29.4: Watambaao

Ujuzi wa Kuendeleza

• Eleza sifa kuu za amniotes
• Eleza tofauti kati ya anapsids, synapsids, na diapsids, na kutoa mfano wa kila
• Tambua sifa za viumbehai
• Jadili mageuzi ya viumbehai

Amniotes -reptilia, ndege, na mamali-wanajulikana kutoka kwa amfibia kwa yai yao iliyobadilishwa na ardhi, ambayo inalindwa na utando wa amniotic. Mageuzi ya membrane ya amniotiki yalimaanisha kuwa majusi ya amnioti yalitolewa na mazingira yao ya majini, ambayo yalisababisha kutegemeana kidogo kwa maji kwa ajili ya maendeleo na hivyo kuruhusu amnioti kuvuka katika mazingira kavu. Hili lilikuwa maendeleo makubwa yaliyowatofautisha na amfibia, ambayo yalizuiwa kwa mazingira yenye unyevunyevu kutokana na mayai yao yasiyo na shell. Ingawa maganda ya aina mbalimbali za amniotic hutofautiana kwa kiasi kikubwa, wote huruhusu uhifadhi wa maji. Makombora ya mayai ya ndege yanajumuisha calcium carbonate na ni ngumu, lakini tete. Makombora ya mayai ya reptile ni ngozi na yanahitaji mazingira ya unyevu. Wanyama wengi hawana mayai (isipokuwa kwa monotremes). Badala yake, kiinitete kinakua ndani ya mwili wa mama; hata hivyo, hata kwa ujauzito huu wa ndani, membrane ya amniotic bado iko.

Tabia za Amniotes

Yai ya amniotic ni tabia muhimu ya amniotes. Katika amniotes zinazoweka mayai, ganda la yai hutoa ulinzi kwa kiinitete kilichoendelea huku kikiwezekana kutosha kuruhusu kubadilishana kaboni dioksidi na oksijeni. Albumini, au yai nyeupe, hutoa kiinitete kwa maji na protini, ilhali yai ya mafuta yenye mafuta ni ugavi wa nishati kwa kiinitete, kama ilivyo kwa mayai ya wanyama wengine wengi, kama vile amfibia. Hata hivyo, mayai ya amniotes yana utando wa ziada wa ziada wa embryonic: chorion, amnion, na allantois (Kielelezo\(\PageIndex{1}\)). Vipande vya ziada vya embryonic ni membrane zilizopo katika mayai ya amniotic ambayo si sehemu ya mwili wa kiinitete kinachoendelea. Wakati utando wa amniotic wa ndani unazunguka kiinitete yenyewe, chorion huzunguka kifuko cha kiinitete na kiini. Chorion inawezesha kubadilishana oksijeni na dioksidi kaboni kati ya kiinitete na mazingira ya nje ya yai. Amnion inalinda kiinitete kutokana na mshtuko wa mitambo na inasaidia usawa. Allantois huhifadhi taka za nitrojeni zinazozalishwa na kiinitete na pia huwezesha kupumua. Katika mamalia, membrane ambayo ni homologous kwa membrane ya ziada ya embryonic katika mayai iko kwenye placenta.

Sanaa Connection

Kielelezo\(\PageIndex{1}\): Vipengele muhimu vya yai ya amniotic vinaonyeshwa.

Ni ipi kati ya taarifa zifuatazo kuhusu sehemu za yai ni uongo?

1. Allantois huhifadhi taka ya nitrojeni na kuwezesha kupumua.
2. Chorion inawezesha kubadilishana gesi.
3. Pingu hutoa chakula kwa kiinitete kinachoongezeka.
4. Cavity amniotic imejaa albumen.

Tabia za ziada zinazotokana na amniotes zinajumuisha ngozi isiyo na maji, kutokana na kuwepo kwa lipids, na uingizaji hewa wa gharama (namba) ya mapafu.

Mageuzi ya Amniotes

Amniotes ya kwanza ilibadilika kutoka kwa mababu wa amfibia takriban miaka milioni 340 iliyopita wakati wa kipindi cha Carboniferous. Amniotes mapema iligawanyika katika mistari miwili kuu mara baada ya amniotes ya kwanza kuinuka. Mgawanyiko wa awali ulikuwa katika synapsids na sauropsids. Sinapsidi ni pamoja na mamalia wote, wakiwemo spishi za mamalia zilizopotea. Synapsids pia hujumuisha therapsids, ambazo zilikuwa viumbehai kama mamalia ambazo mamalia walibadilika. Sauropsids ni pamoja na reptilia na ndege, na inaweza kugawanywa zaidi katika anapsids na diapsids. Tofauti muhimu kati ya sinepsids, anapsids, na diapsids ni miundo ya fuvu na idadi ya fenestrae ya muda nyuma ya kila jicho (Kielelezo\(\PageIndex{2}\)). Fenestrae ya muda ni fursa za baada ya orbital katika fuvu ambazo zinaruhusu misuli kupanua na kupanua. Anapsids hazina fenestrae ya muda, synapsids zina moja, na diapsids zina mbili. Anapsids ni pamoja na viumbe haiko na inaweza, kulingana na anatomy, ni pamoja na turtles. Hata hivyo, hii bado ni ya utata, na turtles wakati mwingine huwekwa kama diapsids kulingana na ushahidi wa Masi. Diapsids ni pamoja na ndege na wanyama wengine wote wanaoishi na wasio na mwisho.

Kielelezo\(\PageIndex{2}\): Linganisha fuvu na fenestra ya muda ya anapsids, synapsids, na diapsids. Anapsids hazina fursa, synapsids zina ufunguzi mmoja, na diapsids zina fursa mbili.

Diapsids iligawanywa katika makundi mawili, Archosauromorpha (“fomu ya kale ya mjusi”) na Lepidosauromorpha (“fomu ya mjusi”) wakati wa kipindi cha Mesozoic (Kielelezo\(\PageIndex{3}\)). Lepidosaurs ni pamoja na mijusi wa kisasa, nyoka, na tuataras. Archosaurs ni pamoja na mamba wa kisasa na alligators, na pterosaurs ya mwisho (“mjusi mwenye mabawa”) na dinosaurs (“mjusi wa kutisha”). Clade Dinosauria inajumuisha ndege, ambazo zilibadilika kutoka tawi la dinosaurs.

Sanaa Connection

Kielelezo\(\PageIndex{3}\): Chati hii inaonyesha mageuzi ya amniotes. Uwekaji wa Testudines (turtles) sasa bado unajadiliwa.

Wanachama wa utaratibu Testudines wana fuvu la anapsid-kama na ufunguzi mmoja. Hata hivyo, tafiti za Masi zinaonyesha kwamba turtles zilishuka kutoka kwa babu wa diapsid. Kwa nini hii inaweza kuwa kesi?

Katika siku za nyuma, mgawanyiko wa kawaida wa amniotes umekuwa katika madarasa ya Mammalia, Reptilia, na Aves. Ndege zinatoka, hata hivyo, kutoka kwa dinosaurs, hivyo mpango huu wa classical husababisha makundi ambayo si clades ya kweli. Tutachunguza ndege kama kikundi tofauti na viumbehai kwa madhumuni ya majadiliano haya kwa kuelewa kwamba hii haionyeshi kabisa historia na mahusiano ya phylogenetic.

Tabia ya Reptiles

Viumbehai ni tetrapods. Reptiles limbless-nyoka na squamates wengine-wana viungo vestigial na, kama caecilians, ni classified kama tetrapods kwa sababu wao ni alishuka kutoka mababu nne limbed. Reptiles huweka mayai yaliyofungwa katika makombora kwenye ardhi. Hata reptilia za majini zinarudi ardhi ili kuweka mayai. Mara nyingi huzalisha ngono na mbolea ya ndani. Aina fulani zinaonyesha ovoviviparity, na mayai yaliyobaki katika mwili wa mama mpaka wawe tayari kuangamiza. Aina nyingine ni viviparous, na watoto waliozaliwa hai.

Moja ya marekebisho muhimu ambayo yaliruhusu reptilia kuishi kwenye ardhi ilikuwa maendeleo ya ngozi yao ya magamba, iliyo na keratin ya protini na lipids ya wax, ambayo ilipunguza kupoteza maji kutoka kwenye ngozi. Ngozi hii ya kawaida ina maana kwamba viumbehai hawawezi kutumia ngozi zao kwa kupumua, kama amfibia, na hivyo wote hupumua kwa mapafu.

Reptiles ni ectotherms, wanyama ambao chanzo kikuu cha joto la mwili hutoka kwenye mazingira. Hii ni kinyume na endotherms, ambayo hutumia joto zinazozalishwa na kimetaboliki kudhibiti joto la mwili. Mbali na kuwa ectothermic, viumbehai vinajumuishwa kama poikilotherms, au wanyama ambao joto la mwili wao hutofautiana badala ya kubaki imara. Viumbehai vina marekebisho ya tabia ili kusaidia kudhibiti joto la mwili, kama vile kuogelea katika maeneo ya jua ili kuogea joto na kutafuta matangazo ya shady au kwenda chini ya ardhi ili kupungua. Faida ya ectothermy ni kwamba nishati ya metabolic kutoka kwa chakula haihitajiki joto mwili; kwa hiyo, reptilia wanaweza kuishi juu ya asilimia 10 ya kalori zinazohitajika na endotherm sawa ukubwa. Katika hali ya hewa ya baridi, baadhi ya viumbehai kama vile nyoka ya garter hupiga. Brumation ni sawa na hibernation kwa kuwa mnyama huwa chini ya kazi na anaweza kwenda kwa muda mrefu bila kula, lakini hutofautiana na hibernation kwa kuwa viumbe vya brumating hazilala au kuishi mbali na hifadhi ya mafuta. Badala yake, kimetaboliki yao imepungua kwa kukabiliana na joto la baridi, na mnyama ni wavivu sana.

Mageuzi ya reptilia

Reptiles zilianza takriban miaka milioni 300 iliyopita wakati wa kipindi cha Carboniferous. Moja ya amniotes ya zamani zaidi inayojulikana ni Casineria, ambayo ilikuwa na sifa zote za amphibian na reptilian. Mojawapo ya reptilia za mwanzo ambazo hazipatikani alikuwa Hylonomus. Muda mfupi baada ya amniotes ya kwanza kuonekana, waligawanyika katika makundi matatu—sinepsids, anapsids, na diapsids—wakati wa kipindi cha Permian. Kipindi cha Permian pia kiliona tofauti kubwa ya pili ya reptilia za diapsid ndani ya archosaurs (watangulizi wa crocodilians na dinosaurs) na lepidosaurs (watangulizi wa nyoka na mijusi). Makundi haya yalibakia haijulikani mpaka kipindi cha Triassic, wakati archosaurs ikawa kundi kubwa duniani kutokana na kutoweka kwa anapsids kubwa na sinepsids wakati wa kutoweka kwa Permian-Triassic. Kuhusu miaka milioni 250 iliyopita, archosaurs ilianza ndani ya dinosaurs na pterosaurs.

Ingawa wakati mwingine huitwa dinosaurs kwa makosa, pterosaurs walikuwa tofauti na dinosaurs ya kweli (Kielelezo\(\PageIndex{4}\)). Pterosaurs walikuwa na idadi ya marekebisho ambayo iliruhusu kukimbia, ikiwa ni pamoja na mifupa mashimo (ndege pia huonyesha mifupa mashimo, kesi ya mageuzi ya kubadilika). Mabawa yao yaliundwa na utando wa ngozi uliounganishwa na kidole kirefu, cha nne cha kila mkono na kupanuliwa pamoja na mwili hadi miguu.

Kielelezo\(\PageIndex{4}\): Pterosaurs, ambayo ilikuwepo kutoka Triassic marehemu hadi kipindi cha Cretaceous (miaka milioni 210 hadi 65.5 iliyopita), alikuwa na mbawa lakini hawaamini kuwa na uwezo wa kukimbia powered. Badala yake, wanaweza kuwa na uwezo wa kuongezeka baada ya uzinduzi kutoka maporomoko. (mikopo: Mark Witton, Darren Naish)

Dinosaurs walikuwa kundi tofauti la viumbehai duniani na spishi zaidi ya 1,000 zilizotambuliwa hadi sasa. Paleontologists wanaendelea kugundua aina mpya za dinosaurs. Baadhi ya dinosaurs walikuwa quadrupeds (Kielelezo\(\PageIndex{5}\)); wengine walikuwa bipeds. Baadhi walikuwa carnivorous, wakati wengine walikuwa herbivorous. Dinosaurs waliweka mayai, na viota kadhaa vyenye mayai ya fossilized vimepatikana. Haijulikani kama dinosaurs walikuwa endotherms au ectotherms. Hata hivyo, kutokana na kwamba ndege wa kisasa ni endothermic, dinosaurs kwamba aliwahi kuwa mababu kwa ndege uwezekano walikuwa endothermic pia. Baadhi ya ushahidi kisukuku ipo kwa ajili ya huduma ya wazazi dinosaurian, na biolojia kulinganisha inasaidia hypothesis hii tangu ndege archosaur na crocodilians kuonyesha huduma ya wazazi.

Kielelezo\(\PageIndex{5}\): Edmontonia ilikuwa dinosaur ya kivita iliyoishi mwishoni mwa kipindi cha Cretaceous, miaka milioni 145.5 hadi 65.6 iliyopita. (mikopo: Mariana Ruiz Villareal)

Dinosaurs iliongoza Era ya Mesozoic, ambayo ilikuwa inajulikana kama “umri wa reptilia.” Utawala wa dinosaurs ulidumu hadi mwisho wa Cretaceous, kipindi cha mwisho cha Era ya Mesozoic. Kupotea kwa Cretaceous-Elimu ya juu kulisababisha kupoteza kwa wanyama wengi wakubwa wa Era ya Mesozoic. Ndege ni wazao tu wanaoishi wa moja ya clades kubwa ya dinosaurs.

Unganisha na Kujifunza

Tembelea tovuti hii ili uone video inayojadili nadharia kwamba asteroidi ilisababisha kutoweka kwa Cretaceous-Triassic (KT).

Watambaazi wa kisasa

Darasa Reptilia linajumuisha aina nyingi tofauti ambazo zinawekwa katika clades nne za kuishi. Hizi ni spishi 25 za Mamba, spishi 2 za Sphenodontia, takriban spishi 9,200 za Squamata, na Testudini, zenye spishi zipatazo 325.

Mamba

Mamba (“mjusi mdogo”) aliondoka na ukoo tofauti na Triassic ya kati; spishi zilizopo ni pamoja na alligators, mamba, na caimans. Crocodilians (Kielelezo\(\PageIndex{6}\)) live throughout the tropics and subtropics of Africa, South America, Southern Florida, Asia, and Australia. They are found in freshwater, saltwater, and brackish habitats, such as rivers and lakes, and spend most of their time in water. Some species are able to move on land due to their semi-erect posture.

Figure \(\PageIndex{6}\): Crocodilians, such as this Siamese crocodile (Crocodylus siamensis), provide parental care for their offspring. (credit: Keshav Mukund Kandhadai)

Sphenodontia

Sphenodontia (“wedge tooth”) arose in the Mesozoic era and includes only one living genus, Tuatara, comprising two species that are found in New Zealand (Figure \(\PageIndex{7}\)). Tuataras measure up to 80 centimeters and weigh about 1 kilogram. Although quite lizard-like in gross appearance, several unique features of the skull and jaws clearly define them and distinguish the group from the squamates.

Figure \(\PageIndex{7}\): This tuatara from New Zealand may resemble a lizard but belongs to a distinct lineage, the Sphenodontidae family. (credit: Sid Mosdell)

Squamata

Squamata (“scaly”) arose in the late Permian, and extant species include lizards and snakes. Both are found on all continents except Antarctica. Lizards and snakes are most closely related to tuataras, both groups having evolved from a lepidosaurian ancestor. Squamata is the largest extant clade of reptiles (Figure \(\PageIndex{8}\)). Most lizards differ from snakes by having four limbs, although these have been variously lost or significantly reduced in at least 60 lineages. Snakes lack eyelids and external ears, which are present in lizards. Lizard species range in size from chameleons and geckos, which are a few centimeters in length, to the Komodo dragon, which is about 3 meters in length. Most lizards are carnivorous, but some large species, such as iguanas, are herbivores.

Figure \(\PageIndex{8}\): This Jackson’s chameleon (Trioceros jacksonii) blends in with its surroundings.

Snakes are thought to have descended from either burrowing lizards or aquatic lizards over 100 million years ago (Figure \(\PageIndex{9}\)). Snakes comprise about 3,000 species and are found on every continent except Antarctica. They range in size from 10 centimeter-long thread snakes to 10 meter-long pythons and anacondas. All snakes are carnivorous and eat small animals, birds, eggs, fish, and insects. The snake body form is so specialized that, in its general morphology, a “snake is a snake.” Their specializations all point to snakes having evolved to feed on relatively large prey (even though some current species have reversed this trend). Although variations exist, most snakes have a skull that is very flexible, involving eight rotational joints. They also differ from other squamates by having mandibles (lower jaws) without either bony or ligamentous attachment anteriorly. Having this connection via skin and muscle allows for great expansion of the gape and independent motion of the two sides—both advantages in swallowing big items.

Figure \(\PageIndex{9}\): The garter snake belongs to the genus Thamnophis, the most widely distributed reptile genus in North America. (credit: Steve Jurvetson)

Testudines

Turtles are members of the clade Testudines (“having a shell”) (Figure \(\PageIndex{10}\)). Turtles are characterized by a bony or cartilaginous shell. The shell consists of the ventral surface called the plastron and the dorsal surface called the carapace, which develops from the ribs. The plastron is made of scutes or plates; the scutes can be used to differentiate species of turtles. The two clades of turtles are most easily recognized by how they retract their necks. The dominant group, which includes all North American species, retracts its neck in a vertical S-curve. Turtles in the less speciose clade retract the neck with a horizontal curve.

Turtles arose approximately 200 million years ago, predating crocodiles, lizards, and snakes. Similar to other reptiles, turtles are ectotherms. They lay eggs on land, although many species live in or near water. None exhibit parental care. Turtles range in size from the speckled padloper tortoise at 8 centimeters (3.1 inches) to the leatherback sea turtle at 200 centimeters (over 6 feet). The term “turtle” is sometimes used to describe only those species of Testudines that live in the sea, with the terms “tortoise” and “terrapin” used to refer to species that live on land and in fresh water, respectively.

Figure \(\PageIndex{10}\): The African spurred tortoise (Geochelone sulcata) lives at the southern edge of the Sahara Desert. It is the third largest tortoise in the world. (credit: Jim Bowen)

Summary

The amniotes are distinguished from amphibians by the presence of a terrestrially adapted egg protected by amniotic membranes. The amniotes include reptiles, birds, and mammals. The early amniotes diverged into two main lines soon after the first amniotes arose. The initial split was into synapsids (mammals) and sauropsids. Sauropsids can be further divided into anapsids (turtles) and diapsids (birds and reptiles). Reptiles are tetrapods either having four limbs or descending from such. Limbless reptiles (snakes) are classified as tetrapods, as they are descended from four-limbed organisms. One of the key adaptations that permitted reptiles to live on land was the development of scaly skin containing the protein keratin, which prevented water loss from the skin. Reptilia includes four living clades: Crocodilia (crocodiles and alligators), Sphenodontia (tuataras), Squamata (lizards and snakes), and Testudines (turtles).

Art Connections

Figure \(\PageIndex{1}\): Which of the following statements about the parts of an egg are false?

1. The allantois stores nitrogenous waste and facilitates respiration.
2. The chorion facilitates gas exchange.
3. The yolk provides food for the growing embryo.
4. The amniotic cavity is filled with albumen.

Answer

D

Figure \(\PageIndex{3}\): Members of the order Testudines have an anapsid-like skull with one opening. However, molecular studies indicate that turtles descended from a diapsid ancestor. Why might this be the case?

Answer

The ancestor of modern Testudines may at one time have had a second opening in the skull, but over time this might have been lost.

Glossary

amniote

animal that produces a terrestrially adapted egg protected by amniotic membranes

allantois

membrane of the egg that stores nitrogenous wastes produced by the embryo; also facilitates respiration

amnion

membrane of the egg that protects the embryo from mechanical shock and prevents dehydration

anapsid

animal having no temporal fenestrae in the cranium

archosaur

modern crocodilian or bird, or an extinct pterosaur or dinosaur

brumation

period of much reduced metabolism and torpor that occurs in any ectotherm in cold weather

Casineria

one of the oldest known amniotes; had both amphibian and reptilian characteristics

chorion

membrane of the egg that surrounds the embryo and yolk sac

Crocodilia

crocodiles and alligators

diapsid

animal having two temporal fenestrae in the cranium

Hylonomus

one of the earliest reptiles

lepidosaur

modern lizards, snakes, and tuataras

sauropsid

reptile or bird

Sphenodontia

clade of tuataras

Squamata

clade of lizards and snakes

synapsid

mammal having one temporal fenestra

temporal fenestra

non-orbital opening in the skull that may allow muscles to expand and lengthen

Testudines

order of turtles