III. Actinopterygii:Actinopterygian fishes

INDEX

CheirolepisCladistia:

Discoserra pectinodon

Fish BonesGuildayichtus carnegeii

Paratarrassius hibbardi

Polypteriformes

Redfieldiidae

http://www.palaeos.com/Vertebrates/Units/090Teleostomi/090.200.html

Fish Bones

The Devonian is frequently called, with ample reason, the "Age of Fishes." The stage for this explosion of aquatic vertebrates was undoubtedly set in the Silurian, perhaps due to the duplication of ancestral hox genes. But, whatever the cause, the earliest Devonian saw the rapid development of chondrichthyans, placoderms, acanthodians, and the two most successful groups of vertebrates ever known: the actinopterygians and sarcopterygians -- collectively, the bony fish, the Osteichthyes.

Much has been written on the unique adaptations of the osteichthyans. Some of these points are summarized in the main entry in these Notes. However, what everyone remembers is that osteichthyans were the first group with endochondral bone.

In the more general vertebrates there are various types of calcified tissues: dentine, enamel (or "enameloids" to be precise) and bone, plus variants, characterized by their ontogeny, chemistry, form and location. However, endochondral bone is said to be unique because it begins life as cartilage. In more basal vertebrates, cartilaginous structures can become

superficially calcified in at least two different modes. Chondrichthyans develop microscopic bone platelets which cover the surface of the cartilage to create prismatic calcified cartilage. All gnathostomes and probably some more basal groups can also produce layers of bone over the surface of cartilage to create dense lamellar or perichondral bone. However, the bone-forming osteoblasts are eventually entombed in their own work product, cut off from all living connections, and drowned in their own metabolic wastes -- rather like post-modern philosophers.

In osteichthyans, the circulatory system actually invades the cartilaginous matrix. This permits the local osteoblasts to continue bone formation within the cartilage and also recruits additional, circulating osteoblasts (who have, presumably, been cruising around looking for some action). Other cells gradually eat away at the surrounding cartilage. The net result is that the cartilage is replaced from within by a somewhat irregular vascularized network of bone. Structurally, the effect is to create a relatively lightweight, flexible, "spongy" bone interior, surrounded by an outline of dense, lamellar periostial bone (since this bone now surrounds other bone, rather than cartilage, it is referred to as periostial rather than perichondral). Developmentally, in a sort of teleological, nineteenth century way, the process is viewed as "pre-forming" bone in cartilage, since the effective result is that a structure created in cartilage is replaced by the same structure composed of bone. This is the unique endochondral bone from which the osteichthyans derived their name, as well as countless structural advantages.

The problem here is that, like a lot of things, it ain't necessarily so.

That is, endochondral bone is not really unique to the osteichthyans. Endochondral bone is found, for example, in the rhinocapsular ossifications of some arthrodire placoderms. Janvier (1996). In the Chondrichthyes there may be a long-term evolutionary trend to incorporate small, but increasing amounts of endochondral bone. Maisey (1988). There have even been reports of endochondral bone in acanthodians, although it seems that these are now discredited. Smith & Hall (1990). Smith & Hall, as well as Janvier, tend to dismiss these occurrences as not really comparable to the wholesale use of endochondral bone in osteichthyans, and certainly there is a significant quantitative difference. However, it would seem that Maisey has the better argument and that endochondral bone is plesiomorphic, a generalized gnathostome character.

Second, it is not clear that endochondral bone was much of an advantage. If one ignores the aberrant tetrapods, the indiscriminate internal calcification of cartilage may be viewed as a relatively short-lived experiment in evolving a fish strong enough to carry around massive armored scales while maintaining a relatively high degree of mobility. The actinopterygians quickly jettisoned their ganoid scales and thus dispensed with the need for most endochondral bone. Sarcopterygians retained their heavy cosmine scales, and endochondral bone, but -- except for the tetrapods -- became virtually extinct in the process.

.

Polypteriformes The Polypteriformes contains the single family Polypteridae, with the single genus Polypterus.  It is known only from the Pleistocene and Recent, although this lineage obviously goes back much further in time. Polypterus, also called "the bichir" is the most primitive living Actinopterygians. Eleven species of bichirs inhabit shallow floodwater areas in tropical Africa rivers, where they feed on worms, insect larvae, and small insects.  This prehistoric looking fish resembles early actinopterygians from the Devonian in having a covering of thick rhombiodal scales, hardly overlapping but connected by fibres.  The scales are covered with ganoin, a dense shiny substance like enamel, which gives the fish an archaic armoured appearance and makes it rather clumsy.

The paired lung-like swim bladders are connected to the esophagus and are used for respiration; the fish die if denied access to the surface to gulp air.  Conversely though, the fish is able to survive for hours out of water.  Compare with the lungfish, another example of living fossil.  In the intestine there is a spiral valve, like that in the dogfish (a type of shark), which is not present in more advanced bony fishes. The skeleton of bichirs is mostly cartilage (again like the shark).  MAK990531

Osteichthyes I. Basic definitions:

A. For our purposes, Osteichthyes (bony fish) is defined as the most recent common ancestor of Actinopterygii (ray-finned fish) and Sarcopterygii (lobe-finned fish and land vertebrates.)

B. Synapomorphies: 1. Lungs: The presence of lungs - outpouchings of the esophagus used to obtain

suplimentary oxygen from "swallowed" air. As we will see, Actinopterygii and Sarcopterygii exploit this synapomorpy in very different ways.

2. Operculum: A large plate of dermal bone suspended from the hyoid arch covering and protecting the gill arches. (Ancestrally consists of three bones, the preopercular, opercular and subopercular.)

3. Tooth bearing dermal bones of mandibular arch: In upper jaw we see premaxilla and maxilla. In ancestral osteichthyans, the maxilla tends to be very long. Meckel's cartilage supports the dentary. Note that many dermal

ossifications of the skull are present, but their homologies across osteichthyan groups are questionable.

Osteichthyes: Andreolepis, Psarolepis? 

Range: From the Late Silurian. Phylogeny: Teleostomi: Acanthodii + *: Actinopterygii + Sarcopterygii. Characters: Pattern of cranial bones, rooted teeth, medial insertion of mandibular muscle in lower jaw; head & pectoral girdles covered with large dermal bones; sclerotic ring has 4 plates; labyrinth contains large otoliths; nostrils completely separated; neurocranium frequently divided into separated anterior and posterior sections divided by fissure; lung or swim bladder, pattern of opercular and pectoral girdle dermal bones; no fin spines; lepidotrichia (bone fin rays); endochondral bone, i.e. bone ossified internally, by replacement of cartilage, as well as perichondrally, as "spongy bone." Links: Biodidac: Osteichthyes (recently revamped with many new images -- and some nice things to say about these Notes); Osteichthyes Catalog (some specimens are linked to images); Fishes - Class Osteichthyes; General Zoology - Subphylum Vertebrata, Class Osteichthyes; Osteichthyes Characteristics; When Fish Bite;  Life, the Universe, and Everything: Fish Resources; OceanLink Answers to Osteichthyes (bony fish) Questions; 14. Class Osteichthyes; MFrefs.html; Class Osteichthyes; FishBase Glossary Searched Term; Wikipedia: Osteichthyes (most material contributed from these Notes); Osteich.htm; Osteichthyes; Gli Osteitti o Pesci Ossei, Osteichthyes (Italian. Very good site); M21.htm; Osteichthyes; osteichthyes.ppt.References: Ahlberg (1999); Zhu et al. (1999). Image: Modified from Zhu et al. (1999). 

Note: Zhu et al.'s (1999) description of Psarolepis from the Upper Silurian and Lower Devonian of China threatens to create chaos out the conventional, orderly treatment of this group. Psarolepis shares a number of characteristics previously believed to be unique to actinopterygians or sarcopterygians. In addition, it has several features, such as the fin spines and characters of the shoulder plate, which are associated with placoderms, chondrichthyans, or acanthodians. In overall appearance, Psarolepis most resembles a sarcopterygian, but the plates in isolation look strikingly like placoderm material. Depending on the data set used, PAUP suggests that it is either (a) the sister group of all (other) osteichthyans or (b) part of a paraphyletic Actinopterygii and sister of all (other) Sarcopterygii. The many strikingly primitive features and the pattern of cranial dermal bones probably favor (a), but these are admittedly a poor basis on which to make major phylogenetic decisions. ATW011116.

II. Fossil Material: The earliest possible osteichthyan fossils are of Silurian age, but the first unambiguous Osteichthyans are from the Devonian.

III. Actinopterygii : If one compares the living species diversities of Sarcopterygii and Actinopterygii, one finds them roughly similar, however most of Sarcopterygian diversity is made up of the land vertebrates. In the water, Actinopterygii form the overwhelming majority. In addition to their living diversity, they have, from the Devonian onward, a rich fossil record. When you consider that we will spend the next eleven lectures covering Sarcopterygii and approximately two thirds of this one on Actinopterygii, it should be clear that we are giving actinopterygians very short shrift and can't really hope to scratch the surface of their diversity. Just as chondrichthyan evolution was marked by a general trend toward ever faster generation and replacement of teeth, actinopterygian evolution is also marked by a few major trends. In the following resume of actinopterygian evolution, we will concentrate on tracking them.

A. From biting to sucking: The feeding apparatus of the ancestral osteichthyan relied on the scissor like action of the upper and lower jaws to bite and hold prey. Most modern actinopterygians employ a suction feeding mechanism, in which the the mouth extends to form a tube while the pharynx is expanded, sucking prey items in. Once inside, prey is dealt with by ay of a variety of jaw, tongue, or pharyngeal teeth. Two basic steps:

1. The anterior maxilla develops a hinged articulation with the braincase and is detached from other dermal bones, so that it can be rotated downward, narrowing the mouth opening to increase suction.

2. The premaxilla becomes mobile, sliding anteriorly along a groove in adjacent dermal bones. When it does so, it carries the posterior corner of the maxilla with is, extending the mouth anteriorly and causing it to assume a tube shape.

B. Controlling the vertebral column and tail: This takes two forms:1. The development of vertebral centra. In actinopterygians, the centra coossify

with neural and haemal arches.2. The neural and haemal arches of the tail are strongly modified.

a. Uroneruals: Neural arches overlap the centra , stiffening the tail in lateral motion.

b. Hypurals: Many haemal arches fuse to form a small number of triangular bone plates to which the tail fin rays attach, stiffening the tail i dorso-ventral motion.

c. While this is going on, the vertebral column of the tail is shortened and curls upward distally. The net effect is to create the familiar fan shaped homocercal fish tail, whose motion is restricted to a single vertical axis.

C. Swim bladder: Lungs were a plesiomorphy for actinopterygians. Some members continued to use them for their original purpose: as a supplimentary oxygen source. Others modified them into a unique organ, the swim baldder. This is used to maintain neutral bouyancy. Gasses are either pumped from the blood into the swim bladder or dissolved from the swim bladder into the blood as circumstances require. Note: Unlike the ancestral lung, the swim bladder does not communicate with the esophagus.

1. Gas exchange facilitated by a counter current flow mechanism capable of moving gas against a concentration gradient.

2. The achievement of neutral bouyance enabled actinopterygians to invade new ecological niches. Ancestrally, all fish had to swim against gravity to stay in the water column. Their general shape - elongate or flat with pectoral fins in a ventral position - reflected their need to rest on the bottom when not moving, as in modern sharks. Once free from this constraint, they could evolve a new, hydrodynamically efficient shape: the deep, laterally compressed body. With it, a fish could hover in one spot or accelerate very quickly. The pectoral fins could move to a position higher on the body where they could exert more effective control over manouverability. Today, fish that need to manouver ina nd out of confined nooks, such as reef fish, tend to have this shape. In the fossil record, we see several groups independently achieving this form, suggesting that all had the swim baldder.

3. The group containing catfish and minnows use the swim bladder to capture sound vibrations, which are transmitted to the otic capsules by specialized bones.

IV. Actinopterygian phylogeny: A. Synapomorphies: Ironically, the presence of fin-rays is a plesiomorphy, not a

synapomorphy of ray-finned fish.1. Single dorsal fin2. Heavily scales on leadig edge of tail

B. Cheirolepis :A reasonable approximation of the ancestral actinopterygian from the Middle to Late Devonian.

C. Cladistia:The most ancestral of all other Actinopterygii. Characterized by a diphycercal tail and a long row of small dorsal finlets. This lineage must have separated from the main actinopterygian tree in the Devonian, but the miracle is that cladistians are still alive! Indeed, types such as Polypterus can be found in aquarium shops. In terms of feeding, tail structure, and lung evolution, these critters represent the ancestral morphotype. Ironcially, their actual fossil record only extends to the Cretaceous.

D. Actinopteri: The most recent common ancestor of sturgeons and teleosts and all of its descendants. There is a myriad of fossil taxa branching between Cladistia and the common ancestor of Actinopteri. Synapomorphies include a number of subtleties of the dermal skull.

In terms of the three trends noted above, the common ancestor of Actinopterii was primitive, however several members and close relatives evolved the deep body form, indicating a swim-bladder.

E. Chondrostei (=cartilage-bone): includes modern sturgeons and their close fossil relatives. Modern representatives are large bottom feeders with large dermal scutes (bony scales).

Saurichthyes: A major predatory fish of the Triassic, closely related to Chondrostei. Picture a sturgeon trying to be a barracuda.

F. Neopterygii: Most recent common ancestor of Ginglymodi (Gars) and Teleostei and all of its descendants.

1. Synapomorphies:a. Upper pharyngeal teeth consolidated into plates.b. Clavicle greatly reduced.c. Maxilla not in contact with palatoquadrate.d. Actinopterygian trends:

a. In Neopterygii, the swim bladder is present.b. The vertebral column of the tail, though not stiffened by any

specialized structures, is noticibly shorter while the tail fin rays are proportionally larger than in primitive actinopterygians.

c. The freeing ot the maxilla fromt he palatoquadrate sets the stage for its future modifications.

2. Ginglymodi: Gar fish. Cretaceous to recent: fresh water predator.

1. Synapomorphies:a. Elongate snout.b. Bones forming lower margin of eye socket become part of jaw

and support teeth. 2. Halecostomi: Includes Amia (bowfin), Teleostei, and fossil relatives.

1. Synapomorphy: a. Mobile maxilla.

2. Interesting fossil representative: Pycnodontida - Cretaceous age deep bodied eater of hard shelled organisms. Probably reef-fish.

3. Actinopterygian trends: a. Only in this group is the maxilla free to rotate.

3. Amiidae: (Amia and fossil relatives): The modern bowfin and fossil relatives. 4. Teleostei: (Jurassic - recent) This important group includes the majority of

actinopterygian diversity. 1. Synapomorphies:

a. Mobile premaxillab. Light scales free of dentine layers.c. Haemal arches of tail consolidated into triangular plates.d. Vertebral column of tail sharply upturned distally.

2. Interesting fossil representatives: a. Ichthyodectiformes: Big nasty predatory fish of Cretaceous,

icluding Xiphactinus, the BIG fish o fthe NMNH.b. Pachycormidae: Group that includes giant suspension feeding

fish of cretaceous. (cf. whale shark and basking shark.)

V. Actinopterygian trends: A. In its outward appearance, the tail has assumed a modern homocercal appearance in

the earliest teleosts, though it lacks a few internal features such as the consolidation of the haemal arches into a small number of triangular plates. By an early point in their history these, too are present.

B. With the mobility of the premaxilla, the modern suction-feeding apparatus was complete in the common ancestor of teleosts.

VI. Enigma -Acanthodii: Now there is a headache we must address: Although course material has referred to three major lineages of gnathostomes. Really, there are four when we consider Acanthodii or "spiny sharks." The acanthodians lived from the Silurian to the end of the Permian.

A. Synapomorphies: Acanthodians encompass a considerable range of diversity but are united by three odd synapomorphies:

1. Paired fins supported by stout spines2. At least one pair of spines intermediate between the pectoral and pelvic fins is

present.3. Unique pattern of scale growth.

B. Diversity: The names of different acanthodian taxa needn't concern us. What matters is that we observe the range of variation in acanthodians, especially with regard to characters that resemble or approach synapomorphies of Osteichthyes.

1. Climatius: (Early Devonian to Mississipian) a. Very heavy fin spines.b. Four pairs of intermediate spines.c. Multiple external gill slits, partially covered by a larger hyoidean gill

cover. (I.e. a gill cover suspended from the hyoid arch. Armored by branchiostegal rays.)

d. anterior and posterior dorsal fin.2. Acanthodes: (Permian)

a. very light fin spinesb. one pair of intermediate spinesc. Gills entirely covered by hyoidean gill cover.d. Anterior dorsal fin lost.

C. Difficulty: Generally speaking, one would expect that in an evolving monophyletic group, the more derived taxa would occur later in time than the more ancestral ones. This is called stratigraphic congruence. Acanthodians display the opposite pattern.

1. Scenario 1: If we use a primitive member of Osteichthyes like Cheirolepis as the outgroup, then the most primitive acanthodians would be ones like Acanthodes, which, like Cheirolepis, lacks multiple intermediate spines, exposed individual gill slits, or heavy spines. Alas, Acanthodes is stratigraphically among the youngest (i.e. most recent) acanthodians.

2. Scenario 2: If we allow stratigraphic age, rather than outgroup comparison, to drive our reconstruction of phylogeny, then Climatius is among the most basal acanthodians, yet there is no obvious outgroup in this case.

3. What might relationships be? Recall that Actinopterygii also have branchiostegal rays.

D. Acanthodian surprise: A Silurian representative exists with paired fin spines, but with shark-like scales. Perhaps the common ancestor of Gnathostomata resembled an acanthodian.

Actinopterygii :   ray-finned fish

Range: from the Late Silurian or Early DevonianPhylogeny: Osteichthyes: Sarcopterygii + *: Cheirolepis + (Cladistia + Actinopteri). 

Description: acrodine cap on teeth; premaxilla fused to other bones; maxilla projects posterodorsally; methyostylic jaw suspension (i.e. based on hyostylic, but palatoquadrate and Meckel's cartilage replaced by dermal bone, hyomandibular reduced to jaw element); single median postrostral; single nasal; 4 sclerotics; 1 pair of suprascapulars; clavicle elongate; pelvic girdle formed by metapterygium (not homologous with other vertebrates); $ fins supported by fin rays; $ skeleton with bone; scales with or approaching peg & socket articulation; $ scales rhombic, with overlying dentine denticles and cancellous bone; enamel ("ganoine") and $ acrodine present.Links: Fossil Actinopterygii; Introduction to the Actinopterygii; Actinopterygii; Class Actinopterygii; Actinopterygii; Peixes marinhos dos Açores; Actinopterygii -- Ray-fins; Class Osteichthyes; actinopterygii.htm (Japanese version; see also English version); URMO: Actinopterygii; Bony fish showcase; Biology 356; IWR: Taxa: Actinopterygii; ISIS - taxon actinopterygii.

References: Janvier (1996); Lund (2000). Note: some of the features in the "description" section are taken from Lund's (2000) synapomorphies of his "basal node" (#23) which is probably not quite Actinopterygii, but close, probably corresponding to the Late Devonian crown group of actinopterygians.

<==(o ACTINOPTERYGII |-------------------------------------------- Cheirolepis |-------------------------------------------- REDFIELDIIDAE (Visit the Berkeley entry) |-------------------------------------------- Howgualepis `--+-----------------------------------------PARAMBLYPTERYIDAE

`--o ACTINOPTERI |-------------------------------------- ÝMimia |-------------------------------------- ÝBorichthys |-------------------------------------- ÝOrvikuina |-------------------------------------- ÝStegotrachelus |-------------------------------------- ÝDialipina |-------------------------------------- ÝMelanecta `--+----------------------------------- ÝRHADINICHTHYIDAE `--+-------------------------------- ÝMoythomasia `--+----------------------------- ÝWoodichthys `--+-------------------------- ÝCoccocephalus |-------------------------- ÝKentuckia `--+----------------------- ÝPteronisculus

`--+--o ÝTERRASIIDAE | |----------------- ÝApholidotos | |----------------- ÝTerrasius | `----------------- ÝParatarrasius `--+----------------- ASCIPENSERIFORMES

`(-o NEOPTERYGII |-------------- ÝOphiosus |-------------- ÝSonganella

|-------------- ÝUarbyichthys

`--o HALECOSTOMI |----------- ÝASPIDORHYNCHIDAE |----------- ÝPACHYCORMIDAE |----------- AMIIFORMES `--+-------- LEPISOSTEIIDAE `--+----- HALECOMORPHI |----- TELEOSTEI `--+-- ÝSEMIONOTIFORMES `-- ÝPYCNODONTIFORMES

Based from Carroll, 1988 and Haaramo, 2001

Basal actinopterygian systematics have been on shaky ground, but at least Chondrostei has some relative stability as basal forms. Basal Neopterygii presents further problems. While cladistic analyses of phenotypic morphology seem to indicate that the old Linnaean grade Holostei is a paraphyletic assemblage of gars (Semiontidae) and amiids (the bowfins of Amiiformes, above) successively closer to teleosts (Gardiner, Maisey, and Littlewood, 1996). However, molecular data tend to suggest a sister-clade status for these two clades in a monophyletic Holostei (Gardiner et al., 1996). This is illustrated:

Neopterygii |--Holostei | |--Semiontiformes | `--Amiiformes `--+?-Pycnodontiformes `--+?Aspidorhynchiformes `--Teleostei

Actinopterygians are what most people know as "fish" today. They dominate the planet among vertebrates as the most common in species number and in individuals. There are more actinopterygians on the planet (well, in the water) than there are mammals and birds combined.

Actinopterygians include a variety of forms. Some "fly," some glow in the dark, some have bony armor covering their body (reminiscient of some jawless vertebrates), some do not have bones, some have spines and inflate, and some walk on land and even climb trees. Such a broad set of environments and lifestyles give an indication of how diverse these animals are, and it is obvious that these pages will take some time to refine.

The most primitive of known actinopterygians include the odd and often grotesque polypterids. Polypteridae is known from only a few species today and are found mostly in Africa. Also known as bichirs, these fish were originally considered close relatives of sarcopterygians. Although they show many features that are primitive to euteleostomes, they are closer to the Chondrostea + Teleostei clade than to sarcopterygians.

Bichirs are often elongate and superficially eel-like. There may be numerous accessory axial fins, a character reminiscent of Acanthodii. However, the skull is of actinopterygian design.

Another group of bizarre, basal actinopterygians are the chondrosteans. Chondrosteans are best known in North America where the spoonbill (Polyodon spathula) is still "grabbed." This animal possesses a large rostrum that is dorsoventrally compressed. The exact function of this adaptation is not fully understood, though chemoreception and feeding are obviously its basic functions. The sturgeons have a similar structure and are also in this group. There are, however, accessory papillae on the snout of the sturgeon. Sturgeon also differ from spoonbills in the presence of bony plates on the surface of their body. Both sturgeon and spoonbills are large fish, but sturgeons can be true giants weighing hundreds of pounds.

The more advanced actinopterygians, the Neopterygii, have traditionally been broken into the Teleostei and the Holostei. However, the latter may not form a monophyletic group. Instead, it may be paraphyletic (not including all descendants of a common ancestor).

Neopterygians are common today only as teleosts. However, the basal neopterygians were important players in their respective times of dominance.

Actinopterygian fishes

Neoselachians - Squalea and Galea Acanthodians - spiny sharks Sarcopterygian fish - Rhipidistians Actinistians Dipnoi

Relationships of three groups

Classic view

Protopterus - 4 species

Very different from Neoceratodus Obligate air breathers Aestivate - w/o any water, forms a cacoon

 

Lungfish phylogeny

Actinopterygians - ray finned fishes

Monophyletic group Specialized fins for locomotion Spread and collapse fins to change locomotor activity lepidotrichia - segmented rays One dorsal fin

contrast to Rhipidistian and Actinistians Ganoin present Complex enamel - like material on the surface of scales and bones, makes scales thick

and shiny

 

Scales from early Actinopterygians have interlocking pegs Most recent actinpoterygians lack this Jugal Pit line detects water displacement, neural mast organ Not present in most living actinopterygians Mandibular sensory cells enclosed in dentary bone

Johannes Müller : 3 groups of ganoid fishes

Chondrostei Cartilaginous bony fish, based on sturgeon and paddlefish Formerly thought to be relatives of sharks Includes fossilized †Chondrosteus Holostei Two taxa from North America Amiiformes and Lepisosteus Based on tail anatomy Teleostei - "higher" bony fish Based on clupeidae and salmonidae based on tail anatomy (Problem for cladistics)

Controversy over the three groups of Teleosts, Amiiformes, and Lepisosteoformes

Classical view

 "Problems" for Teleosts

Basal lineages (non-teleosts) Paleoniscids - are not chondrosteans e.g. †Cheirolepis and †Mimia

4 groups of living non-teleosts

Cladista (Polypteriformes) bichirs and ropefish both from West Africa, usually small Air breathing - recoil respiration (muscles contract body cavity and relax to inspire)

Polypterus

"Many fins" or "wings" on the dorsal tail secondarily homocercal

pectorals- expanded muscular base- 3 skeletal elements for support Reduced pelvic and pectoral girdles

 2nd group -Acipenseriformes

Sturgeons

Sturgeon

Extremely long lived and large in size All species threatened or endangered due to fishing pressure (caviar) loss of habitat

Morphology

Caudal fulcra- have row of "V" shaped forms at the caudal fin 

Solid bony dermal cranial roof - highly variable in form "Anamestic bones" 

Acipenser - 17 species, Europe and N. America Atlantic, White (A. transmontanus), shortnose Huso- 2 species Russia Beluga (anadromous) kaluga (fresh water) Scaphirhynchus - 3 sp shovelnose , N. America Pseudoscaphirhynchus in Asia - 3 extant, 2 extinct Huso and Acipenser, probably related, form fertile hybrids Scaphirhynchus and Pseudoscaphirhynchus, also form fertile hybrids Geographic separation

Conservation of sturgeon

3 Gorges Dam Columbia River

Paddle fish

prolonged rostrum primary fresh water fish stellate bones in rostrum for support Breadth and length of paddle for ampullary organs - electroreception Lateral line canals on paddlefish

Acipenseriform caudal fins

Hypocaudal lobe extended in Paddlefish pelagic versus benthic

Polyodon spathula

up to 300 lbs Specialized filter feeder, fine gill rakers In US southern rivers originally spanned to Great Lakes heavily fished, roe and meat

 

Psephurus in China, rakers larger, a piscivore †Crossophalus also a piscivore

Biogeography of Acipenseriformes

Sturgeon only in Northern hemisphere, Paddlefish in N.America and China example of use of primary freshwater fish information fossils found west of Rockies need explanation

 

Lepisosteidae - 3rd non-teleost

Basal actinopterygian clade Air breathers Only in North America Fossils from S. America, Africa, Europe

Large number of cranial bones Larvae - have a prominent "cement gland" on the snout Allows attchment to substrate while a yolk sac larvae Rhombic scales

Amiiformes - 4 th non-teleost

Amiidae - ~ 50 species , 1 extant Amia calva - bowfin Long dorsal- a secondary specialization

Amiiformes

Fossils from all over the world e.g. †Calamopleurus, Brazil Living sister group of teleosts

Phylogeny of basal actinopterygians

Non -teleosts Note Lepisosteiformes is replaced by Semionotiformes

Two major topics in fish evolution

Jaw development Tail development

Functional morphology of basal actinopterygians

Devonian Paleoniscids, lepisosteiformes, polypteriformes †Chirolepis - limited ability to flare operculum, teeth cannot move this is the case with gar and polypterus

 

 

Halecostomes: Amia and teleosts

Highly developed mobile jaw system

5 Basic Subunits of Halecostomes Jaw

Mouth closing adductor mandibulae, inserts on the lower jaw large muscle covers lower jaw articulation Mouth opening suspensorium can flare to the side, increasing the buccal cavity, important for suction

feeding but does not lower the jaw

Mouth opening,

Opercular chain more important in Amia; complicated in teleosts Levator and Dialator Operculi flare and rotate operculum Opercular /mandibular connection via bone or ligament Together this lowers the jaw

Strap muscles also lower the jaw Muscle action from hypaxials to hyomandibular apparatus(ceratohyal)

Cooperate with epaxial muscles to flare upper jaw for head lift

Teleost jaws

loosening up of the maxillary bones Fused in Polypterus, more free in Amia palatal flaring suspensorium levator-palatine complex movement of the pectoral girdle in polypterus, attached to the skull and integument

in Amia -still attached to the skull, solid foundation for strap muscles

teeth mobility in the maxilla firm in polypterus Suspensorial flaring- allows (and requires) more mobility in the maxilla levator arcus palitine - flares suspensorium/palatine complex

Actinopterygiian Locomotion

Collapsable fins General weight reduction/streamlining for increased flexibility Increased extermal symmetry Only paddlefish and sturgeon have strongly heterocercal tails

 

Other Actinopterygian characters of uncertain phylogenetic significance

Basal fulcra - scales on the front of the caudal fin Picture Acrodin - enamel-like tissue formed on the caps of teeth Myodomes depressions on the wall of the brain case that serve as the site of origin for

extrinsic ocular muscles For rotation of the eye  

Spiracular canal and spiracular sense organ Formed from neuromasts Blind ended pouch in the back of the mouth analogous to the ear canal. Does not connect to external surface Organ like a large mound of neuromast cells Otic innervation, possibly for sound pressure origination

Polypterus pectoral fins - different from all other actinopterygians

3 bones, disk shaped mesapterygium Broad at base Very well muscled for "standing" and swimming Has been a point to argue that polypterus is not a basal actinopterygian 

Lung e.g. in Polypterus - basal feature of actinpterygians Swim bladder - e.g. in acipenseriformes Everted telencephalon forebrain has membranous roof

Phylogeny of Actinopterygii

Actinopterygii (ray-fin fishes)Tarrasiiformes

Paratarrasius hibbardi Cladistia

Discoserra pectinodonGuildayichthys carnegiei

PlatysomiformesPlatysomus sp.

PaleonisciformesAesopichthys erinaceusCyranorhis bergeraciKalops diophrysKalops monophrysProceramala montanensisWendyichthys dicksoni

Paleoniscoids of uncertain affinity unpublished species

 

Teleosts Monophyletic group Presence of uroneurals modified neural arches at the base of the tail Increase tail strength Unpaired basibranchial tooth plates in lower jaw

Variable trait Mobile premaxilla trend of increasing mobility through teleosts

Phylogeny of Basal Teleostei

 

Phylogeny of Ostariophysi

 

 

Phylogeny of the "other" Euteleostei

Cheirolepis

Drawing of fish (after Miller, 1841)

Cheirolepis, shown here in a reconstruction by the 19th-century paleontologist and journalist Hugh Miller, lived in fresh waters of the Middle Devonian in what is now Scotland. It and several related fishes of this time are the most primitive ray-finned fishes known. Note its highly streamlined body, capable of rapid swimming. Cheirolepis also bore pointed teeth in a

large mouth (not visible on this drawing), suggesting it was a predator. Also note its heterocercal (asymmetrical) tail, similar in shape to that of modern sharks and their kin. This is an extremely primitive feature, which almost all living ray-finned fish have lost.

Midden Devoon site Lethen Bar ( Scotland)

Cheirolepis trailli    Devoon   Orkney, Scotlandhttp://www.btinternet.com/~vendian/FOSSILWEB/new_page_11.htmhttp://www.btinternet.com/~vendian/FOSSILWEB/new_page_22.htm

Cheirolepis: Range: Middle Devonian to Late Devonian.Phylogeny: Actinopterygii: (Cladistia + Actinopteri) + *. Description: Possibly earliest actinopterygian with "standard" dermal skull bones; large orbit; long (~50 cm) body; broad-based pelvic fin; fins other than pelvic fin long; strongly heterocercal; fringing scales small or absent; $ minute scales with two ganoine (probably same as enamel) layers; acrodine absent. Links: Cheirolepis; Givetian. Image: Cheirolepis by 19th-century paleontologist and journalist Hugh Miller, reproduced courtesy of University of California Museum of Paleontology. ATW000403.

Cheirolepis trailli Agassiz

 

This medium size fish can reach a length of 30 cm and is well known from the Sandwick Fish Bed but, since it is often not well preserved people don’t bother to collect it. However, it is a very important fish in the fish “history” (see general text on actinopterygians).

It is also found above the Sandwick Fish Bed as isolated scales and dermal plates of the head. It was a top predator like Gyroptychius agassizi and probably acanthodians, lungfish and small osteolepids were its prey. Both lower and upper jaws have rows of small but sharp teeth.

Complete fish from Achanarras, Caithness

 

Complete fish from Sandwick Fish Bed

Incomplete fish from Sandwick Fish Bed

Reconstruction in lateral view (after Traquair, 1895)

Reconstruction of fish in A: lateral and B: ventral view (after Pearson, 1979 ©)

Head in lateral view (after Pearson, 1979 ©)

Head in A: dorsal and B: ventral view (after Pearson, 1979 ©)

Reconstruction of head ready for attack (after Pearson, 1979 ©)

http://fossils.valdosta.edu/fossil_pages/fossils_dev/f9.html

Cladistia:

Range: from the Early CarboniferousPhylogeny: Actinopterygii:: Actinopteri + *: Guildayichthyiformes + Polypteriformes.Description: $ rostral present as separate bone(s); $ postrostrals median & paired; $ maxilla narrow posteriorly; $ median gular absent; $ lateral gulars extended; $ postspiracular bones present; $ parasphenoid extends length of braincase; $ clavicles reduced or absent; $ pectoral fin based on extended lobe; $ caudal fin outline rounded.

Image:Discoserra pectinodon from the Lower Carboniferous of Montana, from Lund (2000). Links: Lund; Untitled Document; Evolution der Fische (German); wpnc.pdf; Cladistia Cope, 1871 after Lund, 2000; Lund; Lecture 2; Untitled Document; New specimens of Serenoichthys kemkemensis; Home; Cladistia.   References: Lund (2000).  ATW021122.

Guildayichthyiformes: Discoserra, Guildayichthys. Deep-bodied marine fish with strong medial bones and unique cheek area.

Discoserra pectinodon (Osteichthyes > Actinopterygii > Cladistia) Cladistia:

Skull bones (left) and fossil (right) of Discoserra pectinodon.

Discoserra is a member of the actinopterygian order Guildayichthyiformes. This elegant little fish has a rounded body, abbreviate-heterocercal tail, pectoral fin high on the flank, and well webbed fins; all of which are features of a fish adapted to living among weeds, sponges, or corals. The snout is like a pincers, with long but weak comb-like teeth, and the gape of the mouth is tiny, thus accentuating suction feeding on small food objects. The skull adaptations are a peculiar mixture of primitive and derived structures. Scale in mm.

Reference: Lund, R. 2000. "The new actinopterygian order Guildayichthyiformes from

the Lower Carboniferous of Montana (USA)". Geodiversitas (MNHN, Paris) 22 (2): 171-206.

2/1/2006

Guildayichtus carnegeii(Osteichthyes > Actinopterygii > Cladistia)Cladistia:

Skull bones (left) and fossil (right) of Guildayichthys carnegiei.

Guildayichthys carnegiei is more plesiomorphous than its sister taxon, Discoserra pectinodon, in a number of ways. The body is a bit less rounded, the mid-dorsal scales overlap backward rather than being forward-pointed hooks, and the scales seem less tall.  The gape of the mouth is a bit longer, the teeth shorter, and the snout less pointed. The bones of the skull, however, show the same peculiar mixture of what appear to be very primitive and highly derived actinopterygian characters.The scale is in mm.

Reference: Lund, R. 2000. "The new actinopterygian order Guildayichthyiformes from

the Lower Carboniferous of Montana (USA)". Geodiversitas (MNHN, Paris) 22 (2): 171-206.

Range: Early Carboniferous of North AmericaPhylogeny: Cladistia: Cladistia: Polypteriformes + *.Description: laterally compressed, discoidal form; mouth small; premaxillae paired and not sutured in midline and $ loosely attached; maxilla does not extend posteriorly past mid-orbit; 8-10 sclerotic bones; 2-3 rows of paired bones over orbit, including supraorbitals; suborbitals ($) in >1 row, numerous, variable within species; infraorbital series of 6-10 bones lacking a specialized postorbital; opercular & gular bones unique; $ narrow dorsal and ventral preoperculars; interopercular bones or rays between preopercular and branchiostegal rays; single large opercular; $ subopercular absent; few branchiostegal rays, not extending forward under mandible; median skull roof bones strongly developed, often unpaired (the rostral, posterior postrostral, and supraoccipital are unpaired in Guildayichthys); supraoccipital ($) prominent on skull roof, dividing parietals and posterior of frontals; parietals similar size to frontals; 3 bones in otic canal series; braincase ossified as several separate bones; parasphenoid extends entire length of braincase; spine with enlarged thoracic supraneurals articulating with $ stiff, overlapping median dorsal scales (also providing very strong base for median musculature); caudal fin somewhat heterocercal; $ clavicle absent; fin rays well spaced; $ dorsal fin long & low; $ dorsal fin base scaled & lobate (as are paired fin bases); tall, rhombic, ganoid scales with peg & socket joints.Note: Lund (2000) believes that the guildayichthyiforms were specialized to have strong medial bones concentrating the force of the bite in the small antorbital jaw and permitting high maneuverability in "geometrically complex environments." The sister group relationship with the polypteriforms is very strong and stable.Image: Guildayichtus carnegeii modified from Lund (2000). The labels on the image reflect my surprise at the identification of the parietal. However, Lund makes a very convincing case that the large, unpaired supraoccipital is homologous to the 'B' bone of Dipnoi (see the diagram at that entry -- the 'J' and 'I' bones are the parietals and postparietals, respectively). See also image at Cladistia.Reference: Lund (2000). ATW010528.

Paratarrassius hibbardi (Osteichthyes > Actinopterygii > Tarrasiiformes)

Paratarrasius hibbardi (top) and Tarrasius problematicus (bottom).

Paratarrasius hibbardi is closely related to the slightly older Scottish Tarrasius problematicus. It ranged from very small to about 7 inches in length.

Scales are small and fine, with an increased number of scale rows relative to body segments. This served to increase body flexibility. The pectoral fins are held high on the flank on long basal lobes and are well webbed paddles. Pelvic fins are absent. The continuous dorsal-caudal-anal fin is well webbed between the fin rays. Fish with this fin disposition today are slow weak swimmers that move either forward or backward, by body undulation, median fin undulation or pectoral paddling. Fish such as these are shelter dwellers in geometrically complex shallow water environments, such as weed or sponge beds.

Paratarrasius has a very small mouth with stout peg-like teeth. The skull has an interestingly primitive-looking actinopterygian snout bone pattern.

Reference: Lund, R., and W. G. Melton jr., 1982. "A new actinopterygian fish from the

Mississippian Bear Gulch Limestone of Montana." Palaeontology 25: 485-498.

Lund, R., and C. Poplin. 2002. "Cladistic analysis of the relationships of the Tarrasiids (Lower Carboniferous Actinopterygians)." Journal of Vertebrate Paleontology 22: 480-486.

2/1/2006

 

Polypteriformes: Polypterus (bichirs), Erpetoichthys (reedfish). Range: From the Late Cretaceous. Phylogeny: Cladistia: Guildayichthyiformes + *. 

Description: Moderate-sized fresh water African fish with unique fins. Body elongated, almost eel-like; acrodine cap on teeth; pineal plate absent; well-ossified skeleton; postcleithrum differentiated from body scales; covered by thick, interlocking ganoid scales; modified heterocercal tail, superficially symmetrical; pectoral fins fleshy (apparently convergent with sarcopterygians); dorsal fin divided into numerous small fins; larval forms may have external gills; adults have two ventral lungs and are obligate air-breathers; air recoil breathing; inhabit edges of streams and flood plains, concealed by day, forage for worms, insect larvae, small fishes by night.Links: Erpetoichthys calabaricus (Rope Fish): Narrative; Actinopterygii--Ray-fins; Bichir. Note: The polypteriforms anchor the crown group Actinopterygii at what is believed to be a very early stage in actinopterygian evolution, and a wide phylogenetic gap lies between the polypteriforms and the next living group (the Chondrostei). Unfortunately, the polypteriforms have little fossil record and are clearly highly specialized. Under these circumstances it is not clear that the proposed synapomorphies for the crown group Actinopterygii have a great deal of credibility. The recent discovery of the Guildayichthyiforms adds substantial clarity to the picture and may change our idea of the Actinopterygii considerably. ATW010528.

Redfieldiidae

During the Triassic and Jurassic, a group of small fishes known as redfieldiids were common in fresh waters.

This one, Redfieldia gracilis, was collected from Triassic deposits at Boontown, New Jersey. Others have been found in Australia, southern Africa, Morocco, and North America.