Tooth Loss Precedes the Origin of Baleen in Whales

Peredo, Carlos Mauricio; Pyenson, Nicholas D.; Marshall, Christopher D.; Uhen, Mark D.

doi:10.1016/j.cub.2018.10.047

Cited by 45 publications

(98 citation statements)

References 38 publications

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“…The reconstructed morphology of other toothed mysticete genera such as the tooth‐bearing Llanocetus (Llanocetidae – Fordyce & Marx, ) or the recently discovered toothless Maiabalaena (Peredo et al. ) is also in line with this hypothesis. Baleen precursors would have been found prevalently at the posterior end of the rostrum, where most of the palatal foramina are found in the fossil skulls, as previously hypothesized (Sawamura, ).…”

Section: Discussionsupporting

confidence: 65%

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Prenatal developmental sequence of the skull of minke whales and its implications for the evolution of mysticetes and the teeth‐to‐baleen transition

Lanzetti

2019

Journal of Anatomy

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Baleen whales (Mysticeti) have an extraordinary fossil record documenting the transition from toothed raptorial taxa to modern species that bear baleen plates, keratinous bristles employed in filter-feeding. Remnants of their toothed ancestry can be found in their ontogeny, as they still develop tooth germs in utero. Understanding the developmental transition from teeth to baleen and the associated skull modifications in prenatal specimens of extant species can enhance our understanding of the evolutionary history of this lineage by using ontogeny as a relative proxy of the evolutionary changes observed in the fossil record. Although at present very little information is available on prenatal development of baleen whales, especially regarding tooth resorption and baleen formation, due to a lack of specimens. Here I present the first detailed description of prenatal specimens of minke whales (Balaenoptera acutorostrata and Balaenoptera bonaerensis), focusing on the skull anatomy and tooth germ development, resorption, and baleen growth. The ontogenetic sequence described consists of 10 specimens of both minke whale species, from the earliest fetal stages to full term. The internal skull anatomy of the specimens was visualized using traditional and iodine-enhanced computed tomography scanning. These highquality data allow detailed description of skull development both qualitatively and quantitatively using threedimensional landmark analysis. I report distinctive external anatomical changes and the presence of a denser tissue medial to the tooth germs in specimens from the final portion of gestation, which can be interpreted as the first signs of baleen formation (baleen rudiments). Tooth germs are only completely resorbed just before the eruption of the baleen from the gums, and they are still present for a brief period with baleen rudiments. Skull shape development is characterized by progressive elongation of the rostrum relative to the braincase and by the relative anterior movement of the supraoccipital shield, contributing to a defining feature of cetaceans, telescoping. These data aid the interpretation of fossil morphologies, especially of those extinct taxa where there is no direct evidence of presence of baleen, even if caution is needed when comparing prenatal extant specimens with adult fossils. The ontogeny of other mysticete species needs to be analyzed before drawing definitive conclusions about the influence of development on the evolution of this group. Nonetheless, this work is the first step towards a deeper understanding of the most distinctive patterns in prenatal skull development of baleen whales, and of the anatomical changes that accompany the transition from tooth germs to baleen. It also presents comprehensive hypotheses to explain the influence of developmental processes on the evolution of skull morphology and feeding adaptations of mysticetes.

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Section: Discussionsupporting

confidence: 65%

“…, ; Peredo et al. , ; Fordyce & Marx, ), whereas other researchers concluded that these structures implied the presence of baleen plates or at least some form of bristle‐like primitive baleen structures (Deméré et al. ; Ekdale et al.…”

Section: Discussionmentioning

confidence: 99%

Prenatal developmental sequence of the skull of minke whales and its implications for the evolution of mysticetes and the teeth‐to‐baleen transition

Lanzetti

2019

Journal of Anatomy

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“…Ancestral reconstruction unambiguously showed that the absence of dorsal canaliculi likely represents the ancestral condition in placental mammals (Data S1) where alveolar branches (IAN and inferior alveolar artery, IAA) pass through the trabecular structures of the bone or directly through tooth roots. In contrast, armadillos (Dasypus novemcinctus, D. pilosus, and Priodontes maximus), sloths (Bradypus tridactylus and Choloepus hoffmanni), and the aardvark (Orycteropus afer) present dorsal canaliculi ( Figures 1, 2E, 2F, 3C, 3D, S1, and S4), the so-called ''dorsal branches'' as previously described in baleen whales [7], whose dorsoventral length increases as the tooth is implanted further from the mandibular canal ( Figures 2E and 2F). Most of these dorsal canaliculi are located in the anterior part of the mandible, where teeth are reduced or simply missing.…”

Section: In Briefmentioning

confidence: 70%

“…A summary description of additional species used to reconstruct the ancestral condition of placental mammals is also provided as Supplemental Information ( Figure S2, Data S1). For cetacean comparisons, we used a dataset that was recently published by Peredo et al [7]. All toothed mammals get teeth innervated and vascularized, but this innervation and vascularization only occasionally happens through dorsal canaliculi.…”

Section: In Briefmentioning

confidence: 99%

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Evolutionary Tinkering of the Mandibular Canal Linked to Convergent Regression of Teeth in Placental Mammals

2019

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Mechanical properties of the California sea lion (Zalophus californianus) and northern elephant seal (Mirounga angustirostris) lower jaws explain trophic plasticity

Nieto-Miranda

Aguilar-Medrano

Hernández‐Camacho

et al. 2023

The Anatomical Record

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The fossil record of pinnipeds documents a suite of morphological changes that facilitate their ecological transition from a terrestrial to an aquatic lifestyle. Among these is the loss of the tribosphenic molar and the behavior typically associated with it in mammals: mastication. Instead, modern pinnipeds exhibit a broad range of feeding strategies that facilitate their distinct aquatic ecologies. Here, we examine the feeding morphology of two species of pinnipeds with disparate feeding ecologies: Zalophus californianus, a specialized raptorial biter, and Mirounga angustirostris, a suction specialist. Specifically, we test whether the morphology of the lower jaws facilitates trophic plasticity in feeding for either of these species. We used finite element analysis (FEA) to simulate the stresses during the opening and closing of the lower jaws in these species to explore the mechanical limits of their feeding ecology. Our simulations demonstrate that both jaws are highly resistant to the tensile stresses experienced during feeding. The lower jaws of Z. californianus experienced the maximum stress at the articular condyle and the base of the coronoid process. The lower jaws of M. angustirostris experienced the maximum stress at the angular process and were more evenly distributed throughout the body of the mandible. Surprisingly, the lower jaws of M. angustirostris were even more resistant to the stresses experienced during feeding than those of Z. californianus. Thus, we conclude that the superlative trophic plasticity of Z. californianus is driven by other factors unrelated to the mandible's tensile resistance to stress during feeding.

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Tooth Loss Precedes the Origin of Baleen in Whales

Cited by 45 publications

References 38 publications

Prenatal developmental sequence of the skull of minke whales and its implications for the evolution of mysticetes and the teeth‐to‐baleen transition

Prenatal developmental sequence of the skull of minke whales and its implications for the evolution of mysticetes and the teeth‐to‐baleen transition

Evolutionary Tinkering of the Mandibular Canal Linked to Convergent Regression of Teeth in Placental Mammals

Mechanical properties of the California sea lion (Zalophus californianus) and northern elephant seal (Mirounga angustirostris) lower jaws explain trophic plasticity

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