Mrs. Ofelia Solano Saludar Department of Natural Sciences University of St. La Salle

1. THE CRANIATES: ANAMNIOTES Mrs. Ofelia Solano Saludar Department of Natural Sciences University of St. La Salle Bacolod City

2. WHO ARE THE CRANIATES? Traditional classification: • Protochordata (Acraniata) are separated from Vertebrata (Craniata) that have a skull. • Vertebrates may be divided into Agnatha(jawless) and Gnathostomata (having jaws). • Gnathostomata is subdivided into Pisces with fins and Tetrapoda, usually with two pair of limbs. • Vertebrates are also divided into Amniota, having an amnion, and Anamniota lacking an amnion. • Many of these groupings are paraphyletic. • Alternative monophyletic taxa are suggested.

3. Cladistic classification: • Some traditional taxa no longer used. • Some cladistic classifications exclude Myxini (hagfishes) from the group Vertebrata because they lack vertebrae, although retaining them in Craniata since they do have a cranium. • Reptiles are paraphyletic because they do not contain all of the descendants of recent common ancestor. • Reptiles, birds and mammals compose a monophyletic clade called Amniota. • Subphylum Vertebrata is a monophyletic group that shares the basic chordate characteristics with the urochordates and cephalochordates.

5. CRANIATE CHARACTERISTICS: GENERAL BODY PLAN • Bilateral symmetry, deuterostome development, chordate “Big 4” • 3 regional components: head, trunk & postanal tail • Marked cephalization: concentrated on head are paired sense organs (olfactory, optic, otic, and lateral line system), a tripartite brain encased in a cranium, jaws and gills in some species • Trunk contains a coelom, surrounded with a body wall. • Several forms have paired appendages. A neck connects structures of the head with those of the trunk

6. Subphylum VERTEBRATA The head of Craniates are opened up a completely new way of feeding for chordates: active predation. Vertebrates get their name from vertebrae, the series of bones that make up the backbone. There are approximately 52,000 species include the largest organisms ever to live on the Earth.

7. Derived characters include: • Two clusters of Hox genes (only one in lancelets & tunicates) may have allowed greater complexity • Other families of genes that produce signaling molecules & transcription factors are also duplicated • Vertebrae to protect the spinal cord and serve as muscle attachment. • Cranium to encase and protect the brain • Pharyngeal clefts evolve into gill slits • Paired sense organs, including 2 semicircular ducts in each ear, electroreception, a lateral line system with multicellularneuromasts • Neural crestcells form near dorsal margins of closing neural tube of embryo

8. Dorsal edgesof neural plate Neuraltube Ectoderm Neuralcrest Ectoderm Migrating neuralcrest cells (a) The neural crest consists of bilateral bands of cells near the margins of the embryonic folds that form the neural tube. Notochord (b) Neural crest cells migrate todistant sites in the embryo. (c) The cells give rise to some of the anatomical structuresunique to vertebrates, including some of the bones and cartilage of the skull.

9. The Origin of Vertebrates • Genetic ties unite echinoderms, hemichordates, protochordates, cephalochordates, and craniates in unknown lineages • Characters shared by protochordates and craniates are derived from a common ancestor

10. The echinoderm tornaria and Ammoecetes larvae of lampreys have similar features with an Amphioxus-like protochordate TORNARIA AMPHIOXUS AMMOECETES

11. The Earliest Vertebrates In 1928, Walter Garstang proposed that the tadpole larvae of tunicates may have led to early vertebrates through paedomorphosis

12. How might the larva cease from being an echinoderm?What selective advantage might have driven these changes?

13. LARVAL ECHINODERM TO CHORDATE TADPOLE: • Neotenic species avoid harsh terrestial winter conditions by remaining larval, yet sexually mature. • Through neoteny or paedomorphism, the larva would have greater adaptive advantage of pelagic mobility • Ammoecoete-like craniate & vertebrate ancestors were derived through heterochronic processes: • Basic chordate plan evolved through elongation of echinoderm larval body. • Segmental musculature, & a stiffened bar (notochord) are replacements for a faltering ciliary system for locomotion; • Pharyngeal slits support suspension feeding.

15. Vertebrates evolved at least 530 million years ago, during the Cambrian explosion. • Pikaia was an early chordate discovered in the Burgess Shale. Cephalochordate? • The most primitive of the early vertebrate fossils are those of the 3-cm-long Haikouella and Haikoicthys. • Eyes and brain present, but no skull. • It is transitional in morphology between cephalochordates and vertebrates, could be a sister taxon of vertebrates.

16. Bony dermal armor of ostracoderms must have developed late in soft-bodied invertebrates or early craniates which already had a notochord, dorsal nerve cord and pharyngeal slits

17. Birthdays and nurseries

18. Superclass: Pisces Class AgnathaClass Placodermii+ ClassAcanthodii+ Class Chondrichthyes Class Osteichthyes Superclass: Tetrapoda Class AmphibiaClass ReptiliaClass Aves Class Mammalia

19. Class AGNATHA • Lack true jaws, appendages • Extinct ostracoderms and living cyclostomes; 45 species

20. OSTRACODERMI- oldest known vertebrates • Fishes that occurred in the late Cambrian period through the Devonian (about 400 - 525 mya) • Jawless vertebrates called 'armored fishes due to bony scale; had flattened appearance • Heterostracans had dermal armor, but lacked paired fins • Osteostracans had paired pectoral fins as well as dermal armor • Anaspidswere more agile and streamlined.

22. CEPHALASPIDOMORPHI - lampreys; sucker-like mouth with teeth; 7 pairs of gill slits and pouches; a sister group to Gnathostomes

23. MYXINI- hagfishes; scavengers; mouth with 4 pairs of tentacles; 5-15 pairs of gill slits and gill pouches; partially hermaphroditic; possibly a sister group to vertebrates Famous for slime production… …and fished for ‘eelskin’ & meat

24. Gill slits Cranium Mouth Skeletal rods GNATHOSTOMES • Have true jaws and paired appendages: Paleozoic placoderms, chondrichthyans, teleostomes (acanthodians &osteichthyans) • Jaws have evolved by modification of the anterior gill arches • Remaining gill slits are no longer required for suspension feeding & remained as main site of respiratory gas exchange. • Another duplication of the Hox genes (now 4 clusters) & other developmental genes • Monophyletic

27. Class PLACODERMII+ • Extinct; evolved from ostracoderms; probably a sister group to chondrichthyans • Armored (bony dermal shields), jawed fishes that first appeared about 420 million years ago (MYA) during the Silurian Period • Were probably predators with large, sharp 'tooth plates' • They came to dominate most marine and freshwater ecosystems before becoming extinct at the end of the Devonian period (355 MYA). • About 200 genera of placoderms have been discovered, with most of these occurring during the Devonian radiations.

28. Class ACANTHODII+ • Spiny fins; bony dermal plates • Extinct jawed fishes; earliest known gnathostomes (Silurian; about 440 mybp) • Probably a sister group to osteichthyans • Small (less than 20 cm long) with large eyes • Most likely died out because of the rapidly increasing number of ray-finned fishes and sharks during the Permian.

30. Class CHONDRICHTHYES • Cartilaginous skeleton, although ancestors had mineralized skeleton; sharks, skates, chimeras: over 800 nearly all marine species • Streamlined body with rigid heterocercal tail; 5-7 gills with separate openings; acute senses • No operculum & swim bladder

31. Subclass Holocephali • Chimeras; 30 marine species; few scales • Gill slits have a fleshy operculum & the spiracle is closed • Bony plates on the jaws instead of teeth; upper jaw fused with braincase • Common ancestor with sharks but an independent line

32. Subclass ELASMOBRANCHII • Have a spiracle, 5-7 naked gill slits, and placoid scales that become teeth on the jaws • 1st pharyngeal slit modified as a spiracle • Naked gill slits (no operculum); mouth located ventrally; 360 shark and 460 ray/skate species

33. Batoidea- rays & skates

34. Cladoselachii- primitive sharks (300-400 mya) • Selachii- modern sharks

35. Class OSTEICHTHYES • Bony fishes; over 17,000 species • Primarily fusiform body but variously modified • Skeleton is partly or chiefly bone • Gill slits are covered by a bony operculum • Skin has scales with typically little bone • Most have a swim bladder

36. Subclass Actinopterygii • Over 27,000 species, 40% occur in fresh water • Ray-finned; thin flexible scales have replaced the bony armor of fishes • Paleozoic fishes had ganoin(a form of enamel) on their large scales, heretocercal tails, well-ossified endoskeleton and lungs • Composed of 3 groups: • Polypterus- have features of paleoniscoids • Chondrosteans– ray fins; most primitive; chiefly Paleozoic (300-400 mya); have largely cartilaginous skeleton, scales lack ganoin; mostly extinct except for sturgeons and paddlefishes • Neopterygians- surviving Mesozoan fishes bowfins and gars; modern teleosts

37. Polypterus paddlefish Chondrosteans sturgeon

38. Neopterygians- bowfins and gars; modern teleosts • Semionotiformes- dominant Mesozoic fishes; possess ganoidscales • 2 extant genera: Lepidosteus - predatory; includes present-day gars and Amia - present-day bowfins BOWFIN GAR

39. Dorsal fin Caudal fin Adipose fin(characteristic oftrout) Swim bladder Spinal cord Brain Nostril Cut edge of operculum Urinary bladder Anal fin Gills Anus Gonad Heart Liver Lateral line Stomach Pelvic fin Kidney Intestine Teleostei– modern ray-finned, bony fishes; form 96% of all surviving fishes; about 40 living orders; well-ossified skeleton; cycloid & ctenoid scales (flexible & overlapping); pelvic fins often located far forward; no spiracle

41. Subclass Sarcopterygii • Resemble early amphibians • Skeleton of fin lobe corresponds closely to proximal skeletal elements of early tetrapodlimbs • Skull similar to that of early amphibians • Had swim bladders that may have been used as lungs

42. Crossopterygii- chiefly Paleozoic except Latimeria

43. Dipnoi - Lungfishes; 3 living genera • African & South American species have inefficient gills & will drown if held under water • Australian species (Neoceratodus spp.) relies on gills unless oxygen content of water is too low

44. Next… evolution of limbs with feet

46. Acanthostega

48. Class AMPHIBIA • 2,400 species; ectothermictetrapods; respiration by lungs, gills, or the skin; skin moist, containing mucous glands, and lacking scales. • Development through larval stage via metamorphosis

49. Subclass Labyrinthodontia • Fish-like features: small bony scales in the skin; fin-rays in the tail (for swimming); a sensory canal system (like the lateral line system) that indicates a primarily aquatic existence • A skull similar to that of some Crossopterygians

50. Subclass Lepospondyli • Ancestry uncertain due to lack of fossil evidence • Probably on a 'side branch' of vertebrate evolution