152 



C.A. MARSICANO AND A. WARREN 



1966. Cosgriff & Zawiskie 1979), Pneumatostega potamia (Cosgriff 

 & Zawiskie 1979), Acerastea wadeae (Warren & Hutchinson 

 1 987) and Trucheosaurus major. The lydekkerinid taxa Lydekkerina 

 (Parrington 1948) and Chomatobatrachits (Cosgriff 1974) and the 

 family Trimerorhachidae (Broom 1913, Olson 1955) were consid- 

 ered as outgroups, taking into account previous cladistic analyses of 

 the Temnospondyli (Milner 1990, 1991). All terminal taxa used in 

 the analysis were examined by one or both of the authors. The taxon- 

 character state matrix (Table 1 ) and character list are included in the 

 Appendix. 



Discussion. The incorporation in the analysis of several taxa 

 represented by poorly preserved specimens greatly increased the 

 instability of the resultant cladogram, and thus the number of 

 equally parsimonious trees. Under these circumstances, four taxa 

 were excluded from the analysis, reducing the number of terminals 

 to twelve. Taxa excluded were: Mahavisaurus sp., Pneumatostega 

 potamia, Acerastea wadeae and Trucheosaurus major, and their 

 relationships are discussed separately. Accordingly, the phylogenetic 

 results are based on an analysis of 18 characters and 12 terminal 

 taxa, using Swofford's (1993) PAUP 3.1. The branch-and-bound 

 search algorithm resulted in 5 1 equally-parsimonious trees with a 

 tree length of 23 steps (CI = 0.83 and RI = 0.89). Fig. 7 depicts the 

 strict consensus tree, showing the consistent nodes among the 51 

 trees. 



The monophyletic group (Indobrachyops + (Boreopelta + 

 Dementia + Laidleria + Peltostega + (Rhytidosteus + Deltasaurus) 

 + Rewana + Arcadia)), that we consider the family Rhytidosteidae 

 (Fig. 7, node 1 ), is supported by the following eight unequivocal syn- 

 apomorphies: orbits located close to the skull margin ( 1 ); otic notch 

 reduced or absent (3): tabular horns reduced or absent (4); straight 

 posterior margin of the palate (7); otic flange absent (8); 'pockets' on 

 the parasphenoid absent (11); cultriform process of the para- 

 sphenoid broad and flat ( 14) and exoccipital condyles horizontally 

 elongated ( 1 6). Two further derived character states of this clade are: 

 the presence of a 'twisted' quadrate ramus of the pterygoid (10), and 

 a reduced palatal tooth row (17), although the former reverses in 

 Derwentia and the latter reverses in Peltostega and Laidleria. The 

 derived condition of character 1 8 ( presence of shagreen on all bones 

 of the palatal series) has long been used as a diagnostic family 



character (Cosgriff & Zawiskie 1979, Warren & Black 1985, Warren 

 & Hutchinson 1987. Shishkin 1994). In the present analysis, this 

 derived character state justifies a more inclusive group which includes 

 theTasmanian 'lydekkerinid' Chomatobatrachus . Moreover, among 

 rhytidosteids, the shagreen is reduced in Derwentia and apparently 

 absent in Laidleria. The condition present in Indobrachyops for 

 characters 7, 8 and 16 is unknown, and their derived states might 

 justify a less inclusive group excluding Indobrachyops. Within 

 Rhytidosteidae, Indobrachyops is the sister group of an unresolved 

 clade which includes all the remaining rhytidosteid taxa: (Boreopelta 

 + Derwentia +Laidleria +Peltostega + {Rhytidosteus +Deltasaurus) 

 + (Rewana + Arcadia)) (Fig. 7, node 2). This monophyletic group is 

 justified by two unequivocal derived character states: skull sculpture 

 with nodules or pustules (5) and lachrymal bone absent (6), although 

 the condition present in Boreopelta and Peltostega for the latter is 

 unknown. Another synapomorphy of this clade is equivocal: the 

 condition of a contact between the palatine and vomer lateral to the 

 choana (15), which is unknown in Rewana, Boreopelta and 

 Peltostega, and reverses in Derwentia and Arcadia. Within the clade, 

 the sister-taxon relationship between the South African Rhytidosteus 

 and the Australian Deltasaurus (Fig. 7, node 3) is justified by the 

 derived condition of characters 12 (exoccipital-pterygoid suture 

 visible in palatal view) and 17 (palatal tooth row absent). Also, the 

 Australian taxa Rewana and Arcadia form a clade (Fig. 7, node 4), 

 justified by the presence of a strikingly low ascending ramus of the 

 pterygoid (9) and the presence of the quadrate condyles well behind 

 the occipital ones (13). It is important to remark that the Australian 

 taxa Arcadia, Rewana and Derwentia share the derived condition of 

 character 2 (the orbits in the anterior half of the skull table ): however, 

 as the presence of this condition is unknown in some of the members 

 of the in-group (Boreopelta and Peltostega), it appears in the analy- 

 sis as an equivocal synapomorphy of the (Rewana + Arcadia) clade. 

 Although not included in the analysis, the taxa Mahavisaurus, 

 Pneumatostega, Acerastea and Trucheosaurus are considered 

 rhytidosteids and in a more derived position than Indobrachyops. 

 This position is supported by the presence in those taxa of a skull 

 sculpture with nodules or pustules, and the absence of lachrymal 

 bones. Both Acerastea and Trucheosaurus appear to be more closely 

 related to the other Australian taxa through the presence of the orbits 

 in the anterior half of the skull, a condition especially marked in 





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Fig. 7 Strict consensus cladogram of 5 1 equally parsimonious trees. 



