On the evolution of extreme structures: static scaling and the function of sexually selected signals

O’Brien, Devin M.; Allen, Cerisse E.; Kleeck, Melissa J. Van; Hone, David W. E.; Knell, Robert J.; Knapp, Andrew; Christiansen, Stuart; Emlen, Douglas J.

doi:10.1016/j.anbehav.2018.08.005

Cited by 55 publications

(80 citation statements)

References 145 publications

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“…Current reconstructions of jaw muscles in these animals place the jaw adductor origins closer to the rostral edge of the supratemporal fenestra, along the midline keel of the frill, and along the inner surface of the squamosal, with the majority of the frill, including its caudal margin, free of musculature (Dodson, 1996; Nabavizadeh, 2018). These differences in frill anatomy between early and late diverging ceratopsians prompted Makovicky (2012) and Makovicky and Norell (2006) to propose that the ceratopsian frill underwent a shift in its primary function within Neoceratopsia from providing an increased area for attachment of jaw adductor muscles as (Haas, 1955; Lull, 1908; Ostrom, 1964; Xu et al., 2002), to serving as a species‐specific display structure with possible social and/or sexual functions (Dodson, 1976, 1993, 1996; Farlow & Dodson, 1975; Hone, Naish, & Cuthill, 2012; Hone et al., 2016; Horner & Goodwin, 2006, 2008; O'Brien et al., 2018; Padian & Horner, 2011; Sampson, Ryan, & Tanke, 1997). Insertion of jaw musculature along the majority of the frill margin in early‐diverging taxa such as Liaoceratops , Yamaceratops (Makovicky & Norell, 2006), and Auroraceratops (Morshhauser et al, 2019) would likely have constrained allometric growth patterns by optimizing muscle orientations and mechanical leverage, a conclusion supported by the observed absence of ontogenetic shape change in Liaoceratops and the LCA of Neoceratopsia (Figure 7a).…”

Section: Discussionmentioning

confidence: 99%

Modularity and heterochrony in the evolution of the ceratopsian dinosaur frill

Prieto-Márquez

Garcia‐Porta

Joshi

et al. 2020

Ecology and Evolution

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The fossil record provides compelling examples of heterochrony at macroevolutionary scales such as the peramorphic giant antlers of the Irish elk. Heterochrony has also been invoked in the evolution of the distinctive cranial frill of ceratopsian dinosaurs such as Triceratops. Although ceratopsian frills vary in size, shape, and ornamentation, quantitative analyses that would allow for testing hypotheses of heterochrony are lacking. Here, we use geometric morphometrics to examine frill shape variation across ceratopsian diversity and within four species preserving growth series. We then test whether the frill constitutes an evolvable module both across and within species, and compare growth trajectories of taxa with ontogenetic growth series to identify heterochronic processes. Evolution of the ceratopsian frill consisted primarily of progressive expansion of its caudal and caudolateral margins, with morphospace occupation following taxonomic groups. Although taphonomic distortion represents a complicating factor, our data support modularity both across and within species. Peramorphosis played an important role in frill evolution, with acceleration operating early in neoceratopsian evolution followed by progenesis in later diverging cornosaurian ceratopsians. Peramorphic evolution of the ceratopsian frill may have been facilitated by the decoupling of this structure from the jaw musculature, an inference that predicts an expansion of morphospace occupation and higher evolutionary rates among ceratopsids as indeed borne out by our data. However, denser sampling of the meager record of early‐diverging taxa is required to test this further.

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Section: Discussionmentioning

confidence: 99%

Modularity and heterochrony in the evolution of the ceratopsian dinosaur frill

Prieto-Márquez

Garcia‐Porta

Joshi

et al. 2020

Ecology and Evolution

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“…ecological selection; [6][7][8]). Since we currently have no way of directly assessing the function of the tusk in nature, we can use the morphological relationships of tusk size with body size to better understand the function of this exaggerated trait [9,10].…”

Section: Introductionmentioning

confidence: 99%

The longer the better: evidence that narwhal tusks are sexually selected

et al. 2020

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Once thought to be the magical horn of a unicorn, narwhal tusks are one of the most charismatic structures in biology. Despite years of speculation, little is known about the tusk's function, because narwhals spend most of their lives hidden underneath the Arctic ice. Some hypotheses propose that the tusk has sexual functions as a weapon or as a signal. By contrast, other hypotheses propose that the tusk functions as an environmental sensor. Since assessing the tusks function in nature is difficult, we can use the morphological relationships of tusk size with body size to understand this mysterious trait. To do so, we collected morphology data on 245 adult male narwhals over the course of 35 years. Based on the disproportional growth and large variation in tusk length we found, we provide the best evidence to date that narwhal tusks are indeed sexually selected. By combining our results on tusk scaling with known material properties of the tusk, we suggest that the narwhal tusk is a sexually selected signal that is used during male–male contests.

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“…As a result, the case for sexual selection in dinosaurs and other extinct reptile lineages has been controversial. In some taxa, however, there is evidence for sexual dimorphism (e.g., Shringasaurus Sengupta, Ezcurra & Bandyopadhyay, 2017) and for the presence of traits that were likely used as socio-sexual signals (O'Brien et al, 2018). Even so, the detection of sexual dimorphism is an important component of understanding sexual selection, and the current lack of evidence for dimorphism in dinosaurs (e.g., Hone, Naish & Cuthill, 2012;Mallon, 2017 and references therein) remains at least a curious anomaly.…”

Section: Introductionmentioning

confidence: 99%

Peer Review #1 of "Ontogeny of a sexually selected structure in an extant archosaur Gavialis gangeticus (Pseudosuchia: Crocodylia) with implications for sexual dimorphism in dinosaurs (v0.1)"

Dodson¹

2020

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Despite strong evidence for sexual selection in various display traits and other exaggerated structures in large extinct reptiles, such as dinosaurs, detecting sexual dimorphism in them remains difficult. Their relatively small sample sizes, long growth periods, and difficulties distinguishing the sexes of fossil specimens mean that there are little compelling data on dimorphism in these animals. The extant gharial (Gavialis gangeticus) is a large and endangered crocodylian that is sexually dimorphic in size, but males also possesses a sexually selected structure, the ghara, which has an osteological correlate in the presence of a fossa associated with the nares. This makes the species a unique model for potentially assessing dimorphism in fossil lineages, such as dinosaurs and pterosaurs, as it is a large, slowly growing, egg-laying archosaur. Here we assess the dimorphism of G. gangeticus across 106 specimens and show that the presence of a narial fossa diagnose adult male gharials. Males are larger than females, but the level of size dimorphism, and that of other cranial features, is low and difficult to detect without a priori knowledge of the sexes, even with this large dataset. By extension, dimorphism in extinct reptiles is very difficult to detect in the absence of sex specific characters, such as the narial fossa.

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On the evolution of extreme structures: static scaling and the function of sexually selected signals

Cited by 55 publications

References 145 publications

Modularity and heterochrony in the evolution of the ceratopsian dinosaur frill

Modularity and heterochrony in the evolution of the ceratopsian dinosaur frill

The longer the better: evidence that narwhal tusks are sexually selected

Peer Review #1 of "Ontogeny of a sexually selected structure in an extant archosaur Gavialis gangeticus (Pseudosuchia: Crocodylia) with implications for sexual dimorphism in dinosaurs (v0.1)"

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