Tadpole with legs

By DawnOfADream

• October 3, 2020

Taxonomy

Kingdom: Animalia
Phylum: Chordata
Class: Amphibia
Order: Anura
Family: Ranidae
Genus: Rana
Species: Rana sp.
Author Citation C.C. Young

Geological Time Scale

Eon: Phanerozoic
Era: Cenozoic
Period: Neogene
Sub Period: None
Epoch: Miocene

Stratigraphy

Shanwang Formation

Provenance

Date Collected: 06/17/2020
Acquired by: Purchase/Trade

Dimensions

Width: 1 cm
Height: 7 cm

Location

Shandong Province
China

• metamorphosis
• shandong
• tadpole

Comments

I purchased this specimen in early 2020. The dealer was under the impression that it originated from the Shanwang formation of China.
After discussions on the forum I came to learn that it may be the species Rana basaltica. 

Seeking to confirm the identification, I contacted Melbourne Museum, who in turn forwarded me to Dr Jim Gardner of the Royal Tyrell Museum, who had this to say (some information removed for the sake of clarity); 

Tadpoles (both living and fossil) are notoriously challenging to identify to species. Assuming your dealer’s information is correct--and I suspect it is, because the Shandong deposits contain many tadpole fossils and the matrix is similar to fossils I have seen from that deposit--your tadpole most likely is from Rana basaltica (or more conservatively, just Rana sp.), which is the most common frog in those deposits and known by both adults and tadpoles.

...

Although I cannot be definitive about the species represented by that fossil, I can say something about its stage of development.  Its well developed hind legs indicate it died during metamorphosis, at approximately Gosner stage 40 before the front legs develop and when tadpoles are still fully aquatic. 

Based on Dr. Gardner’s comments I have decided to conservatively identify this specimen as Rana sp.

Many thanks to the helpful members of the forum, the staff at Melbourne Museum, and Dr Jim Gardner for all your help. 
Literature:

Fossil frogs (Anura) from Shanwang (Middle Miocene; Shandong Province, China) (Wang et al, 2011).

The Fossil Record of Tadpoles (Gardner, 2016).
If there are any mistakes in the information I have provided please let me know!