TELEOSTOMI

Editor's Notes

1. The Teleostomi family includes the acanthodians (a sister group of bony fishes), bony fishes, and their tetrapod offspring Teleostomes give rise to the teleosts (Teleostei), which today make up the majority of live fishes.
2. Acanthodians are represented by spines in the Early Silurian, with some debated evidence that they were present very late in the Ordovician. They reached peak diversity during the Devonian and persisted well into the Permian, long after the placoderms had become extinct. The largest acanthodian was over 2 m in length, but most were minnow sized (under 20 cm) with streamlined bodies. Early acanthodians were marine, but later ones tended to occupy fresh water. Acanthodii means “spiny forms,” Numerous fins (both in-line and paired), most of which were supported at the anterior end by a large spine
3. This figure shows the Teleostomi, phylogenetic relationships. “Rhipidistia” in quotes to notice that, as presently constructed, it may be paraphyletic with one lineage related to Dipnoans and another to derivates from other lineages. “Osteichthyes” in quotes to also notice possible paraphyletic association.
4. Osteichthyans are not the only fishes to contain bone in their skeletons, but the taxonomic term Osteichthyes (meaning “bone” and “fish”) recognizes the pervasive presence of bone, especially throughout the endoskeleton, among members of this class. At least some bone in their skeleton and/or scales. Operculum-Cover for the gill openings. Some have lungs· Fins are often strengthened by lepidotrichia, slender bony rods or “rays” that provide a fanlike internal support. Swim Bladders to adjust depth in the water. Two classes: actinopterygians compose the vast majority of bony fishes and have been the dominant group of fishes since the mid-Paleozoic (figure 3.16). The other group of bony fishes is the sarcopterygians. Although small in numbers today, this group is important to the vertebrate story because it gave rise to the tetrapods, all land vertebrates, and their descendants
5. Ray-finned fishes have been the dominant aquatic vertebrates since the mid-Paleozoic. Actinopterygians are called “ray-finned” fishes because of their distinctive fins, which are internally supported by numerous slender, endoskeletal lepidotrichia (rays). Muscles that control fin movements are located within the body wall, in contrast to the muscles of sarcopterygians that are located outside the body wall along the projecting fin. Some fish biologists divide actinopterygians into chondrosteans, holosteans, and teleosts, each intended to represent primitive, intermediate, page 100 and advanced groups of ray-finned fishes, respectively, representing an increase in ossification In our classification scheme, we use two divisions current at the moment: the Palaeonisciformes, encompassing primitive ray-finned fishes, and the Neopterygii, encompassing derived ones. These two groups are further divided into lower categories
6. Palaeoniscoids occupied marine as well as freshwater habitats The base of each scale was made of bone,the middle of dentin and the surface with an enamel-like substance called ganoine. Hence the name ganoid scales.
7. Sarcopterygians are the second group of bony fishes, the lobe-fin fishes. Unlike in the ray-finned actinopterygians, the paired fins of sarcopterygians rest at the ends of short, projecting appendages with internal bony elements and soft muscles, hence the alternative name “fleshy-finned fish.” Sarcopterygian fins evolved into tetrapod limbs, however these fins do not support the nsarcopterygian body or aid the fish on land. Instead, sarcopterygians appear to use fleshy fins as aquatic devices for pivoting or navigating in shallow waters or working bottom habitats in deeper waters. Sarcopterygians were common in fresh water during most of the Paleozoic, but today, the only surviving sarcopterygians are three genera of lungfishes (dipnoans) living in tropical streams and rare coelacanths, confined to the deep waters of the Indian Ocean. To some, the sarcopterygians were known once as Choanichthyes, in recognition of external nostrils opening internally to the mouth through holes termed choanae.
8. Once sarcopterygians were divided into two subgroups, dipnoans, and all others combined into the crossopterygians (tassle-finned fish) Dipnoi are a monophyletic group, but crossopterygians are now considered to be paraphyletic, including coelacanths (Actinistea) and rhipidistians, which we meet next. Choanae or internal nares- Other than fleshy fins, primitive sarcopterygians differ from other bony fishes in having scales covered with cosmine. These cosmoid scales, initially rhomboidal in shape, tend to be reduced to thin, circular disks without cosmine in later sarcopterygians. Early species usually had two dorsal fins and heterocercal tails
9. Actinistia (Coelacanths) made its first appearance in the Middle Devonian and persisted until the Late Mesozoic, when they were supposed to be extinct. In the 1930s, a “living fossil” was discovered by chance in the waters off the coast of southern Africa. Latimeria, a deep sea fish found in depths of 100–400 meters, was the African fish. Off the coast of Tanzania, on Africa's east coast, more populations have been discovered. A second species, likewise at depth, has been discovered in Indonesian waters.
10. Dipnoi Lungfishes have been found dating back to the Devonian period. The earliest known lungfish, Styloichthys (Early Devonian), shared some characteristics with rhipidistians, implying that it could be a transitional species between rhipidistians and modern lungfishes. Although all Devonian lungfish were marine, modern forms live in freshwater. In continental streams and swamps, three genera have survived. Dipnoans can breathe when oxygen levels in the water drop or when pools of water evaporate during dry seasons because they have paired lungs. Modern lungfishes lack cosmine, have a cartilage-based skeleton, and have a prominent notochord.
11. Ancient tetrapods retained bony scales, although these were generally restricted to the abdominal region. Many were surprisingly large in body length, with proportionately large skulls as well. Eogyrinus, a Carboniferous species, reached 5 m in length The earliest groups of labyrinthodonts date from the Late Devonian. One was Acanthostega, which could be described aptly as a “four-footed fish” because of its close similarity to the rhipidistian fishes from which it evolved
12. Lissamphibia arose within the labyrinthodont radiation, specifically from temnospondyls (figure 3.21), although many labyrinthodont features, such as infolded labyrinthine teeth, have been lost in or by the time lissamphibians debut. The lissamphibia includes fossil and living forms. The term amphibian was once applied to all early tetrapods, but recent taxonomic analysis makes this too encompassing. Today, some would apply it as an equivalent to lissamphibia. But here we restrict it to a subgroup of lissamphibia, namely to all living forms—salamanders, frogs, and caecilians—which date back over 200 million years to the Jurassic and today include almost 4,000 species displaying a wide range of life histories Modern amphibians in some ways stand between fishes and later tetrapods; therefore, they supply us with approximate living intermediates in the vertebrate transition from water to land. Many bones of the ancient skull and pectoral girdle are lost. Scales are absent, except in caecilians which allows respiration to occur through the moist skin. Salamanders appeared first in the Upper Jurassic. When frogs first appeared in the Triassic, they were essentially modern in their skeletal design, already exhibiting the highly derived saltatory (jumping) locomotor system
13. Some features are shared by all living amphibians. Most current forms are small, respire through their skin, have unique pedicellate teeth with a suture separating the tooth base from the tip, and have an auricular operculum, an additional bone connected with the ear. Undergo Metamorphosis wherein it is the transformation of a larval form into an adult form in living amphibians. It can be subtle, as in salamanders, or dramatic, as in the transformation of a tadpole into an adult frog. Currently, most taxonomists consider all live amphibians to be members of the Lissamphibia group.
14. The amniote radiation is composed of two major lineages, the Sauropsida and Synapsida (figure 3.27). As fossils document, they diverged very early, certainly by the Carboniferous and perhaps earlier. The sauropsids include birds, dinosaurs, modern reptiles, and many of the diverse assemblages of the Mesozoic. The sauropsids diversified along two major lineages, the Parareptilia and the Eureptilia. The Synapsida is a monophyletic lineage producing many various forms, including therapsids and modern mammals.
15. The temporal region in amniotes varies in two ways: in the number of openings, termed temporal fenestrae, and in the position of the temporal arches, or bars, made up of defining skull bones.
16. FIGURE 3.28 Amniote skull types. Differences among the skulls occur in the temporal region behind the orbit. Two, one, or no fenestrae may be present, and the position of the arch formed by postorbital (Po) and squamosal (Sq) bones varies. The anapsid skull has no temporal fenestrae. (b) The synapsid skull has a bar above its single temporal fenestra. (c) The diapsid skull has a bar between its two temporal fenestrae. (d) The “euryapsid” skull has a bar below its single temporal fenestra. Rather than being a separate skull type, the euryapsid skull is thought to be derived from a diapsid skull that lost its lower temporal bar and opening.
17. All birds and reptiles, as well as their immediate fossil relatives, are classified as sauropsids, which are amniotes. Amniotes belong to either the sauropsids or the Synapsida, a sister group to the sauropsids that we'll meet later in this chapter (mammals and their fossil relatives). Parareptilia and Eureptilia, as well as similar extinct clades, make up the sauropod clade. The Eureptilia sub-group Diapsida includes all living sauropsids, with the Parareptilia clade having gone out 200 million years ago.
18. In a limited sense, the taxon Reptilia refers to the parareptilia and Eureptilia, which have braincase similarities that separate them from the mesosaurs. This first category was previously referred to as Anapsida, while the second was referred to as Diapsida. Skulls lacking temporal fenestrae were used to identify Anapsida reptiles, while skulls with two temporal fenestrae were used to identify Diapsida reptiles. This simply recognizes that birds are a natural but specialized derivative of earlier reptiles. Reptiles are paraphyletic This simply recognizes that birds are a natural but specialized derivative of earlier reptiles.
19. This became some of the first biological confirmation for continental drift.
20. Parareptilia An assortment of fossil groups (e.g., Pareiasaurus) and lesser-known stem groups They have a distinctive ear region wherein the eardrum is supported by the squamosal (rather than by the quadrate) and by the retroarticular process, a backward projection of the lower jaw. Further, the foot is unique in the way the digits articulate with the ankle bones. The Parareptilia are composed of only fossil forms, with no living representatives (figure 3.30).
21. Within the Eureptilia, the Diapsida is diagnosed by two temporal fenestrae, together with a palatine fenestra within the roof of the mouth.
22. The most basal eureptilian is not an araeoscelidian but a member of the Captorhinidae, also known from the Carboniferous. The captorhinids lack temporal fenestrae and so represent the stage just before appearance of the diapsid condition.
23. Archosauromorpha Encompassed within the archosauromorphs are several groups, small assemblages of diapsids known from fossils, and a very large group, the archosaurs, which includes familiar forms such as crocodiles, dinosaurs, and birds. Archosaurs display a trend toward increasing bipedalism, or two-footed locomotion. Archosaurs display a trend toward increasing bipedalism, or two-footed locomotion. archosaurs include “thecodonts,” the most primitive of the group, crocodiles, birds, pterosaurs, and two large groups, the Saurischia and Ornithischia. Thecodonts take their name from teeth set in deep, individual sockets (thecodont condition) rather than in a common groove. Within the hindlimb, a unique ankle design appeared in some thecodonts along with a tendency to bipedal, upright posture.
24. The first known pterosaur was already specialized for flight with membranous wings. Many were sparrow- to hawk-sized, but the Late Cretaceous Quetzalcoatlus, found in fossil beds in Texas, had an estimated wingspan of 12 m. Pterosaur teeth suggest a diet of insects in some species and strained plankton in other species. Fossilized stomach contents confirm that one species ate fish. The early rhamphorhynchoids are pterosaurs distinguished by long tails and teeth
25. Dinosaurs include two groups of archosaurs: the Saurischia and Ornithischia. The two dinosaur groups differ in the pelvic structure. This FIGURE shows two types of hip structures define each group of dinosaurs. (a) Saurischians all possessed a pelvic girdle with three radiating bones. (b) Ornithischians had a hip with pubis and ischium bones lying parallel and next to each other.
26. Birds outnumber all vertebrates except fishes
27. FIGURE 3.35 Phylogeny of Dinosauria. Dinosaurs are composed of two lineages, the ornithischia (left) and saurischia (right). Within the ornithischia are several clades: (1) Thyreophora, including ankylosaurs and stegosaurs; (2) Ornithopods, including duck-billed dinosaurs; (3) Pachycephalosaurs; and (4) Ceratopsia. Within the saurischia are two major clades: (5) Sauropodomorpha and (6) Theropods, which encompass allosaurs, various other carnivorous dinosaurs, (7) coelurosauria, (8) maniraptora, and (9) birds (Aves).
28. The mammals arose within the therapsid radiation in the Late Triassic, initially small and shrewlike. These Mesozoic mammals contended with a terrestrial fauna then dominated by dinosaurs, especially the saurischians generally. Most Mesozoic mammals were shrew-sized and the largest not much bigger than a cat up until the mass extinctions closed the Mesozoic. The radiation of modern mammal groups began early in the Cenozoic, especially among the eutherian mammals.
29. Living mammals. Monotremes, marsupials, and eutherians are the three groups of mammals living today, the placentals being the largest group.
30. Although the known fossil record indicates that the earliest marsupial and eutherian species arose in the Early Cretaceous of China, the subsequent Cretaceous radiation of marsupials was in North America, and eutherians were there a bit later in the Late Cretaceous, the place of origin and routes of dispersal of therian mammals are still debated. Continental drift was breaking up the Mesozoic's few big continents into smaller landmasses, isolating them by open ocean at the time. Most continents were still in contact, and the Atlantic Ocean was developing but still tiny. Even in polar locations, the Late Cretaceous climate was mild. Marsupials spread to Asia, Antarctica, and Australia during this epoch, while eutherians went to Africa and the New World  These stocks of mammals were carried into semi-isolation as the continents divided further during the Cenozoic, and they served as the founding stocks for the different mammalian groupings that later emerged on the dividing continents.
31. FIGURE 3.46 Therian radiation. Position of the continents during the late Mesozoic is shown. Although today most marsupials live in Australia, their center of origin was apparently the New World (North America) of the late Cretaceous. From there, they spread in two directions. One direction during the Eocene was to Europe and North Africa, although they subsequently became extinct on both those continents (dashed arrows). The other direction in which marsupials spread was through South America and Antarctica to Australia before these continents separated. Eutherians originated in the Old World and spread to the New World via land connections that existed between the continents during the Mesozoic
32. All continents were merged into one huge supercontinent, Pangaea, early in the Mesozoic. In a dynamic Earth, however, this supercontinent began to rift, and by the Late Mesozoic, Pangea had divided into two areas, introducing a north/south geographical division in land masses. As a result, during the Cenozoic, these regions proceeded to split and spin, eventually forming the recognizable continents we see today. During the Late Mesozoic and Cenozoic periods, this fragmentation had an impact on mammalian evolution.
33. FIGURE 3.47 Mesozoic Diversity and Extinctions. The widths of each group subjectively express the estimates of relative abundance. Note the extinctions of not just the dinosaurs but other Mesozoic groups as well; and note that birds and mammals are contemporaries of the dinosaurs but become prominent only after their extinctions.