IB, 3.12, AND 3.14, AND FIGURE 3.10A (CHAPTER 3)

This character was adopted from Maisey 2001 (C22) where is was scored as [?]. New evidence from NMS 2001.7.3 indicates that the notochord o f Acanthodes did extend anteriorly through the parachordal region to at least the anterior tip o f the basioccipital, therefore, in the cladistic analysis this character has been scored with [0] fox Acanthodes.

(38) Endolymphatic duct foramina directed: dorsally (0), or posteriorly (1). PLATES 3.1 A, 3.2 TO 3.3, AND FIGURES 3.1, 3.3B (CHAPTER 3)

Evidence provided by the posterior portion o f the dorsal ridge coupled with the interior endolymphatic duct canals of the endocranial roof strongly suggests that the endolymphatic ducts in Acanthodes (see NMS 2001.7.1 and 5) were indeed posteriorly directed. This character was modified from Coates and Sequeira 2001a (C73); 2001b (C73); also compare my character statement with Maisey 2001 (C8). Endolymphatic duct

(39) Statoliths: absent (0), or present (1).

FIGURE 5.5A-B

Statoliths have only been observed in acanthodid acanthodians, (e.g. Acanthodes spp., Triazeugacanthus, Homalacanthus, and Mesacanthus (for a more comprehensive list o f taxa with statoliths preserved see Sahney and Wilson 2001: 661) which share this character with primitive actinopterygians (e.g. Mimia). The presence o f statoliths have never been reported for the two remaining traditional acanthodians orders (i.e. Climatiiformes or

Diplacanthiformes). Janvier (1996: 242) used the presence o f Targe otoliths, or statoliths’ as evidence supporting a relationship between acanthodians and osteichthyans.

Furthermore, in his ‘odd phylogeny’ Janvier (1996: 330, Fig. 9.1, node 11) used the presence o f ‘three otoliths’ as a character to unite some acanthodians with osteichthyans. (40) Basipterygoid articulation: absent (0), or present (1).

PLATE 3.10 (CHAPTER 3)

The presence o f this articulation in Acanthodes is based on marrying up the

palatoquadrate-hyomandibula complex as seen in NMS 2001.7.1 with the composite braincase model (also based primarily on NMS 2001.7.1) used in this study. This character was adopted from Zhu et al. 1999. (C148); Zhu and Schultze 2001 (C149); and Zhu et al. 2001 (Cl 11)

ENDOSKELETAL MANDIBULAR ARCH (PALATOQUADRATE)

(41) Calcified endoskeletal mandibular arcb present (0), or absent (1). (REVERSE POLARITY option to be tested)

PLATE 3.16

This character statement is based on observations o f acanthodian taxa from all three acanthodian orders. What was observed is a condition o f the palatoquadrate and Meckel’s cartilage which is contrary to what is normally present in non-acanthodian gnathostomes, i.e. the mandibular arch not being preserved in certain taxa, due presumably, to a lack of

calcification o f his region. Calcification o f the mandibular arch appears to be a primitive condition o f gnathostomes as it is present in placoderms, chondrichthyans, osteichthyans, and the majority o f acanthodian taxa. From the ORS strata, climatiids such as Parexus and Euthacanthus lack perichondral ossification o f the mandibular arch but contemporaries such as Climatius have ossified endoskeletal jaws preserved. State [1] also persists in some o f the Canadian MOTH acanthodians such as Brochoadmones and Lupopsyrus which also lack any calcification o f the mandibular arch, but other acanthodian genera found in the same B- MOTH fish layer, e.g. Ischnacanthus and Tetanopsyrus, have ossified palatoquadrates and Meckel’s cartilages.

CHARACTER EVALUATION

(42) Number o f palatoquadrate calcification centre(s) separated by suture(s): single unit without suture (0), or two-unit structure separated by single suture (1), or three-unit structure separated by sutures (2).

SEE ALSO FIGURES 5.6A-B AND 5.7

This character statement follows from Long 1986a; 15 and Long 1986b: 334 who used the term ‘separate ossifications’ o f the palatoquadrate to describe the condition o f the palatoquadrate for some derived acanthodid acanthodians which possess separate ossified bones (quadrate, metapterygoid, and autopalatine, sensu Miles 1973b).

Placed together these bones make up the complete palatoquadrate. Long 1986a and 1986b listed this character as synapomorphies 6 and 11 respectively. The assembly o f this character statement is based on the assumption that there may have been a phyletic delay in fusing the embryonic calcification centres in the adult stage.

(43) Palatoquadrate with anteriorly expanded otic process {sensu Gardiner 1984) absent (0), or present (1).

FIGURE 5.6A-B

This character statement is basically modified from Coates and Sequeira 2001a (C51); 2001b (C51). It informs the systematist about the condition o f articulation between the palatoquadrate and the braincase. An expanded otic process of the palatoquadrate assumes articulation with the postorbital process of the endocranium. This condition o f the upper jaw is by no means restricted to derived acanthodians, e.g. Howittacanthus and Acanthodes, but is also putatively present in the climatiid, Climatius (Fig. 5.7). The alternate condition [state 0] is observed in Tetanopsyrus and Kathemacanthus, where it is assumed that the postorbital articulation is absent despite the fact that the braincases o f either genus is not preserved. (44) Large fenestra on metapterygoid face of palatoquadrate {sensu Miles 1973b): absent (0), or present (1).

FIGURE 5.6B

This large fenestra is present in Lodeacanthus and Cheiracanthus. It appears to be a specialisation o f these aforementioned putative derived mesacanthid acanthodians. Primitive mesacanthids such as Mesacanthus, from the specimens available including the holotype NMS (Powrie) 1891.92.275 (see Watson 1937, PI. 8, Fig. 3) do not exhibit this feature although it has been reported to be present by some workers. This confusion is probably due to

postmortem distortion o f the metapterygoid face o f the palatoquadrate o f some specimens revealing an open space. A clear account o f this feature for Cheiracanthus is given in the above figure.

(45) Palatoquadrate articulation with the rear o f the postorhital process absent (0), or present (1).

FIGURE 5.6B

The polarity o f this character is by no means clear and is coded simply as a presence- absence character in this study. An postorbital (alternatively ‘otic’) articulation is primitively absent in actinopterygians. Maisey 1980: 11 regards such an articulation to be primitively present in elasmobranchs although most living sharks do not show it.

An otic articulation is present in many placoderms (see Young 1986), and it is possible to be a primitive condition for sarcopterygians.

Within the Acanthodii the distribution o f this character is becoming somewhat more clear with the addition o f more taxa with preserved palatoquadrates, however with only one braincase-mandibular arch complex known in any detail (i.e. üom Acanthodes bronni) this character will be subject to speculation by other gnathostome workers. For this analysis, the postorbital articulation is deemed present in climatiid, ischnacanthid, and acanthodid acanthodian, but is absent in all diplacanthid acanthodians.

This characters has been simplified from Coates and Sequeira 1998 (C l6) where this it was discussed more fully with respect to postorbital protuberances which articulated with the palatoquadrate. This character statement was also used in Sequeira and Coates 2000 (C l6) and Coates and Sequeira 2001b (C79); see also Zhu et al. 2001 (C l 10).

(46) Number o f cotyli {sensu Long 1986b) on anterodorsal end o f expanded otic process o f the palatoquadrate: one (0), or two (1).

FIGURE 5.6B

This character statement is based on both Long (1986a: 15) and (1986b: 334) who used the term ‘both otic and auxiliary otic cotyli present on metapterygoid’. He listed it is as a putative synapomorphy o f derived acanthodid acanthodians on his node 6 (Long 1986a:

15) and îor Acanthodes and Acanthodopsis on his node 11 (Long 1986b: 334). State [2] of this character may simply be a specialisaton o f certain derived acanthodiform acanthodians, e.g. Howittacanthus and Acanthodes which may have supported their specialised form of filter feeding.

CHARACTER EVALUATION

(47) Palatoquadrate hinge type: single articular condyle only (0), or single glenoid fossa only (1), or both articular condyle and preglenoid fossa present (2).

FIGURES 5.4 AND 5.6B

This character statement was modified fi'om Coates and Sequeira 2001a (C53 & 54); 2001b (C53 & 54) and Long 1986b: 334 to compose a comprehensive statement about jaw hinge conditions in acanthodians. Long used ‘double mandibular joint’ as a synapomorphic character for his node 2. The presence of a ‘double mandibular joint’ was also used by Janvier

1996: 181, node 2 (see composite cladogram, Fig. 180, p. 180) to illustrate these characters supporting non-ischnacanthid acanthodians based on the classifications o f Miles 1973b and Long 1986b.

The ischnacanthid representatives in this study, i.e. Ischnacanthus (Fig. 5.4) and Poracanthodes (Valiukevicius 1992, PI. II. 1) were scored as state [1], the only distinct group o f acanthodians thus far to exhibit this particular type o f palatoquadrate hinge condition, but caution is advised based on the work o f Long (1986b) where putative ischnacanthid jaws were described and appeared to possess different jaw-hinge conditions (i.e. a mixture of state 1 and

2).

(48) Prominent, dorsally-directed palatobasal process o f palatoquadrate (*autopalatine* sensu Miles 1973b): absent (0), or present (1).

FIGURE 5.6B

This character statement was modified and adopted from Coates and Sequeira (2001a; C84); 2001b (C84). see also the ‘palatobasal connection’ character in Maisey 2001 (C26). This structure is present in members o f all traditionally-known acanthodian subgroups i.e. ischnacanthids, mesacanthids, and acanthodids, but absent in members representing the Climatiiformes and Diplacanthiformes). This feature may be present in Climatius and

Vernicomacanthus based on the expanded otic angle o f the palatoquadrate o f the former and the dermal plate outline on top o f the palatoquadrate area o f the latter taxon. If this type of mandibular arch-braincase articulation is present in climatiids, then the absence o f this structure may be considered the derived, or at the very least, a specialisation o f the diplacanthid acanthodians + Kathemacanthus.

MANDIBULAR ARCH (MECKEL’S CARTILAGE)

(49) Number o f Meckel's cartilage calcification centre(s) separated by suture(s): single unit without suture (0), or two unit structure witb single suture (1).