Watsonella

Last updated

Watsonella
Temporal range: Cambrian Stage 2, c. 530–525  Ma
Ꞓ
O
S
D
C
P
T
J
K
Pg
N
↓
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Mollusca (?)
Genus:† Watsonella
Grabau, 1900
Type species
Watsonella crosbyi
Accepted species
Synonyms

Watsonella is an extinct genus of mollusc known from early (Terreneuvian) Cambrian strata. It has been hypothesized to be close to the origin of bivalves. It contains a single species, Watsonella crosbyi.

Contents

The genus is closely related to Anabarella , with which it bears many morphological similarities, including a laminar internal shell microstructure said to connect it with the early bivalves Fordilla and Pojetaia .

Taxonomy

Watsonella was described by Amadeus William Grabau in 1900, with the type species Watsonella crosbyi. [1] The type specimen was found in a fossil-filled boulder collected by Thomas Augustus Watson, the assistant of Alexander Graham Bell who received the first-ever telephone call. [2] The genus name honors Watson and the species name honors Professor William Otis Crosby. Grabau initially interpreted Watsonella as a heteropod gastropod similar to the modern genus Carinaria . [1] In 1935, E. S. Cobbold named the genus Heraultia based on specimens from France, with the type species Heraultia varensalensis. He tentatively interpreted it as a notostracan crustacean. He noted "striking" similarity between it and Watsonella, but concluded that it was "impossible to bring them together" without more information on the affinities of Watsonella. [3] Because the name Heraultia had already been used for a genus of fly, in 1976 John Pojeta and Bruce Runnegar proposed the name Heraultipegma as a replacement. Pojeta and Runnegar reinterpreted Heraultipegma and Watsonella as the earliest known rostroconchs. [4] In 1988, Martin Kerber hesitantly synonymized Heraultipegma and Watsonella, and Ed Landing affirmed their synonymy in 1989. [5] In 2001, P. Yu. Parkhaev included Watsonella in Stenothecidae and proposed the subfamily Watsonellinae to include it. [6]

Only one species of Watsonella is recognized as valid, the type species W. crosbyi. The species Heraultia varensalensis, Heraultia sibirica, and Heraultipegma yunnanensis are all considered synonyms of W. crosbyi. [7] Another species, Heraultipegma charaulachica, has been reassigned to the genus Xianfengella . [6]

Description

Watsonella was a small, laterally-compressed animal, generally less than 5 millimetres (0.20 in) long. [5] It had a single "pseudobivalved" shell. [5] It is not known with certainty which end of the shell is the front. [8]

The external surface of the shell was ornamented with comarginal growth lines and ribs. [8]

Unlike rostroconchs, Watsonella lacked a pegma, although the curvature of the shell may have served a functionally similar role. [9] Although Pojeta and Runnegar [4] and Landing [5] interpreted a pegma as present, several studies have rejected this interpretation. [9] Li and colleagues interpreted the putative pegma as an artifact of the curvature of the shell. [7]

The shell of Watsonella was probably originally aragonitic in composition. [5] It was composed of two layers with distinct microstructure. The outer layer was composed of regular, tightly-packed prismatic units that were oriented perpendicular to the shell wall. The inner layer was composed of flattened units called lamellae that produced a stepwise texture. [10] Unlike many modern mollusks, the shell was not nacreous. [11]

Paleobiology

Watsonella was probably a burrowing animal. Because of the limited flexibility of its hingeless shell, its burrowing ability would have been less efficient than modern burrowing clams. [5]

Evolutionary relationships

Anabarella was probably the ancestor of Watsonella. [11] Morphological intermediates linking Anabarella and Watsonella are known. [12] The shell microstructure is very similar between Anabarella, Watsonella, and the early bivalves Fordilla and Pojetaia . [11]

A phylogenetic analysis conducted in 2000 by a team of researchers led by J. G. Carter recovered Watsonella as more closely related to bivalves than rostroconchs. [13]

In 2023, a team of researchers led by Hao Song argued that Watsonella was too early to be a stem-group bivalve, based on molecular clock results that suggested that bivalves and scaphopods diverged from each other approximately 520 million years ago. They suggested that Watsonella should be reinterpreted as stem-group members of Diasoma, the clade uniting bivalves and scaphopods. [14]

Biostratigraphic significance

Watsonella has been proposed as an index fossil of the Cambrian, defining a W. crosbyi zone. Notwithstanding the weakness of a first appearance datum as a definition for the base of a period, [15] the species has been proposed as a marker for the base of the presently unratified second stage of the Terreneuvian (i.e. Cambrian Stage 2). However, the species has now been found late in the Fortunian, drawing back its first occurrence. [16] But that said its occurrence in Australia seems to begin rather near the base of Stage 2. [17]

Related Research Articles

<span class="mw-page-title-main">Hyolitha</span> Palaeozoic lophophorates with small conical shells

Hyoliths are animals with small conical shells, known as fossils from the Palaeozoic era. They are at least considered as lophotrochozoan, and possibly being lophophorates, a group which includes the brachiopods, while others consider them as being basal lophotrochozoans, or even molluscs.

<span class="mw-page-title-main">Tusk shell</span> Class of elephant tusk shell molluscs

The tusk shells or tooth shells, technically the Scaphopoda, are members of a class of shelled marine mollusc with worldwide distribution, and are the only class of exclusively infaunal marine molluscs. Shells of species within this class range in length 0.5–18 cm (0.20–7.09 in). Members of the order Dentaliida tend to be larger than those of the order Gadilida.

<span class="mw-page-title-main">Rostroconchia</span> Extinct class of molluscs

The Rostroconchia is a class of extinct molluscs dating from the early Cambrian to the Late Permian. They were initially thought to be bivalves, but were later given their own class. They have a single shell in their larval stage, and the adult typically has a single, pseudo-bivalved shell enclosing the mantle and muscular foot. The anterior part of the shell probably pointed downward and had a gap from which the foot could probably emerge. Rostroconchs probably lived a sedentary semi-infaunal lifestyle. There were probably more than 1,000 species of members of this class.

The Coelosclerithophorans are a polyphyletic group of organisms bearing hollow sclerites made of aragonite, and with a supposedly distinctive microstructure.

<span class="mw-page-title-main">Evolution of molluscs</span> The origin and diversification of molluscs through geologic time

The evolution of the molluscs is the way in which the Mollusca, one of the largest groups of invertebrate animals, evolved. This phylum includes gastropods, bivalves, scaphopods, cephalopods, and several other groups. The fossil record of mollusks is relatively complete, and they are well represented in most fossil-bearing marine strata. Very early organisms which have dubiously been compared to molluscs include Kimberella and Odontogriphus.

<i>Yochelcionella</i> Extinct genus of molluscs

Yochelcionella is an extinct genus of basal molluscs which lived during the Tommotian epoch, the first epoch of the Cambrian period. This genus is often reconstructed to resemble snails.

<span class="mw-page-title-main">Helcionellid</span> Extinct order of molluscs

Helcionellid or Helcionelliformes is an order of small fossil shells that are universally interpreted as molluscs, though no sources spell out why this taxonomic interpretation is preferred. These animals are first found about 540 to 530 million years ago in the late Nemakit-Daldynian age, which is the earliest part of the Cambrian period. A single species persisted to the Early Ordovician. These fossils are component of the small shelly fossils (SSF) assemblages.

The small shelly fauna, small shelly fossils (SSF), or early skeletal fossils (ESF) are mineralized fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Cambrian Period. They are very diverse, and there is no formal definition of "small shelly fauna" or "small shelly fossils". Almost all are from earlier rocks than more familiar fossils such as trilobites. Since most SSFs were preserved by being covered quickly with phosphate and this method of preservation is mainly limited to the late Ediacaran and early Cambrian periods, the animals that made them may actually have arisen earlier and persisted after this time span.

<span class="mw-page-title-main">Mollusca</span> Phylum of invertebrate animals

Mollusca is the second-largest phylum of invertebrate animals, after Arthropoda; members are known as molluscs or mollusks. Around 76,000 extant species of molluscs are recognized. The number of fossil species is estimated between 60,000 and 100,000 additional species. The proportion of undescribed species is very high. Many taxa remain poorly studied.

Stenothecidae is an extinct family of fossil univalved Cambrian molluscs which may be either gastropods or monoplacophorans.

Anabarella is a species of bilaterally-flattened monoplacophoran mollusc, with a morphological similarity to the rostroconchs. Its shell preserves evidence of three mineralogical textures on its outer surface: it is polygonal near the crest of the shell, subsequently changing to both spiny and stepwise. Its internal microstructure is calcitic and semi-nacreous. Its name reflects its provenance from Anabar, Siberia. It has been interpreted as ancestral to the rostroconchs, and has been aligned to the Helcionellidae.

<i>Fordilla</i> Extinct genus of bivalves

Fordilla is an extinct genus of early bivalves, one of two genera in the extinct family Fordillidae. The genus is known solely from Early Cambrian fossils found in North America, Greenland, Europe, the Middle East, and Asia. The genus currently contains three described species, Fordilla germanica, Fordilla sibirica, and the type species Fordilla troyensis.

Stenothecoida is a taxon of bivalved fossils from the Early to middle Cambrian period. They look a bit like brachiopods or bivalve molluscs.

Ribeiria is a genus of rostroconch mollusc with a pegma, once interpreted as an intermediate between helcionellids and primitive scaphopods.

Pojetaia is an extinct genus of early bivalves, one of two genera in the extinct family Fordillidae. The genus is known solely from Early to Middle Cambrian fossils found in North America, Greenland, Europe, North Africa, Asia, and Australia. The genus currently contains two accepted species, Pojetaia runnegari, the type species, and Pojetaia sarhroensis, though up to seven species have been proposed. The genera Buluniella, Jellia, and Oryzoconcha are all considered synonyms of Pojetaia.

<span class="mw-page-title-main">Fordillidae</span> Extinct family of bivalves

Fordillidae is an extinct family of early bivalves and one of two families in the extinct superfamily Fordilloidea. The family is known from fossils of early to middle Cambrian age found in North America, Greenland, Europe, the Middle East, Asia, and Australia. The family currently contains two genera, Fordilla and Pojetaia, each with up to three described species. Due to the size and age of the fossil specimens, Fordillidae species are included as part of the Turkish Small shelly fauna.

<span class="mw-page-title-main">Fordilloidea</span> Extinct superfamily of bivalves

Fordilloidea is an extinct superfamily of early bivalves containing two described families, Fordillidae and Camyidae and the only superfamily in the order Fordillida. The superfamily is known from fossils of early to middle Cambrian age found in North America, Greenland, Europe, the Middle East, Asia, and Australia. Fordillidae currently contains two genera, Fordilla and Pojetaia each with up to three described species while Camyidae only contains a single genus Camya with one described species, Camya asy. Due to the size and age of the fossil specimens, Fordillidae species are included as part of the Turkish Small shelly fauna.

Tuarangia is a Cambrian shelly fossil interpreted as an early bivalve, though alternative classifications have been proposed and its systematic position remains controversial. It is the only genus in the extinct family Tuarangiidae and order Tuarangiida. The genus is known solely from Middle to Late Cambrian fossils found in Europe and New Zealand. The genus currently contains two accepted species, Tuarangia gravgaerdensis and the type species Tuarangia paparua.

Stage 2 of the Cambrian is the unnamed upper stage of the Terreneuvian Series. It lies atop the Fortunian and below Stage 3 of the Cambrian. It is commonly referred to as the Tommotian, after the Cambrian stratigraphy of Siberia. Neither the upper nor lower boundary has yet been defined by the International Commission on Stratigraphy. The preferred definitions for the lower boundary are the first appearance of the molluscs Watsonella crosbyi or Aldanella attleborensis around 529 million years ago. The correlation between the lowest occurrences of A. attleborensis and W. crosbyi with the Zhujiaqing positive carbon isotope excursion (ZHUCE) has led to the conclusion that the combination of these two markers are a reliable indicator of the boundary between the Fortunian and Stage 2. The proposed upper boundary might be the first appearance of trilobites around 521 million years ago.

<span class="mw-page-title-main">Bruce Runnegar</span>

Bruce Norman Runnegar is an Australian-born paleontologist and professor at UCLA. His research centers on using the fossil record to determine how, where, and when life originated and evolved. He has published on a wide variety of topics, including the phylogeny of molluscs, Dickinsonia fossils and oxygen levels, and molecular clock techniques.

References

  1. 1 2 Grabau, Amadeus William (1900). "Palaeontology of the Cambrian Terranes of the Boston Basin". Occasional Papers of the Boston Society of Natural History. 4 (3).
  2. ↑ Watson, Thomas A. (1926). Exploring life: the autobiography of Thomas A. Watson.
  3. ↑ Cobbold, E.S. (1935). "Lower Cambrian faunas from Hérault, France". Annals and Magazine of Natural History. 16 (91): 25–48. doi:10.1080/00222933508655023. ISSN   0374-5481.
  4. 1 2 Pojeta, John; Runnegar, Bruce (1976). "The paleontology of rostroconch mollusks and the early history of the phylum Mollusca". Geological Survey Professional Paper. 968.
  5. 1 2 3 4 5 6 Landing, Ed (1989). "Paleoecology and distribution of the Early Cambrian rostroconch Watsonella crosbyi Grabau". Journal of Paleontology. 63 (5): 566–573. doi:10.1017/S0022336000041196. eISSN   1937-2337. ISSN   0022-3360.
  6. 1 2 Parkhaev, P. Yu (2001). "Molluscs and siphonoconchs". The Cambrian biostratigraphy of the Stansbury Basin, South Australia. pp. 133–210. ISBN   5-7846-0095-8.
  7. 1 2 Li, Guoxiang; Zhao, Xin; Gubanov, Alexander; Zhu, Maoyan; Na, Lin (2011-04-24). "Early Cambrian mollusc Watsonella crosbyi: A potential GSSP Index Fossil for the base of the Cambrian Stage 2". Acta Geologica Sinica - English Edition. 85 (2): 309–319. doi:10.1111/j.1755-6724.2011.00400.x. eISSN   1755-6724. ISSN   1000-9515.
  8. 1 2 Guo, Jun-Feng; Li, Guo-Xiang; Qiang, Ya-Qin; Song, Zu-Chen; Zhang, Zhi-Fei; Han, Jian; Wang, Wen-Zhe (2021). "Watsonella crosbyi from the lower Cambrian (Terreneuvian, Stage 2) Yanjiahe Formation in Three Gorges Area, South China". Palaeoworld. 30 (1): 1–19. doi:10.1016/j.palwor.2020.04.006. ISSN   1871-174X.
  9. 1 2 Peel, J.S. (2021-04-11). "Pseudomyona from the Cambrian of North Greenland (Laurentia) and the early evolution of bivalved molluscs". Bulletin of Geosciences: 195–215. doi: 10.3140/bull.geosci.1827 . eISSN   1802-8225. ISSN   1214-1119.
  10. ↑ Kouchinsky, Artem V. (1999). "Shell microstructures of the Early Cambrian Anabarella and Watsonella as new evidence on the origin of the Rostroconchia". Lethaia. 32 (2): 173–180. doi:10.1111/j.1502-3931.1999.tb00537.x. eISSN   1502-3931. ISSN   0024-1164.
  11. 1 2 3 Vendrasco, Michael J.; Checa, Antonio G.; Kouchinsky, Artem V. (2011). "Shell microstructure of the early bivalve Pojetaia and the independent origin of nacre within the mollusca". Palaeontology. 54 (4): 825–850. doi: 10.1111/j.1475-4983.2011.01056.x . eISSN   1475-4983. ISSN   0031-0239.
  12. ↑ Gubanov, Alexander P.; Kouchinsky, Artem V.; Peel, John S. (1999). "The first evolutionary‐adaptive lineage within fossil molluscs". Lethaia. 32 (2): 155–157. doi:10.1111/j.1502-3931.1999.tb00534.x. eISSN   1502-3931. ISSN   0024-1164.
  13. ↑ Carter, J. G.; Campbell, D. C.; Campbell, M. R. (2000). "Cladistic perspectives on early bivalve evolution". Geological Society, London, Special Publications. 177 (1): 47–79. doi:10.1144/GSL.SP.2000.177.01.04. eISSN   2041-4927. ISSN   0305-8719.
  14. ↑ Song, Hao; Wang, Yunan; Shao, Haojing; Li, Zhuoqing; Hu, Pinli; Yap-Chiongco, Meghan K.; Shi, Pu; Zhang, Tao; Li, Cui; Wang, Yiguan; Ma, Peizhen; Vinther, Jakob; Wang, Haiyan; Kocot, Kevin M. (2023-10-03). "Scaphopoda is the sister taxon to Bivalvia: Evidence of ancient incomplete lineage sorting". Proceedings of the National Academy of Sciences. 120 (40): –2302361120. doi: 10.1073/pnas.2302361120 . eISSN   1091-6490. ISSN   0027-8424.
  15. ↑ 1. Landing, E., Geyer, G., Brasier, M.D., and Bowring, S.A. (2013). Cambrian evolutionary radiation: context, correlation, and chronostratigraphy—overcoming deficiencies of the first appearance datum (FAD) concept. Earth-Science Rev. 123, 133–172.
  16. ↑ Landing, E., and Kouchinsky, A. V. (2016). Correlation of the Cambrian Evolutionary Radiation: geochronology, evolutionary stasis of earliest Cambrian (Terreneuvian) small shelly fossil (SSF) taxa, and chronostratigraphic significance. Geol. Mag. 153, 750–756.
  17. ↑ Jacquet, Sarah M.; Brougham, Thomas; Skovsted, Christian B.; Jago, James B.; Laurie, John R.; Betts, Marissa J.; Topper, Timothy P.; Brock, Glenn A. (2017). "Watsonella crosbyi from the lower Cambrian (Terreneuvian, Stage 2) Normanville Group in South Australia". Geological Magazine. 154 (5): 1088–1104. doi: 10.1017/S0016756816000704 . eISSN   1469-5081. ISSN   0016-7568.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.