Vetulicolia

Vetulicolia Fossil range: Cambrian
Scientific classification
Kingdom:	Animalia
Superphylum:	?Deuterostomia
Phylum:	Vetulicolia Shu, et al. 2001
Classes
Vetulicolida Banffozoa Heteromorphida ? Yunnanozoa ? Yuyuanozoon

Vetulicolia^{[note 1]} is an extinct phylum^[1] encompassing several Cambrian organisms. Their bodies comprise two parts; their front is voluminous and is tipped with a large "mouth" and a row of five round to oval-shaped features on each side which have been interpreted as gills - or at least openings in the vicinity of the pharynx. Their posterior section comprises seven segments. They lack preserved appendages of any kind.^[2] The area where the anterior and posterior parts join is constricted. Their affinity is very uncertain; they have been considered to represent stem- and crown-group arthropods, stem-group vertebrates, and early deuterostomes.

Taxonomy and evolution

When erected, the phylum included the Didazoonidae (Didazoon, Pomatrum, and Xidazoon) and the Vetulicolidae (Vetulicola, and Banffia).^[1] Other groups which may be related include the yunnanozoans.^[1]

The taxonomic placement of the Vetulicolians remains controversial. Shu (2003) has argued that the vetulicolians probably represent an early side-branch of deuterostomes, and that this implies that segmentation in cephalochordates and vertebrates may be derived from the common ancestor of protostomes and deuterostomes. Briggs et al. (2005) described Skeemella from the Middle Cambrian of Utah as having affinity to Vetulicolia, but also as having arthropod features, thus confounding assignment of Vetulicolia to Deuterostomia. Dominguez and Jefferies have argued, based on morphological analysis, that Vetulicola (and by implication, other Vetulicolians) is a urochordate, and probably a stem-group larvacean. However, some question the relation to tunicates and larvaceans, as there is no evidence of segmentation in tunicates, larval or adult, that is comparable to segmentation in vetulicolians, that the anus of urochordates is within the atrium, while that of vetulicolians is positioned at the terminal end of the tail, and, perhaps most importantly, there is no exhalant siphon, or analogous structure, seen in vetulicolians.^[3][4]

Ecology and Lifestyle

From their superficially tadpole-like forms, leaf or paddle-shaped tails, and various degrees of streamlining, it is assumed that all vetulicolians discovered thus far were swimming animals that spent much, if not all, of their time living in the water column.^[4] Some groups, like the genus Vetulicola, were more streamlined (complete with ventral keels) than other groups, such as the tadpole-like Didazoonidae.^[4] Because all vetulicolians had mouths which had no features for chewing or grasping, it is automatically assumed that they were not predators.^[4] Because of their gill slits, many researchers regard the vetulicolians as being planktivores. The sediment infills in the guts of their fossils have led some to suggest that they were deposit feeders. This idea has been contested, as deposit feeders tend to have straight guts, whereas the hindguts of vetulicolians were spiral-shaped. Some researchers propose that the vetulicolians were "selective deposit-feeders" which actively swam from one region of the seafloor to another, while supplementing their nutrition with filter-feeding.^[4]

Classification

• Phylum Vetulicolia
  • Class Vetulicolida
    • Order Vetulicolata
      • Family Vetulicolidae
        • Genus Vetulicola
          • Vetulicola rectangulata
          • Vetulicola cuneata
          • Vetulicola gangtoucunensis
          • Vetulicola monile
      • Family Beidazooidae
        • Genus Beidazoon
          • Beidazoon venustum (synonym = Bullivetula variola)
      • Family Didazoonidae
        • Genus Didazoon
          • Didazoon haoae
        • Genus Xidazoon
          • Xidazoon stephanus
        • Genus Pomatrum
          • Pomatrum ventralis
    • ?Order Yunnanozoa
      • Family Yunnanozoonidae
        • Genus Yunnanozoon
          • Yunnanozoon lividum
        • Genus Haikouella
          • Haikouella lanceolata
  • Class Banffozoa
    • • • • Skeemella clavula
      • Family Banffiidae
        • Genus Banffia
          • Banffia constricta^[5]
  • Class Heteromorphida
    • • Family Heteromorphidae
        • Genus Heteromorphus
          • Heteromorphus longicaudatus (synonym=Banffia confusa)
          • "Form A" (unnamed species)
• incertae sedis Yuyuanozoon magnificissimi ^[6]

Notes

1. ^ The phylum name, Vetulocolia, is derived from the type genus, Vetulicola, which is a compound Latin word composed of vetuli, or "old," and cola, or "inhabitant."

References

• Briggs, D., Lieberman, B., Halgedahl, S. and Jarrard, R. (2005), A new metazoan from the Middle Cambrian of Utah and the nature of Vetulicolia. Palaeontology 48: 681-686.
• Shu, Degan. 2003. A paleontological perspective of vertebrate origin. Chinese Science Bulletin, Vol. 48 No. 8 725-735. April, 2003. [2] - URL retrieved June 22, 2006
• Dominguez, Patricio and Jeffries, Richard. (2003). Fossil evidence on the origin of appendicularians. Paper read at International Urochordate Meeting 2003. Abstract at [3] - URL retrieved June 22, 2006

External links

• New phylum on the block - Accessed January 3, 2008
• Once We Were Worms
• Photos and drawings of fossils of various Vetulicolians - Accessed January 3, 2008