''Baculites'' ("walking stick rock") is an extinct genus of cephalopods with a nearly straight shell, included in the heteromorph

ammonites 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 cuttl ...

. The genus, which lived worldwide throughout most of the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger 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 ''creta'', ...

, 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.

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

, 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 The nautilus (, ) is a pelagic marine mollusc of the cephalopod family Nautilidae. The nautilus is the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina. It comprises six living species in ...

'' 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 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 ...

such as ''

Bassleroceras ''Bassleroceras'' is an elongate upwardly curved, exogastric, genus with the venter on the under side more sharply rounded than the dorsum on the upper. The siphuncle is ventral, composed of thick-walled tubular segments in which connection ring ...

'' and '' Clitendoceras'' from the

Ordovician 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 million years ago (Mya) to the start of the Silurian Period Mya. T ...

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

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

(as suggested by remains of a larval gastropod and a pelagic isopod inside the mouth).

Convergent evolution

''Baculites'' and related

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

straight ammonite cephalopods are often confused with the superficially similar orthocerid

nautiloid 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 specie ...

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 orthocerid

s mostly lived much earlier (common during the

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

Era, possibly going extinct in the Early Cretaceous) 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 Cretace ...

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 Navesink Formation in

Atlantic Highlands, New Jersey Atlantic Highlands is a borough in Monmouth County, New Jersey, in the Bayshore Region. As of the 2010 United States Census, the borough's population was 4,385,Thomas Say Thomas Say (June 27, 1787 – October 10, 1834) was an American entomologist, conchologist, and herpetologist. His studies of insects and shells, numerous contributions to scientific journals, and scientific expeditions to Florida, Georgia, the R ...

in 1820 from a single specimen from the Navesink Formation in

Atlantic Highlands, New Jersey Atlantic Highlands is a borough in Monmouth County, New Jersey, in the Bayshore Region. As of the 2010 United States Census, the borough's population was 4,385,Samuel George Morton Samuel George Morton (January 26, 1799 – May 15, 1851) was an American physician, natural scientist, and writer who argued against the single creation story of the Bible, monogenism, instead supporting a theory of multiple racial creations, p ...

, who published an etching in 1828. After the death of the specimen's owner, the Quaker scientist

Reuben Haines III Reuben Haines III (February 8, 1786 – October 19, 1831) was a Quaker farmer, brewer, abolitionist, scientist, ornithologist, meteorologist, firefighter, philanthropist, and educational reformer from Philadelphia, Pennsylvania. Haines was a found ...

, 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