The one living species of tuatara, Sphenodon punctatus, is on the Ark list. It is the only kind listed as a single species. That presumably means that it’s the only species that belongs to that kind! I have no idea why this species would deserve this distinction. The paper classifying the extant ark kinds notes that S. punctatus and S. guntheri are considered to be a single species, so all living members of Rhynchocephalia would be in that kind. But where does that leave the extinct members?

The list includes one family from the order Rhynchocephalia as its own kind, Gephyrosauridae. But that still leaves an awful lot of the order unaccounted for. No paper on extinct Sphenodonts was ever published so there is no justification provided for this decision. The species currently assigned to this order are shown in the table below:

GephyrosauridaeGephyrosaurusG. bridensisGephyrosauridae
GephyrosauridaeGephyrosaurusG. evansaeGephyrosauridae
DiphydontosaurusD. avonisMissed the Ark
PlanocephalosaurusP. robinsonaeMissed the Ark
RebbanasaurusR. jaini Missed the Ark
PelecymalaP. robustusMissed the Ark
GodavarisaurusG. lateefiMissed the Ark
SphenocondorS. gracilisMissed the Ark
PolysphenodonP. mulleriMissed the Ark
ClevosauridaeBrachyrhinodonB. tayloriMissed the Ark
ClevosauridaeClevosaurusC. bairdi Missed the Ark
ClevosauridaeClevosaurusC. brasiliensisMissed the Ark
ClevosauridaeClevosaurusC. cambricaMissed the Ark
ClevosauridaeClevosaurusC. convallisMissed the Ark
ClevosauridaeClevosaurusC. hadroprodonMissed the Ark
ClevosauridaeClevosaurusC. hudsoniMissed the Ark
ClevosauridaeClevosaurusC. mcgilliMissed the Ark
ClevosauridaeClevosaurusC. minorMissed the Ark
ClevosauridaeClevosaurusC. petilus Missed the Ark
ClevosauridaeClevosaurusC. sectumsempraMissed the Ark
ClevosauridaeClevosaurusC. wangiMissed the Ark
HomeosauridaeHomoeosaurusH. maximiliani Missed the Ark
HomeosauridaeHomoeosaurusH. major Missed the Ark
HomeosauridaeHomoeosaurusH. solnhofensisMissed the Ark
SapheosauridaeKallimodonK. pulchellusMissed the Ark
SapheosauridaeKallimodonK. cerinensisMissed the Ark
SapheosauridaeSapheosaurusS. thiollierei Missed the Ark
SapheosauridaeSapheosaurusS. laticepsMissed the Ark
SapheosauridaeFraserosphenodonF. latidensMissed the Ark
*KawasphenodonK. peligrensisMissed the Ark
*KawasphenodonK. expectatusMissed the Ark
*OpisthiasO. rarusMissed the Ark
EilenodontidaeToxolophosaurusT. cloudi Missed the Ark
EilenodontidaeEilenodonE. robustusMissed the Ark
EilenodontidaePriosphenodonP. minimusMissed the Ark
EilenodontidaePriosphenodonP. avelasiMissed the Ark
EilenodontidaeSphenotitanS. leyesiMissed the Ark
PleurosauridaePalaeopleurosaurusP. posidoniaeSemi-aquatic
PleurosauridaePleurosaurusP. goldfussiAquatic
PleurosauridaePleurosaurusP. ginsburgiAquatic
PleurosauridaeVadasaurusV. herzogiSemi-aquatic
SphenodontidaeSphenodonS. punctatusSphenodon punctatus
SphenodontidaeSphenodonS. diversumMissed the Ark
SphenodontidaeOenosaurusO. muehlheimensisMissed the Ark
SphenodontidaeCynosphenodonC. huizachalensisMissed the Ark
SphenodontidaeZapatadonZ. ejidoensisMissed the Ark
SphenodontidaeSphenoviperaS. jimmysjoyiMissed the Ark
SphenodontidaeTheretairusT. antiquusMissed the Ark
SphenodontidaeDerasmosaurusd. pietrarojaeMissed the Ark
SphenodontidaeAnkylosphenodonA. pachyostosusAquatic
SphenodontidaePamizinsaurusP. tlayuaensisMissed the Ark

As you can see, that’s 43 non-aquatic species that are not assigned to any kind. If they were actually intending to break this order down to the species level like they did for the living tuataras, that would be 43 additional kinds.

The classifications in the table above are mostly based on this paper, which was the most recent I could find. It found that many of the species previously assigned to Sphenodontidae did not belong there. This left several species without assigned family names, which are shown with a “-” or “*”. The ones marked “*” form a natural group at a level similar to the other families, and thus would likely have been grouped together if AiG had used the same standard for the Sphenodonts as they have for the other extinct species. The rest would probably have had their own families. Thus, I estimate that if they had used the same standard as for other orders there would have an additional 13 ark kinds.

While most of the Sphenodonts are small and would probably have been assigned to the larger stacked cages, the Eilenodontidae family members grow up to 1m in length. This is a somewhat significant omission from the Ark list.