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IV.—Notes on Ammonites

Published online by Cambridge University Press:  01 May 2009

L. F. Spath
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Extract

In addition to the variability of the suture-line in a given species, mentioned previously, asymmetry of the elements on opposite sides of the same suture-line is very frequent and probably universal in so far as the minor frillings are concerned, which is only to be expected in organic beings. This phenomenon has lately been illustrated again in Lioceras by Horn, and in Dactylioceras by Swinnerton & Trueman. The latter authors also have some interesting observations on asymmetry associated with lateral displacement of the siphuncle which is of sporadical occurrence in Ammonites.

Type
Original Articles
Information
Geological Magazine , Volume 6 , Issue 3 , March 1919 , pp. 115 - 122
Copyright
Copyright © Cambridge University Press 1919

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References

page 115 note 1 “Die Harpoceraten der Murchisonæ-Schichten d. Donau-Rhein Zuges”: Mitt. Grossherz. Bad. Geol. Land. Anst., vol. vi, pt. i, p. 264Google Scholar.

page 115 note 2 Op. cit., Q.J.G.S., vol. lxxiii, pt. i, pp. 40, 51, 1917Google Scholar.

page 115 note 3 “Beitr. z. Fauna d. Unt. Lias v. Spezia”: Palæontographica, vol. xxix, pt. iii, p. 192, 1882Google Scholar.

page 115 note 4 “Fossil d. Mungo-Kreide”: Geol. v. Kamerun, ii, p. 217, 1904Google Scholar.

page 116 note 1 Spath, L. F., “On the Development of Tragophylloceras Loscombi”: Q.J.G.S., vol. lxx, p. 352, 1914Google Scholar.

page 116 note 2 Canavari (op. cit., 1882, p. 69) has thought that asymmetry of the suture-line was not found in Phylloceratidæ, but he figures as Amaltheus (Sphenodiscus) sinister (ibid., pl. ii, xvi, fig. 17a–c) a form of “Rhacophyllites”, that clearly shows this asymmetry; and both Pompeckj, and Swinnerton and Trueman mention it as occurring in Tragophylloceras, but these are not typical Phylloceratids. It may be suggested for e.g. Meneghiniceras and other “Rhacophyllites”, that, like many modern marine organisms, they were pelagic in the young and littoral when adult.

The form figured by Canavari affords a good illustration of the unsatisfactory results of a morphological classification of Ammonites according to the adult suture-line. Canavari wrote: “A remarkable circumstance in this species is the presence of three lateral lobes. Thus it lets itself be grouped in section B of the Amaltheids, according to Neumayr & Uhlig, which comprises the forms with three or more lateral lobes, and perhaps in the sub-genus Sphenodiscus, Meek, with complicated lobes.” In 1888, Canavari, (“Contribuzione alla Fauna del Lias inferiore di Spezia”: Mem. R. Com. Geol. Ital., vol. iii, pt. ii, p. 34)Google Scholar assigned this form to the genus Oxynoticeras, but its suture-line shows it to be a Rhacophyllitid.

page 117 note 1 Op. cit., 1912, p. 81.

page 117 note 2 “Zur Kenntnis d. Fauna d. Unterst. Lias i. d. Nordalpen”: Abh. k.k. Geol. Reichsanst., vol. vii, pt. v, p. 25Google Scholar.

page 117 note 3 “Das Karwendelgebirge”: Zeitschr. d. D. O. Alpenvereins, vol. xix, pp. 427–8, 1888Google Scholar.

page 118 note 1 Op. cit., p. 55.

page 118 note 2 “Über Ammon. a. d. Hilsbild. Nordd.”: Palæontographica, vol. xxvii, pp. 135–6, 1880–1881Google Scholar.

page 119 note 1 “On the Muscular Attachment of the Animal to its Shell in some Foss. Ceph. (Ammonoidea)”: Trans. Linn. Soc., vol. vii, pt. iv, p. 109, 1898Google Scholar.

page 119 note 2 Owen, R., Lectures on the Compar. Anat. and Physiol. of the Invertebr. Anim., 1843, p. 331Google Scholar.

page 119 note 3 “Geology and Mineralogy, etc.”: Bridgwater Treatise VI, vol. i, sect. iii, “Nautilus,” pp. 310–32Google Scholar; sect. iv, “Ammonites,” pp. 333–57; also sects. v and vi, pp. 357–60; and vol. ii, pp. 58, 59, 62.

This author (p. 62, vol. ii) also stated that the “course of the transverse plates was beneath the depressed and weakest part of the external shell, avoiding the bosses … which from their form were strong”. This is not borne out by the specimen of Hoplites auritus, figured by Swinnerton and Trueman (op. cit., pl. iv, fig. 8), and it seems that in general the septal edge is independent of the position of the tubercles, which are also often irregularly spaced.

page 120 note 1 Op. cit., 1881–5, pp. 332 ff.

page 120 note 2 “Die Cephalopoden Fauna d. Wernsdorf. Schichten”: Denkschr. d. Math.-Naturwiss, Cl. d. k. Akad. d. Wiss., vol. xlvi, p. 61, Vienna, 1883Google Scholar.

page 120 note 3 Op. cit., p. 332.

page 120 note 4 Op. cit., 1912, pp. 67–89.

page 120 note 5 “Beitr. z. Geol. v. Niederländ. Indien”: I, 4, Palæont. Suppl. IV, 1912, p. 173Google Scholar.

page 120 note 6 Whether the earliest representatives were active benthonic animals or attached and sedentary, is not known. But it is probable that from the ancestral capulicone, crytocones and orthocones arose, with elongation of the shell after the manner of tubular structures in Actinozoa, Polyzoa, Annelida, and Gastropoda (“Guide to the Fossil Invertebrata Animals in the Department of Geol. and Pal. in the Brit. Mus. (Nat. Hist.),” 1907, p. 147), and the formation of septa at the end of the cone only after a continued period of elongation and pulling away of the visceral hump from the cone, probably to give it buoyancy. But orthocones and cyrtocones cannot have been active swimmers. (See the interesting paper by Jaekel, O.. “Thesen üb. d. Organis. u. Lebensweise ausgestorbener Cephalopoden”: Z.d.g.G., vol. liv, p. 67, 1902Google Scholar; also Ruedemann, R., “Structure of some Primitive Cephalopods”: Report of New York State Pal. 1903, p. 334Google Scholar, for Piloceras.) They were probably benthonic, and it was only after the shell had become coiled upon itself and bilaterally symmetrical, that the Cephalopod animal could adopt a freely swimming mode of life.

page 121 note 1 “Über Form und Bau'd. Ammonitensepten und ihre Bezieh. z. Sutur-Linie”: 4. Jahresber d. Niedersächs. Geolog. Ver., 1911, p. 212Google Scholar.

page 121 note 2 Op. cit., p. 212.

page 121 note 3 Cat. of Foss. Ceph. in the Brit. Mus. (Nat. Hist.), pt. ii; Nautiloidea, 1891, p. 322Google Scholar.

page 121 note 4 Traité de Paléont., vol. ii, pp. 666–7Google Scholar.

page 121 note 5 Older authors (e.g. Vrolik, & Van Breda, , Ann. Mag. Nat. Hist., vol. xii, p. 173, 1843CrossRefGoogle Scholar) even held that the animal was attached to the shell only by the siphon.

page 122 note 1 See Spath, L. F., Q.J.G.S., vol. lxx, fig. on p. 341, 1914Google Scholar, stages e, f, h, and l.

page 122 note 2 Op. cit., p. 222.