Lesson 22 - Early Vertebrates

22: early vertebrates Thursday, April 4, 2024 6:40 PM which of the following statements about protostomes and deuterostomes is true? a. all protostomes are invertebrates; all deuterostomes are vertebrates ○ it is true that all protostomes are invertebrates which of the following statements about protostomes and deuterostomes is true? a. all protostomes are invertebrates; all deuterostomes are vertebrates ○ it is true that all protostomes are invertebrates ○ some deuterostomes are also invertebrates b. all protostomes have an open circulatory system; all deuterostomes have a closed circulatory system ○ protostome with an open circulatory system: cephalopods and annelids ○ most but not all deuterostomes have a closed circulatory system c. all protostomes have digestive tracts; so do all deuterostomes ○ all deuterostomes have a digestive tract, but not all protostomes do d. all protostomes have bilateral symmetry; so do all deuterostomes echinoderms • • • sea stars, sea urchins, sea cucumbers invertebrate deuterostomes larvae have clear bilateral symmetry characteristics of chordates • • notochord ○ present in all chordate embryos, few adults § most adults lose their notochord during development longitudinal, flexible rod between digestive tube and nerve cord (anterior to ○ posterior) ○ derived from mesoderm § endoderm makes the digestive tract § ectoderm makes the nervous system provides skeletal support ○ § becomes a spine or remains if basal § parallel but not homologous dorsal hollow nerve cord ○ hollow tube that develops into the central nervous system § neurons and nerves regardless of how basal they are § sometimes a brain ○ derived from ectoderm • dorsal hollow nerve cord ○ hollow tube that develops into the central nervous system § neurons and nerves regardless of how basal they are § sometimes a brain ○ derived from ectoderm • muscular, post-anal tail ○ in non-chordates, digestive tract runs body length; the anus is at the end of the body ○ in all embryonic chordates ○ reduced in some adult chordates pharyngeal clefts and slits ○ arches along pharynx develop into slits that open into the pharynx ○ invertebrates: suspension feeding ○ aquatic vertebrates: gills ○ tetrapods: no slits § vestigial, no longer useful (not critical for feeding or breathing) § arches become part of ears, head, and neck • basal chordates • • lancelets ○ notochord protects dorsal hollow nerve cord ○ these larval traits move into adulthood ○ filter-feed using pharyngeal slits tunicates ○ larvae reflect chordate characters ○ adults lose characteristics after metamorphosis § usually sessile, no dorsal hollow nerve cord, no post-anal tail, etc. siphons used for filter feeding and waste removal ○ § from pharyngeal slits (only remaining characteristic) characteristics of vertebrates • • • vertebrae ○ cartilaginous or bony developed nervous system ○ more central nervous system formation ○ cranium protecting brain in less basal species ○ spinal cord ~ 63,000 vertebrate species ○ depending on how species is defined ○ ○ • spinal cord ~ 63,000 vertebrate species ○ depending on how species is defined which of the following statements is true? a. there are half as many beetle species as there are vertebrate species b. there are approximately the same number of beetle and vertebrate species c. there are twice as many beetle species as there are vertebrate species d. there are more than five times as many beetle species as there are vertebrate species a. around 8-9 times more b. 350,000 species of beetles evolution of vertebrates • • • • transitional fossils from 530 MYA ○ vertebrate-like traits but not true vertebrates ○ origin: cambrian explosion earliest vertebrates 500 MYA mineralization ○ started with teeth-like structures earliest gnathostomes (jawed vertebrates) from 440 MYA vertebrates: hagfish & lamprey • • • • • • jawless, no backbone not too speciose rudimentary vertebrae make them basal vertebrates notochord persists in adults ○ insufficient vertebrae support hagfish: ○ reduced sensory structures § scavengers ○ produces slime as defense to hold back predators lampreys: ○ cartilaginous teeth lack collagen § not mineralized adults parasitize fish ○ the evolution of jaws • • rapid radiation of jawed fish after jaws appear ○ the trait demonstrates significance if its appearance is followed by mass diversification hypothesis: jaws originated from the skeletal rods that support gill slits ○ jaws and rods have similar morphology ○ both jaws and rods derived from the same cells in the embryo (other skeletal elements are not) ○ no fossil evidence to confirm § transitional species missing ○ ○ jaws and rods have similar morphology both jaws and rods derived from the same cells in the embryo (other skeletal elements are not) ○ no fossil evidence to confirm § transitional species missing why did jaws lead to an adaptive radiation in fishes? a. they increased the diet breadth of animals b. they represented the origin of predation in chordates ○ predation predates this in the cambrian explosion ○ hagfish, lamprey, etc. ○ jaws advanced predation c. they can increase the attractiveness of male fish, leading to increased female mate choice ○ usually associated with colors or scales d. all of the above gnathostomes: sharks • • • • • fully vertebrates, having a vertebrae and rib cage skeleton of cartilage (derived trait) ○ ancient sharks were bony ○ cartilage makes them lighter mineralized teeth streamlined bodies for hunting ○ reduces drag in the water ○ sharp vision, olfactory bulbs, can detect electric fields/vibrations of animals ○ the largest sharks, though, are filter feeders swim nearly continuously ○ keep them from sinking § still quite heavy and not too buoyant ○ gas exchange § need high oxygenation osteichthyes: ray-finned fish • • meaning "bony fish" over 27,000 extant species ○ most diverse group of vertebrates • • bony fish with rays in fins gills: gas exchange for all of them ○ from pharyngeal slits • over 27,000 extant species ○ most diverse group of vertebrates • • bony fish with rays in fins gills: gas exchange for all of them ○ from pharyngeal slits swim bladder: maintains buoyancy (structurally derived from lungs) ○ ancient fish had lungs (not very functional) ○ selection made them a different function lateral line: detects pressure/vibrations ○ sensory organ for prey and predators • • lobe-fins: coelacanths & lungfish • • • • extant semi-transitional species 8 extant species in total coelacanths: ○ deep-sea fish ○ bones in fins that resemble wrists ○ lobes show structural development of limbs ○ 2 extant species ○ thought extinct, found alive in 1938 lungfish: ○ transition away from the swim bladder to functional lungs ○ breathe air but also have gills § shallow water dwellers ○ fleshy fins, walk short distances underwater § helps with mobility in shallow waters ○ closest living relative to tetrapods