Hubbry Logo
BactritidaBactritidaMain
Open search
Bactritida
Community hub
Bactritida
logo
8 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Bactritida
Bactritida
Bactritida
View on Wikipedia
from Wikipedia

Bactritida
Temporal range: 407–231 Ma Pragian (questionable) or early Emsian – Middle Carnian
Possible descendant taxon Coleoidea survives to present
Diagram showing evolution of Bactritida to Ammonoidea
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Clade: Neocephalopoda
Subclass: †Bactritoidea
Shimanskiy, 1951
Order: †Bactritida
Shimanskiy, 1951
Families[1]

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

[edit]

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

[edit]

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

[edit]

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

[edit]

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

[edit]

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.

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Bactritida

View on Grokipedia
from Grokipedia
Bactritida is an extinct order of cephalopods characterized by orthoconic (straight-conical) shells with a small, marginal ventral siphuncle positioned close to the shell wall, typically comprising 9–16% of the conch diameter, and straight sutures featuring a shallow V-shaped ventral lobe. These features distinguish them as an intermediate form between orthocerid nautiloids and more derived ammonoids, with subcircular to ovate shell cross-sections and sinuous growth lines indicating a nektobenthic or planktonic lifestyle involving vertical migration and low-cost buoyancy regulation. The order first appeared in the fossil record during the Late Silurian to (approximately 428–419 million years ago), with the earliest confirmed occurrences in the Lochkovian stage of the , and persisted through the and eras until the Late Triassic (around 216 million years ago). Systematically placed within the subclass Nautiloidea or as a stem group to and , Bactritida played a pivotal role in cephalopod evolution, giving rise to coiled ammonoids in the and contributing to the diversification of advanced s with improved hydrostatic control. Fossils of Bactritida, dominated by genera such as Bactrites, are primarily known from marine deposits in , , and recently , with soft-tissue attachments like muscle scars preserved in some specimens from the Emsian to Givetian stages, revealing details of their and locomotion. Their discovery in the Argentine Precordillera has expanded understanding of their paleobiogeographic distribution within the Malvinokaffric Realm and refined biostratigraphic correlations for rocks.

Taxonomy

Higher classification

Bactritida is an extinct order of cephalopods classified within the kingdom Animalia, phylum , class , and clade Neocephalopoda. It belongs to the subclass Bactritoidea (Shimanskiy, 1951) and order Bactritida (Shimanskiy, 1951), both named by Soviet paleontologist V. P. Shimanskiy. Shimanskiy introduced the order Bactritida in 1951 to describe early s exhibiting transitional shell features between straight-shelled nautiloids and coiled ammonoids, positioning them as a key link in cephalopod evolution. The status of subclass Bactritoidea remains debated among paleontologists; while traditionally recognized as a distinct subclass, some analyses suggest it better represents a stem group ancestral to both and , based on phylogenetic reconstructions of early divergence.

Families and genera

The order Bactritida encompasses two recognized families: Bactritidae and Parabactritidae. The Bactritidae, established by in 1884, comprise the more diverse and longer-ranging family within the order, featuring long orthoconic to slightly cyrtoconic shells with a small apical angle typically less than 10 degrees and orthochoanitic septal necks. This family includes approximately eight key genera, among them the Bactrites Sandberger, 1843 (ranging from the Lower Lochkovian to Upper Permian, characterized by orthoconic longiconic , a small marginal 9–16% of conch diameter, and straight sutures with a V-shaped ventral lobe), Lobobactrites, Devonobactrites Shimansky, (Emsian , with oblique septa and sub-marginal siphuncle), Ctenobactrites Shimansky, 1951, Cyrtobactrites Erben, 1960, Dillerites, Bactritella, and Hemibactrites. The Parabactritidae, named by Shimansky in 1951, are distinguished by shorter orthoconic or breviconic shells with a larger apical angle exceeding 10 degrees, and are considered transitional forms potentially linked to belemnoid evolution. This family encompasses about five genera, including Parabactrites, Microbactrites ( to ), Aktastioceras Shimansky, 1948 (Early Permian Asselian, with longiconic orthocones, ~9° expansion angle, circular to laterally compressed cross-section, fine transverse lirae, and dorsal orthochoanitic ), Belemnitomimus, and Tabantaloceras. Overall, Bactritida exhibits a total diversity of approximately 13 genera across these families, with Bactritidae demonstrating greater and a broader stratigraphic distribution from the to Permian, while Parabactritidae are more restricted in extent.

Morphology

Shell characteristics

The shells of Bactritida are predominantly orthoconic, featuring a straight, conical phragmocone that extends into a longiconic living chamber, though some genera exhibit slight cyrtoconic . These forms typically measure 10-15 cm in total length, with maximum diameters of 7-8 mm, and possess a subcircular to faintly compressed cross-section that varies ontogenetically. The apical angle is low, ranging from 2° to 5° depending on the family and species, contributing to their elongate profile. The protoconch, or embryonic shell, is small and globular to ovate, with diameters of 0.5-1 mm and a smooth surface, as seen in genera such as Bactrites and Devonobactrites. This compact initial chamber suggests development from small eggs, likely enabling high with numerous offspring per reproductive event. External ornamentation is generally subtle, dominated by fine transverse growth lines that form sinuous patterns, including a ventral hyponomic sinus and dorsal lobe, as observed in Bactrites gracilis. Occasional faint longitudinal or lirae appear on the flanks, with densities up to 30 per 5 mm in some specimens, and rare annular elevations or bands may mark the body chamber base. Compared to shells, Bactritida exhibit a transitional morphology with reduced coiling relative to certain ancestral forms, maintaining an essentially straight that bridges orthoconic nautiloids and the coiled shells of derived ammonoids.

Internal features

The internal structures of Bactritida, particularly the and , exhibit diagnostic features that distinguish them from other Paleozoic cephalopods. The are simple and generally spherical to dome-shaped, with orthochoanitic necks directed forward toward the . These form sutures characterized by V-shaped ventral lobes of varying depth and width, paired with shallow dorsal saddles or lobes, contributing to a slightly tilted dorsal orientation in some specimens. The , a tubular strand connecting the chambers, occupies a marginal ventral position in close proximity to the shell wall, unlike the more central placement typical of nautiloids; this ventral positioning serves as a key synapomorphy linking Bactritida to early ammonoids. It is narrow, with a typically comprising 9–16% of the , and lacks extensive deposits. Preserved soft-tissue attachments, including muscle scars, are known from some Emsian to Givetian specimens. These reveal details such as paired retractor muscles and hyponome attachments, indicating a nektobenthic with capabilities for . The phragmocone is divided into numerous short camerae by the , with cameral ratios (phragmocone to chamber length) ranging from 0.7 to 2.6, indicating relatively compact subdivisions. The body chamber, housing the soft tissues, typically occupies about one-third to one-half of the total shell length, often around 40% in preserved specimens.

Evolutionary history

Origin and derivation

The Bactritida are widely regarded as having originated from orthocerid nautiloids, a diverse order of straight-shelled cephalopods that proliferated during the period. The proposed ancestral lineage traces back to forms exhibiting transitional shell and features, with the earliest potential representative being Bactroceras from the Middle , dated to approximately 460 million years ago. This genus, characterized by a straight orthoconic shell and subcentral , has been suggested as a precursor due to superficial morphological similarities to later bactritids, such as the position and structure of early growth stages. However, a significant stratigraphic gap of about 40–45 million years separates these candidates from the earliest confirmed bactritid records in the Lochkovian stage, approximately 415 million years ago. This hiatus has fueled ongoing debate regarding whether Bactroceras (sometimes synonymized with Eobactrites) represents a true bactritid ancestor or merely a homeomorph—a convergent form with analogous shell traits but distinct phylogenetic affinities within the . Morphological analyses, including differences in protoconch shape and positioning, support the homeomorph interpretation, indicating that Bactroceras lacks the defining ventral marginal of undisputed bactritids. The early evolution of Bactritida is marked by a key transition in siphuncle position, shifting from the subcentral or eccentric placement typical of orthocerids to a distinctly ventral marginal location, which likely facilitated improved control and . Possible precursors, such as forms akin to Eobactrites, have been proposed to bridge this gap, with tentative records from the Late (e.g., single specimens) suggesting an intermediate stage in this migration, though these remain controversial and poorly preserved. Recent discoveries of confirmed Pragian (and Lochkovian) specimens around 410–409 million years ago from the Talacasto Formation in slightly narrow the temporal discontinuity and provide evidence of an earlier diversification phase.

Relationships to other groups

Bactritida is widely regarded as a stem group to both and , serving as a pivotal transitional in during the to periods. This position is supported by morphological evidence, including the shift of the to a ventral position, which facilitated more efficient and control compared to the central siphuncle of ancestral orthocerids. This innovation likely enabled the rapid diversification of descendant lineages by allowing for greater adaptability in shell coiling and locomotion. Within Bactritida, the family Bactritidae exhibits traits closely aligned with early ammonoids, such as straight or slightly curved orthoconic shells and simple sutures, suggesting it as a direct ancestral group to , with the transition documented in strata. Similarly, the subfamily Parabactritinae, or Parabactritidae in some classifications, shares features like reduced shell thickness and internal calcification patterns with early belemnoids, indicating a potential lineage leading to within during the . These connections highlight Bactritida's role in bridging nautiloid-like ancestors to the more dynamic, coiled-shell forms of ammonites and soft-bodied coleoids like squids and octopuses. Phylogenetic analyses have sparked debate over whether Bactritida represents a monophyletic or a paraphyletic assemblage. Cladistic studies, incorporating shell morphology, siphuncle position, and protoconch structure, often position Bactritida as a monophyletic to the + , emphasizing shared synapomorphies like the ventral . However, alternative views propose or even , arguing that some bactritid families may independently derive from orthocerids without forming a cohesive group, based on inconsistencies in septal and soft-tissue attachments. These debates underscore the challenges in resolving early phylogeny due to limited preservation. Bactritida persisted through the Permian-Triassic mass extinction event around 252 million years ago, with records extending into the , but underwent significant decline thereafter, likely due to competition from more specialized ammonoid and coleoid descendants. Surviving traits, such as the ventral and flexible shell architecture, influenced the evolutionary success of modern cephalopods by promoting innovations in mobility and predation avoidance. This endurance highlights Bactritida's foundational impact on the diversification of Neocoleoidea.

Stratigraphy and distribution

Temporal range

The Bactritida first appeared during the Late Silurian or , with the earliest confirmed records from the Lochkovian stage (approximately 419–411 million years ago), although questionable occurrences have been reported from the Late Silurian and possibly earlier in the with forms like Eobactrites. The order persisted through the and into the , with the youngest confirmed fossils dating to the stage of the (around 237–227 million years ago). Bactritida diversity peaked during the and , with multiple genera documented, before declining through the Permian. The group survived the Late Devonian extinction event near the Frasnian-Famennian boundary but was severely impacted by the Permian-Triassic mass extinction at 252 million years ago, leading to low diversity in the aftermath; a brief recovery occurred in the before final extinction in the , possibly linked to the . Due to their stratigraphic consistency, Bactritida serve as valuable index fossils for correlating and marine strata, particularly in regions like and where they co-occur with ammonoids and orthocerids.

Paleobiogeography

Bactritida exhibited a during the , with fossil records documented across major paleocontinents including in (e.g., ), in (e.g., ), and in regions such as , , , and . This broad spread is evidenced by species like Bactrites gracilis, which appears in both Laurasian and Gondwanan assemblages. The group's migration patterns during the were facilitated by oceanic connections, particularly the , which linked Gondwanan and Laurasian realms and enabled faunal exchange. In the , records indicate a more restricted presence, largely confined to equatorial and tropical zones, reflecting environmental constraints following the Permian-Triassic mass extinction. Diversity hotspots for Bactritida were concentrated in the Old World tropics, such as and , where multiple genera including Devonobactrites and Bactrites are well-represented in marine deposits. In contrast, occurrences in polar or high-latitude areas were notably scarce, with no significant assemblages reported from such regions. A pivotal recent development occurred in 2017 with the discovery of bactritids in the Talacasto Formation of west-central , marking the first South American records and including Bactrites gracilis and Devonobactrites? sp. from the Lochkovian–Emsian stages. These findings from the Precordillera Basin confirmed a Gondwanan presence, countering earlier biases toward Laurasian-dominated distributions and underscoring the group's wider global reach.

Paleoecology

Buoyancy and orientation

The ventral in Bactritida, positioned marginally along the external shell wall, facilitated efficient management of gas and fluid within the phragmocone chambers, enabling the organism to achieve and maintain critical for a nektonic . This structure allowed for the removal of cameral liquid through and active , replacing it with gas to balance the weight of the body and shell. The small diameter of the (typically 9–16% of conch width) and absence of significant cameral or siphuncular deposits minimized the energy required for these adjustments, reflecting an suited to relatively stable positions. Bactritida exhibited a predominantly vertical orientation in the water, with the facing slightly oblique downward and the head positioned ventrally, aligning the centers of and along the orthoconic shell axis for hydrostatic stability. The ventral siphuncle's proximity to the shell wall further supported this posture by limiting rotational during fluid exchanges, preventing significant tilting of the . Muscle attachment scars on the internal shell surface indicate soft-tissue arrangements that reinforced this vertical alignment, distinguishing Bactritida from more passively buoyant orthocerids. Locomotion in Bactritida was likely limited, with the organisms functioning as weak swimmers that employed via the hyponome only sparingly for vertical adjustments or short bursts of movement. The shell's slender, straight morphology and —concentrated toward the apex—provided inherent stability, reducing the need for constant and allowing passive orientation in currents. evidence of muscle scars supports a nektonic habit capable of some active maneuvering, though far less agile than later forms. Compared to nautiloids, whose central enabled slower, less responsive control suited to deeper or more stable habitats, the marginal ventral siphuncle of Bactritida offered more dynamic fluid management, foreshadowing the enhanced maneuverability and horizontal swimming capabilities that evolved in ammonoids through shell coiling. This transitional system in Bactritida bridged the passive stability of ancestral nautiloid-like forms to the predatory agility of ammonoids, as inferred from progressive shifts in aperture orientation across their phylogeny.

Lifestyle and predation

Bactritida exhibited an active nektonic , inferred from the morphology of soft-tissue attachment scars on their shells, which indicate enhanced musculature for swimming compared to the more passive, planktonic habits of orthocerid ancestors. This adaptation positioned them as mobile inhabitants of the , facilitating interactions within marine ecosystems during the Early and Middle . Their habitat encompassed offshore, deep-subtidal marine settings, including dysaerobic sequences below the storm wave base, as evidenced by occurrences in formations such as the Wissenbacher Schiefer in and the Tafilalt region in . Although direct evidence of predatory is sparse, the active capabilities suggested by muscle scars imply that Bactritida functioned as mid-level carnivores, likely ambushing or pursuing small in a manner akin to other early s. Sublethal shell injuries on specimens, including potential bactritids, further highlight their vulnerability to larger predators, underscoring a dynamic role in trophic interactions. Reproduction in Bactritida involved the deposition of many small eggs, as indicated by their globular protoconch measuring 0.3–1.0 mm in diameter, which points to a high-fecundity, r-selection strategy with small hatchlings adapted for rapid dispersal in marine environments. Ecologically, Bactritida occupied an intermediate niche in food webs, bridging the planktonic orthocerids and the more specialized ammonoids and coleoids that followed, contributing to the diversification of nektonic cephalopods by the Emsian stage.

References

  1. https://www.cambridge.org/core/journals/journal-of-paleontology/article/first-report-of-devonian-bactritids-cephalopoda-from-south-america-paleobiogeographic-and-biostratigraphic-implications/91E502C6B1DB9B5132AB7D448EAFA852
  2. https://www.app.pan.pl/archive/published/app50/app50-329.pdf
  3. https://www.researchgate.net/publication/286124242_The_cephalopod_macrosystem_A_historical_review_the_present_state_of_knowledge_and_unsolved_problems_1_Major_features_and_overall_classification_of_cephalopod_mollusks
  4. https://www.mindat.org/taxon-P82323.html
  5. https://www.researchgate.net/publication/225773208_The_Cephalopod_Macrosystem_A_Historical_Review_the_Present_State_of_Knowledge_and_Unsolved_Problems_3_Classification_of_Bactritoidea_and_Ammonoidea
  6. https://www.museum.tohoku.ac.jp/pdf/press_info/bulletin/No14/bulletin_14_01.pdf
  7. https://pmc.ncbi.nlm.nih.gov/articles/PMC4786199/
  8. https://royalsocietypublishing.org/doi/10.1098/rsbl.2015.0877
  9. https://www.mindat.org/taxon-3246087.html
  10. https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=82322
  11. https://www.bagniliggia.it/WMSD/HtmFamily/BACTRITIDAE.htm
  12. https://www.bagniliggia.it/WMSD/HtmFamily/PARABACTRITIDAELS.htm
  13. https://www.researchgate.net/publication/288004388_Adolescent_Bactritoid_Orthoceroid_Ammonoid_and_Coleoid_shells_from_the_Upper_Carboniferous_and_Lower_Permian_of_the_South_Urals
  14. https://www.researchgate.net/publication/226349185_On_the_origin_of_bactritoids_Cephalopoda
  15. https://doi.org/10.1007/BF02990181
  16. https://link.springer.com/article/10.1007/BF02990181
  17. https://www.researchgate.net/publication/236901563_Review_of_Early_to_Mid_Ordovician_orthoconic_cephalopods_from_Iran
  18. https://www.researchgate.net/publication/242269620_Some_observations_on_bactritid_cephalopods
  19. https://doi.org/10.1038/s42003-019-0523-2
  20. https://doi.org/10.1007/978-94-017-9633-0_1
  21. https://doi.org/10.1007/s12542-013-0191-3
  22. https://link.springer.com/content/pdf/10.1007/BF02988810.pdf
  23. https://onlinelibrary.wiley.com/doi/10.1111/brv.12341
  24. https://fossil.15656.com/research-pages/bactrites/
  25. https://paleobiodb.org/classic/basicTaxonInfo?taxon_no=182264
  26. https://palaeo-electronica.org/content/2019/2521-cephalopod-hydrostatics
  27. http://app.pan.pl/acta49/app49-235.pdf
  28. https://www.researchgate.net/publication/241792570_Soft-tissue_attachments_in_orthocerid_and_bactritid_cephalopods_from_the_Early_and_Middle_Devonian_of_Germany_and_Morocco
  29. https://www.app.pan.pl/archive/published/app52/app52-749.pdf
Add your contribution
Related Hubs
User Avatar
No comments yet.