Protoconodonts are an extinct taxonomic group of conodonts or, possibly,

Chaetognaths The Chaetognatha or chaetognaths (meaning ''bristle-jaws'') are a phylum of predatory marine worms that are a major component of plankton worldwide. Commonly known as arrow worms, about 20% of the known Chaetognatha species are benthic, and ca ...

(also known as arrow worms) were thought possibly to be related to some of the animals grouped with the

conodont Conodonts (Greek ''kōnos'', "cone", + ''odont'', "tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, which ...

s. The conodonts themselves, however, are thought to be related to the

vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

. It is now thought that protoconodont elements (e.g., '' Protohertzina anabarica'' Missarzhevsky, 1973), are probably grasping spines of chaetognaths rather than the oropharyngeal elements of conodonts. Previously chaetognaths in the Early Cambrian were only suspected from these protoconodont elements (for example '' Phakelodus''), but the more recent discoveries of body fossils have confirmed their presence then.

References

* Middle and Upper Cambrian Protoconodonts and Paraconodonts from Hunan, South China. Dong Xi-Ping and Stig M. Bergström, Palaeontology, September 2001, Volume 44, Issue 5, pages 949–985, * On the evolution and histology of some Cambrian protoconodonts, paraconodonts and primitive euconodonts. Dong Xiping, Science in China Series D: Earth Sciences, July 2004, Volume 47, Issue 7, pages 577–584, * Ion microprobe U–Pb dating and Sr isotope measurement of a protoconodont. Yuji Sano, Kosaku Toyoshima, Akizumi Ishida, Kotaro Shirai, Naoto Takahata, Tomohiko Sato and Tsuyoshi Komiya, Journal of Asian Earth Sciences, Volume 92, 1 October 2014, Pages 10–17,

External links

* * Conodont taxonomy Cambrian conodonts Prehistoric jawless fish orders {{conodont-stub