ArticlePublisher preview available

Exceptionally preserved shark fossils from Mexico elucidate the long-standing enigma of the Cretaceous elasmobranch Ptychodus

The Royal Society
Proceedings of the Royal Society B
Authors:
Romain Vullo at University of Rennes
Romain Vullo
Eduardo Villalobos at University of Vienna
Eduardo Villalobos
Manuel Amadori at University of Vienna
Manuel Amadori
Jürgen Kriwet at University of Vienna
Jürgen Kriwet
Show all 9 authorsHide
Read publisher preview
Download citation
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

The fossil fish Ptychodus Agassiz, 1834, characterized by a highly distinctive grinding dentition and an estimated gigantic body size (up to around 10 m), has remained one of the most enigmatic extinct elasmobranchs (i.e. sharks, skates and rays) for nearly two centuries. This widespread Cretaceous taxon is common in Albian to Campanian deposits from almost all continents. However, specimens mostly consist of isolated teeth or more or less complete dentitions, whereas cranial and post-cranial skeletal elements are very rare. Here we describe newly discovered material from the early Late Cretaceous of Mexico, including complete articulated specimens with preserved body outline, which reveals crucial information on the anatomy and systematic position of Ptychodus. Our phylogenetic and ecomorphological analyses indicate that ptychodontids were high-speed (tachypelagic) durophagous lamniforms (mackerel sharks), which occupied a specialized predatory niche previously unknown in fossil and extant elasmobranchs. Our results support the view that lamniforms were ecomorphologically highly diverse and represented the dominant group of sharks in Cretaceous marine ecosystems. Ptychodus may have fed predominantly on nektonic hard-shelled prey items such as ammonites and sea turtles rather than on benthic invertebrates, and its extinction during the Campanian, well before the end-Cretaceous crisis, might have been related to competition with emerging blunt-toothed globidensine and prognathodontine mosasaurs.
A preview of this full-text is provided by The Royal Society.
Learn more
Content available from Proceedings of the Royal Society B 
This content is subject to copyright.
royalsocietypublishing.org/journal/rspb
Research
Cite this article: Vullo R et al. 2024
Exceptionally preserved shark fossils
from Mexico elucidate the long-standing
enigma of the Cretaceous elasmobranch
Ptychodus.Proc. R. Soc. B 291: 20240262.
https://doi.org/10.1098/rspb.2024.0262
Received: 30 January 2024
Accepted: 21 March 2024
Subject Category:
Palaeobiology
Subject Areas:
palaeontology, evolution, taxonomy and
systematics
Keywords:
Chondrichthyes, Lamniformes, Ptychodontidae,
ecomorphology, Late Cretaceous,
Vallecillo fossil Lagerstätte
Author for correspondence:
Romain Vullo
e-mail: romain.vullo@univ-rennes.fr
Electronic supplementary material is available
online at https://doi.org/10.6084/m9.figshare.
c.7165772.
Exceptionally preserved shark fossils
from Mexico elucidate the long-standing
enigma of the Cretaceous elasmobranch
Ptychodus
Romain Vullo
1
, Eduardo Villalobos-Segura
2
, Manuel Amadori
2
,
Jürgen Kriwet
2,3
, Eberhard Frey
4
, Margarito A. González González
5
,
José M. Padilla Gutiérrez
6
, Christina Ifrim
7
, Eva S. Stinnesbeck
8
and
Wolfgang Stinnesbeck
9
1
Univ Rennes, CNRS, Géosciences Rennes, UMR 6118, Rennes, France
2
Department of Palaeontology, Faculty of Earth Sciences, Geography and Astronomy, University of Vienna,
Vienna, Austria
3
Vienna Doctoral School of Ecology and Evolution, University of Vienna, Vienna, Austria
4
Sonnenbergstraße 27, Pforzheim, Germany
5
Calle Josefa Ortiz de Domínguez 165 norte, Colonia Bella Vista, Sabinas Hidalgo, Mexico
6
Museo del Desierto, Parque de las Maravillas, Nuevo Centro Metropolitano, Saltillo, Mexico
7
Staatliche Naturwissenschaftliche Sammlungen Bayerns, Jura-Museum, Willibaldsburg, Eichstätt, Germany
8
Steinmann-Institut für Geologie, Mineralogie und Paläontologie, Rheinische Friedrich-Wilhelms-Universität,
Bonn, Germany
9
Institute für Geowissenschaften, Ruprecht-Karls-Universität, Heidelberg, Germany
RV, 0000-0002-1900-9991; EV-S, 0000-0001-5475-6143
The fossil fish Ptychodus Agassiz, 1834, characterized by a highly distinctive
grinding dentition and an estimated gigantic body size (up to around 10 m),
has remained one of the most enigmatic extinct elasmobranchs (i.e. sharks,
skates and rays) for nearly two centuries. This widespread Cretaceous taxon
is common in Albian to Campanian deposits from almost all continents.
However, specimens mostly consist of isolated teeth or more or less complete
dentitions, whereas cranial and post-cranial skeletal elements are very rare.
Here we describe newly discovered material from the early Late Cretaceous
of Mexico, including complete articulated specimens with preserved body out-
line, which reveals crucial information on the anatomy and systematic position
of Ptychodus. Our phylogenetic and ecomorphological analyses indicate that
ptychodontids were high-speed (tachypelagic) durophagous lamniforms
(mackerel sharks), which occupied a specialized predatory niche previously
unknown in fossil and extant elasmobranchs. Our results support the view
that lamniforms were ecomorphologically highly diverse and represented
the dominant group of sharks in Cretaceous marine ecosystems. Ptychodus
may have fed predominantly on nektonic hard-shelled prey items such
as ammonites and sea turtles rather than on benthic invertebrates, and its
extinction during the Campanian, well before the end-Cretaceous crisis,
might have been related to competition with emerging blunt-toothed
globidensine and prognathodontine mosasaurs.
1. Introduction
Ptychodus Agassiz, 1834 (Elasmobranchii: Ptychodontidae) is a cosmopolitan
group of fossil sharks occurring in Albian–Campanian (approx. 105 to 75 million
years old) marine deposits of all continents except Antarctica (e.g. [1–10]). This
diverse Cretaceous genus, including at least 16 species, is primarily known from
isolated teeth and partial dentitions. Two species groups, which often co-occur
with each other, can be distinguished: species with low-crowned (uncuspidate)
© 2024 The Author(s) Published by the Royal Society. All rights reserved.
... Despite great progress in recent decades, the taxonomy and systematics of most Mesozoic sharks is still in need of revision (e.g., Amadori et al., 2019bAmadori et al., , 2020aAmadori et al., , 2022bAmadori et al., , 2023Cappetta, 2012;Everhart, 2017;Hamm, 2020;Jambura et al., 2023Jambura et al., , 2024Shimada, 2012;Stumpf et al., 2023;Villalobos-Segura et al., 2023). The taxonomy and systematics of notorious enigmatic sharks, such as the large shell-crusher shark Ptychodus Agassiz, 1834, were the centre of intense debates for centuries (Amadori et al., 2020a;Bassani, 1886;Brignon, 2019;Cappetta, 2012;Casier, 1953;Cuny, 2008;Hamm, 2020;Hoffman et al., 2016;Nicholls, 2010;Parkinson, 1811;Patterson, 1966;Shimada, 2012;Vullo et al., 2024;Woodward, 1912). ...
... Ptychodus (Ptychodontidae; Lamniformes) is an extinct elasmobranch mostly known from the Upper Cretaceous of North America, Europe, Africa, and Asia (e.g., Amadori et al., 2022b;Cappetta, 2012;Hamm, 2020;Vullo et al., 2024;Woodward, 1912). This predatory shark diversified greatly during the Late Cretaceous and reached its diversity peak during the Turonian-Coniacian (Amadori, 2022;Hamm, 2020). ...
... Species of Ptychodus characterised by different tooth morphologies could have targeted different main prey while still keeping a varied diet (e.g., Amadori et al., 2020b;Shimada, 2012). In general, their diet range could have spanned from hard-shelled prey (e.g., bivalves, ammonites and turtles) to soft-bodied prey (e.g., Amadori et al., 2019aAmadori et al., , 2020bAmadori et al., , 2023Cappetta, 2012;Everhart, 2017;Hamm, 2020;Shimada, 2012;Vullo et al., 2024). Recently, complete skeletons of Ptychodus have been documented for the first time from the Turonian (Upper Cretaceous) of Mexico revealing its close relationship with extinct and extant lamniform sharks (Vullo et al., 2024). ...
New insights on the shell-crusher shark Ptychodus decurrens Agassiz, 1838 (Elasmobranchii, Ptychodontidae) based on the first known articulated dentition from the Upper Cretaceous of Croatia
Article
Full-text available
  • Jan 2025
A new lower tooth plate of Ptychodus decurrens from the Turonian (Upper Cretaceous) of the Dalmatian region (southern Croatia) is documented here for the first time. The specimen represents the first articulated dentition of a ptychodontid shark that has been discovered from the Balkan Peninsula and the most complete ever found for the un-cuspidate species P. decurrens up to now. The reconstruction of the entire lower dentition of P. decurrens based on this exceptionally well-preserved dentition shows a wider crushing plate than previously hypothesised with bulgy teeth limited to the central area. Even though a defined cusp is missing, the occlusal surface of the teeth is undeniably raised and bulgy in some un-cuspidate species of Ptychodus (e.g., P. decurrens). This compels us to reconsider the use of terms such as high- and low-crowned as well as cuspidate and un-cuspidate. In addition, specimens previously assigned to dubious species (P. depressus, P. levis and P. oweni) or even varieties (P. polygyrus var. sulcatus and P. decurrens var. multiplicatus) are reassigned here to P. decurrens based on a careful comparison of the type materials. The reassessment of tooth root morphologies provides indicative traits for the identification of different genera of ptychodontid sharks (Paraptychodus and Ptychodus). The taxonomic revision presented here is crucial for securing a stable taxonomy and systematics of the shell-crushing shark P. decurrens, as well as of all ptychodontid sharks. The resulting updated taxonomy, together with the description and reconstruction of the new crushing plate, greatly contribute to a better understanding of one of the most enigmatic families (Ptychodontidae) of Mesozoic elasmobranchs. The detailed investigation of the new dentition of Ptychodus from Dalmatia is also a further step towards the discovery of Upper Cretaceous ichthyofaunas of one of the most palaeontologically important areas of the Balkan Peninsula. Supplementary Information The online version contains supplementary material available at 10.1186/s13358-024-00340-7.
View
... We compiled the neurocranium length (NL; i.e., anteroposterior distance of the skull between the rostral tip and occipital centrum) data from illustrations in the literature in which scale bars and specimen orientation allowed linear calculation of NL as well as radiographic (X-ray or computed tomography) images or neurocranial specimens from non-embryonic shark individuals, each with a known TL. Specifically, we gathered data from the following papers: White (1895), Cappetta (1980), Compagno (1988Compagno ( , 1990, Duffin (1988), Shirai (1992), Goto (2001), Kriwet and Klug (2004), Thies and Leidner (2011), Mollen et al. (2012Mollen et al. ( , 2016, Denton et al. (2018), Weigmann et al. (2020), Pfeil (2021), Vullo et al. (2021Vullo et al. ( , 2024, Jambura et al. (2023), Staggl et al. (2023), Viana and Soares (2023), and White et al. (2024) (Appendices 1-2; note that incomplete fossil specimens or privately owned specimens are not included: e.g., many specimens in Pfeil, 2021). Extant individuals without TL or NL data as well as fossil specimens with missing body parts or unmeasurable TL or NL were not included. ...
... This is interpreted to be due to the fact that the "remaining taxa" are dominated by those with a "conventional shark design", where the range of ways in which "100%" can be divided up into three parts (NP, TP, and CP) under the "conventional" body plan is simply limited. Regardless, one major observation that can be gleaned from Figure 2 is the scattering of lamniforms throughout the dendrogram (Figure 2), likely indicating that Lamniformes exploited wide-ranging combinations of body part proportions, which in turn seems to reflect their broad morphological and ecological diversity (e.g., Compagno, 1990;Ebert et al., 2021;Vullo et al., 2021Vullo et al., , 2024. More importantly in the context of this present study, the close clustering of †Otodus megalodon with Negaprion brevirostris indicates that the slender body plan for †O. ...
Reassessment of the possible size, form, weight, cruising speed, and growth parameters of the extinct megatooth shark, Otodus megalodon (Lamniformes: Otodontidae), and new evolutionary insights into its gigantism, life history strategies, ecology, and extinction
Article
Full-text available
  • Mar 2025
  • PALAEONTOL ELECTRON
Otodus megalodon (Lamniformes: Otodontidae) is an iconic Neogene shark, but the lack of well-preserved skeletons has hampered our understanding of various aspects of its biology. Here, we reassess some of its biological properties using a new approach, based on known vertebral specimens of O. megalodon and 165 species of extinct and extant neoselachian sharks across ten orders. Using the median neurocranial and caudal fin proportions relative to the trunk proportion among non-mitsukurinid/non-alopiid lamniforms, we show that O. megalodon could have had a slender body and possibly reached about 24.3 m in length. Allometric considerations indicate that a stout body plan like the extant white shark (Carcharodon carcharias) for O. megalodon could have incurred excessive hydrodynamic costs, further supporting the interpretation that O. megalodon likely had a slenderer body than C. carcharias. A 24.3-m-long O. megalodon may have weighed around 94 t, with an estimated cruising speed of 2.1–3.5 km h⁻¹. A reanalysis of vertebral growth bands suggests a size at birth of 3.6–3.9 m for O. megalodon, supporting the previous interpretations of its ovoviviparity and embryos’ intrauterine oophagous behavior, but less likely the need for nursery areas. Additional inferred growth patterns corroborated by the known fossil record support the hypothesis that the emergence of C. carcharias during the Early Pliocene is at least partly responsible for the demise of O. megalodon due to competition for resources. These interpretations are working hypotheses expected to serve as reasonable reference points for future studies on the biology of O. megalodon.
View
... However, there is a limit to the information that teeth and their limited character sets can provide for estimates of phylogeny and evolutionary timing [8], and the cartilaginous skeletons of these early crown-group selachians, which would provide more information, have a low preservational potential. Even in those Mesozoic Fossil-Lagerstätten that do preserve potentially information-rich skeletons, these fossils are often flattened [9][10][11][12][13], making it difficult to extract the level of detailed three-dimensional skeletal data that has demystified much of the record of sharks' older, Palaeozoic relatives [14][15][16]. This restricts understanding of key phylogenetic problems at the roots of selachians [17], limits the extent to which traits can be incorporated into macroevolutionary studies [1] and obscures the morphological evolution that led to modern shark biodiversity. ...
Three-dimensional fossils of a Cretaceous collared carpet shark (Parascylliidae, Orectolobiformes) shed light on skeletal evolution in galeomorphs
Article
Full-text available
  • Apr 2025
A rich fossil record of teeth shows that many living shark families’ origins lie deep in the Mesozoic. Skeletal fossils of the sharks to whom these teeth belonged are far rarer and when they are preserved are often flattened, hindering understanding of the evolutionary radiation of living shark groups. Here we use computed tomography to describe two articulated Upper Cretaceous shark skeletons from the Chalk of the UK preserving three-dimensional neurocrania, visceral cartilages, pectoral skeletons and vertebrae. These fossils display skeletal anatomies characteristic of the Parascylliidae, a family of Orectolobiformes now endemic to Australia and the Indo Pacific. However, they differ in having a more heavily mineralized braincase and a tri-basal pectoral fin endoskeleton, while their teeth can be attributed to a new species of the problematic taxon Pararhincodon. Phylogenetic analysis of these new fossils confirms that Pararhincodon is a stem-group parascylliid, providing insight into the evolution of parascylliids’ distinctive anatomy during the late Mesozoic–Cenozoic shift in orectolobiform biodiversity from the Northern Atlantic to the Indo Pacific. Meanwhile both Pararhincodon and extant parascylliids have a distinctive vertebral morphology previously described only in Carcharhiniformes, contributing a skeletal perspective to the picture emerging from macroevolutionary analyses of coastal, small-bodied origins for galeomorphs.
View
... Furthermore, Takeda et al. (2016) identified reptiles, fishes, and various cephalopods (including ammonoids, coleoids, and nautiloids) as key predators in the Western Interior Seaway, spanning the Turonian to the Maastrichtian. Ifrim (2013) and Vullo et al. (2024) hypothesized that the fossil shark Ptychodus was responsible for the ventral injuries observed in the ammonoid Pseudaspidoceras flexuosum from the Turonian of Mexico. Regarding lateral breakage, Fraaye (1996) interpreted the damaged specimen reported by Radwański (1996) as a sublethal injury inflicted by a predatory decapod. ...
Lethal injuries on the scaphitid ammonoid Hoploscaphites nicolletii (Morton, 1842) in the Upper Cretaceous Fox Hills Formation, South Dakota, USA
Article
Full-text available
  • Jan 2025
Predator–prey relationships are considered a major driver for the evolution of organisms, and thus contributed to shaping morphology, ecology, and diversity. During the Late Cretaceous of North America, ammonoid cephalopods were one of the most abundant and diverse marine invertebrates. Despite frequent reports of shell breakage in ammonoids, little is known pertaining to the frequency, position, and size of the shell break through a stratigraphic succession. In this study, we analyze an extensive collection of the scaphitid ammonoid Hoploscaphites nicolletii , which exhibits shell breakage, from the Upper Cretaceous (Maastrichtian) Fox Hills Formation in South Dakota, USA. We focus on four upper Maastrichtian assemblage zones listed stratigraphically from bottom to top—the lower nicolletii Assemblage Zone (LNAZ), the Limopsis - Gervillia Assemblage Zone (LGAZ), the upper nicolletii Assemblage Zone (UNAZ), and the Protocardia - Oxytoma Assemblage Zone (POAZ). Within the collection, we observed two primary types of breakage: ventral and lateral, each displaying a relatively consistent geometry. Lateral breaks, measuring a few centimeters, represent about 20–40% of the maximum conch diameter. Ventral breaks are slightly larger, representing 30–70% of the diameter. Both breakage types occur in the body chamber at approximately 90° from the aperture extending to near the last septum. We find that the incidence of injury increased from 6.6 to 13.7% with some fluctuation across the zones. The breakage size relative to body size does not exhibit a clear change across the assemblage zones. Additionally, no significant difference is apparent in the body size between injured and uninjured specimens within each zone. A weak positive correlation between the size of lateral breaks and maximum conch diameter in LNAZ suggests a tendency for larger predators to target larger individuals. Given the consistency of geometry and size, we presume that these breaks represent lethal injuries from durophagous predators. We propose coleoid cephalopods as the likely culprits for ventral injuries, although fish and crustaceans are plausible alternatives. Concerning lateral injuries, decapod crustaceans appear to be the most probable durophagous predators.
View
... Ptychodus mortoni is known from marine deposits in North America (United States), South America (Mexico), Europe, and Africa (e.g., Applegate 1970;Cappetta 1987;Shimada et al. 2010;Ciampagalio et al. 2013; see review of localities by Blanco-Piñón et al. 2007). Similar to modern durophagous sharks with molariform teeth, the genus Ptychodus is interpreted to be a benthic predator (e.g., Shimada et al. 2009Shimada et al. , 2010) that consumed hard-shelled macroinvertebrates by crushing or crunching (Ciampagalio et al. 2005;Shimada 2012;Amadori et al. 2022), although nektonic turtles and ammonites have also been proposed as components of their diets (Vullo et al. 2024). Thus, lamniform and P. mortoni diets inferred from tooth morphology suggest that there may be some habitat differences or partitioning among the sampled taxa (e.g., offshore vs. nearshore, benthic vs. nektonic). ...
Oxygen isotope composition of teeth suggests endothermy and possible migration in some Late Cretaceous shark taxa from the Gulf Coastal Plain, USA
Article
Full-text available
  • Jan 2025
  • PALEOBIOLOGY
We analyzed the oxygen isotope composition of biogenic apatite phosphate (δ18Op) in fossil tooth enameloid to investigate the paleoecology of Late Cretaceous sharks in the Gulf Coastal Plain of Alabama, USA. We analyzed six different shark taxa from both the Mooreville Chalk and the Blufftown Formation. We compared shark δ18Op with the δ18Op of a co-occurring poikilothermic bony fish Enchodus petrosus as a reference for ambient conditions. Enchodus petrosus tooth enamel δ18Op values are similar between formations (21.3‰ and 21.4‰ Vienna Standard Mean Ocean Water [VSMOW], respectively), suggesting minimal differences in water δ18O between formations. Most shark taxa in this study are characterized by δ18Op values that overlap with E. petrosus values, indicating they likely lived in similar habitats and were also poikilothermic. Ptychodus mortoni and Cretoxyrhina mantelli exhibit significantly lower δ18Op values than co-occurring E. petrosus (P. mortoni δ18Op is 19.1‰ VSMOW in the Mooreville Chalk; C mantelli δ18Op is 20.2‰ VSMOW in the Mooreville Chalk and 18.1‰ VSMOW in the Blufftown Formation). Excursions into brackish or freshwater habitats and thermal water-depth gradients are unlikely explanations for the lower P. mortoni and C. mantelli δ18Op values. The low P. mortoni δ18Op value is best explained by higher body temperature relative to surrounding temperatures due to active heating (e.g., mesothermy) or passive heating due to its large body size (e.g., gigantothermy). The low C. mantelli δ18Op values are best explained by a combination of mesothermy (e.g., active heating) and migration (e.g., from the Western Interior Seaway, low-latitude warmer waters, or the paleo–Gulf Stream), supporting the hypothesis that mesothermy evolved in lamniform shark taxa during the Late Cretaceous. If the anomalous P. mortoni δ18Op values are also driven by active thermoregulation, this suggests that mesothermy evolved independently in multiple families of Late Cretaceous sharks.
View
... Several groups of Mesozoic marine reptiles evolved durophagy, such as the placodont sauropterygians [69], several ichthyosaur lineages [70], and, among mosasaurid squamates, the mosasaurids Globidens, Carinodens [25] and Prognathodon currii [17]. Several sharks such as Heterodon and Ptychodus [71] and actinopterygian fishes such as pycnodontiforms are or were also durophagous. All these taxa are specialized for eating relatively hard prey items (cephalopods, bivalves, echinoderms, corals, sponges, etc.) and, to the extent Carinodens resembles them, it can be assumed to represent a durophage. ...
A New Species of the Durophagous Mosasaurid Carinodens from the Late Maastrichtian Phosphates of Morocco and Implications for Maastrichtian Mosasaurid Diversity
Article
Full-text available
Late Cretaceous marine ecosystems saw a major adaptive radiation of mosasaurids, which evolved highly disparate jaw and tooth morphologies to feed on different prey. A striking pattern seen in mosasaurids was a high diversity of durophagous forms. Durophagy likely evolved several times independently in the mosasaurine genera Globidens, Prognathodon, and Carinodens. Carinodens is unusual in having low, rectangular, laterally compressed teeth. The genus is known from around the world, with the species Carinodens minalmamar and C. belgicus previously reported from the Maastrichtian Phosphates of Morocco. Here, we report a new species of Carinodens, C. acrodon, from the same Maastrichtian Phosphates. It is characterized by teeth with tall crowns, triangular apices, and broad bases. Many of the diagnostic features of this species appear to be plesiomorphies, suggesting the persistence of a primitive species of Carinodens into the latest Maastrichtian alongside the more derived C. minalmamar and C. belgicus. The new species contributes to an emerging pattern of mosasaurid hyperdiversity in the late Maastrichtian of Morocco. A revised faunal list, including stratigraphic range extensions of Khinjaria and Stelladens into the latest Maastrichtian of upper Couche III of the Phosphates of Morocco, suggests at least 16 species of mosasauroid coexisted here.
View
View
Three-dimensional fossils of a Cretaceous collared carpet shark (Parascylliidae, Orectolobiformes) shed light on skeletal evolution in galeomorphs
Preprint
Full-text available
  • Mar 2025
A rich fossil record of teeth shows that many living shark families' origins lie deep in the Mesozoic. Skeletal fossils of the sharks to whom these teeth belonged are far rarer and when they are preserved are often flattened, hindering understanding of the evolutionary radiation of living shark groups. Here we use computed tomography to describe two articulated Upper Cretaceous shark skeletons from the Chalk of the UK preserving three-dimensional neurocrania, visceral cartilages, pectoral skeletons and vertebrae. These fossils display skeletal anatomies characteristic of the Parascylliidae, a family of Orectolobiformes now endemic to Australia and the Indo Pacific. However, they differ in having a more heavily mineralised braincase and a tri-basal pectoral fin endoskeleton, while their teeth can be attributed to a new species of the problematic taxon Pararhincodon. Phylogenetic analysis of these new fossils confirms that Pararhincodon is a stem-group parascylliid, providing insight into the evolution of parascylliids' distinctive anatomy during the late Mesozoic-Cenozoic shift in orectolobiform biodiversity from the Northern Atlantic to the Indo Pacific. Meanwhile both Pararhincodon and extant parascylliids have a distinctive vertebral morphology previously described only in Carcharhiniformes, contributing a skeletal perspective to the picture emerging from macroevolutionary analyses of coastal, small-bodied origins for galeomorphs.
View
View
View
Late Cretaceous coprolite from the Opole area (southern Poland) as evidence for a variable diet in shell-crushing shark Ptychodus (Elasmobranchii: Ptychodontidae)
Article
Full-text available
  • Dec 2023
Background Coprolites, i.e ., fossilized faeces, are an important source of knowledge on the diet and food processing mechanisms in the fossil record. Direct and indirect evidences for the dietary preferences of extinct sharks are rare in the fossil record. The first coprolite attributable to Ptychodus containing prey remains from the European Cretaceous is documented here. Methods A coprolite from the Late Cretaceous of Opole (southern Poland) was scanned using micro-computed tomography to show the arrangement of the inclusions. In addition, the cross-section was examined under the SEM/EDS to analyse the microstructure and chemical composition of the inclusions. Results Brachiopod shell fragments and foraminiferan shells are recognized and identified among the variously shaped inclusions detected through the performed analysis. Conclusions The extinct shell-crushing shark Ptychodus has been identified as the likely producer of the examined coprolite. The presence of brachiopod shell fragments indicates that at least some species of this durophagous predatory shark may have preyed on small benthic elements on the sea bottom.
View
Skeletal convergence in thunniform sharks, ichthyosaurs, whales, and tunas, and its possible ecological links through the marine ecosystem evolution
Article
Full-text available
  • Oct 2023
Tunas, lamnid sharks, modern whales, and derived ichthyosaurs converged on the thunniform body plan, with a fusiform body, lunate caudal fin, compressed peduncle, and peduncle joint. This evolutionary convergence has been studied for a long time but little is known about whether all four clades share any skeletal characteristics. Comparisons of vertebral centrum dimensions along the body reveal that the four clades indeed share three skeletal characteristics (e.g., thick vertebral column for its length), while an additional feature is shared by cetaceans, lamnid sharks, and ichthyosaurs and two more by lamnid sharks and ichthyosaurs alone. These vertebral features are all related to the mechanics of thunniform swimming through contributions to posterior concentration of tail-stem oscillation, tail stem stabilization, peduncle joint flexibility, and caudal fin angle fixation. Quantitative identifications of these features in fossil vertebrates would allow an inference of whether they were a thunniform swimmer. Based on measurements in the literature, mosasaurs lacked these features and were probably not thunniform swimmers, whereas a Cretaceous lamniform shark had a mosaic of thunniform and non-thunniform features. The evolution of thunniform swimming appears to be linked with the evolution of prey types and, in part, niche availability through geologic time.
View
Systematics and Phylogenetic Interrelationships of the Enigmatic Late Jurassic Shark Protospinax annectans Woodward, 1918 with Comments on the Shark–Ray Sister Group Relationship
Article
Full-text available
The Late Jurassic elasmobranch Protospinax annectans is often regarded as a key species to our understanding of crown group elasmobranch interrelationships and the evolutionary history of this group. However, since its first description more than 100 years ago, its phylogenetic position within the Elasmobranchii (sharks and rays) has proven controversial, and a closer relationship between Protospinax and each of the posited superorders (Batomorphii, Squalomorphii, and Galeomorphii) has been proposed over the time. Here we revise this controversial taxon based on new holomorphic specimens from the Late Jurassic Konservat-Lagerstätte of the Solnhofen Archipelago in Bavaria (Germany) and review its skeletal morphology, systematics, and phylogenetic interrelationships. A data matrix with 224 morphological characters was compiled and analyzed under a molecular backbone constraint. Our results indicate a close relationship between Protospinax, angel sharks (Squatiniformes), and saw sharks (Pristiophoriformes). However, the revision of our morphological data matrix within a molecular framework highlights the lack of morphological characters defining certain groups, especially sharks of the order Squaliformes, hampering the phylogenetic resolution of Protospinax annectans with certainty. Furthermore, the monophyly of modern sharks retrieved by molecular studies is only weakly supported by morphological data, stressing the need for more characters to align morphological and molecular studies in the future.
View
The extinct shark, Ptychodus (Elasmobranchii, Ptychodontidae) in the Upper Cretaceous of central-western Russia-The road to easternmost peri-Tethyan seas
Article
Full-text available
  • Feb 2023
Isolated teeth belonging to the genus Ptychodus Agassiz, 1834 (Chondrichthyes; Elasmobranchii) from the Upper Cretaceous of the Ryazan and Moscow Oblast regions (European Russia) are described and discussed in detail herein. The taxonomic composition of the Ptychodus assemblage from the Ryazan region is very diverse including the first records of the cuspidate species P. altior and P. anonymus, which thus is largely consistent with those from other contemporaneous European localities. Ptychodus ubiquitously inhabited epicontinental seas of Europe during most of the Cretaceous with the most diverse assemblages coming from southern England, northern Italy, Belgium, and European Russia. Additionally, the material documented here from the Cenomanian of Varavinsky ravine area (Moscow Oblast) represents the northernmost occurrence of Ptychodus hitherto reported from Europe. It is evident that the Late Cretaceous shallow seas of the Russian platform represented a crucial pathway for the dispersal of Ptychodus from the European peri-Tethys to the eastern margins of the Neo-Tethyan Ocean. The Albian-Campanian records of Ptychodus from Europe indicate that its dominance in the peri-Tethys persisted for most of its evolutionary history. A local temperature drop across most of the European shallow seas probably contributed to the narrowing of its geographic range in the peri-Tethyan seas towards the end of the Mesozoic Era. The fossil remains of Ptychodus documented herein are accordingly of utmost importance for better understanding the taxonomic composition of Russian fossil ichthyofaunas and also inform about the dispersal of Ptychodus towards western and eastern peri-Tethyan seas during the Late Cretaceous.
View
A new cuspidate ptychodontid shark (Chondrichthyes; Elasmobranchii), from the Upper Cretaceous of Morocco with comments on tooth functionalities and replacement patterns
Article
Full-text available
  • Jan 2022
  • J AFR EARTH SCI
The first articulated dentition of †Ptychodus from Africa is described herein. The specimen, likely coming from the Turonian of the Asfla area (Goulmima region, southeastern Morocco), exhibits a well-preserved lower dental plate of a second-level predator. A new species, †P. maghrebianus sp. nov., is erected herein based on this durophagous dentition characterised by imbricated cuspidate teeth. We employed for the first time in †Ptychodus multiple quantitative analyses and statistical parametric and non-parametric tests to process biometrical data taken from articulated, associated and isolated teeth. The quantitative approach (morphospace analysis) is exploited herein to support the traditional taxonomic identification (qualitative examination) of †P. maghrebianus sp. nov. and to separate it from the similar cuspidate species, †P. mortoni. Morphospace reconstructions confirm a marked lower dental heterodonty (mesio-distal patterns) for both species. The analysis protocol employed here also allows assigning indeterminate teeth as belonging to †P. mortoni. The reconstruction of the entire lower dental plate of †P. maghrebianus sp. nov. shows a cuspidate dentition probably able to reduce tooth damages when crushing thin-shelled prey. Both dental morphologies and tooth wear patterns suggest a peculiar food processing and a diet mainly consisting of bivalves, decapods and small fish for this durophagous predator. Trophic reconstructions of the Turonian ichthyofauna inhabiting the middle to outer ramp environment of the Asfla area emphasize that †P. maghrebianus sp. nov. and the batoid †Tingitanius most likely represented second-level consumers, whereas the sclerorhynchiforms †Asflapristis and †Ptychotrygon represented third-level predators. Top positions within the food web were occupied by larger predaceous elasmobranchs (e.g., †Squalicorax).
View
The Italian record of the Cretaceous shark, Ptychodus latissimus Agassiz, 1835 (Chondrichthyes; Elasmobranchii)
Article
Full-text available
  • Nov 2020
Associated and isolated teeth of the extinct elasmobranch Ptychodus latissimus Agassiz, 1835 from the Upper Cretaceous Scaglia Rossa pelagic limestone of northern Italy are described and discussed here in detail for the first time. The dentition of this widely distributed species consists of low-crowned molariform teeth that exhibit marked and strong occlusal ornamentations suitable for crushing hard-shelled prey. The associated tooth sets and isolated teeth analyzed here are heterogeneous in size and crown outline, but unambiguously belong to a single species. Re-examination of this Italian material consisting of ca. 30 specimens mostly coming from historical collections allows for a rigorous assessment of the intraspecific variability of P. latissimus, including the identification of three different tooth “morphotypes” based on their positions within the jaws. The relatively flat crowns and occlusal sharp and thick ridges indicate a high adaptation for crushing hard-shelled prey in P. latissimus indicating that the durophagous adaptations of this species were certainly more pronounced than in all other species of Ptychodus. We hypothesize that P. latissimus was a third-level predator occupying habitats with abundant thickshelled prey, such as inoceramid bivalves and ammonites.
View
TNT version 1.6, with a graphical interface for MacOS and Linux, including new routines in parallel
Article
  • Jan 2023
A new graphical user interface (GUI) for the parsimony program TNT is presented that works under the Linux and Mac operating systems, as well as the Cygwin environment (which runs under Windows). The new interface is based on the GIMP Tool Kit, GTK (version 3). Formerly, only Windows versions of TNT had a GUI. The new interface improves upon the existing Windows GUI in several respects. These changes, together with several additions to the program since the publication of version 1.5, warrant a change in minor version, thus moving from version 1.5 to 1.6. Among the most notable improvements are the possibility to access graphical user dialogs by means of simple commands, to easily save trees in SVG format (“Scalable Vector Graphics”) directly from any tree‐diagram being displayed, and to manage analyses in parallel (using multiple processors, by means of the PVM system or “Parallel Virtual Machine”), as well as a generally more stable and consistent behaviour. As the binaries for the new version are compiled as native 64‐bit applications, this removes the limitations for accessing large amounts of memory in the previous GUI Windows interface (which is a 32‐bit application).
View
Thalassotitan atrox, a giant predatory mosasaurid (Squamata) from the Upper Maastrichtian Phosphates of Morocco
Article
  • Aug 2022
  • CRETACEOUS RES
A B S T R A C T The Cretaceous-Paleogene (K-Pg) transition saw mass extinctions in terrestrial and marine ecosystems. Terrestrial vertebrate diversity patterns across the K-Pg boundary have seen extensive study, but less is known about marine vertebrates. We describe a new mosasaurid from the latest Maastrichtian phosphatic beds of Morocco, showing how mosasaurids evolved to become apex predators in the latest Cretaceous. Thalassotitan atrox n. gen. et sp., from the Oulad Abdoun Basin of Khouribga Province, Morocco is characterized by large size, a broad skull, massive jaws, and reduced cranial kinesis, suggesting it was highly adapted for carnivory. Teeth resemble those of killer whales in their robust, conical shape, and show heavy wear and damage. Phylogenetic analysis recovers Thalassotitan as a close relative of Prognathodon currii and P. saturator within the Prognathodontini. Among the associated fauna, three genera of mosasaurids, elasmosaurid plesiosaur, chelonioid turtle, and enchodontid fish show acid damage, and could be prey ingested by mosasaurids, likely Thalassotitan. Thalassotitan shows mosasaurids evolved to fill the marine apex predator niche, a niche occupied by orcas and white sharks today. Mosasaurs continued to diversify and fill new niches until their extinction at the end of the Cretaceous.
View
A reconsideration of inapplicable characters, and an approximation with step‐matrix recoding
Article
  • Apr 2021
Evidence for phylogenetic analysis comes in the form of observed similarities, and trees are selected to minimize the number of similarities that cannot be accounted for by homology (homoplasies). Thus, the classical argument for parsimony directly links homoplasy with explanatory power. When characters are hierarchically related, a first character may represent a primary structure such as tail absence/presence and a secondary (subordinate) character may describe tail colour; this makes tail colour inapplicable when tail is absent. It has been proposed that such character hierarchies should be evaluated on the same logical basis as standard characters, maximizing the number of similarities accounted for by secondary homology, i.e. common ancestry. Previous evaluations of the homology of a given ancestral reconstruction contain the unintuitive quantity “subcharacters” (number of regions of applicability). Rather than counting subcharacters, this paper proposes an equivalent but more intuitive formulation, based on counting the number of changes into each separate state. In this formulation, x‐transformations, the homoplasy for the reconstruction is simply the number of changes into the state beyond the first, summed over all states. There is thus no direct connection between homoplasy and number of steps, only between homoplasy and extra steps. The link between the two formulations is that, for any region of applicability of any character, a subcharacter can be interpreted as the change into the state that is plesiomorphic in that region. Although some authors have claimed that the equivalence between maximizing explanatory power and minimizing independent originations of similar features (i.e. the standard justification of parsimony) does not hold for inapplicable characters, evaluating homoplasy with x‐transformations clearly connects the two sides of that equation. Furthermore, as the evaluation with x‐transformations provides a direct count and a straightforward interpretation of homoplasy, it extends naturally into implied weighting, and sheds light on problems with additive, step‐matrix or continuous characters. It also allows deriving transformation costs for recoding hierarchies as step‐matrix characters (where recoded states correspond to permissible combinations of states in primary and secondary characters), so that homology of the original observations is properly measured. Those transformation costs set the cost of gaining the primary structure to the maximum difference between “present” states plus cost of loss, and difference between “present” states to the sum of user‐defined transformation costs between secondary features. With such recoding, invoking multiple independent derivations of the structure and similar features will cost as many extra “steps” as the instances of similarities (in both original characters) that are not being homologized. The step‐matrix recoding also can take into account nested dependences. We present a simple convention for naming characters, which TNT can use to automatically convert the original data into a step‐matrix form and set the proper transformation costs. Finally, the basic elements for handling inapplicable characters in the context of maximum‐likelihood inference are outlined, and some quantitative comparisons between different approaches to inapplicables are provided.
View
Manta-like planktivorous sharks in Late Cretaceous oceans
Article
  • Mar 2021
A soaring shark Modern sharks occupy marine ecosystems across the world but display little morphological diversity, being mostly streamlined predators. Vullo et al. describe a new species of shark from the late Cretaceous that shows that the lack of current variation is not due to limited morphological “exploration” in the past. Specifically, Aquilolamna milarcae displays many features similar to modern manta rays, notably long, slender fins and a mouth seemingly adapted to filter feeding, suggesting that it was planktivorous. This finding indicates both that elasmobranchs evolutionarily experimented with other forms and that the planktivorous “soarers” emerged in this group at least 30 million years earlier than previously recognized. Science , this issue p. 1253
View