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Paleovertlecture31.Pdf In Tristychius, the epibranchial has lost the secondary function it performed in the Osteostraci, that of fixing the gills to the cranial cartilage. That function has been taken over by specialized pharyngobranchials In many Chondrichthyes, the hypobranchials are well developed. However, there is no hypohyal. Se cree que el hyophyal puede ser neomórfico para peces osteictios Pectoral fin skeletons support the anterior paired fins, and may be used as functionally simple stabilizers (modern sharks, Stethacanthus, Falcatus), or as a vital component of swimming and maneuvering (modern skates and rays, chimaeroids, Traquairius, Heteropetalus, Harpagofututor). The fin itself is supported by softer tissues that extend quite a distance from the endoskeleton and do not usually preserve Pelvic fins play a role in stabilization of the body during swimming. The bony fish pelvic fin is simple and is supported on a flat-lying triangular plate, somewhat similar to that of the female of the shark Falcatus. Pelvic fins of all sexually mature male chondrichthyans, however, also feature extensions of the fin axis that form sperm conducting ducts for internal fertilization of females. These paired structures, the claspers, are characteristic of adult male Chondrichthyes.Chondrichthyans related to the modern chimaeroids also develop a tall dorsal process and a specialized first radial armed with denticles (pre-pelvic tenaculum), as seen in a relatively primitive state in Echinochimaera snyderi Pueden tb haber dentículos faríngeos presentes en los arcos branquiales (son más pequeños y con menos esmalte q los dientes) No confundir dentículos con gill rakers (rastrillos branquiales cartilaginosos, que alejan particulas de los filamentos branquiales) En placodermos hay sólamente arcos neurales y hemales. No hay interdorsales (interneurales) ni interventrales (interhemales). En lampreas sólo hay arcos basidorsales e interdorsales. En tiburones actuales observamos la presencia de los 4 como elementos (cartilaginosos o calcificados) notochord (green) spinal cord (yellow). In lampreys (top), the vertebral elements are only the basidorsal (red) and the interdorsals (blue). In the gnathostomes, there are in addion ventral elements, the basiventrals (purple) and interventrals (orange), and the notochord may calcify into centra (pink). (Aer Janvier 1996). En tiburones vemos Calcificación sólo de arcos Dentina trabecular, sin esmalte dorsales Amphistylic jaw suspension No clasper in cladoselache! (derived) No anal fin Escamas (denticulos) solo Radials articulate to scapulocoracoid “rayos” basales? en torno a aletas (as in placoderms) y ojos ceratotrichia Sólo dorsal posterior. No hay espinas Escamas sólo a lo largo de la línea lateral No anal fin Placa basal (cartílago) (function unkown) En Fadenia hay pérdida de No palatoquadrate Aletas pélvicas Ligera inclinacion del notocordo Aletas similares a ctenacanthidos Dos aletas anales Radiales por anterior y Doble! posterior, semejante a Neoceratodus (sarcopterygio) Symmoriiformes Denea Falcatus Placa basal de cartílago globular calcificado, espina de dentina Stethacanthus In primitive gnathostomes, the embryonic trabeculae (see Overview) fuse to form a single ossification which includes the entire braincase from the ethmoid plate, anteriorly, to the otic region posteriorly. This region is marked by the orbits, laterally, and often the articulation between the braincase and the palatoquadrate. Its posterior extent was coincident with the original anterior limit of the notochord and the ventral fissure. Ventrally, the ethmosphenoid normally contains foramina for the internal carotid artery and the Vth cranial (trigeminal) nerve, or at least the profundus branch of that nerve. The sphenethmoid also usually bore the basicranial articulation, the old major articulation between the palate and the braincase Dientes pequeños: formados cuando joven Reducción/pérdida del palatocuadrado Dentina trabecular, sin esmalte Amphistylic jaw suspension No clasper in cladoselache! (derived) No anal fin Escamas (denticulos) solo Radials articulate to scapulocoracoid en torno a aletas (as in placoderms) y ojos ceratotrichia Sólo dorsal posterior. No hay espinas Escamas sólo a lo largo de la línea lateral No anal fin Placa basal (cartílago) (function unkown) En Fadenia hay pérdida de No palatoquadrate Aletas pélvicas Ligera inclinacion del notocordo Aletas similares a ctenacanthidos Dos aletas anales Radiales por anterior y Doble! posterior, semejante a Neoceratodus (sarcopterygio) Ctenacanthoid Semejantes a Xenacanthidae As in Xenacanthus! heterodoncia No posterior axis Ceratotrichia Ctenacanthida: ancestros o hermanos de los elasmobranquios actuales ? Al menos, cercanamente relacionados Larger brains! Folded forebrain & cerebellum Los primeros neoselaquios tienen el antiguo diente cladodonto, dos espinas dorsales, aleta anal In more basal forms, there were actually five different couplings which are (roughly from ventral to dorsal): (a) the dorsal aorta, (b) a cotylus or pit for the anterior notochord, (c) connections for the XIth cranial nerve (the spinal accessory or occipitospinal nerve), (d) mechanical coupling for the vertebrae, and (e) the foramen magnum for the spinal cord. The occiput of the Lower Carboniferous shark Akmonistion, shown in Figure 2, illustrates one such arrangement. See Coates & Sequeira (1998). The very complexity of this arrangement may have created the need for an otico-occipital fissure to prevent excessive strain on the various components. Modern sharks are notably different. As shown inFigure 3, the notochord and dorsal aorta have been re-engineered so as not to participate directly in the occiput, and the occipital condyle has become a more prominent, paired structure dorsolateral to the foramen magnum. Myliobatiformes Muchos presentan espina Poseen dos aletas dorsales sin espinas y una aleta anal; con cinco hendiduras branquiales y, normalmente, con espiráculos pequeños situados tras los ojos. Ojos sin membranas nictitantes y unas mandíbulas que se extienden por detrás de los ojos Carpet sharks have two dorsal fins, without spines, and a small mouth that is forward of the eyes. Many have barbels and small gill slits, with the fifth slit overlapping the fourth. The upper lobe of the caudal fin tends to be mostly in line with the body, while the lower lobe is poorly developed, except in the case of the whale shark. While many in the order are small, the whale shark is the largest living fish Dientes Gill rakers: “rastrillos” branquiales Pueden estar compuestos por/llevar “dientes” Bull-face sharks Peces óseos y Acanthodii No claspers! Sólo dentina: no hay esmalte El crecimiento de las escamas recuerda a las ganoideas de los primeros osteictios Enamelina no funcional? (como aves) Dientes sin esmalte, no reemplazables Los arcos branquiales presentan “gill rakers” o rastrillos branquiales Osteichthya Todos los descendientes del ancestro común más reciente compartido por la vaca y un pez dorado -Diverticulo del esófago altamente irrigado: Sacos aéreos (vejiga/pulmon) En actinop no hay escamoso (sq) ! Actinopterygia Hay dermohyal hacia extremo dorsal del hyomandibular (epihyal) Sarcopterygia Huesos Operculares en Actinopterygia Ojo: ya se observaban rayos operculares hyodeos en holocefalos. Su pérdida en elasmobranquios y modificación en sarcopetrygios es derivada Sarcop Actinop: Sarcop Actinop En Osteichthyes, en gral. Arriba, Sarcop (Tetrápodo) Eoherpeton (sarcopterygia: tetrapoda) Dentículos faríngeos en todos los arcos branquiales de Eusthenopteron (sarcop) Amia (actinop) Recuerda la condicion de denticulos en todos los arcos en conodontos, telodontos y tiburones Los dientes verdaderos son de mayor tamaño y de mayor desarrollo de esmalte No confundir con gill rakers (rastrillos branquiales) Una sola dorsal (sarcop: 2) Actinopterygia basal actinop ________ Las mandíbulas faríngeas: Están ausentes en paleonisciformes, pero presentes en condrósteos vivientes .
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