''Baculites'' is an extinct genus of heteromorph

ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

s with almost straight shells. The genus, which lived worldwide throughout most of the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

, and which briefly survived the K-Pg mass extinction event, was named by

Lamarck Jean-Baptiste Pierre Antoine de Monet, chevalier de Lamarck (1 August 1744 – 18 December 1829), often known simply as Lamarck (; ), was a French naturalist, biologist, academic, and soldier. He was an early proponent of the idea that biolo ...

in 1799.

Shell anatomy

The adult shell of ''Baculites'' is generally straight and may be either smooth or with sinuous striae or ribbing that typically slant dorso-ventrally forward. The aperture likewise slopes to the front and has a sinuous margin. The venter is narrowly rounded to acute while the dorsum is more broad. The juvenile shell, found at the apex, is coiled in one or two whorls and described as minute, about in diameter. Adult ''Baculites'' ranged in size from about (''Baculites larsoni'') up to in length. As with other

ammonites Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

, the shell consisted of a series of camerae, or chambers, that were connected to the animal by a narrow tube called a siphuncle by which gas content and thereby buoyancy could be regulated in the same manner as ''

Nautilus A nautilus (; ) is any of the various species within the cephalopod family Nautilidae. This is the sole extant family of the superfamily Nautilaceae and the suborder Nautilina. It comprises nine living species in two genera, the type genus, ty ...

'' does today. The chambers are separated by walls called septa. The line where each septum meets the outer shell is called the suture or suture line. Like other true

, ''Baculites'' have intricate suture patterns on their shells that can be used to identify different species. One notable feature about ''Baculites'' is that the males may have been a third to a half the size of the females and may have had much lighter ribbing on the surface of the shell.

Orientation

The shell morphology of ''Baculites'' with slanted striations or ribbing, similarly slanted aperture, and more narrowly rounded to acute keel-like venter points to its having had a horizontal orientation in life as an adult. This same type of cross section is found in much earlier

nautiloids Nautiloids are a group of cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and species rich, with over 2,500 recorded species. Th ...

such as '' Bassleroceras'' and '' Clitendoceras'' from the

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

period, which can be shown to have had a horizontal orientation. In spite of this, some researchers have concluded that Baculites lived in a vertical orientation, head hanging straight down, since lacking an apical counterweight, movement was largely restricted to that direction. More recent research, notably by Gerd Westermann, has reaffirmed that at least some ''Baculites'' species in fact lived in a more or less horizontal orientation.

Ecology

From shell isotope studies, it is thought that ''Baculites'' inhabited the middle part of the water column, not too close to either the bottom or surface of the ocean. In some rock deposits ''Baculites'' are common, and they are thought to have lived in great shoals. However, they are not known to occur so densely as to be rock-forming, as do certain other extinct, straight-shelled cephalopods (e.g.,

orthocerid Orthocerida, from Ancient Greek ὀρθός (''orthós''), meaning "straight", and κέρας (''kéras''), meaning "horn", also known as the Michelinocerida, is an order of extinct orthoceratoid cephalopods that lived from the Early Ordovician ...

nautiloid Nautiloids are a group of cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and species rich, with over 2,500 recorded species. Th ...

s). Studies on exceptionally preserved specimens have revealed a

radula The radula (; : radulae or radulas) is an anatomical structure used by mollusks for feeding, sometimes compared to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters ...

synchrotron A synchrotron is a particular type of cyclic particle accelerator, descended from the cyclotron, in which the accelerating particle beam travels around a fixed closed-loop path. The strength of the magnetic field which bends the particle beam i ...

imagery. The results suggest that ''Baculites'' fed on pelagic

zooplankton Zooplankton are the heterotrophic component of the planktonic community (the " zoo-" prefix comes from ), having to consume other organisms to thrive. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequent ...

(as suggested by remains of a larval

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

and a pelagic

isopod Isopoda is an Order (biology), order of crustaceans. Members of this group are called isopods and include both Aquatic animal, aquatic species and Terrestrial animal, terrestrial species such as woodlice. All have rigid, segmented exoskeletons ...

inside the mouth).

Convergent evolution

''Baculites'' and related

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

straight

cephalopods are often confused with the superficially similar

cephalopods. Both are long and tubular in form, and both are common items for sale in rock shops (often under each other's names). Both lineages evidently evolved the tubular form independently, and at different times in earth history. The

s mostly lived much earlier (common during the

Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...

Era, possibly going extinct in the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

) than ''Baculites'' (Late

Danian The Danian is the oldest age or lowest stage of the Paleocene Epoch or Series, of the Paleogene Period or System, and of the Cenozoic Era or Erathem. The beginning of the Danian (and the end of the preceding Maastrichtian) is at the Cretac ...

only). The two types of fossils can be distinguished by many features, most obvious among which is the suture line: it is simple in orthocerid nautiloids and intricately folded in ''Baculites'' and related ammonoids.

Species distribution

Cenomanian: ''Baculites gracilis'' is known from the Cenomanian Britton Formation. Turonian: ''Baculites undulatus'', from the upper Turonian of Europe. Campanian: The lower part of the Campanian stage (Upper Cretaceous) in the Western Interior of North America has yielded ''Baculites gilberti'', early ''B. perplexus'', ''B. asperiformis'', ''B. maclearni'', and ''B. obtusus'', followed temporally by late ''Baculites perplexus'' and then by ''Baculites scotti''. The upper part of the upper Campanian has yielded, from older to younger, ''B. compressus'', ''B. coneatus'', ''B. reesidei''. ''B. jenseni'', and ''B. ellasi'', followed sequentially in the lower Maastrictian by ''Baculites baculus'', ''B. grandis'', and ''B. clinolobatis''. ''Baculites pacificum'' is known from the Campanian of Vancouver Island, British Columbia, and ''Baculites leopoliensis'' from the Upper Campanian of Europe. Maastrichtian/Danian: The type species, ''Baculites vertebralis'' is from the upper Maastrichtian and Danian, and is one of the very last species of ammonites. Findings in Denmark and the Netherlands suggest the species survived the K-Pg mass extinction event, albeit being restricted to the

. ''Baculites anceps'' is also known from Europe, although only from the Upper Maastrichtian. Baculites ovatus Say1820 holotype

''Baculites ovatus'' is known from the Maastrichtian deposits of

Ripley Formation The Ripley Formation is a geological formation in North America found in the U.S. states of Alabama, Georgia, Mississippi, Missouri, and Tennessee. The lithology is consistent throughout the layer. It consists mainly of glauconitic sandstone. It ...

in McNairy County, Tennessee, and Severn Formation in

Prince George's County, Maryland Prince George's County (often shortened to PG County or PG) is located in the U.S. state of Maryland bordering the eastern portion of Washington, D.C. As of the 2020 United States census, 2020 U.S. census, the population was 967,201, making it ...

Cultural significance

''Baculites'' fossils are very brittle and almost always break. They are most commonly found broken in half or several pieces, usually along suture lines. Individual chambers found this way are sometimes referred to as "stone buffaloes" (due to their shapes), though the Native-American attribution typically given as part of the story behind the name is likely apocryphal. The Blackfoot have oral traditions that tell a story of the Iniskimm (Buffalo Calling Stone). They are still in use today by Indigenous peoples. ''Baculites ovatus'', the first species of ''Baculites'' described in the Americas, was described by

Thomas Say Thomas Say (June 27, 1787 – October 10, 1834) was an American entomologist, conchologist, and Herpetology, herpetologist. His studies of insects and shells, numerous contributions to scientific journals, and scientific expeditions to Florida, Ge ...

in 1820 from a single specimen from the Navesink Formation in

Atlantic Highlands, New Jersey Atlantic Highlands is a borough in Monmouth County in the U.S. state of New Jersey, in the Bayshore Region. As of the 2020 United States census, the borough's population was 4,414, an increase of 29 (+0.7%) from the 2010 census count of 4,38 ...

. The specimen was later illustrated by

Samuel George Morton Samuel George Morton (January 26, 1799 – May 15, 1851) was an American physician, natural scientist, and writer. As one of the early figures of scientific racism, he argued against monogenism, the single creation story of the Bible, instead sup ...

, who published an etching in 1828. After the death of the specimen's owner, the Quaker scientist Reuben Haines III, in 1831, the specimen was lost for 180 years until it was rediscovered at Haines's home, the historic

Wyck House The Wyck house, also known as the Haines house or Hans Millan house, is a historic mansion, museum, garden, and urban farm in the Germantown, Philadelphia, Pennsylvania, Germantown neighborhood of Philadelphia, Pennsylvania. It was recognized ...

, in 2017 by Matthew Halley.