Macroscaphitidae (

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

μακρός, long and σκάφος, boat) is an extinct family of ptychoceratoid

cephalopods A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, an ...

from the subclass

Ammonoidea 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 cuttle ...

that lived from the Lower Barremian to the Lower

Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...

stages of the

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 th ...

. Fossils of Macroscaphitidae were found all around the world although the abundance of found fossils is rather limited. Known fossils from collections were found largely in Europe (e.g. Italy, France, Czech Republic), South America (Mexico, Venezuela) and Africa (e.g. Mozambique). It is known for some species of which complete specimens were found that these animals developed a hetermorphic shell, i.e. the coiling of the shell was not regular, such that the first whirls formed a planispirally coiled evolute section as seen in homomorphic ammonites, but had an additional straight middle part and a presumably upwards facing aperture. Due to their odd morphology the taxonomic classification of Macroscaphitidae changed often over time since their discovery and may not be finally settled even now.

Classification

The Macroscaphitidae comprise a family in the subclass of

in the class of

Cephalopoda A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, an ...

in the

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...

Mollusca Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

. Due to their curious morphology multiple attempts to classify them into a superfamily were made. While the Macroscaphitidae were at first assigned to Hamitaceae in the 1950s, this was revised in 2000 when they were classified as belonging to the superfamily

Ancyloceratoidea Ancyloceratoidea, formerly Ancylocerataceae, is a superfamily of typically uncoiled and loosely coiled heteromorph ammonoids established by Alpheus Hyatt in 1900, that may contain as many as 11 families, depending on the classification accepted ...

. However, in 2007 it was proposed to assign Macroscaphitidae to the superfamily Ptychoceratiodea, where Macroscaphitidae still belong today. Phylogeny Macroscaphitidae

Taxa

The family includes merely one genus ('' Macroscaphites'' Meek 1876) with two subgenera, the nominative (or type) genus ''Macroscaphites (Macroscaphites)'' Meek 1876 and the other subgenus ''Macroscaphites (Costidscus)'' Uhlig 1883. Some sources suggest more genera, such as ''Acantholytoceras'' Spath 1932, ''Ivaldiceras'' Delanoy 2010 or ''Rugacrioceras'' Vermeulen 2007, but the viability of such claims remains questionable. The type genus ''Macroscaphites (Macroscaphites)'' Meek 1876 contains four species, whereof ''Macroscaphites yuani'' Puzos 1831 constitutes the type species. The subgenus ''Macroscaphites (Costidiscus)'' Uhlig 1883 solely contains one species, ''Macroscaphites (Costidscus) reticostatus'' d’Orbigny 1840. Fm. †Macroscaphitidae Hyatt 1900 :G. †''Macroscaphites'' Meek 1876 ::Subg. †''Macroscaphites (Costidiscus)'' Uhlig 1883 :::†''Macroscaphites (Costidiscus) recticostatus'' d'Orbigny 1840 ::Subg. †''Macroscaphites (Macroscaphites)'' Meek 1876 :::†''Macroscaphites perforatus'' Avram 1984 :::†''Macroscaphites soaresi'' Da Silva 1962 :::†''Macroscaphites striatisulcatus'' d'Orbigny 1841 :::†''Macroscaphites yuani'' Puzos 1831

Morphology

Costidiscus recticostatus (d'Orbigny, 1840)

Due to the scarce amount of fossils found of members of Macroscaphitidae, final remarks about their morphology are difficult to infer. Additionally, just few fossils have been preserved entirely. Nevertheless, a couple of specimens suggest that a wide range of sizes, up to tens of centimeters (e.g. ''Macroscaphites yuani'', see picture at the top). While the general anatomy of members of Macroscaphitidae is supposed to largely follow the one of homomorphic ammonites (i.e. aragonitic shell, supposedly complex suture lines etc.) much remains yet unknown, due to the small number of specimens. However, some complete specimens infer that the shells of ''Macroscaphites'' can be more or less divided into three parts: the planispirally coiled

phragmocone The phragmocone is the chambered portion of the shell of a cephalopod. It is divided by septa into camerae. In most nautiloids and ammonoids, the phragmocone is a long, straight, curved, or coiled structure, in which the camarae are linked by a ...

(as in homomorphic ammonites), a straight part of the living chamber and a hook with an almnost 180 degree bend at the end where the aperture is located. Apart from that little is known about further morphological features.

Life and ecology

It is likely that ''Macroscaphites'' lived similar to other, better known, heteromorphic ammonites. One assumption is that the whole living chamber was filled with the softbody to deduce the center of mass and buoyancy of the ammonite. This commonly used model suggests for hetermorphic ammonites that the center of mass lies vertically below the center of buoyancy (to keep the animal stable in the water column) and thus predicts that the aperture of ''Macroscaphites'' was probably facing upwards. In addition to that it has been proposed for other heteromorphic ammonites that there was a second stable position with the aperture tilted toward the sea floor to prey on bottom dwellers. However, this remains controversial for Macroscaphitidae since e.g. specimens of ''Macroscaphites yuani'' suggest an aperture facing towards the phragmocone, a so-called ancyclocone, and thus preventing it from being tilted towards the sea floor. Thus the exact feeding behavior of ''Macroscaphites'' remains unknown. While it is proposed that members of Macroscaphitidae were fast-moving nektonic carnivores due to there hydrodynamic anatomy, studies of other heteromorphic ammonites suggest a rather nektobenthonic lifestyle. Foraminifera, crustaceans and ostracods found in the guts of some species provide evidence that some heteromorphic ammonites fed on benthic animals, making a epifaunal lifestyle rather likely. Furthermore, all heteromorphic ammonite lack the hyponomic sinus e.g. found in recent ''Nautilius'' that is used for manoeuvreable jetting, thus making a comparable lifestyle to ''Nautilus'' unlikely. In addition most fossil remnants of heteromorphic ammonites, including those of the Macroscaphitidae, were found in clay or marl rather than sandy facies suggesting a substrate dependend lifestyle. It was thus concluded that probably most heteromorphic ammonites, including Macroscaphitidae were bottom dwelling, like a small octopus with a mobile burrow.

Fossils and distribution

Compared to other ammonoid families just very few fossil specimens of Macroscaphitidae are known from collections. While some specimens are well preserved and provide information about the morphology and potentially about the way of living of ''Macroscaphites'', others are merely partly preserved making a comprehensive analysis of the morphology difficult. Fossils of members of Macroscaphitidae have been found in Europe (France, Italy, Serbia, Bulgaria, the Czech Republic, Spain, Georgia), Africa (Egypt, South AfricaW. J. Kennedy, H. C. Klinger, and M. V. Kakabadze. 2009. Macroscaphites Meek, 1876, a heteromorph ammonite from the Lower Aptian of southern Mozambique and northern KwaZulu-Natal. African Natural History 5:37-41 and Mozambique) and South America (Mexico and Venezuela). The fossils have been found in the form of casts, molds, impressions and replacement and occurred mainly in limestoneG. Delanoy, J. A. Moreno-Bedmar, J.J. Ruiz and D. Tolós Lládser. 2013. Xerticeras gen. nov., a new genus of micromorphic heteromorph ammonite (Ancyloceratina, Ancyloceratidae)from the lower Aptian of Spain. Carnets de Géologie otebooks on GeologyCG2013_A02:89-103

References