Mohamad Bazzi

All Publications

• Extinction threatens to cause morphological and ecological homogenization in sharks. Science advances Bazzi, M., Lloyd, W. L., Ebersole, J. A., Sternes, P. C., Al Aswad, J. A., Payne, J. L. 2025; 11 (44): eaea0278

  Abstract

  Global shark biodiversity is in decline, with numerous species facing extinction because of anthropogenic influence. Loss of species richness is expected to diminish trait diversity, encompassing ecological roles and physiological adaptations. We investigate whether the extinction of threatened species, as classified by the International Union for Conservation of Nature, drives morphological and ecological homogenization within Carcharhinus, a speciose genus of requiem sharks. We assembled a dataset of tooth morphology from 30 species and combined it with functional data such as diet, habitat, and body size. Simulated extinction scenarios, where species were sequentially removed from the highest to lowest threat level, revealed that the loss of threatened species would result in marked homogenization of morphology and ecology. Along this extinction trajectory, trait structures become increasingly depauperate, marked by contracting depth ranges and declining body-size diversity. Our results indicate that the diverse dental morphologies, shaped over millions of years, are at risk of disappearing-eroding the genus's capacity to support varied ecological roles.

  View details for DOI 10.1126/sciadv.aea0278

  View details for PubMedID 41160684

• Early gigantic lamniform marks the onset of mega-body size in modern shark evolution. Communications biology Bazzi, M., Siversson, M., Wintner, S., Newbrey, M., Payne, J. L., Campione, N. E., Roberts, A. J., Natanson, L. J., Hall, S., Blake, T., Kear, B. P. 2025; 8 (1): 1499

  Abstract

  Lamniform sharks are amongst the largest-bodied extant fishes and have an evolutionary history spanning ~135 million years (Ma). Fossils correlate their initial development of mega-body size (≥6m) with ecological radiation as marine top-predators during the later part of the mid-Cretaceous (after the late Albian, ~100Ma). Here, we push back this earliest appearance of gigantic lamniforms by ~15Ma (upper Aptian, ~115Ma) with the discovery of enormous cardabiodontid shark remains from northern Australia. We compiled a comprehensive dataset of vertebral centrum diameters versus maximum body length measurements for living lamniforms to calculate length and mass estimates of extinct taxa using both intraspecific and interspecific regression models. Our results show that mega-body size is an ancient lamniform trait, with the Australian cardabiodontid being around 6-8m and over 3 tons. This rivalled some of the largest coeval marine reptiles and suggests that lamniforms invaded top-predator niches from an early stage in their adaptive evolution.

  View details for DOI 10.1038/s42003-025-08930-y

  View details for PubMedID 41139160

• Cretaceous sea turtle soft tissues clarify ancestry of scale loss in chelonioids ISCIENCE Kear, B. P., Nohra, R., Lindgren, J., Rabi, M., Bazzi, M. 2025; 28 (11): 113641

  Abstract

  Scale loss is a quintessential hydrodynamic adaptation in marine reptiles, and paralleled the pelagic specializations of Mesozoic ichthyosaurs, plesiosaurs, and metriorhynchid crocodylians, as well as the modern Leatherback Sea turtle (Dermochelyidae). By contrast, modern hard-shelled sea turtles (Cheloniidae) retain both scutes and scaly flippers, despite evolving from among partially scale-less antecedents after the earliest Eocene, ∼54 million years (Ma) ago. Here, we resolve the ambiguous ancestry of scale loss using the oldest known sea turtle (total-group Chelonioidea) soft tissues preserved in a mid-Cretaceous (middle-to-upper Cenomanian, ∼97 Ma) protostegid (basally divergent chelonioid) from Lebanon. This fossil combines scale-less flipper skin with a scuted carapace similar to other extinct chelonioids, but confirms lineage specific rather than ubiquitous scale loss in an ancestral states analysis. Scale-less skin is therefore an ancient sea turtle trait that was repeatedly modified from scaly ancestors within disparate chelonioid clades during their recurrent independent invasions of oceanic environments.

  View details for DOI 10.1016/j.isci.2025.113641

  View details for Web of Science ID 001607898100013

  View details for PubMedID 41210992

  View details for PubMedCentralID PMC12595121

• The famous fish beds of Lebanon: the Upper Cretaceous Lagerstätten of Haqel, Hjoula, Nammoura and Sahel Aalma JOURNAL OF THE GEOLOGICAL SOCIETY George, H., Bazzi, M., El Hossny, T., Ashraf, N., Saad, P., Clements, T. 2024; 181 (5)

  View details for DOI 10.1144/jgs2023-210

  View details for Web of Science ID 001270254000002

• A unique example of the Late Cretaceous horseshoe crab <i>Tachypleus syriacus</i> preserves transitional bromalites ALCHERINGA Bicknell, R. D. C., Bazzi, M., Meling, C., Rashkova, A., Pankowski, M. V., Botton, M., Cuomo, C. 2024

  View details for DOI 10.1080/03115518.2024.2348748

  View details for Web of Science ID 001228205500001

• Physiology and climate change explain unusually high similarity across marine communities after end-Permian mass extinction. Science advances Al Aswad, J. A., Penn, J. L., Monarrez, P. M., Bazzi, M., Deutsch, C., Payne, J. L. 2025; 11 (13): eadr4199

  Abstract

  Fossil assemblages exhibit a global depletion in taxonomic distinctiveness in the aftermath of the end-Permian mass extinction (~252 million years ago), but little is known about why. Here, we examine whether biotic homogenization can be explained by tropical survivors tracking an expansion of their preferred habitat, measured in terms of the ratio of environmental oxygen supply to metabolic demand. We compare spatial similarity in community composition among marine invertebrate fossils represented by bivalve and gastropod fossils with predictions from an ecophysiological model of habitat that diagnoses areas in the ocean that can sustain the aerobic requirements of marine invertebrates. Modeled biogeographic responses to climate change yield an increase in global similarity of community composition among surviving ecophysiotypes, consistent with patterns in the fossil record and arguing for a physiological control on earliest Triassic biogeography.

  View details for DOI 10.1126/sciadv.adr4199

  View details for PubMedID 40138424

• 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. Palaeontologia electronica (Online) Shimada, K., Motani, R., Wood, J. J., Sternes, P. C., Tomita, T., Bazzi, M., Collareta, A., Gayford, J. H., Türtscher, J., Jambura, P. L., Kriwet, J., Vullo, R., Long, D. J., Summers, A. P., Maisey, J. G., Underwood, C., Ward, D. J., Maisch, H. M., Perez, V. J., Feichtinger, I., Naylor, G. J., Moyer, J. K., Higham, T. E., da Silva, J. P., Bornatowski, H., González-Barba, G., Griffiths, M. L., Becker, M. A., Siversson, M. 2025; 28 (1): 1502

  Abstract

  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 details for DOI 10.26879/1502

  View details for PubMedID 40105087

  View details for PubMedCentralID PMC7617484

• Cautionary tales on the use of proxies to estimate body size and form of extinct animals. Ecology and evolution Gayford, J. H., Engelman, R. K., Sternes, P. C., Itano, W. M., Bazzi, M., Collareta, A., Salas-Gismondi, R., Shimada, K. 2024; 14 (9): e70218

  Abstract

  Body size is of fundamental importance to our understanding of extinct organisms. Physiology, ecology and life history are all strongly influenced by body size and shape, which ultimately determine how a species interacts with its environment. Reconstruction of body size and form in extinct animals provides insight into the dynamics underlying community composition and faunal turnover in past ecosystems and broad macroevolutionary trends. Many extinct animals are known only from incomplete remains, necessitating the use of anatomical proxies to reconstruct body size and form. Numerous limitations affecting the appropriateness of these proxies are often overlooked, leading to controversy and downstream inaccuracies in studies for which reconstructions represent key input data. In this perspective, we discuss four prominent case studies (Dunkleosteus, Helicoprion, Megalodon and Perucetus) in which proxy taxa have been used to estimate body size and shape from fragmentary remains. We synthesise the results of these and other studies to discuss nuances affecting the validity of taxon selection when reconstructing extinct organisms, as well as mitigation measures that can ensure the selection of the most appropriate proxy. We argue that these precautionary measures are necessary to maximise the robustness of reconstructions in extinct taxa for better evolutionary and ecological inferences.

  View details for DOI 10.1002/ece3.70218

  View details for PubMedID 39224151

  View details for PubMedCentralID PMC11368419

• Static Dental Disparity and Morphological Turnover in Sharks across the End-Cretaceous Mass Extinction CURRENT BIOLOGY Bazzi, M., Kear, B. P., Blom, H., Ahlberg, P. E., Campione, N. E. 2018; 28 (16): 2607-+

  Abstract

  The Cretaceous-Palaeogene (K-Pg) mass extinction profoundly altered vertebrate ecosystems and prompted the radiation of many extant clades [1, 2]. Sharks (Selachimorpha) were one of the few larger-bodied marine predators that survived the K-Pg event and are represented by an almost-continuous dental fossil record. However, the precise dynamics of their transition through this interval remain uncertain [3]. Here, we apply 2D geometric morphometrics to reconstruct global and regional dental morphospace variation among Lamniformes (Mackerel sharks) and Carcharhiniformes (Ground sharks). These clades are prevalent predators in today's oceans, and were geographically widespread during the late Cretaceous-early Palaeogene. Our results reveal a decoupling of morphological disparity and taxonomic richness. Indeed, shark disparity was nearly static across the K-Pg extinction, in contrast to abrupt declines among other higher-trophic-level marine predators [4, 5]. Nevertheless, specific patterns indicate that an asymmetric extinction occurred among lamniforms possessing low-crowned/triangular teeth and that a subsequent proliferation of carcharhiniforms with similar tooth morphologies took place during the early Paleocene. This compositional shift in post-Mesozoic shark lineages hints at a profound and persistent K-Pg signature evident in the heterogeneity of modern shark communities. Moreover, such wholesale lineage turnover coincided with the loss of many cephalopod [6] and pelagic amniote [5] groups, as well as the explosive radiation of middle trophic-level teleost fishes [1]. We hypothesize that a combination of prey availability and post-extinction trophic cascades favored extant shark antecedents and laid the foundation for their extensive diversification later in the Cenozoic [7-10].

  View details for DOI 10.1016/j.cub.2018.05.093

  View details for Web of Science ID 000442111300030

  View details for PubMedID 30078565