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Bobo the bear

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I just bought this Permian specimen around 257 myo. With a hope that I would learn to distinguish Goniatite from Ammonite. However this is supposedly Metalegoceras adjaralense...an ammonite. Unfortunately I cannot see any complicated suture pattern I guess due to wear. Couldn't spot an outer siphuncle for same reason. Could any of you guys tell me how else to ID between them?  Size is 6 cm by 3.5 cm wide

IMG_20190404_153137.jpg  IMG_20190404_153220.jpg  IMG_20190404_153241.jpg 


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Barrow Museum

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As a Permian genus, it cannot be an "Ammonite".  It can however, be classified as an "Ammonoid" (Subclass Ammonoidea).  To go a little further along the classification chain, it is in the order Goniatitida (Goniatites).

I was taught (admittedly a few decades ago) that Ammonites meant the suborder Ammonitina, one of the four suborders of the order Ammonitida, which only evolved at the beginning of the Jurassic, and exclude the root-stock suborders of Phylloceratina and Lytoceratina.  The later, mainly Cretaceous suborder Ancycloceratina, often called Heteromorphs (they have irregular coiled shells) are also excluded from the "Ammonites".  However, no-one would object to your calling any Jurassic Ammonitid an ammonite!

Wikipedia succinctly states:

The words "ammonite" and "ammonoid" are both used quite loosely in common parlance to refer to any member of subclass Ammonoidea. However, in stricter usage, the term ammonite is reserved for members of order Ammonitida (or even suborder Ammonitina).
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Bobo the bear

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Quote:
Originally Posted by Barrow Museum
As a Permian genus, it cannot be an "Ammonite".  It can however, be classified as an "Ammonoid" (Subclass Ammonoidea).  To go a little further along the classification chain, it is in the order Goniatitida (Goniatites).

I was taught (admittedly a few decades ago) that Ammonites meant the suborder Ammonitina, one of the four suborders of the order Ammonitida, which only evolved at the beginning of the Jurassic, and exclude the root-stock suborders of Phylloceratina and Lytoceratina.  The later, mainly Cretaceous suborder Ancycloceratina, often called Heteromorphs (they have irregular coiled shells) are also excluded from the "Ammonites".  However, no-one would object to your calling any Jurassic Ammonitid an ammonite!

Wikipedia succinctly states:

The words "ammonite" and "ammonoid" are both used quite loosely in common parlance to refer to any member of subclass Ammonoidea. However, in stricter usage, the term ammonite is reserved for members of order Ammonitida (or even suborder Ammonitina).


Wow...I am really now confused. Always thought Jurassic and cretaceous were ammonites because their siphuncles were exterior and anything before that the siphuncle was interior and called a Goniatite.
I have however this specimen also a Triassic Rhacophyllites neojurensis both of which are claimed to be Ammonites??????  Should they be classed as Goniatites?

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