Abstract:Abstract. The behavior of the maximum body size (body length) in an evolving clade is exemplified by the evolutionary histories of Bivalvia, Cetacea, and Camerata (Crinoidea). Changes of the maximum size with time track closely diversification history: when a clade diversifies exponentially, the maximum size also increases exponentially, and when the number of species changes irregularly (at varying rates), the maximum size also changes in that manner. However, within any given clade, the maximum body size cha… Show more
“…This wide range in size is most likely related to the greater diversity of squalodelphinids included in the sample. High diversity in an evolving clade also generates an increase in the maximum body size [ 67 ]. Figure 15.…”
The South Asian river dolphin (Platanista gangetica) is the only extant survivor of the large clade Platanistoidea, having a well-diversified fossil record from the Late Oligocene to the Middle Miocene. Based on a partial skeleton collected from the Chilcatay Formation (Chilcatay Fm; southern coast of Peru), we report here a new squalodelphinid genus and species, Macrosqualodelphis ukupachai. A volcanic ash layer, sampled near the fossil, yielded the 40Ar/39Ar age of 18.78 ± 0.08 Ma (Burdigalian, Early Miocene). The phylogenetic analysis places Macrosqualodelphis as the earliest branching squalodelphinid. Combined with several cranial and dental features, the large body size (estimated body length of 3.5 m) of this odontocete suggests that it consumed larger prey than the other members of its family. Together with Huaridelphis raimondii and Notocetus vanbenedeni, both also found in the Chilcatay Fm, this new squalodelphinid further demonstrates the peculiar local diversity of the family along the southeastern Pacific coast, possibly related to their partition into different dietary niches. At a wider geographical scale, the morphological and ecological diversity of squalodelphinids confirms the major role played by platanistoids during the Early Miocene radiation of crown odontocetes.
“…This wide range in size is most likely related to the greater diversity of squalodelphinids included in the sample. High diversity in an evolving clade also generates an increase in the maximum body size [ 67 ]. Figure 15.…”
The South Asian river dolphin (Platanista gangetica) is the only extant survivor of the large clade Platanistoidea, having a well-diversified fossil record from the Late Oligocene to the Middle Miocene. Based on a partial skeleton collected from the Chilcatay Formation (Chilcatay Fm; southern coast of Peru), we report here a new squalodelphinid genus and species, Macrosqualodelphis ukupachai. A volcanic ash layer, sampled near the fossil, yielded the 40Ar/39Ar age of 18.78 ± 0.08 Ma (Burdigalian, Early Miocene). The phylogenetic analysis places Macrosqualodelphis as the earliest branching squalodelphinid. Combined with several cranial and dental features, the large body size (estimated body length of 3.5 m) of this odontocete suggests that it consumed larger prey than the other members of its family. Together with Huaridelphis raimondii and Notocetus vanbenedeni, both also found in the Chilcatay Fm, this new squalodelphinid further demonstrates the peculiar local diversity of the family along the southeastern Pacific coast, possibly related to their partition into different dietary niches. At a wider geographical scale, the morphological and ecological diversity of squalodelphinids confirms the major role played by platanistoids during the Early Miocene radiation of crown odontocetes.
“…Finally, the use of maximum size may be sensitive to sampling. It is conceivable that mainland areas are likely to harbour the largest individuals simply because more mainland populations exist (Case & Schwaner, 1993; Trammer, 2005). Especially if a species exhibits strong geographical variation in size on the continent (e.g.…”
Aim The island rule, small animal gigantism and large animal dwarfism on islands, is a topic of much recent debate. While size evolution of insular lizards has been widely studied, whether or not they follow the island rule has never been investigated. I examined whether lizards show patterns consistent with the island rule.
Location Islands worldwide.Methods I used literature data on the sizes of island-mainland population pairs in 59 species of lizards, spanning the entire size range of the group, and tested whether small insular lizards are larger than their mainland conspecifics and large insular lizards are smaller. I examined the influence of island area, island isolation, and dietary preferences on lizard size evolution.
ResultsUsing mean snout-vent length as an index of body size, I found that small lizards on islands become smaller than their mainland conspecifics, while large ones become larger still, opposite to predictions of the island rule. This was especially strong in carnivorous lizards; omnivorous and herbivorous species showed a pattern consistent with the island rule but this result was not statistically significant. No trends consistent with the island rule were found when maximum snout-vent length was used. Island area had, at best, a weak effect on body size. Using maximum snoutvent length as an index of body size resulted in most lizard populations appearing to be dwarfed on islands, but no such pattern was revealed when mean snout-vent length was used as a size index.Main conclusions I suggest that lizard body size is mostly influenced by resource availability, with large size allowing some lizard populations to exploit resources that are unavailable on the mainland. Lizards do not follow the island rule. Maximum snout-vent length may be biased by sampling effort, which should be taken into account when one uses this size index.
“…Many authors argued that in a radiating clade there is a strong correlative relation between the maximum body size and species diversity (Stanley, 1973;Gould, 1988;McShea, 1994;Trammer & Kaim, 1997;Trammer, 2002Trammer, , 2005Gillman, 2007;McClain & Boyer, 2009) such that the continuing increase in size parallels diversification. Other researches (Smith et al 2010) did not provide support for such strong correlation.…”
During the Late Triassic – Jurassic phase of the evolution of dinosaurs, their mean and maximum body size increased concurrently with increasing species diversity. On the contrary, in the Cretaceous, although the number of dinosaur species increased, the body size ultimately decreased. This might have been connected with the increase of the number of land masses and the decrease of their areas in the Late Cretaceous caused by global tectonics
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