Head Skeletal changes of organisms transitioning from water to land

1 head

1.1 head changes in osteichthyes
1.2 head changes in prototetrapod
1.3 head changes in aquatic tetrapods
1.4 teeth , feeding mechanisms

head
head changes in osteichthyes

restoration of osteolepis

the osteolepiformes , elpistostegalia 2 crown groups of rhipidistians respect tetrapods. development of skull roof , cheekbone patterns in these organisms match found in first tetrapods. palatal , nasal skeletal features choanae present in these groups , observed in modern amphibians. indicates incipient air breathing developed, modification of hyoid arch towards stapes development. these characteristics account why osteichthyans accepted sister group of tetrapods.

the elpistostegalid fish considered apomorphic of fish in comparison tetrapods. well-preserved fossils, observed share paltybasic skull eye ridges, , external nares situated on margin of mouth. development of eye ridges , flatting of skull observed in primitive fossil amphibians , reptiles. reason traits adaptive use in aerial vision above waterline. traits enabled animals check area on land safe spots if being chased predator in water, being useful searching prey items above water. water-based lateral line system used substantially these aquatic tetrapods detect danger predators. within osteichthyan diversification, there no changes related respiration in transition can seen nasal region , palatal morphology in elpistostegalid fishes. primary change basic ostelepiform ancestors first elpistostegalid in middle devonian pre-existing roof skulls.

head changes in prototetrapod

restoration of elginerpeton

in elginerpeton pancheni, prototetrapod late frasnian, basic tetrapod characteristics in lower jaw , cranium observed. taxon believed fill gap between elpistostegalid fishes , well-preserved devonian tetrapods. elginerpeton considered more derived elpistostegalid fishes due presence of paired fangs on parasymphysial toothplate, slender shaped anterior coronoid, , in loss of intracranial joint , coronoid fossa. loss of intercranial joint direct functional necessity strengthen broad , long platybasic skull when animal out of water. tubular lower jaw of elginerpeton, compared flat-lamina jaw shape of fishes gave superior cross-sectional force, required when not supported in aquatic setting – allowing opening of mouth outside of water. adaptation may interpreted specialization buccopharyngeal breathing. speculated first step towards aerial respiration in transition fish tetrapod.

head changes in aquatic tetrapods

restoration of acanthostega

in tetrapod , higher clades lower-middle famennian there several defining changes on basis of anatomy of ichthyostega, tulerpeton, , acanthostega. in cranium, there stapes derived hyomandibular of fishes; single bilateral pair of nasal bones, , fenestra ovalis in otic capsule of braincase. opening of otic wall of braincase can considered paedomorphic feature tetrapods , linked stapes functionally. stapes thought structural support between palate , stapedial plate of braincase. in acanthostega, due otic capsule of brain case being mesial stapedial plate, sound picked palate or otic notch allow rudimentary hearing. able perceive vibrations opening mouth way of palate. other factors caused aquatic tetrapods spend more time on land caused development of terrestrial hearing development of tympanum within otic notch , developed convergent evolution @ least 3 times. there change in dermal bones of skull in aquatic tetrapods. involved enlargement of jugal, ceasing contact of maxilla squamosal , single bilateral pair of nasal bones. feature allows stronger bite increasing strength of skull.

teeth , feeding mechanisms

feeding on land different task feeding in water. water more dense , viscous compared air, causing hunting techniques adapted in water less successful when applied on land. main technique used in water suction feeding , used aquatic vertebrates. technique not function in air animals use methods of overtaking prey jaws followed biting down. transitional forms prior developed terrestrial tetrapods such acanthostega, thought have captured prey in water. large coronoid fangs present in fishes eusthenopteron, panderichthys, , tiktaalik, , tetrapod, ventasega. in acanthostega, more derived, large teeth absent. in eusthenopetron , panderichthys, ossified operculum exhibited unlike in tiktaalik, ventastega, , acanthostega. these differences reductions of gill chamber , changes in nature of lower jaw hypothesized indicate reduced reliance on suction feeding in tetrapods in comparison osteolepiform fish. morphological data not enough prove suction feeding less used morphological changes have been found in fish use suction feeding mechanism.

cranial sutures indicators of skull function , morphologies can linked specific feeding modes. transitional feeding changes can observed examining cross sectional morphology of suture in taxa of fish-tetrapod transition. comparing positionally comparable sutures in extant fish allows creation of sutural morphospace. main cause of sutural deformation caused strain during feeding activity, prominent feeding mechanisms involving sucking prey mouth. there tension anteriorly, , compression posteriorly strain patterns observed in polypterus, prey-sucking predator. in terrestrial tetrapod phonerpeton, there compression between frontals , parietals , complex loading between post parietals. there no evidence of tensile strain in sutures. acanthostega fossil records demonstrate no strain pattern exhibited relate prey capture means of suction. load compression similar extant tetrapods. organism captured prey biting in water or near edge of water. finding indicates terrestrial mode of feeding first emerged in aquatic environment.