''Heteromorphus'' is an extinct genus of
banffiid from the
lower Cambrian
The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovici ...
Chengjiang lagerstatte. It contains one broadly accepted species, ''Heteromorphus confusus'', as well as a proposed junior synonym, ''Heteromorphus longicaudatus'' that may prove to be a separate species as additional specimens are examined.
A much smaller species labeled "Form A" is allied with ''Heteromorphus'' at the
class
Class, Classes, or The Class may refer to:
Common uses not otherwise categorized
* Class (biology), a taxonomic rank
* Class (knowledge representation), a collection of individuals or objects
* Class (philosophy), an analytical concept used d ...
level but has not been formally described or assigned to ''Heteromorphus'' itself.
Description
Like ''Banffia'', ''Heteromorphus'' has a two-part body with a notable constriction between the parts, and a crossover that effectively reverses the dorsal and ventral sides between the anterior and posterior sections. The posterior portion is segmented, although the common presence of wrinkling makes counting the segments difficult. The anterior body shape ranges from torpedo-like to more rectangular, with a near-vertical anterior edge.
''Heteromorphus'' is separated from ''Banffia'' by the presence of a lateral groove, similar to that found in the
Vetulicolida
Vetulicolida is a class of vetulicolians. It consists of the order Vetulicolata (which contains the families Vetulicolidae and Didazoonidae) and the genus '' Nesonektris'', which is of uncertain placement. It is distinguished from the Banff ...
.
However, while a 2004 description claimed that four gill openings were present in the groove, later workers have not observed them. The lack of visible gills in banffiids has been speculated to indicate a burrowing lifestyle. A partial "twist" has been described in ''Heteromorphus'', compared to the well-developed torsion in ''Banffia''.
While the initial description of ''H. confusus'' indicated an anus halfway along the ventral surface of the posterior section, later descriptions confirmed the terminal location of the anus.
Taxonomy
''Heteromorphus'' has been grouped with ''Banffia'' and ''Skeemella'' in the family
Banffiidae
Banfiidae is a family of extinct banffozoan animals from North America and China. The family name is sometimes spelt Banffidae. It includes ''Banffia'', ''Heteromorphus'', and possibly ''Skeemella''. The family may be paraphyletic. A ''Heteromorp ...
.
The following cladogram is simplified from Mussini ''et al.'' (2024), using the definition of
Vetulicolidae
Vetulicolidae is a vetulicolian family from the Cambrian Stage 3 Maotianshan Shale and Sirius Passet Lagerstätte that consists of ''Vetulicola'', ''Beidazoon'', and ''Ooedigera''. It is distinguished from the Didazoonidae by a harder body wall a ...
from Li ''et al.'' (2018). It shows ''Heteromorphus'' as part of the earliest steps, corresponding to the class
Banffozoa
Banffozoa (also called Heteromorphida) is an extinct class of bilaterians. Most workers place it in the Vetulicolia, but the protostome-like features of some members have motivated ongoing debate. Banffozoa consists of the order Banffiata (whi ...
, in the
evolutionary grade
A grade is a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit.
Phylogenetics
The concept of evolutionary grades ...
leading to extant
chordates
A chordate ( ) is a bilaterian animal belonging to the phylum Chordata ( ). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics ( synapomorphies) that distinguish them from ot ...
.
An earlier study in 2014 placed vetulicolians as the sister-group to tunicates, but was unable to resolve any relationships among vetulicolians as a group:
''H. confusus'' vs ''H. longicaudatus''
''H. confusus'' was originally described as ''
Banffia confusa'' in 1997, while ''H. longicaudatus'' was described and assigned to the new genus ''Heteromorphus'' in 1999. The discoverers of ''B. confusa'' referred to it as ''H. confusus'' in 2002, accepting its assignment to ''Heteromorphus'' and, according to a comprehensive 2007 review of vetulicolian phylogenetics, indicating that ''H. longicaudatus'' is its junior synonym. However, the same review also noted substantial variation among ''Heteromorphus'' specimens, and that more species (including a distinct ''H. longicaudatus'') may exist.
References
Works cited
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{{Taxonbar, from=Q131424639
Fossil taxa described in 1999
Vetulicolia