Box Relationships Of Neopterygii

The Neopterygii are a vast and diverse group and there is still much contusion over their relationships. Most studies (e.g. Patterson and Rosen, 1977; Lauder and Liem, 1983; Gardiner et al., 1996; Johnson and Patterson, 1996), however, agree on the main points (see cladogram). The basal neopterygians, formerly termed 'holosteans', form a series ot outgroups to the Teleostei. In previous versions, all subsequent taxa formed a series ot outgroups, but new work (Johnson and Patterson, 1996) shows that Clupeomorpha and Ostariophysi pair as the clade Otocephala.

S NEOTELEOSTEI R NEOGNATHI

S NEOTELEOSTEI R NEOGNATHI

A NEOPTERYGII

G HALECOMORPHI P OTOCEPHALA Q EUTELEOSTEI EURYPTERYGII U CTENOSQUAMATA V ACANTHOMORPHA X ACANTHOPTERYGII

H TELEOSTEI F HALECOSTOMI

A NEOPTERYGII

O CLUPEOCEPHALA N ELOPOCEPHALA

G HALECOMORPHI P OTOCEPHALA Q EUTELEOSTEI EURYPTERYGII U CTENOSQUAMATA V ACANTHOMORPHA X ACANTHOPTERYGII

Cladogram showing relationships ot the derived ray-finned bony fishes (Neopterygii), based on the work ot Patterson and Rosen (1977), Lauder and Liem (1983), Gardiner et al. (1996) and Johnson and Patterson (1996). See Figure 7.7 tor context ot Neopterygii. Synapomorphies: A NEOPTERYGII, maxilla and preopercular not in contact with palatoquadrate, maxilla mobile, maxilla with peg-like anterior head, interopercular present, quadratojugal torms brace tor quadrate, symplectic present, upper pharyngeal dentition consolidated, fin rays equal in number to their supports in the dorsal and anal fins, clavicle lost or reduced to a small plate lateral to cleithrum; B, median neural spines, quadratojugal lost or tused with quadrate; C, vomer median; D, large median vomer, coronoid process on mandible, axial lobe ot tail reduced; E, symmetrical tail fin; F HALECOSTOMI, a supramaxilla, quadratojugal absent as independent element; G HALECOMORPHI, symplectic and quadrate bones both contribute to jaw articulation; H TELEOSTEI, mobile premaxilla, unpaired basibranchial toothplates, uroneurals (elongate ural neural arches) present; I, median tooth plate covers basibranchials 1-3; J, enamel layer lost trom most skull bones, cycloid scales; K, vertically keeled rostrum, prearticular element in lower jaw absent, no enamel layer on skull bones, nine or tewer hypurals; L, spiracular canal greatly reduced, loss ot separate surangular bone and appearance ot retroarticular, three epurals; M, tour pharyngobranchials, three hypobranchials; N ELOPOCEPHALA, two uroneurals extend anteriorly over the second ural centrum; O CLUPEOCEPHALA, endopterygoid teeth absent, uroneural 1 extends torward to preural 2; P OTOCEPHALA, epicentrals ossified, hypural 2 and ural centrum 1 tused, extrascapulars and parietals tused; Q EUTELEOSTEI, supraneurals develop in pattern 2, membranous anterodorsal outgrowth ot uroneural 1 present, caudal median cartilages present; R NEOGNATHI, tooth attachment type 4 (hinged), third uroneural absent, cheek and operculum scaled; S NEOTELEOSTEI, rostral cartilage; T EURYPTERYGII, reduction ot second preural neural spine to a halt-spine, tusion ot a toothplate to third epibranchial; U CTENOSQUAMATA, reduction or loss ot pharyngobranchial tour; V ACANTHOMORPHA, true dorsal and anal fin spines, rostral cartilage, median caudal cartilages absent, medial pelvic process ossified distally; W, well-developed ctenoid scales, expansion ot ascending and articular premaxillary processes; X ACANTHOPTERYGII, enlargement ot epibranchials two and three.

In an alternative view, Arratia (1997, 2001) argues that the clade Teleostei should be restricted to node J, as she has evidence that the Pachycormidae, Aspidorhynchidae, Pycnodontiformes and Dapedidae form a clade that is a sister group to a more restricted Teleostei. She also reverses the order of Elopomorpha and Osteoglossomorpha, but confirms the clade Oto-cephala.

Molecular data on relationships of the major neopterygian groups was limited until a flurry of publications appeared in 2003. Gardiner et al. (1996) noted that, among basal neopterygians, mitochondrial and nuclear DNA support a pairing of Amia and Lepisosteus as a resurrection of a clade 'Holostei', separate from teleosts, a result confirmed by Inoue et al. (2003) on the basis of mitochondrial DNA sequencing. New molecular studies of higher teleosts have mainly used mitochondrial DNA. Inoue et al. (2003) confirmed the lower part of the cladogram, including the clade Otocephala. Ishiguro et al. (2003) also found the Otocephala clade, as well as an Esociformes-Salmoniformes clade. Chen et al. (2003) and Miya et al. (2003) found the broad pattern in the upper part of the morphological tree (see cladogram), except that Polymixiiformes and Paracanthopterygii are paired as a side clade.

modifications to the jaw musculature. Living teleosts fall into four main clades, Osteoglossomorpha, Elopomorpha, Otocephala and Euteleostei. In addition, a series of extinct forms fall between the basal neopterygians and these living teleost groups (see Box 7.6).

7.4.1 Basal teleosts

The most primitive teleosts, the pachycormids and aspidorhynchids of the Jurassic and Cretaceous, have long bodies. One of the most astonishing pachy-cormids, Leedsichthys from the Middle Jurassic of England and France (Figure 7.9(a)), was a monstrous scaleless filter-feeder up to 10 m in length (Martill, 1988). Leedsichthys had a huge branchial basket in the throat region, consisting of the ossified gill arches covered with gill rakers each bearing hundreds of teeth (Figure 7.9(b)). As the fish swam with its mouth gaping, water passed into the mouth and out through the gills, and plankton and small fishes were filtered out. The aspidorhynchids, such as Aspidorhynchus (Figure 7.9(c)), were smaller and had long pointed snouts.

The pholidophorids of the Late Triassic and Early Jurassic, such as Oreochima (Figure 7.9(d)), were small hunting fishes that show advances in the jaws: there are two supramaxillae, there is an additional tooth-bearing element, the dermethmoid, beside the tooth-bearing premaxilla and the quadratojugal is fused to the quadrate (Patterson and Rosen, 1977). The leptolepids of the Jurassic and Cretaceous (Arratia, 1997), such as Varasichthys (Figure 7.9(e)) were also small, often as little as 50 mm long, and they may have fed on plankton. These fishes have fully ossified vertebrae and the scales are cycloid (circular, thin and flexible).

Another important extinct group, the ichthyodec-tids of the Jurassic and Cretaceous(Figure 7.9(f, g)), such as Xiphactinus,were mostly large predaceous fishes (Patterson and Rosen, 1977). They swallowed their prey head-first, as is normal among predatory fishes. A specimen of Xiphactinus, 4.2 m long, was found with a 1.6m ichthyodectid in its stomach area, and smaller relatives have been found with as many as ten recognizable fish skeletons preserved inside.

7.4.2 Osteoglossomorpha: bony-tongued teleosts

The osteoglossomorphs, a relatively small group of about 200 species that live in freshwaters mainly of the southern hemisphere, arose possibly in the Late Jurassic (Li and Wilson, 1996). Living forms include Osteoglos-sum from South America (Figure 7.10(a)), which has posteriorly placed elongate dorsal and anal fins, and the elephant-snout fish Mormyrus from Africa (Figure 7.10(b)), which has electric organs in the tail region. Osteoglossiforms are characterized by features of the feeding system (Figure 7.10(c)) that have shifted the

Fossil Fish Book

Fig. 7.9 Basal teleosts,dating from the Jurassic (a-e) and Cretaceous (f,g): (a) the giant pachycormid Leedsichthys; (b) gill rakers on the gill arches ofLeedsichthys,probably used for filter-feeding; (c) the aspidorhynchid Aspidorhynchus; (d) the pholidophorid Oreochima; (e) the leptolepid Varasichthys; (f) the ichthyodectid Xiphactinus; (g) skull of the ichthyodectid Cladocyclus. [Figures (a,b) after Martill, 1988; (c) after Nicholson and Lydekker, 1889; (d) after Schaeffer, 1972; (e) after Arratia, 1997; (f) after Osborn, 1904; (g) modified from Patterson and Rosen, 1977.]

Fig. 7.9 Basal teleosts,dating from the Jurassic (a-e) and Cretaceous (f,g): (a) the giant pachycormid Leedsichthys; (b) gill rakers on the gill arches ofLeedsichthys,probably used for filter-feeding; (c) the aspidorhynchid Aspidorhynchus; (d) the pholidophorid Oreochima; (e) the leptolepid Varasichthys; (f) the ichthyodectid Xiphactinus; (g) skull of the ichthyodectid Cladocyclus. [Figures (a,b) after Martill, 1988; (c) after Nicholson and Lydekker, 1889; (d) after Schaeffer, 1972; (e) after Arratia, 1997; (f) after Osborn, 1904; (g) modified from Patterson and Rosen, 1977.]

primary bite away from the maxilla and the lower jaw (Lauder and Liem, 1983). A bony element in the tongue, and the basibranchial behind, bear large teeth that bite against teeth on the parasphenoid in the roof of the mouth (hence the name osteoglossomorph, which means 'bony-tongue-form').

7.4.3 Elopomorpha: eels and relatives

The elopomorphs (literally 'eel forms') include about 800 species of eels, tarpons and bonefishes, and the group is known from the Early Cretaceous (Forey et al., 1996). The tarpon, Megalops (Figure 7.10(d)), is typically 'fish-shaped' and it seems hard to see how it can be regarded as a close relative of the eel, Anguilla (Figure 7.10(e)). All elopomorphs are characterized by a spe

Fig. 7.10 The osteoglossomorph (a-c) and elopomorph (d—g) teleosts;all extant: (a) Osteoglossum; (b) the elephant fish Mormyrus; (c) internal jaw system of Hiodon, showing toothed tongue and palate elements (lateral jaw bones removed); (d) the tarpon Megalops; (e) the eel Anguilla; (f) the leptocephalus larva of an elopomorph; (g) the skull of the saccopharyngoid eel Eurypharynx. [Figures (a,b,d—f) after Greenwood etal., 1966; (c) after Lauder and Liem, 1983; (g) after Gregory, 1933.]

Fig. 7.10 The osteoglossomorph (a-c) and elopomorph (d—g) teleosts;all extant: (a) Osteoglossum; (b) the elephant fish Mormyrus; (c) internal jaw system of Hiodon, showing toothed tongue and palate elements (lateral jaw bones removed); (d) the tarpon Megalops; (e) the eel Anguilla; (f) the leptocephalus larva of an elopomorph; (g) the skull of the saccopharyngoid eel Eurypharynx. [Figures (a,b,d—f) after Greenwood etal., 1966; (c) after Lauder and Liem, 1983; (g) after Gregory, 1933.]

cialized marine larval stage, the leptocephalus (Figure 7.10(f)) that is thin and leaf-shaped. The leptocephalus larvae can passively migrate long distances before they metamorphose.

Eels have many skeletal modifications including overall elongation of the body, loss of the caudal fin, loss ofthe pelvic girdle, loss ofribs, fusion ofelements in the upper jaw and loss of scales. The deep-sea eels called saccopharyngoids are even more modified, having lost many skull bones. Indeed the skull (Figure 7.10(g)) is really just a huge pair of jaws with a tiny cranium set in front. These fishes float quietly on the deep dark ocean floors and lever their huge mouths open to seize prey animals many times their own size.

7.4.4 Otocephala: herrings and carp

The otocephalans are a new group (Johnson and Patterson, 1996) that includes the Clupeomorpha and Ostariophysi, previously seen as distinct and successive outgroups to Euteleostei, but paired on the basis of morphological and molecular evidence (see Box 7.6).

The clupeomorphs contain over 350 species of extant herring-like fishes and over 150 fossil species that date back to the Early Cretaceous (Lecointre and Nelson, 1996). They are generally small silvery marine fishes, some of which, like the herring (Figure 7.11(a)) and anchovy, occur in huge shoals and feed on plankton. Clupeomorph characters include a peculiar type of abdominal scute, an unusual arrangement of the bones at the base of the tail in which the first hypural has a free proximal end and the second hypural is fused to ural vertebra 1 (Figure 7.11(b)), and a specialized air sac system in most.

The clupeomorph air sac extends into the exoccipital and prootic bones in the braincase. Most bony fishes have a sausage-shaped air sac called the swimbladder in the body cavity that is used to achieve neutral buoyancy. Gas is pumped into the bladder, or removed via the bloodstream in order to match the 'weight' of the fish to the pressure that acts at whatever depth it finds itself. In

Clupeomorphe

Fig. 7.11 The otocephalan teleosts, clupeomorphs (a-c) and ostariophysan (d): (a) the herring Clupea; (b) the tail of a clupeomorph, showing the hypural elements; (c) the Cretaceous clupeomorph Ornategulum; (d) the Weberian ossicles, which transmit vibrations from the swimbladder to the inner ear in ostariophysan fishes (ossicles are shaded and named). [Figure (a) after Greenwood et al., 1966; (b) based on Lauder and Liem, 1983; (c) after Forey, 1973; (d) after Fink and Fink, 1981.]

Fig. 7.11 The otocephalan teleosts, clupeomorphs (a-c) and ostariophysan (d): (a) the herring Clupea; (b) the tail of a clupeomorph, showing the hypural elements; (c) the Cretaceous clupeomorph Ornategulum; (d) the Weberian ossicles, which transmit vibrations from the swimbladder to the inner ear in ostariophysan fishes (ossicles are shaded and named). [Figure (a) after Greenwood et al., 1966; (b) based on Lauder and Liem, 1983; (c) after Forey, 1973; (d) after Fink and Fink, 1981.]

clupeomorphs, the swimbladder has a unique extension into the braincase and is also concerned with hearing.

Clupeomorphs assigned to the Ellimmichthyi-formes arose in the Early Cretaceous and are not known past the early Oligocene. Ornategulum from the Late Cretaceous (Figure 7.11(c)), a possible early clupeo-morph, was a small fish. Abundant herring-like fishes, Knightia, have also been found in the Eocene Green River Formation (see Box 7.7), often preserved in huge masses, suggesting that they lived in vast shoals, like modern herring-like fishes.

The Ostariophysi contains carp, goldfish, minnows, catfish and indeed most freshwater fishes (Fink and Fink, 1996). They are characterized by several features, including a specialized hearing system composed of modified cervical vertebrae, ribs and neural arches, called the Weberian ossicles (Figure 7.11(d)). There are five key bony elements that are connected by ligaments and provide a link between the anterior swimbladder and the ear. The os suspensorium and the tripus rest on the taut surface of the swimbladder. When sound waves reach the fish, the swimbladder vibrates and the Weberian apparatus effectively amplifies the sound. The two bones in contact pivot and the vibrations pass via the intercalarium, scaphium and claustrum to the inner ear.

7.4.5 Euteleostei: salmon, pike and derived teleosts

The largest teleost group, the euteleosts, consists of 17,000 species in 375 families. These may be divided into three main subgroupings, the salmoniforms, the esociforms and the neoteleosts (Lauder and Liem, 1983; Johnson and Patterson, 1996).

The Salmoniformes, the smelts, salmon and trout, possibly includes the early form, the tiny Gaudryella from the mid-Cretaceous (Figure 7.12(a)). True salmon appeared only later. The Esociformes is a small group containing pike and mudminnows that date from the Late Cretaceous to the present. Pike appear primitive because their dorsal fin is set far back and appears symmetrical with the anal fin, as in saurichthyids and gars.

The vast majority of euteleosts, some 15,000 species of advanced teleosts, fall in the clade Neoteleostei. The Neoteleostei are characterized by a specialized muscle in the upper throat region that controls the pharyngeal toothplates in the roof of the pharynx, an important adaptation for manipulating prey. The basal living

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