is a specimen of a member of the Desmospongia, the most diverse
of modern-day sponges. Greater than 90% of the extant 5,000 known
species of sponges are desmosponges. Such a representation in
fossil record is not maintained where less than half the known
genera are of this type, a consequence of the fact that the
not fossilize readily. Desmosponge skeletons are composed of spongin
fibers and/or siliceous spicules. Sponges are known from the
Precambrian, with few localities contributing to the fossil record
over time. The genus Hazelia is perhaps best known from the
Burgess Shale where nine distinct
Hazelia species are described (and several other sponge
also occurs in the House Range
Chengjiang Biota is one such fossil lagerstatte,
with sponges having
the second highest representations among metazoans,
right after the arthropods.
The Chengjiang sponges are though to have been suspension feeders
that used tiering much like crinoids to feed at different heights
in shelves and reefs within the water column.
are, of course, primitive sessile animals that lack nervous,
digestive and circulatory systems; despite their simplicity,
or maybe because of it, they were among the very first animals
remain a robust phylum in modern times. Molecular clocks based
on DNA or amino acid sequences support the appearance
of sponges well prior to the Cambrian
are known from the 580 million year old Ediacaran
Formation, many of which have been placed in Family Demospongiae.
However, the silica spicules
often used to characterize demosponges do not appear in the fossil
record until the Cambrian. The oldest undisputed sponge fossil
date to the Neoproterozoic (~ 700 mya), and molecular biomarkers
suggest an appearance as early as 1800 mya at the end of the Paleoproterozoic.
Some sponge internal skeletons comprise soft spongin protein
interwoven spicules made of calcium carbonate or silicon dioxide
that do preserve well
to their fossil remains.
latest evolutionary biology research suggests that the closest
are choanoflagellates, single-celled organisms very close to
choanocytes. If so, the Metazoa evolved from animals quite similar
to sponges, further suggesting that sponges could be paraphyletic (i.e., sponge ancestors may have given rise to all non-sponge
well as extant sponges).
Walcott, 1920, in the Cambrian of Utah". Journal
of Paleontology (Paleontological Society) 71 (6): 994–997.
doi:10.2307/1306598 (inactive 2014-11-09).
G.D., et al. (2009). "Fossil steroids record
the appearance of Demospongiae during the Cryogenian period".
Nature 457 (7230): 718–721.
C., Manuel, M., Alivon, E., Boury-Esnault, N., Vacelet J.,
and Le Parco,
Y. (2001). "Sponge paraphyly and the origin
of Metazoa". Journal of Evolutionary Biology 14 (1):
Burgess Shale sponges on genus
Hazelia: Hazelia conferta (Walcott, 1920), Hazelia crateria (Rigby,
1986), Hazelia delicatula (Walcott, 1920), Hazelia dignata (Walcott,
1920), Hazelia grandis (Walcott, 1920), Hazelia luteria (Rigby,
1986), Hazelia nodulifera (Walcott, 1920), Hazelia obscura (Walcott,
1920), and Hazelia palmata (Walcott, 1920).