A revision of the Late Jurassic fish Aphnelepis australis from the Talbragar Fossil Fish Bed of New South Wales, Australia

Abstract

The discovery of an exceptionally preserved specimen of the Mesozoic teleost fish Aphnelepis australis from the upper Kimmeridgian (Upper Jurassic) Talbragar Fossil Fish Bed in New South Wales, together with historic confusion over its phylogenetic affinities, has prompted a detailed reassessment of the taxon. The new specimen of A. australis is skeletally complete and exhibits the dorsal fin with long principal dorsal fin rays and characteristic squamation comprising heavy rhombic scales anterior to insertions of the dorsal fin and anal fin, and much lighter and thinner weakly crenulate scales on the posterior half of the body. A cladistic analysis resolves A. australis as a member of Archaeomenidae, along with Archaeomene tenuis, Wadeichthys oxyops, Oreochima ellioti, Gurvanichthys mongoliensis, Zaxilepis quinglongensis, and Aphnelepis australis.

Lynne B. Bean [[email protected]], Research School of Earth Sciences, 142 Mills Road, Australian National University, Acton, Australian Capital Territory 2601, Australia.

Keywords:

• Aphnelepis tenuis
• Talbragar
• Upper Jurassic
• Archaeomenidae

IN 1890, WHEN Arthur Smith Woodward of the then British Museum (Natural History) was sent a shipment of fossil fish from what is now the famous Talbragar Fossil Fish Bed locality by the New South Wales Government Geologist, Charles S. Wilkinson, he was impressed by the occurrence of at least five new species, and also puzzled by the possible age of these fish (Woodward 1895). From his experience, Woodward concluded that the specimens were Jurassic in age, a conclusion supported by subsequent stratigraphical mapping by the Australian government geologists Tennant W. Edgeworth-David and Edward F. Pittman (Edgeworth-David & Pittman 1895). One of the new species was named Aphnelepis australis Woodward, 1895, and is rare in comparison to the abundant small schooling fish from the Talbragar Fossil Fish Bed assemblage, Cavenderichthys talbragarensis (Woodward, 1895) (see Arratia 1997). Aphnelepis australis is distinguished by its heavy ganoid scales covering the anterior section of the body up to the insertion of the dorsal fin and anterior-most insertion of the anal fin; thin circular scales occur posterior to this line.

The rarity and lack of well-preserved specimens of A. australis has limited attention to this taxon in comparison to others in the Talbragar Fossil Fish Bed assemblage. The only descriptions were provided by Woodward (1895) and Wade (1941). Consequently, this paper contributes an updated description based on new specimens. Woodward (1895) placed A. australis in the order Pholidophoriformes. Wade (1941), on the other hand, referred A. australis to Cenogenoidei within Holostei, but erected a new family, Aphnelepidae, because of uncertainty over assignment as a pholidophorid.

Schaeffer & Dunkle (1950, p. 25) noted that A. australis, Semionotus kanabensis Schaeffer & Dunkle, 1950 and Pholidophorus Agassiz, 1832 sensu lato shared a median process on the maxilla, a small gape, shortened maxilla, and reduced suborbital series. This inferred affinity with Pholidophoridae was maintained by Griffith & Patterson (1963, p. 39). At that time, A. australis was included in Archaeomaenidae, which was considered derived from Pholidophoridae based on the shared plesiomorphic states: a medial rostral bearing the ethmoid commissure; premaxillae in contact below the rostral; and nasals in contact along the midline (Griffith & Patterson 1963). López Arbarello et al. (2008) likewise included A. australis in Archaeomaenidae, while Taverne (2011, p. 153), pointed out that the large dorsal and anal fins, unusual squamation and deep body shape excluded A. australis from ‘Pholidophoriformes’.

In 2016, a beautiful specimen of A. australis was recovered by Kerry Mills and Michael Frese (University of Canberra) during excavations at the Talbragar Fossil Fish Bed. The part (AM F141883) and counterpart (AM F141884) add significantly to previous descriptions of the taxon, and permit evaluation of both taxonomic affinities and phylogenetic relationships of A. australis and Archaeomaenidae.

Institutional abbreviations

ANU, Australian National University, Canberra, Australia. AM, Australian Museum, Sydney Australia. GSNSW, Geological Survey of New South Wales (formerly The Mining Museum), Sydney, Australia. NHMUK, The Natural History Museum, London, UK. RB, Rodney Berrell private collection, Perth, Australia.

Geological setting

The stratigraphy and physiography of the Talbragar Fossil Fish Bed have been discussed by Dulhunty (1937), Dulhunty & Eadie (1969), Hind & Helby (1969), Percival (1979) and Pogson & Cameron (1999). The unit comprises a fine-grained mudstone with well-defined thin bedding in sub-horizontal layers. The rich fossil fauna and flora suggests deposition under freshwater lacustrine conditions (Bean 2006, 2017, Beattie & Avery 2012). The maximum thickness of the beds is not more than 2 m, with iron staining from post-depositional weathering penetrating through joint planes to create liesegang bands and being absorbed by many of the fish skeletons. Plant remains are abundant but not usually iron-stained, and occur as white siliceous replacements of the original organic material (Bean 2017).

The Sensitive High-Resolution Ion Microprobe (SHRIMP) analyses at ANU have determined the age of the Talbragar Fossil Fish Bed as 151±4 Mega-annum (Ma) (Bean 2006), or within the upper Kimmeridgian stage of the Upper Jurassic based on the current International Commission of Stratigraphy Chart v2023/09 (https://stratigraphy.org/chart).

Materials and methods

The newly identified specimens of Aphnelepis australis were collected during several field trips to the Talbragar Fossil Fish Beds in 2006 and 2007. These fossils were prepared using dental picks and engraving tools. Some were whitened with sublimate of ammonium chloride for photography. External moulds of skeletal impressions were examined in positive relief using latex peels.

Micro-CT scanning

AM F141883 and AM F141884 were neutron tomography scanned at the Australian Nuclear Science and Technology Organisation (ANSTO) using the Dingo Neutron Imaging device (https://www.ansto.gov.au/user-access/instruments/neutron-scattering-instruments/dingo-neutron-imaging). High resolution Micro-CT scanning was undertaken on the ANU4 system at the ANU National Laboratory for X-ray Micro Computed Tomography (https://ctlab.anu.edu.au/capabilities/micro-ct.php). Unfortunately, however, no internal structures were discernible below the surface bone impressions on the rock.

Anatomical terminology

Cranial bone terminology follows Schultze (2008) and Teng et al. (2019); alternative nomenclature is indicated in square brackets, e.g., parietal [= frontal]: pa [= fr]. Terminology for the vertebral column follows Arratia et al. (2001) and Arratia (2015), whereas caudal endoskeletal terms follow Schultze & Arratia (1988, 1989, 2013), and Arratia & Schultze (1992, 2013). Descriptions of fin rays, scutes, fulcra, procurrent rays, epaxial rudimentary rays, and principal rays follows definitions provided by Arratia (2008, 2009).

Comparative material

Specimens highlighted in bold are described herein; other specimens have otherwise been examined and photographed first-hand. AM F27070, small almost complete specimen; AM F104690, well-preserved head and pectoral fin; AM F 117884 (holotype previously MF267), well preserved with dorsoventral view of skull roof; AM F120491 (previously MF271), well-preserved head and anterior scales; AM F120492, counterpart of 120491; AM F120503, disarticulated head with scales; AM F120506, damaged specimen, partial dorsal fin; AM F120533, complete specimen except dorsal fin; AM F120869, well-preserved specimen, missing cranial roof; AM F141884, (part) well-preserved complete specimen; AM F141883 (counterpart), well-preserved complete specimen; ANU 61126, large broken specimen with well-preserved tail; ANU 61127, large complete but broken specimen; ANU 61112, complete specimen, well-preserved tail; GSNSW 36724, well-preserved dorsal and caudal fins; NHMUK 12411, caudal and anal fins; NHMUK 40501, complete specimen moderately well preserved; NHMLP 40502, head only; NHMUK 40503, dorsoventrally flattened skull roof; NHMUK 12412, well-preserved head; RB 90, damaged complete specimen with head.

Systematic palaeontology

Subclass ACTINOPTERYGII Cope, 1887

Division TELEOSTEOMORPHA Arratia, 2001

Infraclass TELEOSTEI Müller, 1845 (sensu Arratia, 1999)

Family ARCHEOMAENIDAE Wade, 1941

Diagnosis

Emended from Wade (1941) and Bean (2021). Small fusiform fish with an approximate range of 50–150 mm standard length. Cranial roof is broad, with a gentle, downward curve anterodorsally [*]; large flat nasals meeting medially; parietal [=frontal] narrow anteriorly, becoming wider posteriorly; postparietal [=parietal] quadrangular; extrascapula triangular, deeper than long; small mobile premaxilla with no ascending process and tiny teeth; large suborbital covering most of cheek, deeper than long; large infraorbital-3; maxilla tapering anteriorly; mandible longer than maxilla, not very deep, tapering anteriorly; large triangular median gular; paired fins small, on ventral surface; cleithrum with serrated appendages causing parallel ridges in cleithrum; persistent notochord; caudal fin deeply forked, externally symmetrical.

Remarks

The family includes: Archaeomene tenuis Woodward, 1895; Wadeichthys oxyops, Waldman, 1971; Oreochima ellioti Schaeffer, 1972; Gurvanichthys mongoliensis Jakovlev, 1986; Zaxilepis quinglongensis Su, 1994; Aphnelepis australis Woodward, 1895.

Aphnelepis australis Woodward, 1895.

Diagnosis

Emended from Wade (1941). Small fusiform fish with moderately deep body. Maximum length observed 125 mm (For details of measurements see Table 1). Body height one third of standard length. Snout blunt, length about 20% of cranial length. Orbital diameter about 33% of cranial length. A small amount of ornamentation consisting of lunules and tubercles on cranial roof bones; small premaxilla, located adjacent to anterior of maxilla; two supramaxillae, anterior much smaller than posterior; three small supraorbitals; large opercle with ventral margin oblique; preopercle with covered canal and four or five short branches; triangular interopercle; large triangular gular plate; dorsal and anal fin each has a long anterior ray covered with fringing fulcra; the number of fin rays is relatively small, 16 for the dorsal fin and 12 for the anal fin; anterior ray of dorsal fin three times the length of 5th ray, with concave posterior margin [*]; the anterior margin of dorsal fin is 50% of distance between cleithrum and caudal peduncle; a series of supraneurals extends below the dorsal fin reaching almost to the back of the fin, between the tips of the dorsal pterygiophores and above the neural spines [*]; caudal fin hemiheterocercal, deeply forked, with dorsal and ventral scutes that are equivalent in length to about three scale rows; articulations between segments of principal rays straight, except when near bifurcation when Z-shaped. All fins with fringing fulcra; anterior body scales ganoid, rhombic, with tight radiating ridges on the exposed regions producing crenulated posterior margins [*]; posterior to a line joining the anterior insertion of the dorsal fin with the anterior of the anal fin, the scales are lacking ganoine, thinner and with circular exposed profile, also with crenulated posterior border [*]; dorsal ridge scales with small posterior spine between back of head and insertion of dorsal fin. (An asterisk [*] denotes a uniquely derived character or autapomorphy.)

Table 1. Measurements (mm) of examined Aphnelepis australis specimens.

ID No.	ANU 61119	ANU 61112	ANU 61111	AM F141883	AM F141884	AM F120491	AM F117884	GSNSW 36724	ANU 61120
SL	48.14	109.00	?	117.15	120.31	–	100.44	–	53.83
BH	17.10		70.95	38.57	38.33	42.95	39.71	36.82	17.06
CL	17.51	35.69	?	33.31	30.55	33.43	31.11	–	16.89
CL-AF	20.04	49.33	89.14	47.94	53.09	–	45.86	–	22.92
CL-CF	33.63	69.87	126.65	82.86	84.8	–	68.93	–	35.99
CL-DF	16.68	41.04	83.65	40.17	44.35	–	?	–	17.89
CPH	?	15.38	40.77	19.05	19.29	–	19.38	12.33	8.47
DF-AF	2.69	16.69	43.56	21.13	18.33	–	?	45.0	10.15
PAL	?	85.23	?	81.84	83.10	–	75.91	–	39.91
PDL	34.11	75.57	?	72.71	69.70	–	?	–	35.20
PPL	28.71	62.66	?	62.22	57.38	–	59.02	–	29.52
PEC-PEL	11.32	26.48	?	29.80	30.17	–	34.80	–	13.62
Pe-ob-L	2.74 m	8.25	?	5.06	5.71	8.14	7.05	–	3.19
Ob-D	6.11	8.11	?	11.20	11.55	10.35	10.60	–	6.35
Pt-ob-L	8.01	18.84	?	17.86	15.73	14.66	15.02	–	7.35
CL/SL	36.37%	32.7%	?	28.4%	25.4%	–	31%	–	36.4%
Sn/CL	15.6%	23.1%	?	15.2%	18.7%	24.3%	22.7%	–	15.6%
Or/CL	34.9%	22.7%	?	33.6%	37.8%	30.9%	34.1%	–	37.6%
BH/SL	0.355			0.329	0.318		0.395		0.317

Abbreviations: SL, standard length from the tip of snout to the posterior tips of the middle hypurals; BH, body height taken at level of pectoral fin insertion; CL, cranial length from snout to posterior margin of opercle; Cl-AF, distance between posterior margin of cleithrum and beginning of anal fin; Cl-CF, distance between posterior margin of cleithrum and the caudal peduncle; Cl-DF, distance between posterior margin of cleithrum and beginning of dorsal fin; CPH, caudal peduncle height; DF-AF, distance between beginning of dorsal fin and beginning of anal fin; PAL, pre-anal length taken from the tip of the snout to the beginning of the anal fin; PDL, pre-dorsal length taken from the tip of the snout to the beginning of the dorsal fin; PPL, pre-pelvic length taken from the tip of the snout to the beginning of the pelvic fin; Pec-PEL, distance between beginning of pectoral fin and beginning of pelvic fin; Pe-ob-L, length from snout to anterior margin of orbit; Ob-D, diameter of orbit; Pt-ob-L, length from posterior margin of orbit to posterior margin of cleithrum; CL/SL, ratio of cranial length to standard length; Sn/CL, ratio of preorbital (snout) length to cranial length; or/CL, ratio of orbit diameter to cranial length. Average ratio; BH/SL = 0.3428.

Description

Skull roof and braincase

The braincase is obscured by other bones in all examined specimens. The skull roof consists of the nasals, parietals [= frontals], postparietals [= parietals], dermopterotics and the extrascapulae. There is no evidence of fusion between any skull roof bones.

At the anterior part of the head, the nasals are sub-square and flat. They appear to be sutured medially. They carry the anterior section of the supraorbital canal, with one pore in the centre of the nasal bone and another large pore close to the anterolateral margin of the bone. There is no ornamentation on the nasals. Anterior to the nasals is the medial rostral. It is small and sub-rounded, and carries the ethmoidal commissure, with an opening at each lateral end.

The parietals [=frontals] are narrow over the anterior of the orbit and become broader posteriorly. The anterior margin forms a narrowing rounded point that overlaps, or abuts with, the large flat nasals. The parietals are separated by an almost straight suture anteriorly, but in front of the postparietals there is a slight sinusoidal curve. The supraorbital canal is close to the lateral margin of the parietal, AM F117884 (Figs 1A, B). NHMUK 40503 shows the dorsal view of the skull roof with collapsed supraorbital canals on either side and the oblique broad angle of the articulation with the nasals. The surface of the parietals (AM F120491, Fig. 2A) is covered with small lunule bumps with the steep side directed posteriorly. They are most common in the lateral regions above the eye. On AM F120491, the passage of the supraorbital canal is marked by five small pores. There is a large pore at the anterior margin of the parietal, where the canal carries on across the nasal, with a lateral branch that is also marked by a pore. On AM F117884 (Fig. 1) the supraorbital canal has collapsed, and on RB 90 the replacement filling of the supraorbital canal can be seen in an open canal.

Fig. 1. Aphnelepis australis (AM F117884, holotype). A, Lateral view of original specimen with large pectoral fin. B, Head enlarged and whitened with ammonium chloride to show the dorsal view of skull roof. Grid divisions = 10 mm.

Fig. 2. Aphnelepis australis. A, AM F120491, peel of lateral view of head whitened with ammonium chloride. B, Interpretive drawing of head based on AM F120491. Abbreviations: ang, angular; ao, antorbital; br, branchiostegal ray; cl, cleithrum; de, dentary; dpt, dermopterotic; dsp, dermosphenotic; exc, extrascapula; gu, gular; io 1–5, infraorbitals 1–5; iop, interopercle; mx, maxilla; n, nasal; op, opercle; pa, parietal bone [= fr, frontal of traditional terminology]; pcl, postcleithra; pmx, premaxilla; pop, preopercle; ppa, postparietal bone [= pa, parietal bone of traditional terminology]; ps, parasphenoid; ptt, posttemporal; r, rostral bone; scl, supracleithrum; smx, supramaxilla; sob, suborbital; sop, subopercle; suo, supraorbital bone.

The postparietals [= parietals] are almost square. They have similar small ornamentation to the parietals. The suture between the postparietals is almost straight. Lateral to the postparietals are the dermopterotics that are also almost square and have similar ornamentation. The middle pit line crosses the boundary between the postparietal and the dermopterotic. There is a trace of the middle pit line in the dermopterotic, and a trace of the anterior pit line in the postparietal almost intersecting the dorsal end of the middle pit line (AM F120491; Fig. 2A, B).

The depth of the extrascapula is equal to the total depth of the postparietal and dermopterotic. Each extrascapula is like an isosceles triangle, with rounded apices, and with the base located partially overlapping the supracleithrum. It seems that the extrascapulae meet medially but are not sutured. The temporal commissure has not been observed.

Orbit and circumorbital series

Above the orbit there are three supraorbitals. The first and second are long and narrow, with rounded ends, but the third is quite small and may be pointed posteriorly to fit against the dermosphenotic. The triangular antorbital is almost adjacent to the anterior end of the first supraorbital, and is also adjacent to the nasal, but it is difficult to determine whether they are sutured or not. Below the orbit there are three infraorbitals. Infraorbital 1 and 2 can be seen on AM F120491 (Fig. 2B), with a slight ridge following the path of the infraorbital canal. These two bones are not preserved on RB 90 or AM F117884. Infraorbital 3 is very large and sub-rounded. It fills the space between the orbit, the upper jaw, the preopercle, suborbital and infraorbital 4. Woodward (1895) and Wade (1941) identified infraorbital 3 as the circumorbital. It has a ridge covering the infraorbital canal that runs parallel, and quite close, to the margin of the orbit, and has two short branches that end ventrally as pores.

The posterior margin of the orbit is formed by two small bones, infraorbitals 4 and 5, that sometimes are not well preserved and appear to be covered by the suborbital (AM F120491). The two bones, or their traces, can be seen on AM F141883, AM F104690, AM F141884, ANU 61112a and RB 90.

The dermosphenotic is a small irregular triangular bone, with an anterior apex, and its canal that is a continuation of the infraorbital canal. There is no evidence of it connecting with the supraorbital canal. It fills the space between the orbit, the posterolateral margin of the parietal, the anteroventral margin of the dermopterotic, and the dorsal margin of the infraorbital 5 (Figs 2, 3). Part of a sclerotic ring can be seen at the top of the orbit on AM F120491. No other specimens observed in this study have preserved any remnants of the sclerotic ring.

Fig. 3. Aphnelepis australis (AM F120492). A, Lateral view of lower head showing two supramaxillae, possible symplectic, and pores on dentary; B, Interpretative drawing with labels. Abbreviations: ang, angular; br, branchiostegal ray; cl, cleithrum; de, dentary; dsp, dermosphenotic; gu, gular; io 1–5, infraorbitals 1–5; iop, interopercle; mx, maxilla; n, nasal; op, opercle; orb, orbit; pmx, premaxilla; pop, preopercle; ps, parasphenoid; r, rostral bone; smx, supramaxilla; sob, suborbital; sop, subopercle; suo, supraorbital bone.

Upper jaw

The upper jaw consists of the premaxilla, maxilla and two supramaxillae. The premaxilla is small, adjacent to the anterior of the maxilla, with about six tiny conical teeth on the oral margin and is interpreted here as mobile.

The maxilla is shorter than the lower jaw and is mobile. There are about six needle-like conical teeth at the anterior of the maxillary oral margin (AM F120491), then a short gap followed by small conical teeth extending about two thirds of the length of the oral margin. This gap is not seen on other specimens. The posterior margin of the maxilla is almost perpendicular to the oral margin, and slightly concave. The maxilla is narrow anteriorly and becomes wider, doubling its depth by about 2/3 of its length.

On AM F120491 (Fig. 2) there appears to be only one supramaxilla that is located over the posterior half of the maxilla. It has a series of slight ridges that parallel the dorsoposterior margin and are interpreted as growth stages, although they are sometimes described as ornamentation. The front part of the dorsal margin of the maxilla is covered by the displaced infraorbital 1. In comparison, on specimen AM F120492 (Fig. 3), there is clearly a smaller supramaxilla 1 that is overhung by an anterodorsal process of the second supramaxilla and therefore confirms the presence of two supramaxillae.

Lower jaw

The dentary is rounded anteriorly, with some small pores that may represent the terminations of mandibular sensory canal (Fig. 3B). The surface of the dentary and angular is smooth, with a low ridge of bone covering the passage of the mandibular canal. There are three or four large pores marking the path of this canal. The coronoid process of the dentary is usually covered by the maxilla.

Suspensorium, hyoid arch, and urohyal

The suspensorium is not usually exposed. The top of the hyomandibular is visible on RB 90 adjacent to the suborbital bone. It has not been possible to see any processes on the hyomandibular.

The quadrate is not fully exposed in any of the specimens available. On AM F120491 there is a small thin pointed bone, dorsal to the anterior of the preopercle, adjacent to the articulation of the mandible and quadrate that appears to be the symplectic (Fig. 3A).

The anterior ceratohyal is flat and sub-rounded (AM F120491). Hypohyals have not been preserved on any of the observed specimens, nor the posterior ceratohyal. There is no evidence of a urohyal.

Opercular bones, branchiostegal rays and gular plate

The opercle has a smooth surface. It is deeper than long, with a rounded top and its anteroventral angle is approximately level with the position of infraorbital 3 (Fig. 2). The size of this angle is about 70°, and the ventral margin is oblique. The subopercle is up to half as deep as the opercle and the ventral margin is more rounded than the ventral margin of the opercle.

The interopercle is quite large (Figs 2, 3), located between the preopercle dorsally and subopercle posteriorly. The interopercle can be seen on AM F120491, AM F120492, RB 90 and AM F141884.

The preopercle is almost vertical, moderately narrow and only slightly bent at the anteroventral tip, with the upper part of the dorsal section usually covered by the suborbital. The preopercular sensory canal is usually covered by a low ridge, is slightly closer to the anterodorsal margin, and has four or five short broad branches ending in pores but not reaching the posteroventral margin of the bone (Figs 2–4, 6).

There are about eight branchiostegal rays on each side of the head on AM F120492 and AM F104690 (Figs 3, 6). Their shape is spathiform. Those on AM F 120492 (Fig. 3A) show ornamentation that is rows of tiny pits. They occupy the space posterior to the gular plate, ventral to the interopercle and anterior to the cleithrum.

The median gular is quite large and triangular, extending from about a quarter of the length of the dentary to the posterior margin of the angular, becoming wider posteriorly (Fig. 3).

Vertebral column and intermuscular bones

The pattern of scale arrangement, which is unusual among fishes from the Talbragar Fossil Fish Bed assemblage, obscures the endoskeleton anteriorly. Behind the line joining the front of the dorsal fin and front of the anal fin the scales are lacking ganoine or enamel, thus traces of the underlying bones can occasionally be seen. AM F141884 (Fig. 4A) shows the dorsal and anal pterygiophores, as well as supraneurals, neural spines and haemal spines. The vertebrae are not completely ossified and there is a persistent notochord (RB 90). The posterior nine members of a series of supraneural bones can be seen below the dorsal fin, behind the demarcation line between scale types. They are located between the ventral tips of the dorsal pterygiophores, and the dorsal tips of the neural spines. Traces of 19 neural spines and about the same number of short haemal spines can be seen, but it is unclear whether neural spines of the caudal region are paired or a single median spine due to conditions of preservation. The locations of many of these features can be seen on the reconstruction (Fig. 4C).

Fig. 4. Aphnelepis australis. A, AM F141884. Original rock in lateral view showing scale pattern. B, Lateral view of counterpart (AM F141883) showing traces of endoskeleton on posterior half of body. Abbreviations: apt, anal pterygiophores; dpt, dorsal pterygiophores; hs, haemal spines; ns, neural spines; sne, supraneural spines. C, Reconstruction of Aphnelepis australis based on AM F141883.

RB 90 (Fig. 5) also has traces of the posterior nine supraneurals, and the 12 posterior neural spines. Only about seven haemal spines have left traces. AM F120869 has some traces of neural and haemal spines, as does AM F120533. These few specimens suffer from poor preservation, so detailed descriptions are not possible.

Fig. 5. Aphnelepis australis. RB 90 showing traces of supraneurals (sn), neural spines (ns) and haemal spines (hs) posterior to the thick rhombic ganoid scales of anterior section.

Pectoral girdle and pectoral fin

The posttemporal is posterior to, and partly overhung by the extrascapula. The exposed bone is less than half as wide as the extrascapula.

The cleithrum is arcuate and clearly visible on AM F120491 (Fig. 2). On AM F104690 the cleithrum can be seen posterior to and overlapped by the branchiostegal rays (Fig. 6). The region of the cleithrum dorsal to the pectoral fin has serrated appendages represented by parallel low ridges. The supracleithrum appears posterodorsal to the opercle on AM F120491 and there is an impression of it where it is overhung by the opercle, dorsal to the cleithrum. There is a similar situation with AM F104690 (Fig. 6). Of the 18 examined specimens of Aphnelepis australis, only one shows details of the posterodorsal region of the cranium. AM F120491 (Figs 2, 6) shows two postcleithra that are large scale-like structures ventral to the lateral line.

Fig. 6. Aphnelepis australis (AM F104690) whitened latex peel showing cranial bones and pectoral fins exposed by rotation of the body.

The pectoral fins are low on the body. On the holotype, AM F117884, the pectoral fin is quite large (Fig. 1A), as can be seen also on AM F 104690 (Fig. 6), where the pectoral fin is exceptionally well preserved due to rotation of the body, and up to16 rays can be counted. In some other cases only 10 rays are discernible because of damage. The first ray is simple, not fused to a basal fulcrum, does not bifurcate, and has small fringing fulcra on the anterior side of the ray for its whole length. The proximal section of each ray is long, followed by a bifurcation and then small segments.

Pelvic fin and pelvic girdle

The pelvic fins are small and located low on the body. They are located about mid-way between the head and the caudal fin, slightly closer to the anal fin than to the pectoral fin (Figs 1A, 4, 7B). There are six rays, with fringing fulcra along the whole length of the leading ray.

Fig. 7. Aphnelepis australis (AM F141883). A, Dorsal fin (df) showing long anterior ray with concave posterior margin of fin and ridge scales (rs) anterior to dorsal fin. B, Anal (af) and pelvic (pf) fins showing fringing fulcra with cloaca (c).

Dorsal and anal fins

The insertion of the dorsal fin is almost opposite the insertion of the pelvic fin. The best-preserved example of the dorsal fin is AM F141883 (Fig. 7A). The dorsal fin has 16 rays, with four procurrent rays anteriorly. Principal rays 1 and 2 are very long and fine, being more than twice as long as rays 5 and 6. Thus, the posterior margin of the dorsal fin is strongly concave. Fringing fulcra cover the whole extent of the leading ray. There are 16 or 17 pterygiophores including those supporting the procurrent rays, but they are not always well preserved, especially posteriorly. The first principal ray does not bifurcate, but the second ray bifurcates after half its length. This specimen is the only one seen where the dorsal fin is not damaged. In subsequent rays the first bifurcation occurs at about half the total length of the rays. There is a second bifurcation after another quarter of the length. The first pterygiophore, which is not bifurcated, supports the first two procurrent rays, and the second supports procurrent rays 3 and 4. The long first ray on the dorsal fin is also visible on ANU 61112a, AM F27070, AM F120869, GSNSW 36724 and NHMUK 12412.

The anal fin (Fig. 7B) has one long, unsegmented fin ray followed by 11 segmented fin rays (12 rays in total). The proximal segment of each ray is about half the total length of the ray, followed by a bifurcation and shorter segments. There are two or three small procurrent rays, and fringing fulcra cover the whole leading edge of the fin. There are 11 pterygiophores, with the last one supporting the last two rays. The base of the anal fin is considerably shorter than for the dorsal fin. The posterior margin of the anal fin is slightly concave.

Caudal fin and endoskeleton

The caudal fin (Fig. 8) is hemiheterocercal, deeply forked with the five central principal rays about half as long as the epaxial and hypaxial lobes. The epaxial margin is covered anteriorly by a single caudal scute, followed by six or seven epaxial basal fulcra, and a series of small fringing fulcra extending along the whole of the epaxial margin of the fin.

Fig. 8. Aphnelepis australis (AM F120533). A, Caudal fin in lateral view whitened with ammonium chloride. B, Reconstruction of tail from peel (reversed). Abbreviations: d.sc, dorsal caudal scute; E1–3, epural 1–3; ebf, epaxial basal fulcra; ff, fringing fulcra; H, hypural (unnumbered); hbf, hypaxial basal fulcrum; hpr, hypaxial procurrent ray; hsPU2?, possible preural haemal spine 2; PR 1–20, principal rays 1–20; ud, urodermals; un 1–3, uroneural 1–3; v.sc, ventral caudal scute.

The hypaxial margin has a single scute that is slightly smaller than the epaxial scute. There are four hypaxial basal fulcra, followed by a series of small fringing fulcra along the hypaxial margin.

There are 19 principal rays with the epaxial and hypaxial rays not being bifurcated, and the inner 17 rays bifurcating at least once. AM F141883/4 has 19 principal rays with a single procurrent ray on both the epaxial and hypaxial margins that are segmented but not divided, but only extend for about half the length of the lobes. ANU 61112 has the same arrangement of rays, as does AM F120533. The latter specimen is well preserved, but in the central section of the tail it is difficult to count the rays. It also has one short hypaxial procurrent ray. AM F120869 also has 19 principal rays and one hypaxial procurrent ray. The articulations between segments of the principal rays are generally straight, except in the segments approaching a bifurcation of the ray, where they are Z-shaped. There is a patch of 10 or 12 diamond-shaped urodermals arranged in two parallel rows at the commencement of the epaxial lobe of the fin.

There is no complete exposure of the caudal endoskeleton as it is covered by scales. Some incomplete details are observable on the following specimens. AM F120533 (Fig. 8) has traces of at least five hypurals, but the dorsal-most hypurals are hidden by the urodermals. It is difficult to identify with surety the number of hypurals, which trace might be a parhypural, and which trace represents the preural haemal spine, because there is no detail of the proximal ends of these structures. Labels in Fig. 8 should not be considered definitive. ANU 61112 has traces of three epurals and several hypurals. ANU 61126 has a clear large dorsal scute, and traces of the five ventral haemal spines and hypurals supporting the hypaxial lobe. AM F 120869 has a large hypaxial scute and traces of at least seven hypurals. GSNSW 36724 has a large dorsal scute, at least eight hypurals, and three epurals.

Fig. 9. Aphnelepis australis (AM F27070) in lateral view, showing division between rhombic ganoid scales anteriorly (as) and circular scales posteriorly (ps). Grid divisions = 10 mm.

Scales

The pattern of the squamation is one of the distinguishing features of this taxon. There is a clear demarcation between anterior and posterior scales. This is marked by the line joining the anterior insertion of the dorsal fin with the anterior insertion of the anal fin (AM F141884, AM F120492, AM F120869, AM F27070 (Fig. 9)). In front of this line the scales are ganoid, deeper than long, sub-rectangular shape, with crenulated posterior margins, especially in the mid-flank region. Anteriorly there are 18 vertical rows of scales with the five central horizontal rows of scales that are more than twice as deep as they are long. The crenulations are very small (AM F120503; Fig. 10), being the terminations of fine radiating ridges on the posterior field of the scales. Each of the dorsal ridge scales between the back of head and dorsal fin has a short posterior spine projecting over the next scale.

Fig. 10. Aphnelepis sp. (AM F120503) anterior body scales with almost parallel fine ridges resulting in crenulations at their posterior margin. Anterior is to the left. Pectoral fin rays (pf).

The posterior scales are not enamelled, are smaller, almost circular on exposed area and still have crenulated posterior margins. They are lighter/thinner, so some features such as the positions and shape of fin radials and vertebral column elements are apparent. They are semi-transparent, making 18 vertical rows of scales. Posterior to the dorsal and anal fins there are nine horizontal rows of scales. The position of the lateral line makes a clear line parallel to the spine down the middle of the side of the fish. Anterior to the dorsal fin there is a row of dorsal ridge scales. Six of these scales can be seen anterior to the dorsal fin (Fig. 7A).

There is also a rarely preserved structure (Fig. 7B) in advance of the anal fin that appears to be a cloaca surrounded by small scales.

Phylogenetic analysis

The phylogenetic dataset set up in Mesquite 3.81 consists of 201 characters and 43 taxa. It is based on the matrix of Arratia (2017), which comprises 195 characters, but modified with five additional taxa and two characters (N = 197) for the analysis of Archaeomenidae by Bean (2021). Two archaeomenid taxa, Zaxilepis quinglongensis and Gurvanichthys mongoliensis were deleted herein because no specimens were available for re-examination. Coding for Archaeomene tenuis, Wadeichthys oxyops and Oreochima ellioti was checked with differences listed in Supplementary Data 1. Aphnelepis australis was added, and Anaethalion White, 1938, Lycoptera middendorffi Müller, 1845, and Siemensichthys siemensi Arratia, 2000 (sensu Arratia 2017) deleted to remove excessive missing data. All characters were unordered with equal weighting. User designated outgroup taxa included: Amia calva Linnaeus, 1766, Amia pattersoni Grande & Bemis, 1998, Lepisosteus Lacépède, 1803, Obaichthys Grande 2010 and Watsonulus Brough, 1939.

The four additional and one modified characters for this analysis are described as follows:

• Character 180. Caudal fin (modified) without epaxial lobe or few epaxial rays, long notochord extending to tip of fin or close to it, and hypurals following its path (heterocercal) [0]; Notochord upturned, but not extending into epaxial lobe (hemiheterocercal) [1]; epaxial lobe developed, short notochord, and hypurals in a fan-shape distribution (homocercal tail) [2]. This has been changed from Bean (2021) to accommodate the hemiheterocercal condition. All taxa were coded by referring to published descriptions (see Supplemental Data 1).

• Character 196. Includes a rewording of the description of the suture between opercle and subopercle. Opercle-subopercle suture: nearly horizontal [0]; oblique [1]; curved, not straight [2].

• Character 198. Compares the size of the anal and dorsal fins. Base of anal fin longer than base of dorsal fin [0]; anal shorter than dorsal fin [1]; approx. equal length [2].

Characters 199 and 200 are unique conditions for Elopomorpha. Elops Linnaeus, 1766 and Megalops Valenciennes, 1847 are extant, but Anaethalion is a fossil member of Elopomorpha.

• Character 199. Leptocephalous larvae is a character shared by Elops and Megalops. The presence of leptocephalous larvae have only been observed in extremely well-preserved fossils of Anaethalion (Arratia 1997, pp. 56–58), so all fossil fishes except the Elopomorpha have been coded [?].

• Character 200. The unusual morphology of the spermatozoa flagellum is also a synapomorphy of Elopomorpha (Wiley & Johnson 2010). The list of taxa in the analysis includes the extant A. calva, Lepisosteus, Heterotis Rüppell, 1828 and Hiodon Lesueur, 1818. Character 201 in this analysis is the same as Character 197 in Bean (2021).

The phylogenetic analysis was carried out with PAUP 4.0a 169 (Swofford 2002). A heuristic search retained four most parsimonious trees (length = 644; Consistency Index = 0.4658; Homoplasy Index = 0.6025; Retention Index = 0.7509) and resolved A. australis as a member of Archaeomenidae at Node D. Other cladograms (Fig. 11) for major clades include: Node L, Varasichthyidae as a sister group of crown teleosts; Node E, Pholidophoridae; Node G, Ankylophoridae as a sister clade; Node C, Prohalecites as sister to other Teleostei. Aspidorhynchidae and Pachycormidae also form a monophyletic sister lineage to Teleostei, thus comprising Teleosteomorpha (see Arratia 2001, 2013, 2017).

Fig. 11. Strict consensus and majority-rule majority trees placing Aphnelepis australis within Archaeomenidae. Black numbering above branch indicates >50% clade resolution; bootstrap values shown in red below the lines. †Fossil taxa.

Character state distributions

Node B represents the clade Teleosteomorpha, and is supported by seven synapomorphies: Character 13 [0], the autosphenotic is absent; Character 45 [0], tube-like canal bearing anterior arm of antorbital is absent; Character 56 [1], a complete ring of two sclerotic bones oriented anterior and posterior to eye is present; Character 104 [0], an occipital condyle is absent; character 128 [1], the first principal ray of the pectoral fin is compound, fused with a basal fulcrum; Character 162 [1], each hypural normally articulated with a few caudal rays; Character 187 [1], ganoid scale rows at mid-flank between postcleithra and pelvic fins have three rows of distinctively deeper than long scales.

Node C defines Teleostei and groups Prohalecites and the Archaeomaenidae clade with all other teleosts. It is supported by five synapomorphies: Character 39 [1], supraorbital canal with simple tubules; Character 61 [1], the premaxilla is mobile, lying lateral to the rostral; Character 126 [1], there are four pectoral proximal radials; Character 167 [0], epaxial lobe of the caudal fin without rudimentary ray; Character 197 [0], shape of opercle: sub-rectangular, deeper than long.

Node D has four characters supporting Archaeomenidae with all other teleosts: Character 3 [1], the orbital region of the skull roof is slightly narrower than the postorbital region; Character 53 [1], there is one suborbital bone; Character 70 [1], the quadrate-mandibular articulation is below the posterior half of orbit; Character 178 [1], there is a long dorsal caudal scute.

Synapomorphies

Aphnelepis australis is supported by five apomorphies: Character 64 [1], the posterior margin of the maxilla is slightly concave; Character 120 [1], the lateral line emerges from the supracleithrum at its posteroventral margin; Character 152 [4], number of ural neural arches modified as uroneurals is three or less; Character 196 [1], the suture between the opercle and the subopercle is oblique; Character 197 [2], the shape of the opercle is tapering anteroventrally.

Archaeomene tenuis has the following autapomorphies: Character 95 [1], preopercular sensory canal with long tubules opening on the ventral and posteroventral borders of the preopercle; Character 122 [1], postcleithra are formed by external cycloid scaly elements; Character 132 [1], there are no fringing fulcra on the pelvic fin; Character 138 [1] and Ch. 140 [1],) there are no fringing fulcra on the leading edge of the dorsal or anal fins; Character 181 [2], the scales are of the elasmoid cycloid type; Character 198 [0], the anal fin is longer than the dorsal fin.

Wadeichthys oxyops is supported by five characters: Character 3 [0], the skull roof has no distinct broadening between the orbital and postorbital regions; Character 41 [1], the middle pit-line groove is absent from the dermopterotic; Character 50 [1], the posterior margin of infraorbital 4 is serrated; Character 67 [0], there is only one supramaxillary bone; Character 99 [1], the preopercle is crescent-shaped.

Oreochima ellioti is supported by four characters: Character 21 [1], the posterior margin of the extrascapula bone is serrated; Character 48 [1], infraorbital 4 is an expanded, broad bone; Character 101 [1], the posterior margin of the preopercle is serrated; Character 188 [1], the caudal fin is without a well-defined, small lobe of ganoid scales extending dorsally and covering the base of the dorsal principal rays.

Discussion

Morphology of Aphnelepis australis

Woodward (1895) placed Aphnelepis australis in the family Semionotidae. However, these taxa show significant differences in the squamation, shape of the snout, infraorbital series, and structure of the jaws (Olsen & McCune 1991). Wade (1941) alternatively placed Aphnelepis in the monospecific family Aphnelepidae, which is rejected here. Nelson et al. (2016, p. 124) described Semionotidae as having dorsal ridge scales (present in A. australis), and an epiotic with a large posteriorly directed process (not identified in A. australis), yet these features occur in other non-teleostean fishes (Olsen & McCune 1991; López-Arbarello & Codorniú, 2007; Gibson 2013). The ridge scales of A. australis overlap each other posteriorly, but their low spines are not as prominent, and no other archaeomenids possess ridge scales. Similar differentiation between anterior and posterior scales has been observed in Hemicalypterus Schaeffer, 1967, which is assigned to Dapediidae (Gibson 2016).

The anterior section of the dentary in A. australis (Fig. 3A) exhibits small pores just above the trace of the mandibular canal. These resembles the pores on the anterior section of the dentary in Archaeomene tenuis (Bean 2021).

An autapomorphy of A. australis is the series of supraneural bones extending to near the posterior end of the dorsal pterygiophore series. They are visible because of the light scales that occur posterior to the dorsal–anal line. Supraneural bones are common in teleosts, such as in members of Orthogonikleithridae, including Cavenderichthys talbragarensis and Waldmanichthys koonwarri (Waldman, 1971) (see Bean & Arratia 2019); however, they do not usually extend beyond the first and second dorsal pterygiophores. The preserved squamation also usually prevents observation of the supraneurals in fossils of these taxa.

Phylogenetic placement of Aphnelepis australis

The phylogenetic analysis supports placement of Aphnelepis australis within Archaeomenidae. It also accords with previous assessments of Griffith & Patterson (1963) and López-Arbarello et al. (2008), who referred A. australis to Archaeomenidae without phylogenetic testing. By contrast, attribution of A. australis to Aphnelepidae by Wade (1941), and assignment of Archaeomenidae to Pholidophoriformes (sensu Arratia 2013) are not supported.

Aphnelepis australis displays a unique character state combination amongst archaeomenids.

• The squamation arrangement comprising rhombic ganoid scales found anterior to a line joining the anterior margins of the dorsal and anal fins, together with lighter scales that lack ganoine situated behind this line, is also found in a few other neopterygians, including some members of the family Dapediiformes (Thies & Waschkewitz 2015, Gibson 2016), and also Aetheolepis mirabilis (Woodward, 1895) from the Talbragar Fossil Fish Bed.

• The very long first dorsal fin ray occurs in no other archaeomenids.

• The series of supraneural bones extending almost to the back of the dorsal fin is comparable to those of Jurassic teleosts, such as Ascalabos voithii Münster, 1839 Leptolepides Blainville, 1818, and Anaethalion (Arratia 1997), but the supraneural series of these taxa does not extend between the dorsal pterygiophores and the neural spines as far as the rear of the dorsal fin. Most teleosteomorphs, like pholidophorids, otherwise have ganoid scales covering the entire body (Arratia 2013), thus the presence or absence of supraneural rays not observable. Notably, though, supraneurals are not present in the exposed endoskeleton of Tharsis Giebel, 1848 (Arratia et al. 2019).

• While not pronounced, the presence of dorsal ridge scales between the back of the cranium and anterior of the dorsal fin is distinctive for Aphnelepis australis.

Some distinguishing character states of A. australis are not resolved as autapomorphies: moderately deep body; cranial bones ornamented with small tubercles and rugae (Character 42), and the large opercle with the oblique ventral margin (Character 196). The position of the dorsal fin level with the pelvic fin is similar to the condition in Zaxilepis quinglongensis (Bean 2021), but contrasts with the posterior location of the dorsal fin in Archaeomene tenuis, Wadeichthys oxyops, and Oreochima ellioti.

The following character states unite all archaeomenids, but are not unique to the family: a short snout with a gentle anteroventral curve (Character 201); two large flat nasal bones joined medially (Characters 24 and 28); postparietal bones that are quadrangular; triangular extrascapulae; small premaxillae with tiny teeth but no ascending process (Character 59); two supramaxillae on each side (Character 67); a single large suborbital filling each cheek (Character 54); a large medial triangular gular (Character 103); small paired fins located on the ventral surface; serrated appendages located on the cleithrum (Character 123); a persistent notochord (Character 111); hemiheterocercal caudal fin structure (Character 180).

The family diagnosis for Archaeomenidae provided in Bean (2021) included two character states that are no longer valid: suture between the opercle and subopercle being almost horizontal, which is otherwise present in A. tenuis, W. oxyops, O. ellioti, Z. quinglongensis and Gurvanichthys mongoliensis, but not A. australis; and the dorsal fin being posterior to the pelvic fin, which is common to A. tenuis, W. oxyops and O. ellioti, but not A. australis and Z. quinglongensis.

In summary, this re-evaluation of A. australis based on new specimens has robustly defined its relationships amongst Mesozoic neopterygians, and confirms its position within the family Archaeomenidae. Future research on other coeval taxa, especially A. mirabilis, must therefore be undertaken to resolve the faunal diversity and the community palaeoecology of the spectacular Jurassic fossil fish assemblage from the Talbragar Fossil Fish Bed of New South Wales, Australia.

Acknowledgements

Thanks to Gloria Arratia (Kansas University) for supervision and support. Mark Wilson (Loyola University) assisted with the phylogenetic analysis. Matthew McCurry (AM) allowed access to material. The Research School of Earth Sciences at ANU supported my postdoctoral research. Duncan Bean enabled digitization of illustrations. Two reviewers and the Editorial Board of Alcheringa contributed improvements on this paper.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplemental data

Supplemental data for this article can be accessed online at https://doi.org/10.1080/03115518.2024.2311092.