Trigonoceratid nautilids from the Early Carboniferous Imo Formation of Arkansas, Midcontinent North America

Niko, Shuji; Mapes, Royal H.

doi:10.2517/1342-8144(2007)11[293:tnftec]2.0.co;2

Cited by 5 publications

(1 citation statement)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Reports of the numbers of septa and shell diameters at the hatched stage in other Paleozoic nautiloids are relatively few (for Tainocerataceae, Ruzhencev and Shimansky, 1954;Mapes et aI., 2007;and for Trigonicerataceae, Ruzhencev and Shimansky, 1954;Niko and Mapes, 2007). Both the number of septa and the shell diameter at the hatching stage of M mcchesneyi (5 septa and 9.5 rom in diameter) are within the range of those in the previously reported Paleozoic nautiloids (2-7 septa and 4.9-20 mm in diameter).…”

Section: Hatchlings and Maturitymentioning

confidence: 99%

Conservative evolution in nautiloid shell morphology: Evidence from the Pennsylvanian nautiloidMetacoceras mcchesneyifrom Ohio, USA

Wani

Mapes

2010

J. Paleontol.

Self Cite

View full text Add to dashboard Cite

Morphometric analyses of shell morphology in the Pennsylvanian nautiloid Metacoceras mcchesneyi Murphy, 1970 (Cephalopoda, Mollusca) recovered from coal mines in Madison Township, Columbiana County, Ohio, USA, reveal the ontogenetic change from hatching to maturity as well as intra-specific variation of shell morphology. The shell shape of M. mcchesneyi has isometric relationships, and the umbilicus diameter between umbilical shoulders has a positive allometric relationship with shell diameter. These show that the relative whorl shape was constant through the ontogeny, but the umbilicus became relatively broader with growth. The siphuncle position moved from a ventro-central position toward the center with growth until 420° of the total rotational angle had been attained. A constriction was recognized on the early whorl at 9.5 mm in shell diameter, and the interval angles of succeeding septa were changed at the 5th septum, indicating that hatching occurred at this diameter. The ventral apertural wall, the disappearance of ornamentation toward the last preserved aperture, and the last whorl separating from the previous whorl indicate that M. mcchesneyi attained maturity at ca. 70 mm in shell diameter. Most characteristics of shell morphology in M. mcchesneyi (the relative shell shape and ornamentation through ontogeny) are comparable to those in modern and younger fossil nautilids, irrespective of taxonomy and age, supporting the conclusion that evolutionary rates of shell morphology are conservative in nautilid history.

show abstract

Section: Hatchlings and Maturitymentioning

confidence: 99%