; clp, clinoid process; co, crista oesophagea; ds, dorsum sellae; epar, epipterygoid ascending ramus; epdp, epipterygoid dorsal plate; epft, epipterygoid footplate; ic, internal carotid foramina; ltcr, oblique crests of the lateral wall; obacr, orbitosphenoid vertical crest; obasu, lateral sulci of the median vertical process; obdfo, orbitosphenoid dorsal fossa; obgu, orbitosphenoid gutter; obvp, orbitosphenoid vertical process; obsp, orbitosphenoid spine process; obw, orbitosphenoid wings; ofc, olfactory cavity; PRB, parasphenoid rostrum + basipresphenoid; ps, parasphenoid (light blue) rostrum; psc, parasphenoidal crests; psf, parasphenoidal foramen; pss, parasphenoidal sulcus; pt amp, anteromedial process of the pterygoid; pt gr, pterygoid dorsal groove; ptmp, pterygoid median plate; ptqr, quadrate ramus of the pterygoid; stu, sella turcica. Scale bars equal 5 mm. The first scale serves for (A-C), the second for (D-F), the third for (G-H), the fourth for (I-K) and the fifth for (L-N).

Figure 8 in X-ray microcomputed and synchrotron tomographic analysis of the basicranial axis of emydopoid dicynodonts: implications for fossoriality and phylogeny

Figure 8. The braincase of the Malawian cistecephalid DMMM-PK-16-1: ventral region of the braincase in (A) dorsal, (B) right lateral and (C) ventral views; the left exoccipital (pink) in (D) anterior and (E) posterior views; and right exoccipital (pink) in (F) medial view. Anterior wall: right prootic (blue) in (G) ventrolateral, (H) anterior; (I) lateral, (J) medial, (K) ventral and (L) posterior views. Posterior wall of the braincase: opisthotic (golden) and supraoccipital (dark green) in (M) anterior, (O) posterior and (P) right lateral views; opisthotic in (N) medial view. ap, alar process of the prootic; aptr, anterior (palatal) pterygoid ramus; ascc, attachment of the anterior semicircular canal; bo, basioccipital (lime green); boc, basioccipital condyle; bod, basioccipital ventral depression; bok, basioccipital dorsal knob; bosr, basioccipital lateral ridges; bplr, basisphenoidal lateral recess; cc, attachment of the crus communis; clp, clinoid process; co, crista oesophagea; ds, dorsum sellae; eoat, exoccipital anterior tuberosity; eodc, exoccipital dorsal component; eopsu, exoccipital posterior sulcus; epi, epipterygoid; fa, facial foramen; flo, floccular fossa; fm, foramen magnum; fo, fenestra ovalis; gap, gap between the prootic and the parabasisphenoid; hf, hypoglossal foramen; ic, internal carotid foramina; jf, jugular foramen; lscc, attachment of the lateral semicircular canal; oac, opisthotic anterior crests; oad, opisthotic anterior depression; obg, opisthotic anterior bulge; od, opisthotic posterior depression; op, opisthotic; opc, opisthotic posterior crests; opp, opisthotic posterior process; ovmp, opisthotic ventromedial process; pa, pila antotica; pbl, prootic blade-like process; pbs, parabasisphenoid; pr, prootic; ps, parasphenoid rostrum; pss, parasphenoid rostrum dorsal sulcus; pssc, attachment of the posterior semicircular canal; pt, pterygoid; ptf, posttemporal fenestra; pt ltr, pterygoid lateral trench; ptqr, pterygoid quadrate ramus; pt vsc, pterygoid ventral sulcus; sap, supraoccipital anteriorly projected crest; slr, supraoccipital lateral recess; sp, supraoccipital; ssd, supraoccipital semicircular depressions; su, supraoccipital; stu, sella turcica; tgn, passage of the trigeminal nerve (V); tmp, 'tympanic process' of Cox (1959); us, U-shaped suture; uz, unossified zone; ve, vestibular area. Scale bars equal 5 mm, except for (G) which equals to 1 mm. The first scale serves for (A-C), the second for (D-F), the third for (G), the fourth for (H-L) and the fifth for (M-P).

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Data from: A new taxon of cistecephalid dicynodont from the upper Permian Kundaram Formation of India

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Data from: The evolution of the dicynodont sacrum: constraint and innovation in the synapsid axial column

Constraint is a universal feature of morphological evolution. The vertebral column of synapsids (mammals and their close relatives) is a classic example of this phenotypic restriction, with greatly reduced variation in the number of vertebrae compared to the sauropsid lineage. Synapsids generally possess only three sacral vertebrae, which articulate with the ilium and play a key role in locomotion. Dicynodont anomodonts are the exception to this rule, possessing seven or more sacral vertebrae while reaching a range of body sizes rivaled among synapsids only by therian mammals. Here we explore the evolution of this unusual sacral morphology in dicynodonts by 1) hypothesizing homologies of the additional sacral vertebrae, 2) using ancestral state reconstruction and phylogenetic regressions (e.g., logistic regression, Poisson regression) to track the coevolution of sacral count and body size, and 3) proposing mechanisms by which additional sacral vertebrae were incorporated during dicynodont evolution. We find that sacral vertebra morphology covaries with sacral count in consistent ways across dicynodonts, implying that sacra with a given number of vertebrae are composed of homologous elements. There is a correlation between increased sacral count and larger body size, especially at the shift from four to five sacrals near the origin of Bidentalia. Based on position, morphology, and the consistent number of presacral vertebrae among dicynodonts, we hypothesize that the additional sacrals anterior to the plesiomorphic three are duplications of the first sacral, and that a single caudosacral was incorporated by a shift in the identity of the anteriormost caudal vertebra. Although changes in sacral count appear to be correlated with shifts in body size in dicynodonts, the evolution of general morphological conservativism in the synapsid sacrum remains to be further explored.

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Data from: The evolution of the dicynodont sacrum: constraint and innovation in the synapsid axial column

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Figure 5 in Do extraordinarily high growth rates in Permo-Triassic dicynodonts (Therapsida, Anomodontia) explain their success before and after the end-Permian extinction?

Figure 5. Phylogenetic distribution of mean channel density and enlarged vascular channels amongst therapsids. Mean channel density optimized using squared-change parsimony and equal branch lengths; enlarged vascular channels optimized using parsimony. Topology modified from Angielczyk (2007), Botha, Abdala & Smith (2007), Fröbisch (2007), and Liu, Li & Cheng (2002), Higher level taxonomy of anomodonts follows Kammerer & Angielczyk (2009).

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Figure 2. Permian dicynodont bone histology. A in Do extraordinarily high growth rates in Permo-Triassic dicynodonts (Therapsida, Anomodontia) explain their success before and after the end-Permian extinction?

Figure 2. Permian dicynodont bone histology. A, adult Galeops humerus SAM-PK-12261a; B, early subadult Eodicynodon femur NMQR2996a; C, late subadult Eodicynodon femur NMQR3153a; D, late subadult Diictodon SAM-PK-K7725; E, subadult Endothiodon tibia SAM-PK-5605c; F, adult Endothiodon humerus SAM-PK-K6618a. Arrows indicate enlarged midcortical channels. Enlarged channels are absent in Galeops, Diictodon, and Endothiodon. However, subadult Endothiodon reveals rapid, sustained growth with an average channel area of 13%. Scale bars: B, C = 500 mm; A, D, E, F = 413 mm.