Emuellidae

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Emuellidae
Temporal range: 517  Ma
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late Botomian
BalcoracaniaDailyi.png
Balcoracania dailyi  of the family Emuellidae
Lower Cambrian Emu Shale
Kangaroo Island, South Australia
© Dave Simpson
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class:† Trilobita
Order:† Redlichiida
Superfamily:† Emuelloidea
Family:† Emuellidae
Pocock, 1970
Genera

Emuellidae are a small family of trilobites, a group of extinct marine arthropods, that lived during the late Lower Cambrian (late Botomian) of the East Gondwana supercontinent, in what are today South-Australia and Antarctica.

Contents

Description

Emuellidae can be recognized among trilobites in having a set of unique features. The headshield or cephalon has large genal spines reaching back as far as the 3rd to 6th segment of the thorax. The eye-ridges contact the back of the frontal lobe of the glabella and extend laterally and backwards, roughly parallel to the frontal and lateral rim of the cephalon. There are small, clearly incised pits at the junction between the eye-ridge and the frontal lobe of the cephalic axis (or glabella). The thorax reaches its greatest width at the 6th segment. The frontal part or prothorax consists of 6 segments, with number 5 and 6 fused, and the 6th carrying very large trailing spines. The rear part or opistothorax consists of a variable but extremely large number of segments (up to 97). [1]

(See the Trilobite article for a definition of morphological terms)

Cephalon: Cranidium subquadrate, glabella cylindrical, slightly contracted at S3, three pairs of glabellar furrows, preglabellar field short or absent, eye ridge wide, long, directed slightly postero-laterally, palpebral lobe cresentic, posterior area of fixigena with fulcrum, free cheeks (or librigenae) with long spines; hypostome conterminant, attached to a narrow rostral plate.

The thorax is divided into a prothorax of six segments (the 6th carrying very large, trailing, pleural spines) and extremely long opisthothorax of up to 97 segments (Balcoraciana dailyi holds the record for greatest number of thoracic segments in a trilobite species).

Pygidium: A minute, segmented disc.

Taxonomic history

Fossils now assigned to the Emuellidae were first discovered by Dr. B. Daily, of the Geology Department, University of Adelaide in 1956. [2]

Position of the Emuellidae within the Redlichiida

Originally, the Emuellidae were described as part of the Redlichiina. The primitive features prompted the theory that the Emuellids actually represented the stem group of all trilobites, with the Olenellina having secondary fused facial sutures. [2] Later, the Emuellidae were placed in their own superfamily (Emuelloidea), recognizing that trilobites lacking facial sutures (i.e. the Olenellina) are the stem group. [3] This was followed by the clustering of the Emuellidae in a new superfamily Ellipsocephaloidea. [4] Most recently, the Emuellidae are regarded an early branch of the Redlichiina suborder, the closest relatives being the genera Bigotina, Abadiella, and the close-knit group of the families Estaingiidae, Ichangiidae and Ellipsocephalidae. [1]

Genera assigned to the Emuellidae

Holyoakia has previously been assigned to the Emuellidae. [5] The tailshiel (or pygidium) in Holyoakia is about the same size as its cranidium, with a well-defined axis, eight axial rings, well-developed pleural ribs and furrows, and a spiny margin. The pygidia of Emuella and Balcoracania however are poorly differentiated, minute, and have a smooth margin. Later scholars therefore placed Holyoakia in the Dorypygidae. [1]

Distribution

Balcoracania dailyi occurs in the late Lower Cambrian (late Botomian) of South Australia (White Point conglomerate, Cape d' Estaing and Emu Bay sections, Kangaroo Island; [6] Warragee Member, Billy Creek Formation, Flinders Range; [6] [7] Coads Hill Member, Billy Creek Formation, Reaphook Hill). [8] Balcoracania sp. has been collected from the Lower Cambrian of Antarctica (Shackleton Limestone, central Transantarctic Mountains). [5]

Emuella dalgarnoi is found in the late Lower Cambrian (late Botomian) of South Australia (Emu Bay Shale, Kangaroo Island). [6]

Emuella polymera has been collected from the late Lower Cambrian (late Botomian) of South Australia (Cape d' Estaing section, Kangaroo Island). [6]

Key to the species

1Cephalon subpentagonal. Glabella contacts the frontal margin of the cephalon. Axis at the 3rd thorax segment much wider than each of the pleural zones. Up to 58 thorax segments. → 2
-Cephalon semicircular. There is a short distance between the glabella and the frontal margin of the cephalon. Axis at the 3rd thorax segment almost as wide as each of the pleural zones. Up to 103 thorax segments. South Australia and Antarctica.
→ Balcoracania dailyi Pocock, 1970
2Rear border of the cephalon narrower between the midline and the intergenal angle than between the intergenal angle and the genal angle. South Australia. → Emuella polymera Pocock, 1970
-Rear border of the cephalon wider between the midline and the intergenal angle than between the intergenal angle and the genal angle. South Australia. → Emuella dalgarnoi Pocock, 1970

Related Research Articles

<span class="mw-page-title-main">Redlichiida</span> Extinct order of trilobites

Redlichiida is an order of trilobites, a group of extinct marine arthropods. Species assigned to the order Redlichiida are among the first trilobites to appear in the fossil record, about halfway during the Lower Cambrian. Due to the difficulty to relate sediments in different areas, there remains some discussion, but among the earliest are Fallotaspis, and Lemdadella, both belonging to this order. The first representatives of the orders Corynexochida and Ptychopariida also appear very early on and may prove to be even earlier than any redlichiid species. In terms of anatomical comparison, the earliest redlichiid species are probably ancestral to all other trilobite orders and share many primitive characters. The last redlichiid trilobites died out before the end of the Middle Cambrian.

<i>Balcoracania</i> Extinct family of trilobites

Balcoracania dailyi is a small trilobite of the family Emuellidae. Its fossils have been found in south Australia and Antarctica.

<i>Emuella</i> Extinct genus of trilobites

Emuella is a genus of Cambrian trilobites of the family Emuellidae. Its fossils have been found in South Australia.

<span class="mw-page-title-main">Olenellina</span> Extinct suborder of trilobites

Olenellina is a suborder of the order Redlichiida of trilobites that occurs about halfway during the Lower Cambrian, at the start of the stage called the Atdabanian. The earliest trilobites in the fossil record are arguably Olenellina, although the earliest Redlichiina,Ptychopariida, and Eodiscina follow quickly. The suborder died out when the Lower Cambrian passed into the Middle Cambrian, at the end of the stage called Toyonian. A feature uniting the Olenellina is the lack of rupture lines in the headshield, which in other trilobites assist the periodic moulting, associated with arthropod growth. Some derived trilobites have lost facial sutures again, but all of these are blind, while all Olenellina have eyes.

<span class="mw-page-title-main">Redlichiina</span> Extinct suborder of trilobites

Redlichiina is a suborder of the order Redlichiida of Trilobites. The suborder contains three superfamilies: Emuelloidea, Redlichioidea and Paradoxidoidea. These trilobites are some of the oldest trilobites known. They originated at the beginning of the Cambrian Period and disappeared at the end of the middle Cambrian.

<i>Redlichia</i> Extinct genus of trilobites

Redlichia is a genus of redlichiid trilobite in the family Redlichiidae, with large to very large species. Fossils of various species are found in Lower Cambrian (Toyonian)-aged marine strata from China, Korea, Pakistan, the Himalayas, Iran, Spain, southern Siberia, and Antarctica, and from Middle Cambrian (Ordian)-aged marine strata of Australia.

<i>Olenelloides</i>

Olenelloides armatus is an extinct, small sized olenelloid redlichiid trilobite arthropod. It lived during the later part of the Botomian stage, which lasted from approximately 524 to 518.5 million years ago. This faunal stage was part of the Cambrian Period. The most conspicuous feature is the hexagonal head shield that carries 6 ray-like spines..

<i>Holyoakia</i> Genus of trilobites

Holyoakia is a genus of very small trilobites of the family Dorypygidae, from the late Lower Cambrian of South Australia and Antarctica.

<i>Tsunyidiscus</i> Genus of trilobites

Tsunyidiscus is a trilobite belonging to the Suborder Eodiscina. Tsunyidiscus appeared near the end of the Lower Cambrian, during the late Atdabanian stage of geologic time and some collections suggest it may have survived into the Botomian. The genus is very small, oculate and isopypous with a narrow dome-shaped glabella and a narrow bullet-shaped pygidial axis. Thorax consists of three segments. Tsunyidiscus is the only genus currently attributed to the family Tsunyidiscidae.

<i>Nephrolenellus</i>

Nephrolenellus is an extinct genus of trilobite, fossil marine arthropods, of relatively small size. Currently two species are attributed to it. Nephrolenellus lived at the end of the Lower Cambrian. Species are known from the Great Basin of California, Nevada and Arizona, with one specimen from Canada.

<i>Mesonacis</i>

Mesonacis is an extinct genus of trilobite that lived during the Botomian, found in North-America, and the United Kingdom. Some of the species now regarded part of Mesonacis, have previously been assigned to Angustolenellus or Olenellus (Angustolenellus). Angustolenellus is now regarded a junior synonym of Mesonacis.

<i>Fallotaspis</i> Cambrian Period genus of trilobites

Fallotaspis is a genus of redlichiid trilobites found in Early Cambrian-aged strata of the United States and Morocco.

<i>Emucaris</i> Extinct genus of arthropods

Emucaris fava is an extinct species of soft-shelled trilobite-like arthropod of the nektaspid order from the Lower Cambrian of South Australia. It is the only species classified under the genus Emucaris.

<i>Biceratops</i>

Biceratops is an extinct genus of olenelloid redlichiid trilobites, of average size, with the largest specimen 8 centimetres or 3.1 inches long, not including the huge pleural spines of the 3rd segment of the thorax. It lived during the Toyonian stage, in what is today the South-Western United States. Biceratops can easily be distinguished from other members of Biceratopsidae by the absence of genal spines, in combination with effaced features of the raised axial area of the head shield, that is bordering the two horn-like projections that carry the eyes. Biceratops nevadensis is the only known species in this genus.

Mesolenellus is an extinct genus of trilobites that lived during the lower Cambrian (Botomian), found in Greenland and Spitsbergen.

<i>Bristoliinae</i>

The Bristoliinae is an extinct subfamily of trilobites, fossil marine arthropods, with species of small to average size. Species belonging to this subfamily lived during the Botomian and Toyonian stage (Olenellus-zone), 522-513 million years ago, in the former continent of Laurentia, including what are today Mexico, the Appalachian Mountains and the south-western United States, and Canada.

<i>Emigrantia</i>

Emigrantia is an extinct genus of trilobites, fossil marine arthropods, of small to average size. It lived during the Toyonian stage, in what is today the South-Western United States. Emigrantia can easily be distinguished from other trilobites by the sturdy but not inflated genal spines, that are attached at midlength of the cephalon, in combination with effaced features of the raised axial area of the head shield.

Bolbolenellus is an extinct genus of trilobites, fossil marine arthropods, with five species attributed to it currently. It can be easily distinguished from all other trilobites by the combination of the absence of dorsal sutures in the head shield like all Olenellina, and a distinctly bulbous frontal lobe (L4) of the raised axial area in the head called glabella. The species lived at the end of the Lower Cambrian.

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

Eodiscina is trilobite suborder. The Eodiscina first developed near the end of the Lower Cambrian period and became extinct at the end of the Middle Cambrian. Species are tiny to small, and have a thorax of two or three segments. Eodiscina includes six families classified under one superfamily, Eodiscoidea.

The Calodiscidae Kobayashi, 1943 [nom. transl. Öpik, 1975 ex Calodiscinae Kobayashi, 1943] are a family of trilobites belonging to the order Agnostida that lived during the Lower Cambrian. They are small or very small, and have a thorax of two or three segments. The Calodiscidae includes five genera.

References

  1. 1 2 3 Paterson, J.R.; Edgecombe, G.D. (2006). "The Early Cambrian trilobite Family Emuellidae Popock, 1970: Systematic position and revision of Australian Species". Journal of Paleontology. 85 (3): 496–513. doi:10.1666/0022-3360(2006)80[496:TECTFE]2.0.CO;2.
  2. 1 2 Pocock, K.J. (1970). "The Emuellidae, a new family of trilobites from the Lower Cambrian of South Australia". Palaeontology. 13: 522–562.
  3. ↑ Zhang, W.T.; Lu, Y.H.; Zhu, Z.L.; Qian, Y.Y.; Li, H.L.; Zhou, Z.Y.; Zhang, S.G.; Yuan, J.L. (1980). "Cambrian trilobite faunas of Southwestern China". Palaeontologica Sinica. 159: 1–497.
  4. ↑ Lin, T.R. (1990). "Application of custer analysis to taxonomy of superfamilies and families of superorder Redlichiina (Trilobita)". Acta Palaeontologica Sinica. 29: 94–105.
  5. 1 2 Palmer, A.R.; Rowell, A.J. (1995). "Early Cambrian trilobites from the Shackleton Limestone of the Central Transantarctic Mountains". Paleontological Society Memoir. 45: 1–28.
  6. 1 2 3 4 Popock, K.J. (1970). "The Emuellidae, a new family of trilobites from the Lower Cambrian of South Australia". Palaeontology. 13: 522–562.
  7. ↑ Moore, P.S. (1979). "Stratigraphy and depositional environments of the Billy Creek Formation (Cambrian), central and northern Flinders Range, South Australia". Transactions of the Royal Society of South Australia. 103: 197–211.
  8. ↑ Moore, P.S. (1980). "Stratigraphy and depositional environments of the Billy Creek Formation (Cambrian), east of the Flinders Range, South Australia". Transactions of the Royal Society of South Australia. 104: 117–132.

Further reading

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