Harajicadipterus youngi, Clement, 2009

Clement, Alice M., 2009, A new genus of lungfish from the Givetian (Middle Devonian) of central Australia, Acta Palaeontologica Polonica 54 (4), pp. 615-626 : 616-620

Harajicadipterus youngi sp. nov.

1985 “dipnoan”; Young 1985: 246, 249, fig. 8J. 1993 “dipnoan indet.”; Young 1993: 248.

Figs. 2 , 3 , 5J–K .

Etymology: In honour of Dr. Gavin Young who has contributed much time and effort in the study of the Amadeus Basin geology and fauna. Type material: Holotype: NMV P228725, skull roof and cheek bones, with also tooth plates, operculum and partial pectoral girdle ( Fig. 2A–D ); paratype: CPC 24697, a cranium showing the pattern of most skull roofing bones ( Fig. 2E, F ).

Type locality: All specimens were collected from “locality 6” of the Amadeus Basin , Northern Territory, Australia. Locality 6 is 2km southwest of the southern end of Stokes Pass .

Type horizon: The Harajica Sandstone Member of the Parke Siltstone has been dated as Givetian–Frasnian ( Young 1985). Locality 6 has three horizons that contain fish material, most of which is referable to the antiarch Bothriolepis , but that also contains some osteichthyans ( Young 1985).

Material.—NMV P229314, an isolated left pterygoid tooth plate ( Fig. 3A, B ); CPC 24698, 7 vertebral centra ( Fig. 3C, D ); and CPC 24699 contains some possible partial operculo−gulars and an isolated dermal scale ( Fig. 3E, F ).

Diagnosis.— Dipterus −like pterygoid tooth plates with seven tooth rows; teeth that coalesce towards the postero−mesial margin of the tooth plate; scattered denticles between tooth rows. Broad B bone with median projection; K present; single D bone separates C from F; paired C and E bones; C bones elongate. Postorbital cheek longer than orbit diameter. Ossified, differentiated disc centra; rounded scales partially covered with ridged dermal ornament.

Description

General features.—A small to mid−sized dipnoan with a Dipterus −like skull roof pattern ( White 1965) and a long postorbital cheek. Specimen NMV P228725 consists of two parts of the same individual, labelled herein as A and B. NMV P228725−A shows detail of the skull roof, operculum, shoulder girdle and the tooth plates. NMV P228725−B shows skull−roofing bones, the shoulder girdle and the position of the orbit relative to the operculum. CPC 24697 is an impression of a second dipnoan skull of the same taxon that was first figured by Young (1985: text−fig. 8J) but will be re−described here. NMV P229314 is an isolated left pterygoid tooth plate. CPC 24698 shows 7 vertebral centra, and CPC 24699 contains some possible partial operculo−gulars and scales.

Skull roof.— Harajicadipterus youngi has a short and broad median B bone with a distinctive median projection and elongate, paired C bones ( Figs. 2E, F , 5G, H ). There is a single D bone, and paired E bones lying anteriorly. The I and J bones are both large relative to Y1 and Y2 which seem to be variable in size between specimens. Unlike Dipterus where the X bone can sometimes fail to develop ( White 1965), both X and K bones are present in these specimens of Harajicadipterus ( Fig. 2 ). Bones L and M have fused on the right side of CPC 24697 to form a compound bone ( Fig. 2E, F ). There has been some disarticulation of the anterior portion of the skull roof, with the D, E and F bones displaced slightly.

Bone 3 has a long orbital margin and is strongly curved ( Fig. 2C, D ). Pores and a thickening of the bone indicate the path of the lateral line branch passes into bone 3. Bone 2 ( Fig. 2C, D ) is very small with a short orbital margin. Although very few of the cheek bones have been preserved, the distance between the orbit and the median skull roof bones (B and C) is comparable to that of other “long−cheeked” dipnoans such as Iowadipterus ( Schultze 1992) , Adololopas ( Campbell and Barwick 1998) and primitive dipnoans such as Dipnorhynchus ( Campbell and Barwick 1982) and Uranolophus ( Denison 1968) . There is no ornamentation on the skull roof bones, indicating that they were possibly covered by cosmine unlike the distinct dermal ornamentation seen on the Mount Howitt lungfishes Howidipterus and Barwickia , which were also studied from latex casts ( Long 1992, 1993). Unfortunately the state of preservation is too poor to more accurately determine the presence or absence of this tissue. The canal entering bone 3 is the only evidence of sensory canals or pit−lines.

Operculum and pectoral girdle.—The size and shape of the operculum can be determined from NMV P228725 A and B ( Fig. 2A–D ). The operculum measures approximately 19 mm in diameter and has a horizontal dorsal edge. The specimens have not preserved evidence of muscle attachment scars or any ornamentation.

Specimen NMV P228725 shows the clavicle on parts A and B, and the cleithrum on part B only. The clavicle ( Fig. 2A–D ) is a long, thin bone, which is slightly trapezoidal in shape. The cleithrum is loosely articulated with the clavicle on part B, and the ventral portion is pentagonal in shape with an elongated point. The dorsal shaft is not seen ( Fig. 2C, D ). The clavicle and cleithrum in Fig. 2C, D comprise the right shoulder girdle which shows no evidence of dermal ornamentation on its external surface, however, this is possibly an artefact of poor preservation. There is a large bone at the anterior end of the specimen lying below the tooth plates that appears narrow and elongate, and this is likely to be part of the submandibular or subopercular series disarticulated and partially exposed ( Fig. 2A–D ).

Mandible.—Some of the prearticular (the main internal dermal bone) can be seen still attached to the lower tooth plate on the holotype ( Fig. 2A, B ). The visible portion shows that it is a thick, smooth bone that supports the radial tooth plates.

Tooth plate.—NMV P229314 is an isolated upper left tooth plate with the oral surface exposed. It resembles that of the holotype ( Fig. 2A, B ) and has been assigned to Harajicadipterus . The discovery of further material will be vital to either support or disprove this association. The tooth plate is deeply concave and triangular in shape, not ovoid like Eoctenodus ( Long 1987) . Seven well−defined tooth rows are visible, and there is a possibility of an eighth ( Fig. 3A, B ). The tooth plate contains 8 or 9 teeth in the medial rows, and as few as 6 in the lateral rows. The angle between the medial row and the lateral−most row is 67°. Like those in lungfish such as Tarachomylax ( Barwick et al. 1997) and Stomiahykus ( Bernacsek 1977) , all tooth rows originate from the posterior of the pterygoid and radiate anteriorly and anterolaterally. There are no postero−laterally radiating ridges. The teeth are rounded and they decrease in size and coalesce towards the centre of radiation. They appear neither sharp nor pointed, possibly due to wear. The tooth rows are not as clearly defined or widely separated as in Adololopas ( Campbell and Barwick 1998) , and there are relatively shallow clefts between the rows without any obvious wear facets. Unlike the condition seen in Dipterus ( White 1965; Jarvik 1980), Harajicadipterus has some small denticles between

Diabolepis Diabolepis

Dipnorhynchus sussmilchi Dipnorhynchus sussmilchi

Speonesydrion Speonesydrion

Ichnomylax Ichnomylax

Stomiahykus

Uranolophus

Uranolophus Jessenia

Jessenia Stomiahykus

Tarachomylax Tarachomylax

Melanognathus Holodipterus gogoensis

Holodipterus gogoensis H. (Asthenorhynchus) meemannae

H. (Asthenorhynchus) meemannae H. (Robinsondipterus) longi

H. (Robinsondipterus) longi Griphognathus whitei

Griphognathus whitei Chirodipterus australis

Andreyevichthys Pillararhynchus

Fleurantia Gogodipterus

Howidipterus Adololopas Barwickia Andreyevichthys

Fleurantia

Sagenodus

Scaumenacia

Howidipterus

Ctenodus Barwickia

Neoceratodus Scaumenacia

Gnathorhiza Sagenodus

Soederberghia Ctenodus

Conchopoma Neoceratodus

Orlovichthys

Gnathorhiza

Soederberghia

Harajicadipterus

Conchopoma

Chirodipterus australis

Sorbitorhynchus

Gogodipterus

Pillararhynchus Dipterus

Sorbitorhynchus Orlovichthys

Adololopas Harajicadipterus

Dipterus Melanognathus the tooth rows. The outline of the shape and size of the corpus (the anterior portion of the parasphenoid) can be inferred from the shape of the tooth plates. The corpus appears short and broad, with long pterygoid to pterygoid contact. The pterygoid reaches backwards towards the mandibular articulation and there is a prominent ridge extending postero−laterally ( Fig. 3A, B ), similar to that seen in Dipterus ( White 1965) . The pterygoid distinctly differs in shape from those of Tarachomylax ( Barwick et al. 1997) and Adololopas ( Campbell and Barwick 1998) which have a distinct edge into which a ploughshare−shaped parasphenoid can fit, the posterior edge of the pterygoid is not so prominent in Harajicadipterus ( Fig. 3A, B ). The tooth plates of Howidipterus , another Australian Middle Devonian tooth−plated genus, differ from Harajicadipterus in having twice as many tooth rows, with only three to five cusps in each tooth row ( Long 1992).

Vertebrae.—Like the Recent genera, most Devonian dipnoans do not possess ossified vertebral centra ( Ahlberg and Trewin 1995; Arratia et al. 2001), however, some impressions of centra are evident in CPC 24698. There appears to be a row of seven centra, six of which are articulated and none of the associated vertebral elements such as neural or haemal arches or spines are preserved ( Fig. 3C, D ). Unlike Howidipterus or Barwickia that exhibit a mineralised column rather than individual centra (Long and Clement in press), those of Harajicadipterus are clearly differentiated. The average height of the centra is 6.5 mm. Harajicadipterus does not have prominent neural arches or supraneural spines, which is unlike the condition seen in Dipterus ( Ahlberg and Trewin 1995) and Uranolophus ( Denison 1968) . The centra are compact and independent and resemble those of Rhynchodipterus ( Schultze 1969; Arratia et al. 2001). They may be comparable to the disc centra of genera such as Griphognathus ( Campbell and Barwick 2002) and Soederberghia ( Ahlberg and Trewin 1995) , but further comparisons cannot be made due to the state of preservation in Harajicadipterus ( Fig. 3C, D ).

Scales.—Some isolated scales present in CPC 24699 are poorly preserved, but dermal ornament is present and cosmine was most likely absent. The scales are cycloid and approximately 20 mm in diameter. Individual scales may overlap, and the thin, wavy ridged ornament covers a roughly triangular area one−third the length of the scale ( Fig. 3E, F ). The ornament is less dense than that of Scaumenacia ( Cloutier 1996) and more pronounced than that of Eoctenodus ( Long 1987) . It resembles most closely that of Howidipterus ( Long 1992) .

Figures

Fig. 2. Dipnoan fish Harajicadipterus youngi gen. et sp. nov. from the Harajica Sandstone Member (Givetian), central Australia. Holotype, NMV P228725, skull−roofing bones, operculum, tooth plates and pectoral girdle in opposing views (A, C); interpretive drawing of same (B, D). E. CPC 24697, skull roof in dorsal view. F. Interpretive drawing of same. All specimens are latex casts of impressions in rock and whitened with ammonium chloride. Dashed lines represent approximate extent of cleithrum in D and approximate position of orbit.

Fig. 3. Dipnoan fish Harajicadipterus youngi gen. et sp. nov. from the Harajica Sandstone Member (Givetian), central Australia.A. Photograph of upper left pterygoid tooth plate, NMV P229314, latex cast impression whitened with ammonium chloride. B. Interpretive drawing of same. C. Articulated vertebral centra, CPC 24698. D. Drawing of same. E. Isolated scale in external view showing ornament CPC 24699. F. Drawing of same.

Fig. 5. Comparison between dorsal and right lateral views of skull roof pattern of Devonian dipnoans. A, B. Chirodipterus australis from the Gogo Formation (Frasnian), Australia, redrawn from Miles (1977:232−233); comparison between dorsal and right lateral views. C, D. Holodipterus (Asthenorhynchus) meemannae from the Gogo Formation (Frasnian), Australia, redrawn from Pridmore et al. (1994: 152). E. Dipterus valenciennesi from the Old Red Sandstone (Middle Devonian) of Scotland, redrawn from Campbell and Barwick (1990: 154). F. Dipterus valenciennesi from the Old Red Sandstone (Middle Devonian) of Scotland, redrawn from Jarvik (1980: 413). G, H. Howidipterus donnae from Mount Howitt (Givetian), Victoria, Australia, redrawn from Long (1992: 306). I. Amadeodipterus kencampbelli from the Amadeus Basin (Emsian–Eifelian), central Australia, redrawn from Young and Schultze (2005:20). J, K. Harajicadipterus youngi gen. et sp. nov. from the Harajica Sandstone Member (Givetian), central Australia, drawn from specimens NMV P228725 and CPC 24697. Abbreviation: Op, operculum.