Labechiida Temporal range: Possible reports as young as the Triassic | |
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Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Porifera |
Class: | † Stromatoporoidea |
Order: | † Labechiida Kühn, 1927 |
Labechiida is an extinct order of stromatoporoid sponges. They lived from the Early Ordovician (Floian stage) [1] to the Late Devonian (Famennian stage), [2] though a few putative fossils have been reported from younger sediments. [3] [4] Labechiids were the first order of stromatoporoids to appear and were probably ancestral to all other orders in the main Paleozoic radiation (Stromatoporoidea sensu stricto). [2] They were most diverse and abundant during the Middle-Late Ordovician and the Famennian, when they were a major group of reef-building sponges. However, they were relatively uncommon through most of the Silurian and Devonian, in contrast to other stromatoporoids. [5]
Labechiids can be differentiated from other stromatoporoids by having an internal structure emphasizing cysts (pockets roofed by flat or convex cyst plates) and pillars (solid rods perpendicular to the surface). [2] [6] [7] The pillars may extend all the way to the surface and project out a short distance as small bumps known as papillae. Cyst plates may bear denticles (pointed thorns) or crenulations (pinched deflections) pointing upwards within the skeleton. Laminae (regular horizontal plates) are comparatively difficult to distinguish due to the more unorganized internal structure of labechiids compared to other stromatoporoids.
Mamelons are found in some species, while astrorhizae are indistinct or absent. Many labechiid fossils are poorly preserved, as their emphasis on cysts affords a lower skeletal density than other stromatoporoids. As a result, some traits used to distinguishing between taxa (such as pillar microstructure) may instead be taphonomic rather than biological in origin. [2]
From The Treatise on Invertebrate Paleontology (Part E, Revised): [2]
The earliest reported labechiid species is Cystostroma primordia , from the Floian stage (Early Ordovician) of South China. [1] This species was rare and small, but massive reefs appeared simultaneously worldwide in the mid- to upper-Darriwilian stage, near the end of the Middle Ordovician (~460 Ma). [9] During the Darriwilian, 4 genera occur in the Chazy Group of eastern North America, 9 in the Machiakou Formation of North China, and several others are dispersed among Russia, Kazakhstan, Korea, and Malaysia. [5] Most specialists agree that the ancestral labechiid was a member of the family Rosenellidae, but disagreement persists over which genus serves as the ancestral form. Studies focusing on North America and China generally consider the widespread Pseudostylodictyon [9] or Cystostroma [1] to be ancestral to other labechiids, while Russian paleontologists point to the Siberian Priscastroma . [9] [10] Labechiids as a whole may be descended from non-stromatoporoid sponges in the order Pulchrilaminida. [9] [11]
In the Sandbian stage of the Late Ordovician, labechiids spread to regions equivalent to Scotland and Australia, and some former Chinese endemics (such as the tree-shaped aulaceratids) populated Laurentia (North America) for the first time. [5] During the Katian stage, labechiids reached their maximum diversity and were abundant in tropical reef ecosystems worldwide. They were significantly less common in temperate areas corresponding to Central Asia. [5] Most Late Ordovician labechiid genera were cosmopolitan, while endemics were few. Global cooling in the first pulse of the Late Ordovician mass extinction (~445 Ma) led to the extinction of the short-lived family Stromatoceriidae, and Hirnantian-age stromatoporoid fossils are limited to only a few localities in Canada and Northern Europe. [5] Only two labechiids ( Aulacera and Pachystylostroma ) retain any semblance of commonness during the extinction interval. [5]
Labechiids which survived into the Llandovery Epoch (early Silurian) were inconspicuous relative to other diversifying stromatoporoid orders such as clathrodictyids and actinostromatids. South China and Siberia were notable exceptions where labechiids temporarily remained the most diverse group of stromatoporoids. [5] Even as stromatoporoids collectively reached their maximum Silurian diversity in the Wenlock Epoch (middle Silurian), labechiids were not among the beneficiaries. [5] Labechiids were still rare in the Ludlow and Pridoli epochs (late Silurian), though the typical Ordovician genus Lophiostroma made an unexpected recovery in Baltica (Eastern Europe) and Turkey. [5]
No unambiguously new labechiid genera evolved through the entire Early and Middle Devonian, nor the Frasnian stage (the first part of the Late Devonian). Labechiid fossil occurrences during this time were spotty and consist entirely of hardy relicts which purportedly originated in the Ordovician. [5] Stromatoporoid specialists have mixed interpretations of this phenomenon. The Devonian relicts may truly be the same as their Ordovician predecessors, persisting as rare and reclusive ‘Lazarus taxa’. Alternatively, they could be misidentified fragments or new labechiid lineages acquiring a similar set of characteristics, so-called ‘Elvis taxa’. [12] In any case, Devonian labechiids never managed to repopulate southeast Laurussia (eastern North America) or high-latitude environments at any time during the period. [5]
Unlike other stromatoporoids, labechiids were not adversely affected by the Kellwasser event (Late Devonian mass extinction) at the end of the Frasnian (~372 Ma). Instead, they experienced a diversification in the Famennian stage, reacquiring a level of diversity and dominance in their niche not experienced since the Ordovician. [5] Most new genera arose from the families Stylostromatidae and Platiferostromatidae, which helped to form dense reef habitats alongside the older relict forms. [12] The labechiid resurgence was strongest in shallow water and the Eastern Hemisphere. [12] [5]
Despite being reinvigorated after the Kellwasser event, labechiids and their reef ecosystems presumably did not survive the Hangenberg event (~359 Ma), a second mass extinction which marked the end of the Famennian stage and Devonian period. [11] This extinction is generally considered absolute, but several possible exceptions have been reported to imply post-Devonian survival: Labechia carbonaria (from the Viséan stage of Carboniferous England) [3] and Lophiostroma boletiformis (from Triassic rocks of the Pamir Mountains). [2] These discontinuous reports pose the same set of questions applied to Early and Middle Devonian occurrences. [12] Labechiid-like fossils are abundant in early Pennsylvanian (Bashkirian) reef deposits of the Akiyoshi Limestone Group in Japan, representing a Panthalassan seamount. [4]
The Devonian is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.3 million years from the end of the preceding Silurian period at 419.2 million years ago (Ma), to the beginning of the succeeding Carboniferous period at 358.9 Ma. It is named after Devon, South West England, where rocks from this period were first studied.
The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period 485.4 Ma to the start of the Silurian Period 443.8 Ma.
The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago (Mya), to the beginning of the Devonian Period, 419.2 Mya. The Silurian is the shortest period of the Paleozoic Era. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by a few million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera were wiped out.
Archaeocyatha is a taxon of extinct, sessile, reef-building marine sponges that lived in warm tropical and subtropical waters during the Cambrian Period. It is believed that the centre of the Archaeocyatha origin is now located in East Siberia, where they are first known from the beginning of the Tommotian Age of the Cambrian, 525 million years ago (mya). In other regions of the world, they appeared much later, during the Atdabanian, and quickly diversified into over a hundred families.
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Discosorida are an order of cephalopods that lived from the beginning of the Middle Ordovician, through the Silurian, and into the Devonian. Discosorids are unique in the structure and formation of the siphuncle, the tube that runs through and connects the camerae (chambers) in cephalopods, which unlike those in other orders is zoned longitudinally along the segments rather than laterally. Siphuncle structure indicated that the Discosorida evolved directly from the Plectronoceratida rather than through the more developed Ellesmerocerida, as did the other orders. Finally and most diagnostic, discosorids developed a reinforcing, grommet-like structure in the septal opening of the siphuncle known as the bullette, formed by a thickening of the connecting ring as it draped around the folded back septal neck.
Lituitida is an order of orthoceratoid cephalopods. They correspond to the family Lituitidae of the Treatise, reranked as an order and combined with other orthoceratoids. They are considered to be more closely related to the Orthocerida than to the Ascocerida or Pseudorthocerida which are also included.
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Reticulosa is an extinct order of sea sponges in the class Hexactinellida and the subclass Amphidiscophora. Reticulosans were diverse in shape and size, similar to their modern relatives, the amphidiscosidans. Some were smooth and attached to a surface at a flat point, others were polyhedral or ornamented with nodes, many were covered in bristles, and a few were even suspended above the seabed by a rope-like anchor of braided glass spicules.
Trimerellida is an extinct order of craniate brachiopods, containing the sole superfamily Trimerelloidea and the families Adensuidae, Trimerellidae, and Ussuniidae. Trimerellidae was a widespread family of warm-water brachiopods ranging from the Middle Ordovician to the late Silurian (Ludlow). Adensuidae and Ussuniidae are monogeneric families restricted to the Ordovician of Kazakhstan. Most individuals were free-living, though some clustered into large congregations similar to modern oyster reefs.
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Olev Vinn is an Estonian paleobiologist and paleontologist.
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