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COMPARISONS WITH OTHER PUTATIVE HALLUCIGENIA SPECIES
Articulated specimens of putative hallucigeniids are known from both the Chengjiang
biota (H. fortis) and the slightly younger Guanshan biota (H. hongmeia, H. sparsa) in
China [1, 2]. In all species, spines have non-flaring bases and pointed ends; but spines
differ in shape both between species and within species – even within a single specimen.
H. hongmeia, for instance, typically has small conical spines in the middle of the body,
with spines increasing in length and becoming more slender towards the posterior – a
pattern that recalls Luolishania [3]. Whereas the spines in H. hongmeia are generally low
and broad, H. sparsa spines are long and slender, with the spines of H. fortis intermediate
between these two [1].
Unfortunately, the surface detail in the spines of H. hongmeia and H. fortis is poorly
preserved, impeding a direct comparison with H. sparsa. A pock-marked pattern is
present in H. hongmeia [1], with ovoid structures seemingly comparable in size to the
triangular scales observed in H. sparsa. These ovoid elements were described as holes
partially filled by Fe-minerals, perhaps indicating differential preservation of labile
tissues during early diagenesis [4]. The identification of these ovoid elements as holes
suggests comparison with other Cambrian lobopods such as Microdictyon and
Onychodictyon [1], which would distance H. hongmeia from the hallucigeniids. On the
other hand, given the effects of severe weathering and the discrete preservational mode
active in the Chinese material, the ovoid structures may simply represent poorly
preserved scales. Because body specimens of H. hongmeia and Chinese material
attributed to H. sparsa are incomplete or fragmentary, it remains difficult to categorically
determine the generic synonymy of these three species.
References
1.
Steiner M., Hu S.X., Liu J., Keupp H. 2012 A new species of Hallucigenia from
the Cambrian Stage 4 Wulongqing Formation of Yunnan (South China) and the structure
of sclerites in lobopodians. Bulletin of Geosciences 87(1), 107-124.
2.
Hou X., Bergström J. 1995 Cambrian lobopodians--ancestors of extant
onychophorans? Zoological Journal of the Linnean Society 114(1), 3-19.
3.
Ma X., Hou X., Bergström J. 2009 Morphology of Luolishania longicruris (Lower
Cambrian, Chengjiang Lagerstätte, SW China) and the phylogenetic relationships within
lobopodians. Arthropod Structure & Development 38(4), 271-291.
4.
Gabbott S.E., Hou X.G., Norry M.J., Siveter D.J. 2004 Preservation of Early
Cambrian animals of the Chengjiang biota. Geology 32, 901-904.