Bactritida

Bactritida; Temporal range: 407–231 Ma PreꞒ Ꞓ O S D C P T J K Pg N Pragian (questionable) or early Emsian – Middle Carnian ; Possible descendant taxon Coleoidea survives to present
	Diagram showing evolution of Bactritida to Ammonoidea
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Clade:	Neocephalopoda
Subclass:	† Bactritoidea ; Shimanskiy, 1951
Order:	† Bactritida ; Shimanskiy, 1951
Families
	† Bactritidae ; † Parabactritidae ; † Ammonoidea?; Coleoidea?; Bactritida incertae sedis † Cochleiferoceras ; † Cyclobactrites ; ;

Last updated December 31, 2023

The Bactritida are a small order of more or less straight-shelled (orthoconic) cephalopods that first appeared during the Emsian stage of the Devonian period (407 million years ago) with questionable origins in the Pragian stage before 409 million years ago, and persisted until the Carnian pluvial event in the upper middle Carnian stage of the Triassic period (231 million years ago). They are considered ancestors of the ammonoids, as well as of the coleoids (octopus, squid, cuttlefish, and the extinct belemnites).

Bactritids are distinguished from the more primitive nautiloids by the small size and globular shape of the protoconch, the so-called embryonic shell. Nautiloids have relatively large embryonic shells, and living species lay a few large eggs. In contrast, bactritids and ammonoids produced large numbers of small eggs, each housing a small embryonic shell.

Classification and description

Bactritida (Erben 1964) are characterized by orthoconic to cyrtoconic shells that may be long or short with a narrow siphuncle invariably in contact with the ventral wall and sutures uniformly with V-shaped ventral lobes. Septal necks are orthochoanitic to cyrtochoanitic, the apical angle may be small or large, and the protoconch is globular to egg-shaped. The Bactritida comprise two families, the Bactritidae and the Parabactritidae.

Bactritidae

The Bactritidae^[2] are characterized by long orthoconic to cyrtoconic shells with a small apical angle (less than 10°) and septal necks that are orthochoanitic. Chamber length is variable. The Bactritidae contain eight recognized genera. Bactrites has the longest range, from the Lower Devonian to the Upper Permian, and even possibly from the Silurian. The Bactritidae gave rise to the Ammonoidea in the Early Devonian starting with an early Bactrites and going with increasingly tight curvature from Lobobactrites to Cyrtobactrites, leading to the gyroconic Anetoceras of the Anarcestida (Ammonoidea).^[2]^[3]

Parabactritidae

The Parabactritidae^[2] are characterized by orthoconic and breviconic shells with a large apical angle (greater than about 10°) and septal necks that are vary from orthochoanitic or suborthochoanitic to cyrtochoanitic. The Parabactritidae contain some five described genera and are thought to have given rise to the Belemnoidea (Coleoidea).

Derivation

The Bactritida have their origin in the Orthocerida, nautiloid cephalopods that first appeared in the Ordovician.

Bactroceras (Eobactrites), an early middle-Ordovician cephalopod, is considered as a true bactritid by some paleontologists,^[2] because of its spherical apex and ventral siphuncle.^[4]

This view is challenged by more recent research. The shell of Bactroceras has important differences from those of true bactritids. For instance, the first chamber of Bactroceras resembles that of other Ordovician orthocerids, such as Archigeisonoceras and Hedstroemoceras: it is about 10 mm in diameter, and is short, forming a spherical cap. True bactritids more strongly resemble late Silurian and Devonian orthocerids, whose first chamber is only about 5 mm across. Moreover, a large stratigraphic gap of nearly 50 million years occurs between Bactroceras and the next orthocones with a spherical apex and ventral siphuncle.^[5]

Paleoecology and lifestyle

Bactritids, especially the Bactritidae, seem to have lived in a vertical orientation, head down, as probably did many of the Orthocerida such as Michelinoceras and Buttsoceras , or these forms without extensive internal ballast may simply have been more flexible in their vertical orientation than the well-ballasted bottom-dwellers such as the actinocerids and endocerids. The ventral siphuncle of the Bactritida would have facilitated chamber dewatering in either horizontal or vertical orientation or in between. A central siphuncle would have made horizontal or near-horizontal dewatering more difficult, though.^[4]^[3] Bactritids, like cephalopods in general, were probably active predators with tentacles of some sort. As with other externally shelled forms, they were probably not active swimmers in the sense of fish or squid. Rather, they were likely stalkers and ambush predators hiding among the seaweeds, snatching prey found below.

Related Research Articles

<span class="mw-page-title-main">Nautiloid</span> Extant subclass of cephalopods

Nautiloids are a group of marine cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living Nautilus and Allonautilus. Fossil nautiloids are diverse and speciose, with over 2,500 recorded species. They flourished during the early Paleozoic era, when they constituted the main predatory animals. Early in their evolution, nautiloids developed an extraordinary diversity of shell shapes, including coiled morphologies and giant straight-shelled forms (orthocones). Only a handful of rare coiled species, the nautiluses, survive to the present day.

Orthoceras is a genus of extinct nautiloid cephalopod restricted to Middle Ordovician-aged marine limestones of the Baltic States and Sweden. This genus is sometimes called Orthoceratites. Note it is sometimes misspelled as Orthocera, Orthocerus or Orthoceros.

Orthocerida, also known as the Michelinocerida, is an order of extinct orthoceratoid cephalopods that lived from the Early Ordovician possibly to the Late Triassic. A fossil found in the Caucasus suggests they may even have survived until the Early Cretaceous, and the Eocene fossil Antarcticeras is sometimes considered a descendant of the orthocerids although this is disputed. They were most common however from the Ordovician to the Devonian.

Neocephalopods are a group of cephalopod mollusks that include the coleoids and all extinct species that are more closely related to extant coleoids than to the nautilus. In cladistic terms, it is the total group of Coleoidea. In contrast, the palcephalopoda are defined as the sister group to the neocephalopoda.

Aulacocerida is an order of primitive coleoid cephalopods, possibly derived from michelinoceraitids (Orthocerida) early in the Devonian, which in turn gave rise to the Belemnites.

Boletzkyida is a primitive order of teuthid coleoid cephalopod: the boletzkyids are thought to be the earliest forms of coleoid cephalopods, and appear to form a link between nautiloid orthocerids and more advanced coleoids. Boletzkyida was named and described by Bandel, Reitner, and Sturmer in 1983 (B.R.&S) from specimens found in the Lower Devonian black slate in Germany.

<span class="mw-page-title-main">Oncocerida</span> Extinct order of nautiloids

The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian, in which the connecting rings are thin and siphuncle segments are variably expanded. At present the order consists of some 16 families, a few of which, such as the Oncoceratidae, Brevicoceratidae, and Acleistoceratidae contain a fair number of genera each while others like the Trimeroceratidae and Archiacoceratidae are represented by only two or three.

The Ellesmeroceratidae constitute a family within the cephalopod order Ellesmerocerida. They lived from the Upper Cambrian to the Lower Ordovician. They are characterized by straight and endogastric shells, often laterally compressed, so the dorso-ventral dimension is slightly greater than the lateral, with close spaced sutures having shallow lateral lobes and a generally large tubular ventro-marginal siphuncle with concave segments and irregularly spaced diaphragms. Connecting rings are thick and layered, externally straight but thickening inwardly with the maximum near the middle of the segment so as to leave concave depressions on internal siphuncle molds. Septal necks are typically orthochoanitic but vary in length from almost absent (achoanitic) to reaching halfway to the previous septum (hemichoanitic) and may even slope inwardly (loxochoanitic).

Pseudorthocerida is an order of generally straight longiconic orthoceratoids with a subcentral to marginal cyrtochoanitic siphuncle composed of variably expanded segments which may contain internal deposits that may develop into a continuous parietal lining.. Cameral deposits are common and concentrated ventrally. Apices typically have a slight to moderate exogastric curvature

Osbornoceras is a genus of Lower Silurian cyrtoconic nautiloid cephalopods known from Ohio and possibly Manitoba, one of five general currently included in the oncocerid family Karoceratidae.

Bactroceras is a genus of orthoceratoid cephalopods that lived during the early Middle Ordovician, from about 472—464 mya, existing for approximately 8 million years.

Baltoceratidae is an extinct family of orthoconic cephalopods belonging to the subclass Nautiloidea endemic to what would be Asia, Australia, Europe, North America, and South America during the Ordovician living from about 480–460 mya, existing for approximately 20 million years.

Geisonoceratidae is an extinct family of orthoceroid cephalopods endemic to what would be Asia, Europe, and North America from the Middle Ordovician to the Middle Devonian living from about 470—380 mya, existing for approximately 90 million years. With the possible addition of an Early Cretaceous orthocerid from the western Caucasus the range of this group increases dramatically to some 350 million years, thus making it one of the longest lived families of the Nautiloidea.

Parasphaerorthoceras is an extinct orthocerid genus, a nautiloid cephalopod, that lived in what would be Europe and north Africa during the Silurian from 422.9 to 418.1 mya, having existed for approximately 4.8 million years.

Sactoceras is an extinct nautiloid cephalopod that lived during the Ordovician and Silurian in what would become North America, Europe, and Asia.

Orthoceratoidea is a major subclass of nautiloid cephalopods. Members of this subclass usually have orthoconic (straight) to slightly cyrtoconic (curved) shells, and central to subcentral siphuncles which may bear internal deposits. Orthoceratoids are also characterized by dorsomyarian muscle scars, extensive cameral deposits, and calciosiphonate connecting rings with a porous and calcitic inner layer.

Oncoceratidae is a family of nauatiloid cephalopods in the order Oncocerida established by Hyatt, 1884, that range from the Middle Ordovician to the Upper Silurian.

Wutinoceras is a genus of now extinct nautiloid cephalopods of the Wutinoceratidae family. It exhibits orthoconic actinocerids with ventral siphuncles composed of broadly expanded segments.

Temperoceras is a genus of orthoconic nautiloid cephalopods that lived in what is now north Africa, Europe, and Asia during the early Paleozoic. It was named by I. V. Barskov in 1960.

Dolorthoceras is a nautiloid cephalopod from the upper Paleozoic found in Lower Devonian to Lower Permian strata in North America, Europe, Asia, and Australia.

References

↑ "†order Bactritida Shimanskiy 1951 (mollusk)" (html). Fossilworks. Retrieved 17 December 2021.
1 2 3 4 Erben H.K. 1964; Bactritoidea, in the Treatise on Invertebrate Paleontology Vol K Nautiloidea, K491 –, Teichert, C and Moore R.C. Eds, GSA and Univ Kansas Press. 1964)
1 2 Klug, C. and Korn, D. 2004. The origin of ammonoid locomotion. Acta Palaeontologica Polonica 49 (2): 235–242
1 2 Holland, Charles H. (2003). "Some observations on bactritid cephalopods" (PDF). Bulletin of Geosciences. 78 (4): 369–372. ISSN 1214-1119.
↑ Kröger, B.; Mapes, R. H. (2007). "On the origin of bactritoids (Cephalopoda)". Paläontologische Zeitschrift. 81 (3): 316–327. doi:10.1007/BF02990181. S2CID 129091196.

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[Fossilworks-1] "†order Bactritida Shimanskiy 1951 (mollusk)" (html). Fossilworks. Retrieved 17 December 2021.

[erb-2] 1 2 3 4 Erben H.K. 1964; Bactritoidea, in the Treatise on Invertebrate Paleontology Vol K Nautiloidea, K491 –, Teichert, C and Moore R.C. Eds, GSA and Univ Kansas Press. 1964)

[klug-3] 1 2 Klug, C. and Korn, D. 2004. The origin of ammonoid locomotion. Acta Palaeontologica Polonica 49 (2): 235–242

[Holland_2003-4] 1 2 Holland, Charles H. (2003). "Some observations on bactritid cephalopods" (PDF). Bulletin of Geosciences. 78 (4): 369–372. ISSN 1214-1119.

[Kroger_&_Mapes_2007-5] Kröger, B.; Mapes, R. H. (2007). "On the origin of bactritoids (Cephalopoda)". Paläontologische Zeitschrift. 81 (3): 316–327. doi:10.1007/BF02990181. S2CID 129091196.

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