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Character states of edaphosaurids used to construct the phylogenetic hypotheses in Figure 15.

Character states for Gordodon

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
1 0 0 1 0 1 0 2 1 0 1 1 1 1 1 1 1 1 ? ?

Character descriptions

All characters taken from Mazierski and Reisz (2010), which was based on a data matrix developed by Modesto (1995). Corrections and modifications are noted below:

1. Marginal teeth: taper gradually (0) or slightly bulbous (1). The marginal teeth of Gordodon are slightly swollen near their tips (1).

2. Marginal teeth: cutting edges absent (0) or present (1) on mesial and distal surfaces. No indications of cutting edges are visible on the marginal teeth of Gordodon (0).

3. Premaxillary dentition: larger than (0) or equal to or smaller than maxillary teeth (1) in basal cross section. The greatly enlarged premaxillary teeth of Gordodon are unique among basal synapsids (0).

4. Caniniform region: present (0) or absent (1). No caniniform (or indeed, any) teeth are present in the anterior maxilla of Gordodon (1).

5. Caniniform tooth: absent (0) or present (1). The states for characters 4 and 5 are confusingly described as the reverse of each other in previous edaphosaur studies. Modesto (1995) listed this character as absent (0) or present (1) but coded his matrix oppositely. Mazierski and Reisz (2010) corrected the coding for all taxa except Edaphosaurus novomexicanus, which they coded as possessing a caniniform tooth (1). Our examination of the holotype of E. novomexicanus found no indication of a caniniform tooth, and we have coded it as absent (0) in this study.

6. Maxilla: long, extends past orbit (0) or short, does not extend past orbit (1). The maxilla of Gordodon stops beneath the middle of the orbit (1).

7.Maxillary and dentary alveolar ridges: straight (0) or twisted (1). Although the posterior maxillary teeth of Gordodon are pushed outward slightly from being compressed against the underlying dentary, there is no indication of the twisted alveolar tooth row that is present in Edaphosaurus (0).

8. Maxillary dentition: 30-40 tooth positions (0), 20 to 30 tooth positions (1), or less than 20 tooth positions (2). Gordodon and Edaphosaurus have a comparable number of maxillary teeth (<20), although the teeth of Gordodon are proportionally smaller and limited to the posterior half of the maxilla (2).

9. Prefrontal: ventral process tongue-like (0) or expanded medially (1). The ventral process of the prefrontal extends medially into the orbit in Gordodon (1).

10. Frontal: lateral lappet broad (0) or narrow (1). In Gordodon, a broad lappet of the frontal extends laterally between the pre- and postfrontals to make up ~25% of the dorsal margin of the orbit (0).

11. Supraorbital margin: interorbital width less than the frontal sagittal length (0) or expanded laterally (1). As in Edaphosaurus, the supraorbital bones extend laterally beyond the orbit in Gordodon (1).

12. Parietal: in dorsal view, lateral margin is straight or convex (0) or concave (1). Concave in Gordodon (1).

13. Postorbital: contacts squamosal (0) or separate from squamosal (1). The postorbital does not contact the squamosal in Gordodon (1).

14. Quadratojugal: large, forming the ventral margin of the posterior cheek (0) or small, covered laterally by the squamosal (1). The quadratojugal appears to be a small element in Gordodon (1).

15. Quadrate: separate, distinct condyles (0) or broad, saddle-shaped articular surface (1). The articular surface of the quadrate is saddle-shaped in Gordodon (1).

16. Jaw suspension: level with maxillary tooth row (0) or offset ventrally from maxillary tooth row (1). The jaw suspension in Gordodon is offset ventrally, although not as dramatically as is seen in Edaphosaurus (1).

17. *Skull: Length greater than 30% of presacral length (0) or less than 25% of presacral length (1). Mazierski and Reisz (2010) compared skull length to dorsal vertebrae for this character: eight or more dorsal centra in length (0) or five or fewer dorsal centra in length (1). The skull of Gordodon measures 6-7 dorsal centra in length and we opted to use the skull length character from Benson (2012) (1).

18. *Postorbital region: shorter than antorbital region (0), equal to antorbital region (1), longer than antorbital region (2). As in characters 17 and 22, Gordodon occupies a transitional state between the states described in Mazierski and Reisz (2010). We replaced it with the 3-state character used by Benson (2012) (1).

19. Pterygoid: transverse flange present (0) or absent (1). Obscured in Gordodon (?).

20. Pterygoid: palatal ramus ≥ 2x longer than quadrate ramus (0) or < 2x length of quadrate ramus (1). Obscured in Gordodon (?).

21. Occluding palatal and mandibular tooth plates absent (0) or present (1). Although the palatal tooth plates are obscured in Gordodon, we infer their presence from the mandibular tooth plate visible on the left jaw (1).

22. *Mandible: dorsoventral height:length less than .26 (0), greater than .3 (1). As in characters 16 and 17, this character in Gordodon is in between the two states described in Mazierski and Reisz (2010). The comparable character from Benson (2012) is used here (1).

23. Dentary: 70% or more of total jaw length (0) or 66% or less of total jaw length (1). The dentary is relatively long in Gordodon (0).

24. Splenial: lateral exposure 1/5 or less of total anterior jaw height (0) or 1/3 or more total anterior jaw height (1). The splenial makes up approximately 1/3 of the total anterior jaw height in Gordodon (1).

25. Cervical centra: length ≥ mid-dorsal centra length (0) or shorter than mid-dorsal centra (1). The length of the cervical centra is subequal to the length of the dorsal centra in Gordodon (0).

26. Presacral neural spines: short (0) or long (more than 5x centrum height) (1). Long in Gordodon (1).

27. Presacral neural spines: centrum length: neural spine height ratio is less than 1:5 (0), 1:6 to 1:12 (1), or 1:13-1:20 (2). Extremely long in Gordodon (2).

28. Presacral neural spines: laterally compressed in distal cross section (0) or subcircular (1). Although the neural spines in Gordodon are laterally compressed, it is unclear how much of this is due to post-mortem crushing. Additionally, we interpret this character as differentiating between rod-like and blade-like neural spines, and the proportions of the neural spines of Gordodon are more rod-like (1).

29. Presacral neural spines: lateral tubercles absent (0); moderately sized (1); or large, gall-like (2). The lateral tubercles of Gordodon are among the smallest known for any edaphosaur (1).

30. Presacral neural spines: anterior spines are slender (0) or club-shaped (1). None of the neural spines of Gordodon show the club-shaped morphology seen on the anterior spines of E. cruciger and E. pogonias (0).

31. Neural arches: possess lateral excavations (0) or no excavations (1). No lateral excavations are visible on the neural arches of Gordodon (1).

32. Dorsal vertebrae: moderately developed transverse processes (0) or elongate transverse processes (1). The right transverse processes on the dorsal vertebrae are too heavily eroded in NMMNH P-70796 to determine their extent (?).

33. Sacral/caudal vertebrae: neural spine tips smooth (0) or rugose (1). Unknown in Gordodon (?).

34. Sacral/caudal vertebrae: smooth spines (0) or spines with longitudinal ridges (1). Unknown in Gordodon (?).

35. Caudal vertebrae: neural spines rectangular in lateral view (0) or wider distally (1). Unknown in Gordodon (?).

36. Caudal vertebrae: neural spines short and square (0) or long and pointed (1). Unknown in Gordodon (?).

37. Dorsal ribs: curved proximally only (0) or curved throughout their length (1). Although only the proximal portion of the anterior ribs are known for Gordodon, these are relatively straight and there is no indication of the barrel-like curvature seen in Edaphosaurus (0).

38. Dorsal ribs: flange-like tubercles (0) or low tuberosities (1). The articular facets of the right ribs have been eroded from NMMNH P-70796 and the tubercula on the left side of the body are obscured beneath the vertebrae (?).

39. Ilium: anterodorsal process smaller than posterodorsal process, convex (0) or longer, triangular (1). Unknown in Gordodon (?).

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