Zoneait

Name: Zoneait ‭(‬Large tooth‭)‬.
Phonetic: Zone-ate.
Named By: Eric W.‭ ‬Wilberg‭ ‬-‭ ‬2015.
Classification: Chordata,‭ ‬Reptilia,‭ ‬Crocodylomorpha,‭ ‬Thalattosuchia,‭ ‬Metriorhynchoidea.
Species: Z.‭ ‬nargorum‭ (‬type‭)‬.
Diet: Carnivore/Piscivore.
Size: Unavailable.
Known locations: USA,‭ ‬Oregon‭ ‬-‭ ‬Snowshoe Formation,‭ ‬Weberg member.
Time period: Aalenian of the Jurassic.
Fossil representation: Partial skulls and post cranial remains of several individuals.

       Named in‭ ‬2015,‭ ‬Zoneait was an important discovery for those interested in marine crocodiles.‭ ‬Zoneait represents a transitional genus and possible sister taxon of the Metriorhynchidae,‭ ‬the group that features many famous genera of marine crocodiles such as Metriorhynchus and Geosaurus.‭ ‬In addition to this the Zoneait holotype fossils were found in fossil bearing deposits estimated to have come from the Aalenian age of the Jurassic,‭ ‬meaning that at the time of the first description of the genus,‭ ‬Zoneait is the oldest marine crocodile that we know about.
       However as is often the case,‭ ‬although Zoneait is the oldest marine crocodile at the time of its discovery,‭ ‬it is not the most primitive form known to us.‭ ‬Both Teleidosaurus and Eoneustes are known from the Bajocian stage of the Jurassic,‭ ‬and yet both are more primitive in form when compared to Zoneait.‭ ‬Zoneait has been stablished as a marine crocodile upon the basis that all remains have so far been found in what would have been a shallow marine environment,‭ ‬and the eyes were also orientated to look out to the sides instead of above like in modern day semi-aquatic crocodiles which ambush animals that are above them.‭ ‬Passages for enlarged blood vessels have also been found on Zoneait skulls,‭ ‬strongly suggesting that these were for carrying blood to a salt gland which would have extracted the unusually high levels of salts from the blood which would have been absorbed by living in a salt water environment.
       Ultimately though,‭ ‬Zoneait was not as well adapted to a marine lifestyle as later metriorhynchid crocodiles such as Tyrannoneustes and Plesiosuchus.‭ ‬Key to this understanding is the forelimbs which are not shaped into paddles like in true metriorhynchids.‭ ‬In addition the forelimb only shows some shortening of the lower ulna‭ (‬one of the lower forelimb bones‭)‬,‭ ‬while no reduction is apparent in the humerus‭ (‬upper arm limb bone‭)‬.‭ ‬This tells us two things,‭ ‬one being‭ ‬that forelimb reduction in marine crocodiles would have started in the lower extremities of the limb,‭ ‬before eventually progressing into the upper forelimbs of later descendants.‭ ‬Second is that Zoneait might not have spent as much time in the water as true metriorhynchids,‭ ‬and possibly spent more time on the coastlines to rest.‭ ‬It is for these reasons that Zoneait has been placed within the Metriorhynchoidea,‭ ‬making the genus a metriorhynchoid.‭ ‬Here Zoneait is treated as a sister taxon to the metriorhynchids of‭ ‬the‭ ‬Metriorhynchidae,‭ ‬evolving alongside their ancestors,‭ ‬though possibly not being ancestral to them.‭ ‬Only future research and discoveries will allow us to be sure.

Further reading
-‭ ‬A new metriorhynchoid‭ (‬Crocodylomorpha,‭ ‬Thalattosuchia‭) ‬from the Middle Jurassic of Oregon and the evolutionary timing of marine adaptations in thalattosuchian crocodylomorphs.‭ ‬-‭ ‬Journal of Vertebrate Paleontology‭ ‬35‭ (‬2‭)‬:‭ ‬e902846.‭ ‬-‭ ‬Eric W.‭ ‬Wilberg‭ ‬-‭ ‬2015.



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