First direct evidence of ammonoid ovoviviparity

DWhatley

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First direct evidence of ammonoid ovoviviparity
Aleksandr A. Mironenko, Mikhail A. Rogov 2015 (subscription)

Ammonoids had high evolutionary rates and diversity throughout their entire history and played an important role in the high-resolution sub-division of the Mesozoic, but much of their palaeobiology remains unclear, including the brooding habitat. We present our study of the first recorded ammonite embryonic shell clusters preserved with calcified embryonic aptychi in situ within the body chambers of mature macroconch shells of the Early Aptian (Early Cretaceous) ammonite Sinzovia sazonovae. The following support the idea that the clusters are egg masses, which developed inside ammonite body chambers: the absence of post-embryonic shells and any other fossils in these clusters, the presence of the aptychi in all embryonic shell apertures and peculiarities of adult shells preservation. These facts confirm earlier speculations that at least some ammonoids could have been ovoviviparous and that, like many modern cephalopods, they could have reproduced in mass spawning events. The aptychi of ammonite embryonic shells are observed here for the first time, indicating that they were already formed and calcified before hatching. Our results are fully congruent with the peculiar modes of ammonoid evolution: quick recovery after extinctions, distinct evolutionary rates, pronounced sexual dimorphism and the nearly constant size of embryonic shells through ammonoid history. We assume that adaptation to ovoviviparity may be the reason for the presence of these features in all post-Middle Devonian ammonoids.
 

tonmo

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Cool! Had to Google it, of course :rolleyes:

Ovoviviparity, ovovivipary, or ovivipary, is a mode of reproduction in animals in which embryos that develop inside eggs remain in the mother's body until they are ready to hatch.
 

DWhatley

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I wonder if this was translated to English since this statement, "These facts confirm earlier speculations that at least some ammonoids could have been ovoviviparous and that, like many modern cephalopods, they could have reproduced in mass spawning events. " does not make a lot of sense. Extant cephalopods do not keep fertilized eggs internally.
 

Architeuthoceras

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Would be nice to see this fossil, and see if there is a way of telling whether the eggs were laid inside the egg layer's shell or just an empty, convenient shell. Anyone have a spare copy of this paper ;)
 

cuttlegirl

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Hmmm... may have to spring for the $6 for access to this... blurry pictures in preview look interesting. But I too would question whether deposited in an empty shell.
 

DWhatley

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I'm curious to know if they are really ammonite eggs laid by the original occupant or eggs laid in an empty shell. Current species behavior makes me think the later is most likely.
 

cuttlegirl

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In reading the preview, it appears that the evidence of ovoviviparity is that all the eggs are of the same developmental stage (if they had been laid in an empty shell, by multiple ammonites then the eggs would have different developmental stages) AND there were no other artifacts in the shell (like fish scales, other shells or plant remains).
 

cuttlegirl

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Well, then it would have to be freshly dead, no algae growth, no other debris from the ocean floor - at least that is their stance on this. When I have an extra 48 hours, I am going to spring for the $6 and I will share a synopsis.
 

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