The Phylogenetic Relationships of Eucynodontia (Amniota: Synapsida)

Abstract

The phylogeny of Eucynodontia is an important topic in vertebrate paleontology and is the foundation for understanding the origin of mammals. However, consensus on the phylogeny of Eucynodontia remains elusive. To clarify their interrelationships, a cladistic analysis, based on 145 characters and 31 species, and intergrating most prior works, was performed. The monophyly of Eucynodontia is confirmed, although the results slightly differ from those of previous analyses with respect to the composition of both Cynognathia and Probainognathia. This is also the first numerical cladistic analysis to recover a monophyletic Traversodontidae. Brasilodon is the plesiomorphic sister taxon of Mammalia, although it is younger than the oldest mammals and is specialized in some characters. A monophyletic Prozostrodontia, including tritheledontids, tritylodontids, and mammals, is well supported by many characters. Pruning highly incomplete taxa generally has little effect on the inferred pattern of relationships among the more complete taxa, although exceptions sometimes occur when basal fragmentary taxa are removed. Taxon sampling of the current data matrix shows that taxon sampling was poor in some previous studies, implying that their results are not reliable. Two major unresolved questions in cynodont phylogenetics are whether tritylodontids are more closely related to mammals or to traversodontids, and whether tritylodontids or tritheledontids are closer to mammals. Analyses of possible synapomorphies support a relatively close relationship between mammals and tritylodontids, to the exclusion of traversodontids, but do not clearly indicate whether or not tritheledontids are closer to mammals than are tritylodontids.

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Acknowledgements

We thank James Hopson, Hans-Dieter Sues, Marina Bento Soares, and especially Fernando Abdala for fruitful discussions. The comments from Zhe-Xi Luo, Fernando Abdala, Agustín G. Martinelli, and John R. Wible greatly improved this paper. The cooperation and hospitality of the staff of various museums and institutions greatly facilitated our comparative studies. We would like to thank Tom Kemp (Oxford University Museum of Natural History, UK); Ray Symonds (University Museum of Zoology, Cambridge, UK); Sandra Chapman (Natural History Museum, London, UK); Fernando Abdala and Bruce Rubidge (Bernard Price Institute for Palaeontological Research, Johannesburg, South Africa); Jennifer Botha and Elize Butler (National Museum, Bloemfontein, South Africa); Roger Smith and Sheena Kaal (Iziko Museums–South African Museum, Cape Town, South Africa); Johann Neveling (Council for Geosciences, Pretoria, South Africa); Stephany Potze (Transvaal Museum, South Africa); Ana Maria Ribeiro (Museu de Ciências Naturais, Fundação Zoobotânica do Rio Grande do Sul, Porto Alegre, Brazil); Maria C. Malabarba (Museu de Ciências e Tecnologia, Pontifïcia Universidade Católica do Rio Grande do Sul, Porto Alegre, Brazil); Marina B. Soares and Cesar L. Schultz (Universidade Federal do Rio Grande do Sul, Porto Alegre RS, Brazil); Jaime E. Powell (Universidad Nacional de Tucumán, Argentina); Alejandro Kramarz and Agustín G. Martinelli (Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Buenos Aires, Argentina); Guillermo F. Vega (Museo de Antropología, Universidad Nacional de La Rioja, Argentina); Ricardo Martinez (Museo de Ciencias Naturales, Universidad Nacional de San Juan, Argentina); Marcelo Reguero and Rosendo Pascual (Museo de La Plata, Argentina); Charles R. Schaff and Wu Shaoyuan (Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, USA), Hans-Dieter Sues and Matthew Carrano (National Museum of Natural History, Washington, D.C., USA), James A. Hopson (University of Chicago, Chicago, USA), Olivier Rieppel, Elaine Zeiger, and William F. Simpson (Field Museum of Natural History, Chicago, USA); and John Flynn (American Museum of Natural History, New York, USA). Special thanks to Corwin Sullivian for reading the manuscript and greatly improving the writing.

Financial support for this project was provided by Columbia University through a Faculty Fellowship, the Climate Center of Lamont-Dohert Earth Observatory, Theodore Roosevelt Memorial Fund of AMNH, and Chinese Academy of Sciences (KZCX2-YW-BR-07). The Field Museum provided grants that make possible a study visit to Chicago.

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Correspondence to Jun Liu.

Appendices

Appendix I: List of Morphological Characters

The following abbreviations are used to identify authors that previously used a particular character in data matrices: R, (Rowe 1988); W, (Wible 1991); WH, (Wible and Hopson 1993); LL, (Lucas and Luo 1993); L, (Luo 1994); LC, (Luo and Crompton 1994); M, (Martinez et al. 1996); H, (Hopson and Kitching 2001); LCS, (Luo et al. 2001); B, (Bonaparte et al. 2003); S, (Sidor and Smith 2004); MA, (Martinelli et al. 2005), BO, (Bonaparte et al. 2005); SH, (Sidor and Hancox 2006); A, (Abdala 2007). The number following the abbreviation indicates the position of the character in the author’s matrix. Italics indicate that the definition of the character provided by the previous author(s) differs from that provided here. Asterisk indicates that the polarity of the character differs, or current states are part of the original states. A pound sign (#) preceding the character definition indicates that the character is ordered in some analyses.

Rostrum

  1. 1.

    #Premaxillary extranasal process: absent or with very little exposure (0); large but not contacting nasal (1); contacting nasal (2). [R2, W36, L82, M14, A1]

  2. 2.

    Septomaxilla facial process: long, extending far beyond posterior border of external naris (0); short, almost limited in external naris (1). [S1, A2]

  3. 3.

    #Snout in relation to temporal region: longer (0); subequal (1); shorter (2). [A11]

  4. 4.

    Position of paracanine fossa in relation to upper canine: anteromedial (0); medial or posteromedial (1); anterior (2); paracanine fossa absent (3). [A14*]

  5. 5.

    Premaxilla: does not form (0) or does form (1) posterior border of incisive foramen. [M19, H1, B21, BO27, MA24, A13]

  6. 6.

    Maxillary platform lateral to tooth row: absent (0); present (1). [M15, H77, BO15, A23]

  7. 7.

    Maxilla: excluded from (0) or participates in (1) border of subtemporal fenestra. [R15, W14, L62, M16, A21]

Skull roof

  1. 8.

    Profile of skull roof (relationship of sagittal crest with part of skull roof just anterior to it): nearly flat (0); remarkably concave (1); convex (2). [S7, A65]

  2. 9.

    Parietal foramen: present (0); absent (1). [R8, W12, LL34, L64, M31, H7, B24, BO34, MA28, A7]

  3. 10.

    Interparietal (postparietal) in adult: separate bone (0); absent or fused with other bones (1). [R21, W15, LL36, M34]

  4. 11.

    #Lateral expansion of braincase in parietal region: absent (0); moderate (1); well developed (2). [L67, M33]

  5. 12.

    Sagittal crest: does not (0) or does (1) extend posteriorly to reach or closely approach the posteriormost part of the lambdoidal crest.

Orbital region

  1. 13.

    Prefrontal: present (0); absent (1). [R4, W1, M28, H3, B22, BO30, MA25, A4]

  2. 14.

    #Postorbital: present and forms postorbital bar (0); present but does not form postorbital bar (1); absent (2). [R7, W2, LL33, L55, M29, H5, B23, B40, BO31, BO32, MA 50, A6]

  3. 15.

    #Palatine: does not meet frontal (0); meets frontal but neither element contributes significantly to medial orbit wall (1); meets frontal and both elements contribute significantly to medial orbit wall (2). [R6, R31, W17, W37, L56, L60, M24, M30, H23, B29, BO46, MA38, A63]

  4. 16.

    Sphenopalatine foramen: absent (0); present (1). [L57, M26]

Zygomatic arch

  1. 17.

    Dorsoventral height of zygomatic arch as a proportion of skull length: moderately deep (10∼18%) (0); very deep (>18%) (1); slender (<10%) (2). [R16, W40, L54, M39, H18, S5, BO40, MA33, A69]

  2. 18.

    Anteroventral corner of zygomatic arch: lies at same level as (0) or lies significantly higher than (1) postcanine line.

  3. 19.

    Infraorbital process: absent (0); suborbital angulation between maxilla and jugal (1); descending process of jugal (2). [M18, H21, H41, A25, B38, BO29, BO44, MA36, MA46, A70]

  4. 20.

    #Maximum dorsal extent of zygomatic arch: below middle of orbit (0); above middle of orbit but below upper border (1); above upper border of orbit (2). [H19]

  5. 21.

    Maximum posterior extent of jugal along zygomatic arch: near quadratojugal notch of squamosal (0); near squamosal glenoid (1); receding from glenoid (2). [L28]

  6. 22.

    Posteroventral process of jugal: low, forming less than half the height of the zygomatic arch (0); high, forming more than half the height of the zygomatic arch. [H20, BO43, A71]

  7. 23.

    Width of temporal fossa: greatest near middle (0); constant or nearly constant along its length (1); strongly increasing toward the posterior end (2). [H39, BO42, MA44, A74]

  8. 24.

    Squamosal groove for external auditory meatus: an incipient depression (0); deep (1). [M55, H22, B28, S18, BO45, MA37, A73]

  9. 25.

    Posterior extension of squamosal, dorsal to squamosal sulcus in zygomatic arch: incipient (0); well developed (1) [A72]

  10. 26.

    Notch separating lambdoidal crest from zygomatic arch: shallow (0); deep, V-shaped (1). [H43, S17, BO55, A75]

Palatal complex

  1. 27.

    Palatine: excluded from subtemporal border of orbit (0); participates in subtemporal border by displacing pterygoid posteriorly (1). [L58]

  2. 28.

    Vomer exposure in incisive foramen (at anterior ends of maxillae on palate): present (0); absent (1). [M21]

  3. 29.

    Vomer: with (0) or without (1) vertical septum extending posteriorly beyond level of secondary palate. [SH65]

  4. 30.

    Ectopterygoid: present, but does not contact maxilla (0); present and contacts maxilla (1); absent (2). [R32, H9, S15, A20]

  5. 31.

    Interpterygoid vacuity between pterygoid flanges: present (0); absent (1) in adults. [M27, H10, B25, BO35, MA29, A25]

  6. 32.

    Secondary palatal plate on maxilla: does not extend to midline (0); extends to midline (1). [H12, S11, A16]

  7. 33.

    Secondary palatal plate on palatine: does not extend to midline (0); extends to midline (1). [H13, S12, A16]

  8. 34.

    Osseous secondary palate: terminates well anterior to last upper postcanine tooth (0); terminates near or well posterior to last upper postcanine tooth (1). [R30, W16, L68, M23, LCS40, H14, B26, BO36, MA30, A18]

  9. 35.

    #Osseous secondary palate: terminates anterior to (0), at approximately the level of (1), or posterior to (2) anterior border of orbit. [H15, B27, BO38]

  10. 36.

    Anteroposterior extent of osseous secondary palate: 45% of skull length or less (0); more than 45% of skull length (1). [A17]

  11. 37.

    Contribution of palatine to osseous secondary palate: short (less than 1/3 anteroposterior length of osseous secondary palate) (0); long (greater than 1/3) (1) [M22, H40, B37, BO53, MA45, A19]

  12. 38.

    Middle of pterygoid: smooth (0); bears a boss (1); bears a distinct median crest (2). [LL12, L71, A26]

  13. 39.

    Nasopharyngeal roof posterior to transverse process of pterygoid: narrow, deep, forms a ventral keel (0); flat, minimum width greater than half width of transverse process of pterygoid (1).

  14. 40.

    Quadrate ramus of pterygoid: present (0); absent (1). [R38, W47, LC10, M40, H30, B34, BO52, S20, MA43, A30]

  15. 41.

    Quadrate articulation with quadrate ramus of epipterygoid: absent (0); present (1). [LC11, M53, A31]

Basicranium and lateral wall of braincase

  1. 42.

    Frontal-epipterygoid contact: present (0), absent (1). [R39, W48, L61, H35*, S24*, A64*]

  2. 43.

    Epipterygoid ascending process at level of trigeminal foramen: greatly expanded (0); moderately expanded (1). [H32*, B35*, A67*]

  3. 44.

    Anterior part of basisphenoid: narrow (0); wide, and width greater than half width of transverse process of pterygoid (1). [L69, LCS44]

  4. 45.

    Parasphenoid ala (basisphenoid wing): at same level as basicranium (0); ventrally expanded below basicranium (1). [H17, BO39, MA32, A29]

  5. 46.

    #Parasphenoid ala: long, bordering fenestra vestibuli (0); slightly shorter and excluded from fenestra vestibuli, but overlapping entire prootic pars cochlearis (a part of the petrosal) (1); much shorter and overlapping prootic pars cochlearis (2); basisphenoid does not overlap prootic pars cochlearis (3). [R40, W49, L74, M41, M49, LCS37, A28]

  6. 47.

    #Extent of basioccipital overlap on pars cochlearis: covers entire pars cochlearis (0); covers medial side of promontorium (1); no overlapping (2). [LCS38]

  7. 48.

    Internal carotid foramina in basisphenoid: present (0); absent (1). [R42, W50, WH23, LL14, L72, M45, H26, B31, BO48, MA40, A27]

  8. 49.

    Prootic and opisthotic: separate (0); fused at early ontogenetic stage to form petrosal (=periotic) (1). [R51, W5, WH29, L34, BO56, A37]

  9. 50.

    Promontorium: absent (0); present (1). [R52, W6, LL1, L35, LCS9, BO57, A35]

  10. 51.

    Internal auditory meatus: open (0); walled (1). [R53, W7, WH12, L39, M47, H36, B36, A38]

  11. 52.

    #Space for trigeminal ganglion (semilunar ganglion): open ventrally (0); partly floored by prootic (1); completely floored by prootic (2). [W54, A34]

  12. 53.

    Lateral trough floor anterior to tympanic aperture of prootic canal and/or primary facial foramen: absent (0); present (1). [R49, LL6, L43, M44, LCS 15*]

  13. 54.

    Vascular foramen in posterior part of lateral flange (Foramen “X” of Rougier et al. 1992: 205): absent (0); present (1). [LL30, L53, M43, LCS29]

  14. 55.

    Foramen and passage of prootic sinus in lateral trough: absent (0); present (1). [R50, W28, LL3, L45, MA49, BO58, A36]

  15. 56.

    Route of venous drainage from back of cavum epiptericum: only vascular groove on lateral flange (0); absent (1); vascular canal on lateral flange (foramina on lateral surface) (2). [W53, WH22, H27]

  16. 57.

    #Maxillary and mandibular branches (V2+3) of trigeminal nerve exit: via single foramen between prootic and epipterygoid (0); via two foramina between prootic and epipterygoid (1); via separate foramina, some enclosed by anterior lamina of prootic (petrosal) (2). [L50, M48, H28, B33 BO51, S27, MA42, A66]

  17. 58.

    Pterygoparoccipital foramen: squamosal does not contribute to enclosure of foramen (0); squamosal contributes to enclosure of foramen (1); open as a notch (2). [LL23, L51]

  18. 59.

    Lateral flange of prootic: lacks vertical component (0); includes vertical component, so that flange is L-shaped and forms vertical wall adjacent to pterygoparoccipital foramen. [L52, LCS25]

  19. 60.

    Anterior part of paroccipital process: lateral aspect covered by squamosal (0); lateral aspect exposed due to dorsal withdrawal of squamosal (1). [L47, LCS22]

  20. 61.

    Hyoid (stapedial) muscle fossa on paroccipital process: absent (0); present (1). [R55, W56, WH35, LL7, L40, M59, LCS32, MA48, BO61, A39]

  21. 62.

    Paroccipital process: undifferentiated (0); differentiated into a posterior process and a bulbous anterior process (1); differentiated into mastoid and quadrate processes (2). [R56, W18, L46, L47, M50, LCS21, LCS30, BO66, A44*]

  22. 63.

    Fenestra rotunda and jugular foramen: confluent (0); completely and widely separated (1). [R60, W29, LL10, L42, M46, HK42, LCS33, B39, BO60, A41]

  23. 64.

    Paroccipital process: does not contact quadrate (0); contacts quadrate (1). [R19, W41, M52, H29, A33]

Occipital region

  1. 65.

    Paroccipital process in base of posttemporal fossa: absent (0); present (1). [H24, A45]

  2. 66.

    Tabular: present (0); absent (1). [R22, LL19, L80, LCS 47]

  3. 67.

    Relationship of hypoglossal foramen (condylar foramen) with jugular foramen: confluent or sharing a depression (0); at least one foramen completely separated from jugular foramen (1). [LL11*, L75*, M51*, LCS39*, BO65]

  4. 68.

    Shape of occipital condyles (in lateral view): bulbous (0); ovoid to cylindrical (1). [LL15, L77, LCS51]

Craniomandibular joint

  1. 69.

    Rotation of dorsal plate relative to trochlear axis of quadrate: small (less than 10 degrees) (0); about 45 degrees (1); around 90 degrees (2); parallel to trochlear axis (3). [L30, LC1]

  2. 70.

    Contact facet on posterior side of dorsal plate of quadrate: flat or convex (0); concave (1). [L29, LC2, M56]

  3. 71.

    Trochlear condyles of quadrate: lateral condyle larger than medial condyle (0); medial condyle at least as large as lateral condyle (1). [LC3]

  4. 72.

    Shape of trochlea of quadrate: cylindrical (0); trough-shaped (1). [LC4]

  5. 73.

    #Lateral margin of dorsal plate of quadrate: straight (0); flaring posteriorly (1); flaring and rotated posteromedially (2). [LC5]

  6. 74.

    #Medial margin of dorsal plate of quadrate: straight (0); flaring anteriorly (1); flaring and rotated anterolaterally (2). [LC6]

  7. 75.

    Dorsal margin of dorsal plate of quadrate: with a pointed dorsal process (“dorsal angle”) (0); rounded (1) [L31, LC7]

  8. 76.

    #Lateral notch and neck of quadrate (separating lateral margin of contact facet from trochlea): lateral notch absent or poorly developed (0); lateral notch developed, separating lateral margin of contact facet from lateral end of trochlea (1); lateral notch broader, separation of lateral margin of contact facet from trochlea wider, lateral margin shifted medially (2); neck developed, displacing contact facet away from trochlea (3). [L32, LC8]

  9. 77.

    Articulation of quadrate with squamosal: via an anteriorly open and concave recess in the squamosal (0); anteriorly open squamosal recess is absent (1); quadrate having little or no contact with the squamosal (2). [WH7, LC12, M54, H31, A61]

  10. 78.

    Articulation of quadrate with stapes: via broad recess on medial margin and medial end of trochlea (0); stapedial contact restricted to medial end of trochlea (1); via projection from medial margin of dorsal plate (2); via medial vertical ridge on neck of quadrate (3); via projection from neck of quadrate (4). [R20, W42, L33, LC14]

  11. 79.

    Craniomandibular articulation: quadrate/articular (0); primarily quadrate/articular, secondarily surangular/squamosal (1); incipient dentary/squamosal (2); primarily dentary/squamosal (3). [R66, R67, W9, W60, L23, L24, M60, H25, LCS 70, B30, S19, BO26, MA39, A59]

  12. 80.

    Craniomandibular articulation: around dorsoventral level of postcanine line (0), much lower than postcanine line (1); much higher than postcanine line (2). [L25, A60].

  13. 81.

    Squamosal articular surface for mandible: absent (0); formed by small and medially or anteromedially facing facet (1); wide glenoid cavity directed approximately ventrally (2). [L26, B19, BO37, MA22, A58]

Mandible

  1. 82.

    Dentary symphysis: unfused (0); fused (1). [R68, W10, L19, LCS56, H44, B17, S34, BO21, MA21, A62]

  2. 83.

    #Lateral crest of dentary: absent (0); incipient (1); moderately developed (2); strongly projecting (3). [A48]

  3. 84.

    Angle of dentary: close to anteroposterior position of postorbital bar (0); close to jaw joint (1). [A55]

  4. 85.

    Anteroposterior position of dorsal contact between dentary–surangular, relative to postorbital bar and jaw joint: around midway between these landmarks (0); closer to jaw joint (1). [H48, A56]

  5. 86.

    Inner side of coronoid process (including coronoid bone): relatively thin (0); mediolaterally thick (1). [M66, H50, A52]

  6. 87.

    Splenial: large and deep, reaches ventral border of dentary (0); thin splint covering dentary groove (1). [M64]

  7. 88.

    #Postdentary bones: large, including tall surangular (0); angular, surangular, and prearticular medium in height and lying in dentary groove (1); single gracile rod in postdentary trough (2). [R74*, W59*, M65*, H49*]

  8. 89.

    Posterior extent of reflected lamina of angular: greater than 1/2 distance from angle of dentary to jaw joint (0); less than l/2 this distance (1). [H51]

  9. 90.

    #Reflected lamina of angular in lateral view: spoon-shaped plate bearing slight depressions (0); hook-like lamina (1); thin process (2) [M62, H52, S44, A57*]

  10. 91.

    Mandibular movement during occlusion inferred from wear facets: orthal movement during power stroke (0); posteriorly directed power stroke (1); moderate rotation along longitudinal axis during power stroke (2). [R79, W62, L2, LCS74*, B2, BO2]

Dentition

  1. 92.

    Postcanine occlusion: no consistent pattern of contact between upper and lower tooth rows (0); bilateral, interdigitating occlusion between multiple cusps (1); precise unilateral occlusion (2) [R84, R86, W33, L1, L14, M8, LCS 73, LCS 81, B1, BO1, MA1, A88]

  2. 93.

    Wear facets on postcanines: absent (0); simple longitudinal facet present on crown (1); main cusp bears two distinct facets (2); multiple cusps each bear one or two transverse and crescentic facets (3). [L17, B16, MA19, BO20]

  3. 94.

    Number of upper incisors: five or more (0); four (1); three or less (2). [R81, W63, L5, M1, H53, B3, S45, BO3, MA3, A76]

  4. 95.

    Number of lower incisors: four or more (0); three (1); two or less (2). [L5, M2, H54, B4, S46, BO4, MA4, A78]

  5. 96.

    Incisors: all small (0); some or all large (1). [H56, B5, B6, BO5, MA5, MA6, MA7, A79]

  6. 97.

    Incisor cutting margins: smoothly ridged (0); serrated (1); denticulated (2). [H55, A80]

  7. 98.

    Distinct diastema between upper incisor and canine: present (0); absent (1). [A82]

  8. 99.

    Upper canine: large (0); small (height <10% of skull length) (1); absent (2). [L6, H57, A84]

  9. 100.

    Lower canine: large (0); small (1); absent (2). [L6, H58, A85]

  10. 101.

    Canine serrations: absent (0); present (1). [H59*, A86*]

  11. 102.

    Upper postcanine: sectorial, lacking cingulum or with incipient lingual cingulum (0); sectorial, with well-developed lingual cingulum (1); bucco-lingually expanded (2). [L13, M5, M9, H60, H62, A7, S51, S55, B10, BO8, A90]

  12. 103.

    #Single-cusped tooth as anteriormost postcanine: present in juveniles and adults (0); present only in juveniles (1); absent (2).

  13. 104.

    #Gomphodont tooth as posteriormost postcanine: absent (0); absent in juveniles but present in adults (1); present in both juveniles and adults (2). [H80]

  14. 105.

    Main cusps of posterior postcanine teeth: not strongly curved (0); strongly curved (1). [S52, A91]

  15. 106.

    Upper postcanine roots: single (0); divided into two longitudinally aligned roots (1); multiple roots (more than two) (2). [R88, W65, W66, L9, M6, LCS77, B8, BO6, MA9, A96]

  16. 107.

    Lower postcanine roots: single (0); divided (1). [R88, W65, L9, M7, B8, BO6, MA9, A95]

  17. 108.

    Buccal (external) cingulum on sectorial upper postcanines: absent (0); present (1). [R85, H61, B9, BO7, MA10, A92]

  18. 109.

    Transverse crest in upper postcanines: absent (0); present with two cusps (1); present with three or more cusps (2) [H63, A93]

  19. 110.

    Position of transverse row of upper postcanines: midcrown (almost to posterior margin) (0); on anterior half of crown (1); at posterior margin of crown (no posterior cingulum) (2). [H64*]

  20. 111.

    Central cusp of transverse row of upper postcanines: absent (0); midway between buccal and lingual cusps (1); closer to lingual cusp (2). [H65]

  21. 112.

    Alignment of main cusps of upper postcanines: single longitudinal row (0); multiple cusps in multiple rows (1). [L13, LCS78]

  22. 113.

    Contacts between adjacent lower postcanines: simple, with no interlocking (0); distal cuspule of anterior molar fits into embayment between cusps of succeeding molar (1). [L11, B14, BO18]

  23. 114.

    Number of cusps in transverse row of lower postcanines: two (0); three or more (1). [H73]

  24. 115.

    Lingual cingulum on lower postcanine: present (0); vestigial or absent (1) [L12, LCS80, B11, B12, BO9, BO10, S56, A94]

  25. 116.

    Lower posterior basin: absent (0); present (1). [H75]

  26. 117.

    Axis of posterior part of maxillary tooth row: directed lateral to subtemporal fossa (0); directed toward center of fossa (1); directed toward medial rim of fossa and diverged curved (2); directed toward medial rim of fossa and straight (3). [R80, M12, H78, B13, MA17, MA20, BO14, BO16, BO17, A87]

  27. 118.

    Posterior end of upper tooth row: below orbit and anterior to subtemporal fenestra (0); anterior to orbit (1); posterior to anterior border of subtemporal fenestra (2). [H79, A76]

  28. 119.

    Postcanine replacement pattern: alternating (0); delayed (1); sequential addition of postcanines, no replacement (2). [L7, H81, LCS89, B7]

Postcranial skeleton

  1. 120.

    Vertebral centra: amphicoelous (0); platycoelous (1). [R108, H101, B51, BO78, MO61]

  2. 121.

    Axial centrum: cylindrical (0); depressed (1). [R98]

  3. 122.

    Dens: absent or vestigial (0); strongly developed (1) [R99]

  4. 123.

    Posterior thoracic vertebrae (or mid-dorsal vertebrae): neural spines nearly vertical or slightly inclined (0) or strongly inclined (1). [R102]

  5. 124.

    Anapophysis: absent (0); present (1).

  6. 125.

    Expanded costal plates on dorsal ribs: absent (0); present (1). [H82]

  7. 126.

    The ridge on lumbar costal plates overlapping preceding rib: absent (0); present (1). [H83]

  8. 127.

    #Acromion process: absent (0); weakly to moderately developed (1); strongly developed and close to level of glenoid (2). [R115*, H85*]

  9. 128.

    Scapular constriction below acromion: absent (0); present (1). [H86]

  10. 129.

    Scapular elongation between acromion and glenoid: absent (0); present (1). [H87, B41, BO68, MO51]

  11. 130.

    Procoracoid contribution to glenoid fossa: present (0); barely present or absent (1). [R116, H88, B42, BO 71, MO52]

  12. 131.

    Procoracoid contact with scapula: longer than coracoid contact (0); equal to or shorter than coracoid contact (1). [H89, B43, BO72, MO53]

  13. 132.

    Ectepicondylar foramen in humerus: present (0); absent (1). [R124, H90, B44, BO73, MO54]

  14. 133.

    Olecranon process of ulna: unossified or poorly ossified (0); well ossified (1). [R128, H91, B45, MO55]

  15. 134.

    Number of phalanges present in manual digit III: four (0); three (1). [H92]

  16. 135.

    Number of phalanges present in manual digit IV: four (0); three (1). [H93]

  17. 136.

    Dorsal profile of ilium in lateral view: strongly convex (0); straight to concave (1). [R130, H96, B48, BO75]

  18. 137.

    Length of anterior process of ilium anterior to acetabulum: less than 1.5 times diameter of acetabulum (0); greater than 1.5 times diameter of acetabulum (1). [H94*, B46*, BO74, MO56*]

  19. 138.

    Lateral surface of iliac blade: concave or nearly flat (0); convex (1); divided by longitudinal ridge into dorsal and ventral portions (1). [R131]

  20. 139.

    Posterior iliac spine: robust and extends beyond acetabulum (0); small nub that lies entirely anterior to acetabulum (1). [R132, R133]

  21. 140.

    Cotyloid (acetabular) notch: lies between ischial and iliac parts of acetabulum, but mainly on ilium (0); lies entirely on ischium, between acetabular facet and pubic process (1). [R134]

  22. 141.

    Diameter of obturator foramen: less than or equal to that of acetabulum (0): greater than that of acetabulum (1). [R139]

  23. 142.

    Head of femur: rounded and predominantly in plane of shaft (0); subspherical and inflected dorsally (1). [R141]

  24. 143.

    Greater trochanter of femur: continuous with femoral head (0); separated from femoral head by distinct notch (1). [R143, H98, B49, BO76, MO59]

  25. 144.

    Lesser trochanter: on ventromedial surface of femoral shaft (0); on medial surface of femoral shaft (1). [R144*, H100, B50, BO77, MO60]

  26. 145.

    Lesser trochanter: far distally from femoral head (0); near level of femoral head (1). [BO80, MO63]

Appendix II. Data Matrix

Distribution of the character-states for the characters listed in Appendix I among 31 taxa considered in this analysis. A=0&1, B=1&2, a=0/1, b=1/2. ?=unknown, dash=inapplicable

  1 11111111112 2222222223 33333333334 4444444445 5555555556 6666666667 7777777778
  1234567890 1234567890 1234567890 11234567890 1234567890 1234567890 1234567890 1234567890
Procynosuchus delaharpeae 0000000100 0000000000 0000000000 0000000000 0000000000 0000000000 0001A00000 0000000000
Galesaurus planiceps 0100000000 0000000010 0000100001 1000000000 0000000000 0000000000 0000000000 0000000100
Thrinaxodon liorhinus 01A0000000 0000000000 0000000000 1110000000 0000000000 0000000000 0000000000 0010010100
Platycraniellus elegans 0110000000 0000000011 0000000001 0110000000 ??00000000 ?000000000 0000000000 101??10100
Cynognathus crateronotus 0000000000 0000001021 0021100000 1110000101 1100010100 ?000000000 0000100000 1110010110
Diademodon tetragonus A000000000 0000001022 0121110001 1110000001 1100010100 000000A000 0000000000 0010010111
Trirachodon berryi 11100100A0 0000001121 0111110100 1110100201 1100010100 0000021000 0000000011 0111020110
Sinognathus gracilis 1020?10010 0000??1101 0011110?1? 1?1010?001 1000010100 ???????000 00?000?011 0111020110
Langbergia modisei 0010000000 0000000121 0111110100 1110100001 10000101?0 ?000?21??0 000000001? 0?11????10
Pascualgnathus polanskii 1020?10010 0000001122 012111011? 1110100001 ??000101?0 ???0?2?000 00???0?0?? ????????a0
Luangwa drysdalli ??00?1000? 0000010121 001111???? 1110?00001 ???0010100 0000?2??00 000???0??? ????????10
Massetognathus pascuali 0111110010 0000001101 0111110112 1110200001 0000010100 0000121100 0000000011 0111020110
Exaeretodon argentinus 0011111010 0000111121 0121110112 11101A0001 0?00010100 0100021100 00000000?1 01????0110
Scalenodon angustifrons ??10?1?000 0000??1101 012111???? ?1101?0??1 ??00010100 ?000021100 0000?000?? 0?????0?a0
“Scalenodon” hirschoni ???0010??? ??001?11?? ???1110112 11101?0?0? 0??00????? ???????1?0 00?0?????1 ??1?0?0?a?
Chiniquodon theotonicus 1110101010 0000101011 000001011B 1111211001 1000010100 0000010000 00000000?1 ?01???1110
Lumkuia fuzzi ??10001010 00000?0000 0000010?12 0110100101 0100010010 ?000000100 0000000000 0010000110
Ectenion lunensis 001??00210 0000200000 0000000?1a 1110000201 1100010100 ?100010100 0000000011 0011021110
Probainognathus jenseni 0110100210 0000100101 1000010112 1111101001 1100010000 0000110000 0000000011 0011021110
Prozostrodon brasiliensis 11?010?2?? ??0121?1?? ???????11? ?1111?1??? ?????????? ?????????? ?????????? ??????????
Therioherpeton cargnini ?????0?21? 11122?2100 ??0??????? ?1111????? ?????????? ?????????? ?????????? ??????????
Riograndia guaibaensis 0113101211 111221?1?? ??000??112 0111211011 0001020000 ?000010200 0010001121 102?13????
Pachygenelus monus 2013101211 1112212100 1000000112 0111211011 0001020000 1000010200 00101??121 1022131320
Brasilodon quardangularis a00??01211 1112212000 1000?00?12 011121?211 0001021001 ?0?112220? 0011101121 1022131320
Tritylodon longaevus 102-111111 0112211102 0011110112 1110211211 0000110110 1101021211 1101101031 1022031202
Oligokyphus major b??-1111?1 0112???102 010110?1?2 ?1??21???? ????110?10 110102?211 1101100031 0022031202
Bienotherium yunnanense 102-111111 01122111?2 01?1110112 1110211211 0000110110 110?02?011 11?110?031 ??22131?02
Kayentatherium wellesi 102-11111? 0112211102 0111111112 0110211211 0000110110 1101021211 11?110?031 1022131202
Adelobasileus cromptoni ???????011 21?2?????? ?????????? 0??????211 0001021011 ?211122100 00101110?? ??????????
Sinoconodon rigneyi 0002?01011 2112212000 1000?01?12 1111211211 0011031011 ?211122210 11101010?? ??????0?30
Morganucodon oehleri 0?02?01011 2112212000 2?00001111 1111211211 0011032011 1211122201 1211111121 1022132430
  8888888889 1 1111111111 1111111111 1111111111 1111111111 11111
  1234567890 9999999990 0000000001 1111111112 2222222223 333333333 44444
   1234567890 1234567890 1234567890 1234567890 41234567890 12345
Procynosuchus delaharpeae 0000000100 0000000100 010000000- -00-000000 0000000-0 0000000000 00000
Galesaurus planiceps 0010000000 0001100100 000010000- -00-100000 0001100??? ?00??0??00 00000
Thrinaxodon liorhinus 0010000011 0001100000 010000000- -00-100000 0001100-0 0000000000 ?0000
Platycraniellus elegans 0?1010?0?? 0001?0?100 000000000- -0?-0?000? ?????????? ?????????? ?????
Cynognathus crateronotus 1120101112 0001101000 100010000- -00-100100 0000111000 0001100000 00000
Diademodon tetragonus 1120101112 1131101000 1200100010 0100?00010 0001111000 0001100000 00000
Trirachodon berryi 1110101112 1131101000 1211100020 110100101? ??01111000 000????000 00000
Sinognathus gracilis 11101011?? 1131200000 02?0?00?20 1100?0201? ?????????? ?????????? ?????
Langbergia modisei 1110101112 1131101000 1200100020 110100101? ????1????? ?????????? ?????
Pascualgnathus polanskii ?1201011?? 1132100000 02bb000-11 0100-12010 ???1101??0 000??10000 00000
Luangwa drysdalli 11201011?? 1131101000 12bb000-20 2100-12010 ???1101100 00???11000 00000
Massetognathus pascuali 11B01011?? 1131102111 0211000-22 2100-12010 0000101101 000??11000 00000
Exaeretodon argentinus 11211011?? 1132110101 02bb000-12 0100-12210 0000001101 0011111000 00000
Scalenodon angustifrons ?12??011?? 1131101000 12bb000-20 2100-1201? ?????????? ?????????? ?????
“Scalenodon” hirschoni ?1???011?? 1132210010 02bb000-22 2100-1201? ?????????? ?????????? ?????
Chiniquodon theotonicus 1120101112 0001100000 000010000- -00-100000 ??00001101 0001110000 ?0000
Lumkuia fuzzi 1120100012 0001100000 000010000- -00-10000? ????001??? ?????????0 ?????
Ectenion lunensis 11001011?? 0001100000 1a0010000- -00-?00000 ???1??110? ?0?????0?? ?????
Probainognathus jenseni 2100101112 0001100000 010000000- -00-001100 00?000110? ??0??11000 ?0000
Prozostrodon brasiliensis ?0301111?? 0000000000 110000000- -00-001000 ???000???? ?0???11111 10000
Therioherpeton cargnini ?????????? 000??????? ?0?0?0000- -00-?00000 ??1?00???? ?????11111 10011
Riograndia guaibaensis 00301111?? 0012110011 00b000000- -00-10100? ?????????? ?????????? ?????
Pachygenelus monus 2030111112 0012210010 001000010- -00-002001 ???0001111 101??11111 11111
Brasilodon quardangularis ?0301111?? 0011100?01 011000010- -01-00101? ?????0111? ?11??????? ?????
Tritylodon longaevus 00311111?? 1132210-22 -222-21-2- 1100-03221 ??????210? ?????1???? ?1111
Oligokyphus major 00311111?? 1132110-22 -222-21-2- 1100-03221 11100?2101 111??11211 11111
Bienotherium yunnanense 00311111?? 1132110-22 -222-21-2- 1100-03221 ??????210? ?11??????1 11111
Kayentatherium wellesi 0031111112 1132110-22 -222-21-2- 1100-0322? 1110002101 1?1111121? ?1111
Adelobasileus cromptoni ?????????? ?????????? ?????0???? ?0??1????? ?????????? ?????????? ?????
Sinoconodon rigneyi 20301112?? 2001000001 001001110- -00-10101? ?????????? ?????????? ?????
Morganucodon oehleri 2030111212 2221000001 011001110- -01-001011 1111001111 111??11211 11111

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Liu, J., Olsen, P. The Phylogenetic Relationships of Eucynodontia (Amniota: Synapsida). J Mammal Evol 17, 151–176 (2010). https://doi.org/10.1007/s10914-010-9136-8

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Keywords

  • Phylogeny
  • Eucynodontia
  • Tritheledontidae
  • Tritylodontidae
  • Traversodontidae
  • Mammal