Thirteen echinoid taxa are described from Coniacian marl-limestone alternations in three sections south and east of Djebel Metlili, on the southwestern margin of the Aures Mountains in northeastern Algeria. The biostratigraphic framework, based on ammonites and inoceramids, indicates an early to middle Coniacian age. The identified taxa include: Rachiosoma rectilineatum, Phymosoma tamarinense, P. cf. P. mansour, Gomphechinus meslei, Coenholectypus subcrassus, Parapygus coquandi, Petalobrissus trigonopygus, P. rimula, Hemiaster sp., and Mecaster fourneli. Three new species are described, Orthopsis metliliae sp. nov., Coenholectypus sulcatus sp. nov. and a new genus and species referred to the family Phymosomatoidae, Triboporus luluatus gen. et sp. nov. A large amount of well-documented material, comprising 579 specimens, was collected, with the fauna being dominated by the spatangoid Mecaster fourneli. At the genus level, the fauna exhibits characteristics typical of the Tethyan realm, and includes Rachiosoma, Gomphechinus, Mecaster, Parapygus and Petalobrissus. However, at the species level, most taxa are restricted to Algeria. Some are also found in adjacent countries such as Tunisia and Egypt.

This study investigates the biostratigraphic and paleobiogeographic significance of Hemipneustes africanus Deshayes, 1848, with a special attention on its temporal extent and geographical distribution during the Late Cretaceous. The overarching scientific question investigated herein tackles the significance of the distribution and stratigraphic position of this taxon in elucidating its faunal provincialism and dispersal limits within the southern Tethys.

A newly discovered and well-dated occurrence of H. africanus is described in a new area of the Aurès Basin, within the Beni Fedhala syncline (Maafa–Djebel Gueroun, Algeria). This taxon was found associated with the ammonite index species Nostoceras (Bostrychoceras) polyplocum (Roemer, 1841), within the Total Range Zone of the planktic foraminifer Globotruncana calcarata Cushman, 1927, which indicates a Late Campanian age.

The present record represents one of the earliest chronostratigraphically constrained reports of the genus Hemipneustes in the upper Campanian. The limited geographic distribution of the species, restricted to Algeria, Tunisia and Spain, suggests low dispersal ability, further contributing to our general understanding of the regional faunal differentiation within the southern Tethyan region during the Late Cretaceous.

A comprehensive study of the lithological, sedimentological and palaeontological characteristics of deposits belonging to the middle Turonian to Coniacian age in the Bellezma-Batna Mountains was carried out in order to establish a new biostratigraphic framework and interpret the evolution of the palaeoenvironment and sea-level fluctuation during this period. The studied sequences, exposed at Chaabet (Djebel Boukezzez) and Chihat, are mostly composed of marls and limestones. They are mainly composed of three formations: the Marly Limestone of the Chaabet Formation, the Upper Limestone of the Berriche Formation and the Marls of the Chaabet Formation. Biostratigraphic interpretations were based mainly on planktic and benthic foraminifera (H. helvetica, Marginotruncana cf. sigali, Discorbis turnicus, Nezzazatinella picardi HENSON), ostracods (Ovocytheridea sp., Brachycythere ekpo), and rudists Vaccinites praegiganteus, from the lower limestone member at both the Chaabet and Chihat sections, which is considered as a good indicator of the Upper Turonian age. Fourteen types of microfacies were identified and grouped into three facies assemblages- outer, middle, and inner ramp—based on sedimentological and palaeontological features. Sequence stratigraphic analysis establishes five sedimentary sequences that mark successive cycles of transgression and regression. A significant rise in sea level during the middle Turonian led to deep open marine conditions, followed by a regression in the late Turonian and early Coniacian that led to progressively shallower environments. These fluctuations reflect the combined effects of eustatic changes and regional tectonic movements.

A comprehensive study of the lithological, sedimentological and palaeontological characteristics of deposits belonging to the middle Turonian to Coniacian age in the Bellezma-Batna Mountains was carried out in order to establish a new biostratigraphic framework and interpret the evolution of the palaeoenvironment and sea-level fluctuation during this period. The studied sequences, exposed at Chaabet (Djebel Boukezzez) and Chihat, are mostly composed of marls and limestones. They are mainly composed of three formations: the Marly Limestone of the Chaabet Formation, the Upper Limestone of the Berriche Formation and the Marls of the Chaabet Formation. Biostratigraphic interpretations were based mainly on planktic and benthic foraminifera (H. helvetica, Marginotruncana cf. sigali, Discorbis turnicus, Nezzazatinella picardi HENSON), ostracods (Ovocytheridea sp., Brachycythere ekpo), and rudists Vaccinites praegiganteus, from the lower limestone member at both the Chaabet and Chihat sections, which is considered as a good indicator of the Upper Turonian age. Fourteen types of microfacies were identified and grouped into three facies assemblages- outer, middle, and inner ramp—based on sedimentological and palaeontological features. Sequence stratigraphic analysis establishes five sedimentary sequences that mark successive cycles of transgression and regression. A significant rise in sea level during the middle Turonian led to deep open marine conditions, followed by a regression in the late Turonian and early Coniacian that led to progressively shallower environments. These fluctuations reflect the combined effects of eustatic changes and regional tectonic movements.

The Aptian sedimentary succession exposed in the southern Bellezma Mountains contains a low diversity trace fossil assemblage, with ichnofossils being common in the middle part of the studied section. The recorded trace fossils comprise eight ichnogenera: Archaeonassa, Cochlichnus, Chondrites, Gyrochorte, Palaeophycus, Protovirgularia, Rhizocorallium, and Thalassinoides. Ethologically, these ichnogenera display feeding, crawling, and dwelling activities of epi- and infaunal organisms. The presence of these trace fossils is mainly related to the activity of the deposit feeders, due to the accumulation of nutrients on the seafloor in unconsolidated, poorly sorted, soft substrate after storms under good environmental conditions. Together with sedimentological features, the ichnoassemblage suggests that the studied Aptian sedimentary succession was deposited in the upper offshore zone, corresponding to the Cruziana ichnofacies. These trace fossils are reported herein for the first time in the Bellezma Mountains. Furthermore, this study represents the first investigation of Mesozoic trace fossils in eastern Algeria.

This article reports cases of growth anatomical anomalies in two echinoid species, Macraster douvillei (Gauthier) and Mecaster pseudofourneli (Péron and Gauthier), from the Cenomanian deposits of the Bellezma-Batna mountains (northeastern Algeria). Such a topic is first reported in Algeria ever. The large collection (400 specimens) made it possible to distinguish several types of these rare pathologies, each one being illustrated by explanatory drawings. Three types of deformation directly concerning the pentamery, are presented. They are most often resulting from an additional growth zone (6 ambulacra), a complete tetramery represented by a missing growth zone (4 ambulacra) and constrictions or strangulation of the ambulacres. Abnormalities can develop in the rudiment as soon as the larva enters metamorphosis, or shortly afterwards in juvenile broods. They may alter the plate arrangement and the general shape of the test or, on the contrary, result in local deformations, influencing the arrangement or shape of the ambulacra, etc. These malformations resulted from either intrinsic (genetic) or extrinsic (ambiental) conditions.