Vertebrate Zoology Chapter 10 Tetrapods PDF

Tetrapods Chapter 10 Simplified Phylogeny of Sarcopterygian Fishes & Tetrapods Evolution of Tetrapods Tiktaalik from Rocks in Newfoundland NOT a tetrapod, but an advanced crossopterygian fish Ray fins (no limbs), scales, gills (no operculum), very modest girdles, etc. Beginnings of elb...

Tetrapods Chapter 10 Simplified Phylogeny of Sarcopterygian Fishes & Tetrapods Evolution of Tetrapods Tiktaalik from Rocks in Newfoundland NOT a tetrapod, but an advanced crossopterygian fish Ray fins (no limbs), scales, gills (no operculum), very modest girdles, etc. Beginnings of elbow & wrist with some flexion at wrist (push-up) Head and body are flat with eyes on the top of its skull Shoulders are not connected to its skull, giving it a functional neck Has ribs like some of the earliest tetrapods Figure 10.3 A tetrapodomorph fish and two early tetrapods (Part 1) Figure 10.3 A tetrapodomorph fish and two early tetrapods (Part 2) Figure 10.3 A tetrapodomorph fish and two early tetrapods (Part 3) Tetrapod Origins Transition onto Land  Could be… Hypotheses - –Seasonal droughts caused lakes and ponds to dry up and fish had Why Animals to move to new places to survive Moved Onto Land –Searching for food, dispersing offspring, laying eggs in moist environments, and basking in the sun Forelimb Development in Fish and Tetrapods Fins and limbs are homologous –Coded for by the same Hox A/D cluster Hands and feet are the result of differential expression of the same genes that make fin rays –Hox11 and Hox13  What are the differences animals encounter when they shift from water to land-dwelling? Transition to What novel systems might the Land transition to land require? How do these novel systems relate to surface area to volume relationships? Transition to Land – 4 Major Environmental Considerations 1.O2 – 20X higher in air compared to water, & it diffuses more rapidly; what are the implications? 2.Fluid density (gravity effect) – air is 1000X less dense than water; what are the implications? 3.Thermal environment – temperature fluctuations are more extreme in air; implications? 4.Resources – huge array of new environments, abundant resources (vascular plants, some snails & arthropods had already made this transition), fewer predators; implications?  Locomotion In fish, muscles are only used for locomotion In tetrapods, muscles are also used to stabilize the trunk so that they body doesn’t twist as they walk Modification Breathing in Early Large tetrapods wouldn’t have been able to release Tetrapods CO2 through their skin –Surface area to volume ratio issue –Scaly skin Maybe used dermal bone to buffer acidosis while they were on land  4 limbs with digits Eyelids Internal nostrils/olfactory epithelium Muscular tongue Stapes + tympanum Tetrapod Skull with 2 occipital condyles Synapomorphies 1 cervical & 1 sacral vertebra Pelvic girdle attached to backbone There are 2 main groups of tetrapods: Non-amniotes (modern amphibians) Amniotes (reptiles, birds, and mammals) Radiation of Non- Amniote Tetrapods Early tetrapods are not like modern amphibians, or Lissamphibians Large, crocodile-like, and closely related to amniotes Non-amniote tetrapods reached their peak diversity in the Late Carboniferous and Early Permian  Insect diversity greatly increased during the Pennsylvanian period Most early tetrapods were carnivorous – All extant adult amphibians are Radiation of carnivorous Non-Amniote Most early tetrapods were mostly or completely aquatic Tetrapods – Several modern amphibians have (cont’d) reverted to this ancestral state There are several extinct groups of nonamniotes, and scientists are not sure which group modern amphibians evolved from  Modern Amphibians This grouping includes frogs, salamanders, and caecilians Amniotes Named for their amniotic egg Appeared in the mid- Carboniferous, but radiated in the Permian 3 major groups: – Synapsida (mammals) – Parareptilia (e.g. mesosaurs) – Eureptilia (extant reptiles and birds) Other Amniote Characteristics Skin diversity – scales, hair, feathers, nails, beaks, and horns, all formed from keratin Internal tongue muscles No palatal teeth Rib ventilation of lungs Ossified ribs that connect to the sternum Longer necks created space for more nerves to control forelimbs Ankles that allow them to use their limbs for locomotion Internal fertilization Amniotic egg  Distinctive Features of the Amniotic Egg The chorion and amnion develop from outgrowths of the body wall at the edges of the developing embryo and spread outward and around the embryo until they meet. At their junction, the chorionic and amniotic membranes merge and leave an outer membrane (the chorion), which surrounds the entire contents of the egg, and an inner membrane (the amnion), which surrounds just the embryo. The allantoic membrane develops as an outgrowth of the hindgut posterior to the yolk sac and lies within the chorion.  Amniotes are classified by the number of holes in their heads, or temporal fenestration – Anapsids – No holes, turtles and early amniotes – Synapsids – Single arch, mammals – Diapsids – Double arch, birds and reptiles  Important for how muscles attach to the head and jaws and allow different groups to grab food and chew