The fossil conchs of ammonoids provide valuable information about the life habits of this extinct group. A new conch measurement, the apertural surface area, is introduced here along with modelled sizes of the buccal mass and the hyponome, based on ratios of these organs in comparison with the aperture height from the Recent Nautilus pompilius. A principal components analysis was performed using the three main characters (1) apertural surface area index (i.e., the ratio of the apertural surface and the conch diameter), (2) buccal mass area index (i.e., the ratio between the buccal mass area and the apertural surface area) and (3) coiling rate of the conch and reveals an ecomorphospace where life history traits can be tentatively assigned to species of the Ammonoidea. In this morphospace, Recent Nautilus has a marginal position, being one of the ectocochleate cephalopods with best properties for active life (capacity for handling large food items, rather good mobility). In contrast, most ammonoids possessed, at comparable conch sizes, much smaller buccal apparatuses and hyponomes, suggesting a more passive life history with reduced mobility potential and reduced capacities for larger prey items.
Species list
List of species investigated. MB.C. = Museum für Naturkunde, Berlin
Supplementary Table 1.xlsx
Ontogenetic data
List of the conch parameters, whorl expansion rate (WER), apertural surface area index (ASAI) and buccal mass area index (BMAI) for all half whorl measurements for each specimen and their PCA values.
Supplementary Table 2.xlsx
Supplementary Fig 1
Simple dm/ASarea plot to outline the position of the various studied cross sections. The nine specimens divide into three groups: 1) Forms with a high ASA (*Nautilus*, *Macrocephalites* and in the adult stage *Hammatocyclus*), 2) Forms with a moderate ASA (*Revilloceras* and *Joannites*, *Metalegoceras* in the adult stage) and 3) Forms with low ASA (*Choffatia* and *Sageceras*).
Supplementary Fig 2
Simple ASarea/BMAI plot to outline the position of the various studied cross sections. In the nine highlighted specimens, it is clear to see that for a given ASA there can be a range of BMAIs. The disparity in BMAI increases from the hatchling stage through to the adults. In the subadult/adult stages, some specimens possess relatively small buccal apparatus (*Revilloceras* and *Joannites*) restricting them to smaller food items whereas other specimens were capable of eating larger prey (*Nautilus*, *Sageceras*).
Supplementary Fig 3
Simple WER/ASAI plot to outline the position of the various studied cross sections. The blue lines indicate the relationship between the ASAI and WER for simple geometric apertural shapes, the three lines from the top represent depressed ellipsoids of decreasing intensity, the fourth line a circle and the bottom two lines compressed ellipsoids.
Supplementary Fig 4
Ontogenetic trajectories of the conch width index, umbilical width index and whorl expansion rate, as well as the two new parameters, apertural surface area index and buccal mass area index, of three ammonoid species: A – *Hammatocyclus pollex* Ebbighausen, Korn & Bockwinkel, 2010, specimen MB.C.18601.7 (Early Carboniferous, Gourara, Algeria), B – *R**evilloceras granofalcatum *(Kullmann, 1961),
specimen MB.C.9090.1 (Early Carboniferous, Anti-Atlas, Morocco) and C – *Metalegoceras sundaicum*
(Haniel, 1915), specimen MNHN Paris 1925-16 B7532 (Early Permian, Timor)*.*
Supplementary Fig 5
Ontogenetic trajectories of the conch width index, umbilical width index and whorl expansion rate, as well as the two new parameters, apertural surface area index and buccal mass area index, of three ammonoid species: A – *J**oannites cymbiformis *(Wulfen, 1793), specimen MB.C.6352.2 (Late Triassic, Austria), B – *Sageceras haidingeri* (Hauer, 1849), specimen MB.C.6008.4 (Late Triassic, Austria) and C – *Tropites subbullatus *(Hauer, 1849), specimen MB.C.7724 (Late Triassic, Austria).
Supplementary Fig 6
Ontogenetic trajectories of the conch width index, umbilical width index and whorl expansion rate, as well as the two new parameters, apertural surface area index and buccal mass area index, of two ammonoid species and a *Nautilus* species: A – *Macrocephalites macrocephalus *(Schlotheim, 1813), specimen MB.C.26518 (Middle Jurassic, Westphalia), B – *Choffatia isabellae* Bonnot et al., 2008, specimen MB.C.26550 (Middle Jurassic, Normandy) and C – *Nautilus pompilius* Linnaeus, 1758, specimen GPI Tübingen 1431-K1.
