*Petrolacosauruksen* rekonstruktio
**Diapsidit** (Diapsida) on sauropsidien ryhmä, jolle kehittyi kallon molemmille puolelle kaksi ohimoaukkoa. Ensimmäiset diapsidit kehittyivät noin 307 miljoonaa vuotta sitten Pennsylvania-kaudella. Diapsidit ovat monimuotoisin sauropsidiryhmä, johon kuuluvat esimerkiksi krokotiilieläimet, liskot, käärmeet, alkuliskot, kalaliskot, joutsenliskot, mosasaurit, lentoliskot, kilpikonnat ja linnut. Vaikka kilpikonnat luetaan perinteisesti anapsidien ryhmään (joiden kallosta puuttuu ohimoaukot), nykyään nekin luetaan kladistisesti diapsideihin, sillä ne ovat kehittyneet diapsideista, jotka menettivät ohimoaukkonsa.

Tuntomerkit
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Diapsidinen kallo.
Diapsideihin on perinteisesti luokiteltu vain ne matelijat, joilla on molemmat ohimoaukot kallon kummallakin puolella silmien takana. Tämä mahdollisti monille diapsideille suuremmat ja vahvemmat leukalihakset sekä laajemmin avautuvat leuat. Toinen diapsidien epämääräinen ominaisuus on melko pitkä värttinäluu, verrattuna olkaluuhun.

Luokittelu
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Diapsidit olivat ennen yksi neljästä matelijoiden alaluokasta, jonka kaikilla lajeilla on diapsidinen kallo. Kolme muuta matelijoiden alaluokkaa olivat Synapsida (jonka lajeilla oli yksi alempi ohimoaukko kallon molemmilla puolilla; "nisäkäsliskot"), Anapsida (jonka lajeilta puuttuu kaikki ohimoaukot; kilpikonnat ja niiden sukupuuttoon kuolleet sukulaiset) ja Euryapsida (jonka lajeilla on yksi ylempi ohimoaukko kallon molemmilla puolilla; sisälsi monia merimatelijoita).
Nykyisessä fylogeneettisessä systematiikassa tätä luokittelua ei kuitenkaan enää käytetä. Nykyään synapsidit ovat sauropsidien sisarryhmä (nisäkkäät ja niiden sukupuuttoon kuolleet sukulaiset), kun taas euryapsidit ja anapsideista kilpikonnat luetaan nykyisin diapsideihin, mikä tarkoittaisi, että euryapsidit on polyfyleettinen ryhmä ja anapsidit on parafyleettinen ryhmä. Kladistisesti myös linnut (jotka ovat diapsidisten matelijoiden jälkeläisiä) luetaan nykyisin diapsideihin. 

### Kladogrammi

Alla oleva Kladogrammi Bicklemannin (2009) ja Reiszin (2011) mukaan kuvaa diapsidien sukulaisuussuhteita:


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| Sauropsida | 

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| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Parareptilia | 

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| --- | --- |
|   | Millerettidae  |
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| unnamed | 

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| --- | --- |
|   | *Eunotosaurus* |
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| Hallucicrania | 

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| --- | --- |
|   | Lanthanosuchidae  |
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| Procolophonia | 

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| --- | --- |
|   | Procolophonoidea  |
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|   | Pareiasauromorpha  |
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| Eureptilia | 

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|   | Captorhinidae  |
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| Romeriida | 

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| --- | --- |
|   | *Paleothyris* |
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| **Diapsida** | 

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| --- | --- |
|   | Araeoscelidia |
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| Neodiapsida | 

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|   | *Orovenator* |
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|   | *Lanthanolania* |
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|   | Tangasauridae |
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|   | Younginidae |
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|   | *Claudiosaurus* |
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| --- | --- | --- | --- | --- | --- | --- | --- |
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| --- | --- |
|   | *Palaeagama* |
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|   | *Saurosternon* |
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| --- | --- |
|   | *Coelurosauravus* |
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| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
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| --- | --- |
|   | Thalattosauria |
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|   | Hupehsuchia |
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|   | Ichthyopterygia |
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| Sauria | 

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| --- | --- |
|   | Lepidosauromorpha |
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|   | Archosauromorpha |
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Katso myös
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* Anapsidit
* Synapsidit
* Sauropsidit
* Vesikalvolliset
* Reptiliomorpha

Lähteet
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Aiheesta muualla
----------------

* Fossil Wikin diapsideja käsittelevä sivu (englanniksi)

|  |  |  |
| --- | --- | --- |
| 

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| --- | --- |
| Taksonitunnisteet | 
* Wikidata: Q134688
* Wikispecies: Diapsida
* EoL: 42329830
* Fossilworks: 135387
* ITIS: 564527

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Alkuperäinen artikkeli: en:Diapsid