Lesson 1: General Concepts of Comparative Anatomy PDF

Lesson 1: General Concepts of Comparative Anatomy Comparative anatomy | Lecture | Module 1 COMPARATIVE ANATOMY Comparative anatomy is the study of similarities and differences Fish scales are dermal (= formed in derma) bones like skull roof in the anatomy of different species....

Lesson 1: General Concepts of Comparative Anatomy Comparative anatomy | Lecture | Module 1 COMPARATIVE ANATOMY Comparative anatomy is the study of similarities and differences Fish scales are dermal (= formed in derma) bones like skull roof in the anatomy of different species. bones meanwhile in reptiles one must differentiate between scales and osteoderms (= scutes). Scutes are widespread HOMOLOGY among reptiles, and they are like fish scales in that they are Intrinsic similarity indicative of a common evolutionary origin. produced in derma and are ossified. They may be unlike superficially but can be proven to be equivalent. Homology refers to features of two or more organisms sharing common ancestry. Similarity of anatomical construction Similar topographical relation to the animal body Similar course of embryonic development Similarity or identity of specific physiological function or mechanism. HOMOPLASY Features of two or more organisms that may are related by EXAMPLES OF HOMOLOGY similarity of appearance but cannot be explained by either The arm of a human, the wing of a bird or a bat, the leg of a homology or analogy. dog and the flipper of a dolphin or whale. Usually also analogous and frequently also both analogous and homologous. Homoplastic structures are unusual unless the chance resemblance is superficial. EXAMPLE OF HOMOPLASY Sailfish and pelycosaur; similarities from mimicry and camouflage. CONVERGENCE OR PARALLELISM ANALOGOUS STRUCTURE Structures present striking similarities of appearance usually Structures that have similar functions (jobs) but were not associated with living in a common environment. inherited from a common ancestor. EXAMPLE OF CONVERGENCE EXAMPLES OF ANALOGOUS STRUCTURES Fish and whale; porpoise and fish Wings of a hummingbird and humming moth – both can hover to feed. DIVERGENCE Animals which are closely related by descent but differ greatly in general appearance after long sojourn in different environments. EXAMPLES OF DIVERGENCE seals and cats; bat and man; whale and man. RECAPITULATION THEORY OR LAW OF BIOGENESIS ANALOGY During the development, an individual passes through certain Similarity of general function or of superficial appearance not ancestral stage through which the entire race passed in its associated with similarity of intrinsic anatomical construction or evolution and that the embryo of higher forms in certain ways of embryonic origin and development. resemble the adults of lower forms. EXAMPLES OF ANALOGY The embryo of lower forms resembles the embryo of higher Fish and snakes are covered with scales for purposes but forms. investigation of the two types of scales shows that they are histologically dissimilar and differ in their made of origin. MODULE 1 | 1  ONTOGENY 1. RADIAL SYMMETRY Individual life history Symmetry of a wheel Birth to death. The body parts of a radially symmetrical PHYLOGENY animal are arranged around a central axis so Species history that each part extends from the center. Racial history Animals that exhibit radial symmetry tend to Ancestral Origin be sessile (immobile). Radial symmetry Evolutionary change within related organism allows them to reach out in all directions. SYMMETRY AND BODY SHAPES ANIMAL SYMMETRY Asymmetrical Symmetrical - Radially symmetrical - Bilaterally symmetrical 2. BILATERAL SYMMETRY - Spherical symmetry Symmetry of a plank - Biradial symmetry One cut along the longitudinal axis will produce identical halves of a bilaterally ASYMMETRICAL symmetrical animal. Asymmetrical animals have no pattern of Bilateral symmetry is best for motile animals. symmetry. Body Plan Includes: o Anterior and The simplest animals (sponges) are Posterior Ends asymmetrical. o Dorsal and Ventral Surfaces o “Right” and “Left” sides are mirror images. SYMMETRY 3. SPHERICAL SYMMETRY Arrangement of body parts with regards to foregoing axes and Symmetry of a ball planes. Any section through the center divides the Axis-longitudinal, or anterior, posterior/ sagittal, Or organism into symmetrical halves. dorsoventral 4. BIRADIAL SYMMETRY Planes-median, sagittal, horizontal, frontal, transverse, Symmetry of an oval or cross planes. Only two sections vertical ones at right angles to each other divide the organism into symmetrical halves. EVOLUTION OF SYMMETRY The evolutionary sequence progressed from asymmetrical animals, to radial, and then to bilaterally symmetrical animals. 2  EVOLUTIONARY CHANGES IN THE ANIMAL BODY BODY CAVITIES The body cavity is a space that separates the gut and internal organs from the rest of the body. It isolates the internal organs from body-wall movements. The body cavity of a coelomate animal (called a coelom) is It also bathes the internal organs in a liquid through which located within the mesoderm. nutrients and wastes can diffuse. THREE MAJOR BILATERAL BODY PLANS Acoelomates Pseudocoelomates Coelomates o Each plan consists of 3 cell layers: endoderm, mesoderm, ectoderm. GASTROVASCULAR CAVITY (GVC) Gastrovascular Cavities (GVC) are areas where food is digested. If they have only one opening, the process is limited. CEPHALIZATION Two openings designate a digestive tract The term “Cephalo” allowing food to be digested more means “head”. thoroughly. In animals with bilateral ARRANGEMENT OF ECTODERM, MESODERM, AND symmetry, there is a ENDODERM greater increase in the An acoelomate animal does not have a body cavity. nerve tissue concentrated in the anterior end (the head) as animals increase in complexity. For example, brains have formed with accessory organs for seeing, hearing, tasting, etc. SEGMENTATION Many animals have segmented body parts. In some cases, the parts repeat repeatedly, as with earthworms. A pseudocoelomate animal has a body cavity (called a pseudocoelom) located between endoderm and mesoderm. In other animals, the segments are modified, such as with insects they essentially have 3 segments: the head, thorax, and abdomen. 3  CLEAVAGE PATTERNS One opening will become the mouth, the other will become the anus. 3 MAJOR DIFFERENCES BETWEEN PROTOSTOMES AND DEUTEROSTOMES CHARACTERISTICS PROTOSOME DEUTEROSTOME Early Cleavages Slight angle (spiral Straight Down cleavage) (radial cleavage) First Infoldings of Mouth Anus Archenteron Coelom develops Split in tissue at Outpouching of from sides of archenteron wall EMBRYONIC DEVELOPMENT archenteron During early development, the fertilized egg divides, or cleavages, to produce a solid ball of cells. Then, cell migration 6 MAJOR TRENDS IN EVOLUTION results in a hollow ball called a blastula. 1. multicellularity 2. Development of tissues, first none (sponges), then 2 (cnidarians), then 3 3. Development of symmetry, first none (sponges), then radial (cnidarians), then bilateral 4. Development of a gut, first none (sponges), then sac- like (cnidarians, flatworms), then complete 5. Development of a body cavity, first none (flatworms), then a pseudocoelom (roundworms), then a coelom 6. Development of segmentation; segmentation evolved in protostomes (annelids and arthropods) Some cells of the blastula migrate inward and form a independently of that which evolved in three-cell layered embryo called a gastrula. deuterostomes. The opening is the blastopore. The internal cavity is called the archenteron. SUMMARY OF EVOLUTIONARY TRENDS The Gastrula will become the gut (digestive tract) of the mature animal. In species that have a separate mouth and anus, the tube will eventually extend through the length of the embryo and fuse with the opposite side. 4 EVOLUTIONARY TRENDS 5