Baculites

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Baculites
Temporal range: Late Cretaceous
SouthDakotaBaculites.jpg
Baculites fossils from South Dakota. Some
still have traces of the original nacre (shells).
Scientific classification e
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Family: Baculitidae
Genus: Baculites
Lamarck, 1799
Type species
Baculites vertebralis
Lamarck, 1801[1] vide Meek, 1876[2]
Species

See text

Baculites ("walking stick rock") is an extinct cephalopod genus with a nearly straight shell that is included in the heteromorph ammonites. The genus, which lived worldwide throughout the Late Cretaceous period, was named by Jean Baptiste Lamarck in 1799.[3]

A fossil cast of the shell of a Baculites grandis on display at the North American Museum of Ancient Life in Lehi, Utah.

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 a centimeter in diameter. Adult Baculites ranged in size from about seven centimeters (Baculites larsoni) up to two meters 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.

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.[4]

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).

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.

Baculites and related Cretaceous straight ammonite cephalopods are often confused with the superficially similar orthocerid 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 orthocerid nautiloids lived much earlier (common during the Paleozoic Era and extinct by the end of the Triassic Period) than Baculites (Late Cretaceous Period 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.

Studies[5] on exceptionally preserved specimens have revealed a radula by synchrotron imagery. The results suggest that Baculites fed on pelagic zooplankton (as suggested by remains of a larval gastropod and a pelagic isopod inside the mouth).[6]

Species[edit]

Baculites specimen in the field; western South Dakota, Pierre Shale, Late Cretaceous. Part of the phragmocone (left) and part of the body chamber (right) are present.
Baculites showing sutures and remnant aragonite; western South Dakota, Late Cretaceous.
Baculites from the Late Cretaceous of Wyoming. The original aragonite of the outer conch and inner septa has dissolved away, leaving this articulated internal mold.

Numerous species have been designated from the fossil record since the initial description of the genus in 1799.[7]

  • Baculites anceps
  • Baculites aquilaensis
  • Baculites asper
  • Baculites asperiformis
  • Baculites baculus
  • Baculites bailyi
  • Baculites buttensis
  • Baculites capensis
  • Baculites chicoensis
  • Baculites clinolobatus
  • Baculites compressus
  • Baculites crickmayi
  • Baculites fairbanksi
  • Baculites fuchsi
  • Baculites grandis
  • Baculites haresi
  • Baculites incurvatus
  • Baculites inornatus
  • Baculites jenseni
  • Baculites kirki
  • Baculites knorrianus
  • Baculites lechitides
  • Baculites lomaensis
  • Baculites mclearni
  • Baculites meeki
  • Baculites minerensis
  • Baculites nugssuaqensis
  • Baculites occidentalis
  • Baculites obtusus
  • Baculites ovatus
  • Baculites pseudovatus
  • Baculites rectus
  • Baculites reesidei
  • Baculites scotti
  • Baculites subanceps
  • Baculites teres
  • Baculites undatus
  • Baculites undulatus
  • Baculites vaalsensis
  • Baculites vertebralis

References[edit]

  1. ^ Lamarck, J. P. B. A. de M. de (1801): Systeme des Animaux sans vertebres. The author; Deterville, Paris, vii + 432 pp.
  2. ^ Meek, F. B. (1876): A report on the invertebrate Cretaceous and Tertiary fossils of the upper Missouri country. In Hayden,F. V. Report of the United States Geological Survey of the Territories, 9, lxiv + 629 pp., 45 pis
  3. ^ Lamarck, J. P. B. A. de M. de (1799): Prodrome d'une nouvelle classification des coquilles. Mem. Soc. Hist. Nat.Paris, (1799), 63-90.
  4. ^ Westermann, G. E. G. l996. Ammonoid life and habitat. In N. H. Landman, K. Tanabe, and R. A. Davis (editors), Ammonoid Paleobiology, pp. 607–707. New York: Plenum Press.
  5. ^ Kruta, I.; Landman, N.; Rouget, I.; Cecca, F.; Tafforeau, P. (2011). "The Role of Ammonites in the Mesozoic Marine Food Web Revealed by Jaw Preservation". Science 331 (6013): 70–72. Bibcode:2011Sci...331...70K. doi:10.1126/science.1198793. PMID 21212354.  edit
  6. ^ Neil H. Landman, Neal L. Larson and William A. Cobban (2007). Chapter 13. Jaws and Radula of Baculites from the Upper Cretaceous (Campanian) of North America. In N. H. Landman et al. (eds.), Cephalopods Present and Past: New Insights and Fresh Perspectives, 257–298. © 2007 Springer.
  7. ^ Baculites-Paleobio
  • 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.