Neopterygii

Taxa on This Page

1. Ginglymodi
2. Halecomorphi
3. Halecostomi
4. Ionoscopiformes X
5. Lepisosteiformes
6. Macrosemiiformes X
7. Neopterygii
8. Parasemionotidae X

Neopterygii: same old wings, but a new jaw

Neopterygii means "new wings."  Despite this portentious name, the experienced student -- hardened to the bitter disappointments of scientific nomenclature -- will be unsurprised to learn that neopterygians were neither new nor wingèd. True, there are some changes in the fins by comparison to earlier actinopterygians. A 1:1 ratio between radials and basals in the dorsal and anal fins is diagnostic of this taxon. The caudal fin also becomes more symmetrical. However, the truly homocercal (symmetrical) tail fin is not achieved until the teleosts. Thus, the changes in the "wings" at the level of the Neopterygii are actually rather mundane and unimpressive.

The irony of this name is that almost everything else about the Neopterygii really does involve significant novelties. For example, heavily mineralized scales, a hallmark of osteichthyan integument since the Silurian, begin to be shed. The vertebral centra show significant ossification. The clavicle disappears. These are osteological signals that the whole scheme of locomotion was being changed.

Like the advent of the automobile, the new locomotion created dramatic changes in life style. Greater speed generated, not just quick hunters, but also fast food. However, fish lack the ability (or patience) to use Drive-Thru windows. Thus it became necessary to evolve some anatomical equivalent to those elaborately indifferent young persons whose function it is to thrust randomly chosen packages of tepid, lard-soaked paper through car windows.

This, eventually, was the triumph of the teleost jaw. The mechanics of this instrument will be taken up elsewhere. In essence, teleosts drop the posterior end of the upper jaw, rather than the anterior end of the lower jaw. The flexible branchiostegal rays at the bottom of the mouth cavity flex, and the whole mouth expands (and also moves forward) while the anterior jaws barely open. Done very quickly, this creates a surprisingly large pressure difference which sucks in food items like a straw. In fact, a human uses a straw in much the same way except that humans are able to use muscular lips as a substitute for bone and cartilage.

The foundations for this incredible edifice of evolution were laid by the Permian and Jurassic neopterygians. As the image of Amia shows, early neopterygians probably still relied on engulfing prey. But even this feeding method is advantaged by attaining greater flexibility in the posterior parts of the jaw. Initially, neopterygians evolved a symplectic, a sort of alternate quadrate lying medial (interior) to the original quadrate, the symplectic also articulated with the lower jaw and presumably allowed the lower jaw to drop at its posterior end while remaining strongly braced against the body of pillar of the hyomandibular. In Amia, as in all other neopterygians, the upper jaw is no longer bound to the opercular series, and is free to swing ventrally at its posterior end. Among the Halecostomi, the maxilla actually develops an anterior ball-in-socket joint with the neurocranium   (Compare the mechanism used by the Chondrostei).

In addition, the Neopterygii developed more flexibility in the branchiostegal rays. The system of branchiostegals was not new Neopterygii.  Cheirolepis, and even acanthodians, clearly have them. See section on gular osteology. However, the Neopterygii were able to make more, and more flexible, use of these overlapping plates to expand the oral cavity by interposing an interopercular bone (actually an exapted branchiostegal ray) between the large operculars and the small branchiostegals.

Image:  adapted from several figures in Carroll (1988). An equivalent photograph of the skull bones can be found at Fish Skull. APW 040806.

Neopterygii: gars + teleosts

Description: mouth terminal; maxilla short with posterior freed from cheek; jaw swings laterally and increases oral volume; symplectic attaches to suspensorium and frees jaw (lost in later forms); interopercular separates subopercular from branchiostegal rays; adductor not confined by bone; anterior maxilla free of operculars so that posterior rotates forward – creating circular mouth opening; increase suction, size (Teleostei); lower jaw articulates with the vertical quadrate and neomorphic symplectic bone; reduction or loss of ganoid and reduction of scales also required ossification of vertebra to resist flexion; #rays = #basals in dorsal & anal, upper lobe of caudal reduced (symmetric); $ heterocercal caudal becomes homocercal fin reduced weight allows this); $ clavicle absent; swim bladder increasingly used for buoyancy control rather than auxiliary respiratory device?; feeding changes complimentary to locomotor changes?

Links: Neopterygii; BONY FISHES; 209 lec s02/20905s02.pdf; bodyskeleton.pdf; Untitled Document; Home.

Notes: capable of rapid and complex movement, efficient respiratory systems, variability in diet. Note that virtually all living fish have adopted very lightweight scales or lost them, as well as reducing the amount of bone. At some point in the Cretaceous, or perhaps earlier, weight reduction and rapid mobility seem to have become critical for survival. Another significant change at this level is the more flexible floor of the branchial chamber. A rigid floor requires ram ventilation, respiration using movement of the operculum, spiracular ventilation, etc. Branchiostegal rays give more room for ventilation through the mouth and a more efficient way of forcing water past the gills. The most important change is in the structure of the jaw in teleosts. The jaw mechanics are discussed in more detail (with crude diagrams) in connection with the premaxilla. APW 040806.

Ginglymodi: gars & extinct relatives

Range: from the Late Triassic?, in fresh waters of North America, Europe and Africa. Presently restricted to North America.

Phylogeny: Neopterygii: Halecostomi + *: Macrosemiiformes + Lepisosteiformes.

Characters:  rostrum elongate; infraorbital bones that bear teeth; quadrate extends well past the anterior portion of the orbit;  elongate maxillary and lower jaw bones with heavy dentition; elongate body; posterior dorsal & anal fins; heavy ganoid scales; convexly rounded caudal fin [GB98]; typically found in slow moving warmish water; classic "sit and wait" ambush predators.

Links: Untitled Document; Agnatha - Jawless; Untitled Document; Evaluation of knowledge of advanced actinopterygians at the ....

References: Grande & Bemis (1998) [GB98]. APW 040806.

Macrosemiiformes: Aphanepygus, Disticholepis, Enchelyolepis, Histionotus, Legnonotus, Macrosemius, Notagogus, Orthurus, Petalopteryx, Propterus.

Range: Late Triassic? to Late Cretaceous of Europe, Asia, North America (Mexico) & Africa

Phylogeny: Ginglymodi: Lepisosteiformes + *.

Characters: supramaxilla absent [C88]; 7 unique scroll shaped infraorbitals [C88]; 2 additional tubular bones postorbitally [C88]; quadratojugal retained [C88]; symplectic does not articulate with lower jaw [C88]; some with elongate dorsal fin [C88].

Image: Propterus from Solnhofen Fishes (Rotonda Rock)

Links: Macrosemiiformes; Welcome (Aphanepygus); 151histionotus Histionotus); Pagefossil1; Histionotus); LEGNONOTUS; The presence of the Macrosemiidae; Verkaufs- und Tauschliste. Macrosemius);  

References: Carroll (1988) [C88]. APW 040806.

Lepisosteiformes: gars, Lepisosteus, Atractosteus.

Description: maxilla reduced; sclerotic ring absent [GB98]; suborbitals present [GB98]; preoperculum L-shaped [GB98]; quadrate extends well anterior to orbit; exoccipital ventral (or proximal) processes do not reach posterior margin of occiput [GB98]; paired vomers; 3 branchiostegal rays; gular or interopercular absent; teeth of upper jaw on infraorbital series; needle-like teeth; opisthocoelous (! very unusual in an actinopterygian); caudal series reduced, and ventral elements enlarged to form triangular hypurals; parapophyses fused to abdominal centra [GB98]; dorsal fin far posterior (ambush predators evolved to accelerate quickly); few dorsal rays; 5-10 & rarely >10 ural centra [GB98]; approximately 1:1 ratio of caudal fin rays to hypurals [GB98]; moderate degree of ossification retained; largely retain primitive interlocking ganoid scales; ambush predation with lateral snapping movement; facultative air breathers with vascularized swim bladder. Chiefly freshwater, in brackish water occasionally; very rarely marine; occurs usually in shallow, weedy areas.

Links: MEANING OF GAR(FISH); FishBase; Master Index of Freshwater Fishes; BioMed Central - Normal embryonic stages of the Longnose Gar, ....

References: Grande & Bemis (1998) [GB98]. APW 040806.

Halecostomi: (Note: thumbnail links to a large image (1440 x 1067) in a new window

Range: from the Triassic

Phylogeny: Neopterygii: Ginglymodi: + *: Halecomorphi + ((Semionotiformes + Pycnodontiformes) + (Pachycormiformes +  Teleostei)).

Characters: Evolution of a third series of muscles in the jaw series see note); anterior ball-in-socket joint between maxilla and neurocranium; median neural spines fused to vertebrae (??).

Note: Actinopterygians generally have two series of muscles that facilitate jaw opening: (i) an epaxial series which elevates the head, and (ii) a hypaxial series which lowers the mandible (lower jaw). The Halecostomi possess a third series (including the m. dilator operculi) that attach the cranium and lower jaw to the opercular bone series. The significance of this third attachment series is that there are now four ways for the fish to open its mouth: (1) elevation of the head via the epaxials, (2) depression of the mandible via the hypaxials, (3) swing down of the maxillary bone, and (4) contraction of the opercular muscles to open the mouth in a medial direction. This, again, results in greater flexibility of jaw opening, greater "suction-like" ability for feeding, and generally a greater range of options for feeding mode which likely promoted ecological diversification and, ultimately, speciation in teleosts. From Untitled Document with minor changes. See image at that site.

Links: Untitled Document (Best on the Web); Sinapom Portuguese); Bony Fishes; feeding.pdf. APW 040806.

Halecomorphi: Amia only living genus). A. calva Linnaeus 1766.

Description: $ notch or concavity on posterior margin of maxilla [GB98]; $ 1 supramaxillary bone [GB98]; $ ventral extension of symplectic articulates with lower jaw as does quadrate (but not present in most parasemionotids) [GB98] [C88]; lateral cranial fissure bridged over in various ways except some parasemionotids) [C88]; primitively, caudal fin is forked [GB98].

Image: Amia calva. Photograph by Konrad P. Schmidt. Reproduced by permission.

References: Grande & Bemis (1998) [GB98]; Carroll (1988) [C88].

Parasemionotidae: Albertonia, Broughia, Devillersia, Helmolepis, Icarealcyon, Jacobulus, Lehmanotus, Ospia, Parasemionotus, Piveteaunotus, Praesemionotus, Promecosomina, Stensionotus, Thomasinotus, Watsonulus. 

Range: Early Triassic to Late Triassic of Australia, China, Europe, Greenland, Madagascar & North America (Canada).

Phylogeny: Halecomorphi: (Ionoscopiformes + Amiiformes) + *.

Characters: sclerotic ring present [GB98]; $ preopercular ovoid & fused with suborbital [GB98]; sensory canal runs along poster edge of preopercular; supraneurals numerous [GB98].

Links: Parasemionotiformes; Vertebrates; PAST LIVES- CHRONICLES OF CANADIAN PALEONTOLOGY - Chapter 27 Albertonia); "_ _"; PALEOGUY Online! (Parasemionotus); Phylogenetic analyse of Eoeugnathus megalepis; Swimming patterns of Malagasyan Triassic fishes and environment; Mesozoic Fishes - 2- Systematics and Fossil Record discussion of Arratia paper).

References: Grande & Bemis (1998) [GB98]. APW 040806.

Ionoscopiformes: Ionoscopus, Macrepistius, Ophiopsis, Oshunia

Range: Early Jurassic to Late Cretaceous of Europe, South America & South Asia.

Phylogeny: Halecomorphi:: Amiiformes + *.

Characters: rostral bone V-shaped, with lateral horns [GB98]; dermosphenotic sutured into & forming part of skull roof [GB98]; $ dermosphenotic with flange inside orbit bearing sensory canal tube [GB98]; $? parietal relatively long (length >= width) [GB98]; sclerotic ring present [GB98]; 1+ suborbitals [GB98]; preoperculum crescentic, long & narrow [GB98]; supraotic ossification encloses dorsal parts of anterior and posterior semicircular canals; supraotic exposed on skull roof at posterior midline; vertebral centra with 2 lateral fossae in at least some genera [GB98]; numerous supraneurals [GB98].

Image: Ionoscopus from Verkaufs- und Tauschliste.

Links: Elasmobranch and actinopterygian remains from the Jurassic and ...; Verkaufs- und Tauschliste.; FORMAÇÃO SANTANA; Fossilien aus dem Plattenkalk von Solnhofen und Eichstätt ( ... -;  ARARIPE HOME PAGE; The Axelrod Fish Fossil Collection...continued; Abbildungen Sonderangebot Santana-Fische.

References: Grande & Bemis (1998) [GB98]. APW 040806.