Observations of juvenile sandbar sharks Carcharhinus plumbeus (Nardo, 1827) around the Bojana River delta (Southern Adriatic Sea)

The sandbar shark (Carcharhinus plumbeus) is considered rare in the Adriatic Sea and the majority of records originate from the northern Adriatic, where a nursery area for this species close to the Po delta system has been repeatedly proposed. This study provides 5 new records and analyses the previously published records of sandbar sharks recorded around the delta of the River Bojana (in Montenegro, in the south-eastern Adriatic). The River Bojana located on the border between Montenegro and Albania, is the second largest river flowing into the Adriatic Sea, where it forms a highly productive ecosystem already known as a local hotspot for smooth-hound sharks (Mustelus spp.). New records of sandbar sharks have emerged as a result of citizen science (a social media survey) and direct reports from fishermen. The total length of C. plumbeus juveniles ranged from approximately 800 mm to 1100 mm, and most (n=5) were caught by set gillnets. The data presented here show that juveniles are consistently present around the estuary and indicate the importance of this fragile estuarine ecosystem for sandbar sharks. Additionally, this study also provides morphometric data collected from a single individual

Rostral and body shape analyses reveal cryptic diversity of Late Jurassic batomorphs (Chondrichthyes, Elasmobranchii) from Europe

The fossil record of chondrichthyans (chimaeras, sharks, rays and skates) consists largely of isolated teeth, with holomorphic specimens being extraordinary exceptions. However, numerous of these more or less completely preserved specimens are known from several Upper Jurassic deposits of Europe, enabling detailed analysis of their morphology. Batomorphs (rays and skates) resembling modern guitarfishes and wedgefishes (Rhinopristiformes) are among the most common Jurassic chondrichthyans found, but they have been only sporadically studied up to now, resulting in large knowledge gaps concerning their taxonomy and phylogeny. Here, we present the most detailed revision of Late Jurassic holomorphic batomorphs to date, quantitatively analysing body proportions of specimens from Germany (Solnhofen Archipelago), France (Cerin) and the UK (Kimmeridge), using both geometric and traditional morphometrics. Furthermore, we identify qualitative morphological characters for species discrimination, to clarify the taxonomic identity and diversity of Late Jurassic batomorphs based on holomorphic specimens. Our results support the validity of Belemnobatis sismondae, Kimmerobatis etchesi and Spathobatis bugesiacus, as well as that of the previously doubtful Asterodermus platypterus. Moreover, we describe Aellopobatis bavarica, a new taxon, which has hitherto been considered to be a large-sized morphotype of Spathobatis bugesiacus. Our results highlight that the diversity of holomorphic batomorphs during the Late Jurassic was greater than previously thought, and suggest that this group was already well-established and diverse by this time. This study thus provides vital information about the evolutionary history of Late Jurassic batomorphs and has direct implications for batomorph species that are based on isolated teeth only

Articulated remains of the extinct shark Ptychodus (Elasmobranchii, Ptychodontidae) from the Upper Cretaceous of Spain provide insights into gigantism, growth rate and life history of ptychodontid sharks.

Due to their cartilaginous endoskeleton and the continuous tooth replacement, the chondrichthyan fossil record predominantly consists of isolated teeth, which offer diagnostic features for taxonomic identifications, but only provide very limited information of an organism's life history. In contrast, the calcified vertebral centra of elasmobranchs (sharks, skates and rays) yield important information about ecological and biological traits that can be utilized for constructing age-structured population dynamic models of extant species and palaeoecological reconstructions of such aspects in extinct groups. Here, we describe two large shark vertebrae from the Santonian (Upper Cretaceous) of Spain, which show a unique combination of characters (asterospondylic calcification pattern, with concentric lamellae and numerous parallel bands that are oriented perpendicular) that is only known from ptychodontid sharks, a distinct, extinct group of giant durophagous sharks of the Cretaceous era. Based on linear regression models for large extant sharks a total length between 430 and 707cm was estimated for the examined specimen. Our results indicate that ptychodontid sharks were large viviparous animals, with slow growth rates, matured very late and, therefore, show typical traits for K-selected species. These traits combined with a highly specialized feeding ecology might have played a crucial role for the success but also, eventually, extinction of this group

Reply to Soldo, A.; Lipej, L. Comment on “Balàka et al. Updated Checklist of Chondrichthyan Species in Croatia (Central Mediterranean Sea). <i>Biology</i> 2023, <i>12</i>, 952”

Balàka et al [...

Tooth sections of an orthodont (<i>Carcharhinus leucas</i>), pseudoosteodont (†<i>Hemipristis serra</i>) and osteodont shark (<i>Isurus oxyrinchus</i>).

<p>The white line indicates the plane of the section. (A), (B), (C) <i>Carcharhinus leucas</i> (EMRG-Chond-T-15) has a hollow pulp cavity surrounded by tightly packed orthodentine; (D, E, F) fully mineralized tooth of †<i>Hemipristis serra</i> (EMRG-Chond-T-11) with a thick layer of orthodentine, surrounding the osteodentine core; (G, H, I) the crown of <i>Isurus oxyrinchus</i> (EMRG-Chond-T-14) is fully filled by osteodentine. Orthodentine is absent in this species. en, enameloid; mc, Meckel’s cartilage; or, orthodentine; os, osteodentine; pc, pulp cavity; pq, palatoquadrate.</p

Micro-CT images of tooth series of the sphyrnid shark <i>Sphyrna zygaena</i>.

<p>Tooth files showing the number of teeth, tooth stages and mineralization. (A) LMC3 (lower jaw), (B) LPC3 (upper jaw) of <i>Sphyrna zygaena</i> (EMRG-Chond-J-8). Scalebar = 0.5cm. en, enameloid; mc, Meckel’s cartilage; or, orthodentine; pc, pulp cavity; pq, palatoquadrate.</p

Micro-CT images of tooth series of the carcharhinid sharks <i>Galeocerdo cuvier</i>, <i>Prionace glauca</i>, and <i>Rhizoprionodon acutus</i>.

<p>Tooth files showing the number of teeth, tooth stages and mineralization in (A) RMC3 (lower jaw) <i>Galeocerdo cuvier</i>, (B) RPC3 (upper jaw) <i>Galeocerdo cuvier</i> (EMRG-Chond-J-13), (C) LMC3 <i>Prionace glauca</i>, (D) LPC3 <i>Prionace glauca</i> (EMRG-Chond-J-6), (E) LMC3 <i>Rhizoprionodon acutus</i>, (F) LPC3 <i>Rhizoprionodon acutus</i> (EMRG-Chond-J-7). Scalebar = 0.5cm. en, enameloid; mc, Meckel’s cartilage; or, orthodentine; pc, pulp cavity; pq, palatoquadrate.</p

Micro-CT images of tooth series of sharks of the family Hemigaleidae.

<p>Tooth files showing the number of teeth, tooth stages and mineralization in (A) LMC3 (lower jaw) <i>Chaenogaleus macrostoma</i>, (B) LPC3 (upper jaw) <i>Chaenogaleus macrostoma</i> (CD042), (C) LMC3 <i>Hemigaleus microstoma</i>, (D) LPC3 <i>Hemigaleus microstoma</i> (CD045), (E) LMC3 <i>Paragaleus randalli</i>, (F) LPC3 <i>Paragaleus randalli</i> (CD046). Scalebar = 0.5cm. en, enameloid; mc, Meckel’s cartilage; or, orthodentine; pc, pulp cavity; pq, palatoquadrate.</p