Bio310 Lecture 4: Fish Skeleton, Skin, and Scales PDF

Bio310 – Fish Skeleton, Skin, and Scales Peter J. Park, PhD Lecture Outline Fish Evolution (Extant and Extinct) Fish Development Bone Evolution and Development Fish Cranial Skeleton Fish Postcranial Skeleton Fish Median Fins Fish Paired Fins Fish Scales...

Bio310 – Fish Skeleton, Skin, and Scales Peter J. Park, PhD Lecture Outline Fish Evolution (Extant and Extinct) Fish Development Bone Evolution and Development Fish Cranial Skeleton Fish Postcranial Skeleton Fish Median Fins Fish Paired Fins Fish Scales KEY TERMS Vertebrata includes all craniates (may or may not exclude Myxiniformes [hagfishes], which have no trace of vertebrae) Craniata includes any organism ancestrally with a chondrocranium, which includes Myxiniformes Gnathostomata includes all vertebrates except Petromyzontiformes (and Myxiniformes); Osteichthyes includes all gnathostomes except Chondrichthyes; Sarcopterygii includes all osteichthyans except Actinopterygii Jawless Fishes hagfish [living] ostracoderms [extinct] lamprey [living] ostracoderms [extinct] ORIGIN OF JAWS Placoderms (first vertebrates to have true hinged jaws) [extinct] Chondrichthyes (sharks, skates and rays, chimaera) [living] Acanthodii [extinct] †Acanthodii Actinopterygii – basal groups [fishes with many plesiomorphic traits] bichir [living] palaeonisciform [extinct] sturgeon [living] gar [living] bowfin [living] Actinopterygii – teleosts (derived groups) [living] Actinopterygii – teleosts (derived groups) [living] Actinopterygii – teleosts (derived groups) [living] Lecture Outline Fish Evolution (Extant and Extinct) Fish Development Bone Evolution and Development Fish Cranial Skeleton Fish Postcranial Skeleton Fish Median Fins Fish Paired Fins Fish Scales  Synapomorphies of Vertebrata (1) Predation instead of active suspension feeding, but some species have reverted to this (2) Bone and cartilage (3) Head (brain, braincase) (4) Neural crest cells, which form numerous unique vertebrate structures (5) Thyroid (derived from endostyle) (6) nephrostomes or renal corpuscles or nephron instead of flame cells  Basic Vertebrate Structure (compared to amphioxus-like chordates) - Segmentation (= metamerism = serial homology) is a characteristic feature of the vertebrate body plan. - Repeated segments allows a subset of the segments to “evolve” while the remaining segments continue to carry out previous function(s) FISH DEVELOPMENT zebrafish  Gastrulation (NOTE: This diagram is not of a fish, but overall concept is similar to that which occurs in fish.)  Splanchnopleur vs. Somatopleur Splanchnopleur - a layer of tissue in a vertebrate embryo comprising the endoderm and the inner layer of mesoderm, and giving rise to the gut. - mostly involved in feeding Somatopleur - a layer of tissue in a vertebrate embryo comprising the ectoderm and the outer layer of mesoderm, and giving rise to the body around the gut. - carries out the other major categories of functions, including locomotion, which is involved in: - Defense (Predator avoidance and deterrence) - Reproduction Evolution of the ability to capture larger, more active prey probably played a major role in the origin of the vertebrates.  Generalized Vertebrate Body Plan Dorsal Hollow Nerve Cord Notochord Mouth Post-anal Tail Pharyngeal Liver Anus Gill slits Anterior  Cephalochordate (NOT a craniate or vertebrate)  Splanchnopleur (Feeding) Primary vs. secondary splanchnic segmentation PRIMARY SPLANCHNIC SEGMENTION: Pharyngeal gill slits represent primary splanchnic segmentation (and hypertrophy). “Primary" because they represent an adaptation to the functional demands imposed by the environment for feeding. The gill slits allow the animal to eliminate water taken in with food at the mouth. Food could now be concentrated then swallowed. SECONDARY SPLANCHNIC SEGMENTION: Other segmented structures associated with the gill slits represent secondary splanchnic segmentation. They represent adjustments of the body to support and supply the gill slits. Subsequently, they evolved later. Examples: - brachial arches strengthen the pharynx. - aortic arches provide circulation to gills  Somatopleur (Locomotion) Primary vs. secondary somatic segmentation PRIMARY SOMATIC SEGMENTATION: The myomeres represent primary somatic segmentation. “Primary” because they represent an adaptation to the functional demands imposed by the environment for locomotion in water. Myomeres allow localized muscular contraction. Contraction is limited to each myomere, and all the muscle fibers of a myomere contract together. Successive myomeres contract individually and in sequence from front to back so a wave throws the body into a series of S- curves that push water backward. SECONDARY SOMATIC SEGMENTATION: Other segmented structures associated with myomeres represent secondary somatic segmentation. They represent adjustments to support and supply myomere function. Subsequently, they evolved later. Examples: - Nerves that serve the myomeres. - Ribs - Vertebrae Lecture Outline Fish Evolution (Extant and Extinct) Fish Development Bone Evolution and Development Fish Cranial Skeleton Fish Postcranial Skeleton Fish Median Fins Fish Paired Fins Fish Scales  THE FISH SKELETON Cranial Skeleton Neurocranium - Chondrocranium – protect brain and inner ear (found in jawless fishes and gnathostomes; in gnathostomes, the cartilage is replaced by bone (endochondral or replacement bone)) - Dermatocranium (found in bony fishes only) Splanchnocranium (visceral skeleton) – gill arches - Mandibular Arch = jaw -- sharks: palatoquadrate is upper jaw and mandibular cartilage (Meckel’s cartilage) is lower jaw [both components of jaw are cartilage] -- bony fishes: premaxilla + maxilla is upper jaw and dentary is lower jaw [both bone] - Hyoid Arch – helps suspend jaws - Branchial Arches – gill arches Postcranial Skeleton Axial Skeleton - Vertebral Column (and Notochord) - Ribs - Median Fins Appendicular Skeleton - Pectoral girdle and appendages - Pelvic girdle and appendages  Cranial Skeleton Cartilaginous Fishes Bony Fishes (chondrichthyes) (actinopterygii, sarcopterygii) Skull Skull Jaw Jaw Gills Jaw Jaw Gills Support Support Extinct Agnathans - Ostracoderms had large cephalothoracic bony shield that covered the head dorsally and laterally, comparable with the dermatocranium. - Several extinct agnathan groups were armored with dermal bone, but internal skeleton was cartilage. - Thus, dermal bone is phylogenetically older than Chondrichthyes Bony Fishes: In living bony fish taxa, there are two types of bone: (a) Cartilage replacement (endochondral) bones - have cartilage precursor which is then replaced by bone (b) Dermal bones – never have cartilage precursor; develops directly into bone. Bony Fish and Tetrapods: Internal skeleton (e.g., ribs, arms, legs) is comprised of endochondral bone Sheets of dermal bone are incorporated into roof of skull Dermal bone used as armor in many forms and locations Lecture Outline Fish Evolution (Extant and Extinct) Fish Development Bone Evolution and Development Fish Cranial Skeleton Fish Postcranial Skeleton Fish Median Fins Fish Paired Fins Fish Scales  Evolution of the Skull - There is an evolutionary trend toward fusion and reduction in bony elements in ancient actinopterygians to more advanced teleosts and in aquatic sarcopterygians to tetrapods. - A fossil chondrostean (actinopterygian) fish may have more than 150 skull bones while humans have 28 skulls bones. - The earliest living craniate is the hagfish, which has a small chondrocranium and cartilaginous visceral arches associated with pharyngeal pouches - Lamprey lack a dermal component to the cranial skeleton, which probably resulted from a secondary loss of dermal bones because most jawless vertebrates had dermal bones. Also, dermal bones are present in the anapsids (sister group of lamprey). - Lamprey’s cranial skeleton consists only of a small chondrocranium and a series of eight visceral arches, which are united to form a cartilaginous pharyngeal basket - The pharyngeal basket is superficial, lying peripheral to gill pouches, and its elements are fused cartilage https://youtu.be/_v22dSMHKGo?feature=shared  Cranial Skeleton NOTE: Dermatocranium never found in cartilaginous fishes  CARTILAGINOUS FISH: chondrocranium (dorsal view) In cartilaginous fishes, neurocranium = chondrocranium Photos by Simon De Marchi Owner-operator at Elasmo-Morph In bony fishes, neurocranium = chondrocranium + dermatocranium (Bones of the dermatocranium evolved from scales that became attached to the chondrocranium) BONY FISH:  BOWFIN (Amia) [Basal bony fish] https://reptileevolution.com/amia.htm NEUROCRANIUM (BONY FISHES) Yellow Perch [Highly derived bony fish] EARLY GNATHOSTOME (Loosely based on a Shark) Jaw patterning in cartilaginous fish classes Placodermii, Chondrichthyes, and Acanthodii. Meckel’s cartilage is found in Chondrichthyes and Acanthodii. Dentary is found in Placoderms.  Jaw patterning in actinopterygian fishes. dermatocranial bones viscerocranial elements only dermatocranial bones shown Dentary is found in Actinopterygii (Ray-finned fishes) BRANCHIOCRANIUM / VISCERAL CRANIUM / SPLACHNOCRANIUM (BONY FISHES) Mandibular Arch - The palatoquadrate of cartilaginous fishes is replaced in bony fishes by maxilla and premaxilla - The Meckel’s cartilage of cartilaginous fishes is replaced in bony fishes by the dentary  3-D Skull: https://sketchfab.com/3d-models/largemouth-bass-labelled-skull-e9118acf81044ea388474fda96f66976 Feeding Video: https://www.westernbass.com/article/mouth-largemouth-bass-works-video BRANCHIOCRANIUM / VISCERAL CRANIUM / SPLACHNOCRANIUM (BONY FISHES) Palatine Arch Hyoid Arch (includes Suspensorium)  BONY FISHES: Yellow Perch - The suspensorium (part of the hyoid arch) of bony fishes attaches the lower jaw and opercular apparatus to the neurocranium. It consists of just the hyomandibula and symplectic. Branchiostegal Rays Jaw Suspension varies across fishes! There are three basic types of jaw suspension: Amphistylic: palatoquadrate connected to the braincase directly and indirectly by the hyomandibula; jaw supported by both hyomandibular and chondrocranium (ancient chondricthyans, acanthodians, early bony fishes). Hyostylic: palatoquadrate connected to the braincase indirectly by the hyomandibula; jaws supported solely by the hyomandibular (most derived chondricthyans, most bony fishes). Autostylic: palatoquadrate connected to the braincase directly without support from the hyomandibula; jaws supported by chondrocranium; hyomandibular not involved (dipnoans, tetrapods) NOTE: This is not an evolutionary progression.  LAMPREY: GNATHOSTOMES: Lamprey - pharyngeal basket are superficial, lying peripheral to gill pouches, and its elements are fused cartilage Gnathostomes - Visceral arches lie deeply next to lumen of pharynx and composed of articulated segments Conclusion: Visceral arches between jawless fishes and gnathostomes are likely NOT homologous. BRANCHIOCRANIUM / VISCERAL CRANIUM / SPLACHNOCRANIUM (BONY FISHES) Opercular apparatus Branchial Complex (NOTE: Opercular bones removed) Lecture Outline Fish Evolution (Extant and Extinct) Fish Development Bone Evolution and Development Fish Cranial Skeleton Fish Postcranial Skeleton Fish Median Fins Fish Paired Fins Fish Scales Cephalochordate (NOT a craniate or vertebrate) Major Organ Systems of Craniates (Based on a generalized craniate) Major Organ Systems of Craniates (Based on a generalized craniate) POSTCRANIAL SKELETON Vertebral Column (2 sections): 1. Trunk (Precaudal) vertebrae - skull to end of body cavity/gut) 2. Caudal vertebrae - end of body cavity/gut to tail) Precaudal Vertebra consists of: - Neural Spine and Neural Arch (surrounds spinal cord) - Centrum (surrounds notochord) - Parapophyses (attachments for ribs, if ribs present; ribs only cover body cavity). - Haemal Arch (surrounds dorsal aorta) present only in last several trunk vertebrae Trunk Vertebra consists of: - Neural Spine and Neural Arch (surrounds spinal cord) - Centrum (surrounds notochord) - Haemal Arch always present and now also have Haemal Spine - No ribs Precaudal vertebrae Caudal vertebrae POSTCRANIAL VERTEBRAE (NOTE: Left pectoral fin removed.) Tails of modern fishes look “Symmetrical” but this is only superficial – these tails are actually internally (i.e., supporting skeletal elements) asymmetrical: - Hypurals are enlarged haemal spines that support the main caudal fin rays of the caudal fin. - Some hypurals fuse to form a hypural plate - Epurals are enlarged neural spines. - Epurals + last haemal spine support the very top of caudal fin  Caudal Fin Types Protocercal tail - ancient undifferentiated caudal fin that extends around the posterior end Found in lancelets, agnathans, and large of derived fishes) Heterocercal tail – vertebral axis turns upward into an expanded dorsal lobe of the tail; plesiomorphic for gnathostomes Found in osteostracans, most chondrichthyans, early actinopterygians and sarcopterygians Homocercal tail – reduced centra of several terminal vertebrae have fused to form a spike-like urostyle, which tips upward; most of the caudal fin is comparable with the ventral portion of the heterocercal tail; caudal fin rays arrayed symmetrically and attach to a series of hypural bones (enlarged haemal spines) posterior to (behind and below) the last vertebra that supports the caudal fin rays – these “plates” are ventral to urostyle; in some species, some of the hypurals fuse to form a hypural plate (e.g., stickleback, flatfishes, mackerel). Found in teleosts Abbreviated heterocercal tail – intermediate between heterocercal and homocercal types Early neopterygians - Amia, Lepisosteus Leptocercal (or Diphyrcercal) tail – vertebral axis straightened out; dorsal and ventral lobes equal in size Evolved independently in lungfishes and coelacanths, whose ancestors had heterocercal tails Isocercal tail – the last vertebrae (not the original urostyle) has been secondarily modified into a small plate to which caudal fin rays attached Found in cods  Homocercal Heterocercal Abbreviated heterocercal Diphycercal Lecture Outline Fish Evolution (Extant and Extinct) Fish Development Bone Evolution and Development Fish Cranial Skeleton Fish Postcranial Skeleton Fish Median Fins Fish Paired Fins Fish Scales Chondrichthyes have ceratotrichia - Horny fin rays made of elastin Bony fishes have lepidotrichia - Replaces ceratotrichia - Bony rays (derived from scales) - Includes spines, soft rays, and finlets - If single, then all soft - If double then anterior spines + posterior soft  Bony fishes have lepidotrichia - fin rays that are bony - Notice how the arrangement of the dorsal fin indicates that the rays are derived from scales Transverse section through dorsal fin of a bony fish Median Fins include Dorsal Fin (which can 1 or 2 fins) and Anal Fin (Paired Fins include Pectoral Fins and Pelvic Fins) Pterygiophores are the cartilaginous elements (in cartilaginous fishes) or bony elements (in bony fishes) that support the fins of a fish Lecture Outline Fish Evolution (Extant and Extinct) Fish Development Bone Evolution and Development Fish Cranial Skeleton Fish Postcranial Skeleton Fish Median Fins Fish Paired Fins Fish Scales Placoderms (extinct) - had pectoral fins and small pelvic fins. - Pectoral girdle: well-developed thoracic dermal plates (cleithral elements and clavicle) that covered the front of the trunk, comparable to the dermal part of a pectoral girdle Lateral view of thoracic plates of Dunkleosteus BONY FISHES: Bones of the Pectoral Girdle BONY FISHES: Bones of the Pelvic Girdle Lecture Outline Fish Evolution (Extant and Extinct) Fish Development Bone Evolution and Development Fish Cranial Skeleton Fish Postcranial Skeleton Fish Median Fins Fish Paired Fins Fish Scales