''Baculites'' ("walking stick rock") is an extinct genus of cephalopods with a nearly straight shell, included in the heteromorph ammonites. The genus, which lived worldwide throughout most of the Late Cretaceous, and which briefly survived the K-Pg mass extinction event, was named by Lamarck in 1799.

Life

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, 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'' 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 ammonites, ''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 such as '' Bassleroceras'' and '' Clitendoceras'' from the Ordovician 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 nautiloids). Studies on exceptionally preserved specimens have revealed a

radula The radula (, ; plural radulae or radulas) is an anatomical structure used by molluscs 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 ...

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 magnetic field which bends the particle beam into its closed p ...

imagery. The results suggest that ''Baculites'' fed on pelagic zooplankton (as suggested by remains of a larval

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

and a pelagic

isopod Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, an ...

inside the mouth).

Convergent evolution

''Baculites'' and related Cretaceous straight

ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...

cephalopods are often confused with the superficially similar

orthocerid Orthocerida is an order of extinct Orthoceratoid cephalopods also known as the Michelinocerida that lived from the Early Ordovician () possibly to the Late Triassic (). A fossil found in the Caucasus suggests they may even have survived until ...

nautiloid 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

nautiloids mostly lived much earlier (common during the Paleozoic Era, possibly going extinct in the

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

) than ''Baculites'' (Late Cretaceous/ Danian 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 The Britton Formation is a geologic formation deposited during the Middle Cenomanian to the Early Turonian ages of the Late Cretaceous in modern-day East Texas. It forms the lower half of the Eagle Ford Group in the northern portion of East ...

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

''Baculites ovatus'' is known from the Maastrichtian

Navesink Formation The Navesink Formation is a 66 to 70 mya greensand glauconitic marl and sand geological formation in New Jersey. It is known for its Cretaceous period fossil shell beds and dinosaur bones. Description The Navesink Formation, named after Navesin ...

in Atlantic Highlands, New Jersey.

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 in 1820 from a single specimen from the

in Atlantic Highlands, New Jersey. The specimen was later illustrated by Samuel George Morton, 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, in 2017 by Matthew Halley.

References

*Arkell ''et al.'', 1957, Mesozoic Ammonoidea, Treatise on Invertebrate Paleontology Part L. Geological Soc. of America, Univ of Kansas Press. R.C. Moore, (Ed) *W. A. Cobban and Hook, S. C. 1983 Mid-Cretaceous (Turonian) ammonite fauna from Fence Lake area of west-central New Mexico. Memoir 41, New Mexico Bureau of Mines&Mineral Resources, Socorro NM. *W. A. Cobban and Hook, S. C. 1979, ''Collignoniceras woollgari wooollgari'' (Mantell) ammonite fauna from Upper Cretaceous of Western Interior, United States. Memoir 37, New Mexico Bureau of Mines&Mineral Resources, Socorro NM. {{Taxonbar, from=Q1061311 Ammonitida genera Turrilitoidea Late Cretaceous ammonites Late Cretaceous cephalopods of North America Late Cretaceous genus first appearances Late Cretaceous genus extinctions Paleozoic life of Africa Paleozoic life of Asia Paleozoic life of Australia Paleozoic life of Europe Paleozoic life of North America Paleozoic life of Oceania Paleozoic life of South America Paleozoic life of Alberta Paleozoic life of British Columbia Paleozoic life of Saskatchewan Fossils of Angola Fossils of Antarctica Fossils of Argentina Fossils of Australia Fossils of Austria Fossils of Belgium Fossils of Brazil Fossils of Canada Fossils of Chile Fossils of Denmark Fossils of Egypt Fossils of France Fossils of Germany Fossils of Greenland Fossils of Haiti Fossils of India Fossils of Japan Fossils of Jordan Fossils of Mexico Fossils of Mozambique Fossils of the Netherlands Fossils of New Zealand Fossils of Nigeria Fossils of Romania Fossils of Russia Fossils of South Africa Fossils of Spain Fossils of Sweden Fossils of Tajikistan Fossils of Tunisia Fossils of Turkey Fossils of Turkmenistan Fossils of Great Britain Fossils of the United States Fossils of Uzbekistan Fossils of Venezuela Fossil taxa described in 1799 Cephalopods described in 1799 Taxa named by Jean-Baptiste Lamarck