[dinosaur] Nocturnalism in Triassic Archaic Mammals (free pdf)

Ben Creisler
[email protected]


A new paper with free pdf:

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Barry G. Lovegrove (2019)
Obligatory Nocturnalism in Triassic Archaic Mammals: Preservation of Sperm
Quality?
Physiological and Biochemical Zoology 92(6):544–553
DOI: 10.1086/705440
https://urldefense.proofpoint.com/v2/url?u=https-3A__www.journals.uchicago.edu_doi_10.1086_705440&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=L8ogB_Ny4WQKB-bbQqox6YyvAQoy4jderY6i0598hS4&s=yScdgwLXMVG1dVXLmOUAN9TZdPbAYHZSaJe_fnYg5sc&e= 

Free pdf:
https://urldefense.proofpoint.com/v2/url?u=https-3A__www.journals.uchicago.edu_doi_pdfplus_10.1086_705440&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=L8ogB_Ny4WQKB-bbQqox6YyvAQoy4jderY6i0598hS4&s=cFGghZZZt_hzfyVIcPUATKN6cN52G_diTR_STmS7EXY&e= 

Archaic mammals became exclusively nocturnal by the Late Triassic, and
today, the majority of extant mammals remain nocturnal. Although there is
ample morphological and physiological evidence supporting Late Mesozoic
nocturnalism, a succinct hypothesis for why mammals became nocturnal
remains elusive. Here, I propose a hypothesis that, with the onset of body
size miniaturization in the Triassic and the concomitant evolution of fur
and increased mass-specific metabolic rate and hence body temperature,
small mammals became obligatorily nocturnal in order to avoid poor sperm
quality, hyperthermia, and high rates of evaporative water loss and to
maximize foraging time. The hypothesis hinges heavily on the assumption
that, with the absence of externalized testes, the maximum optimum
temperature of about 36°C for spermatogenesis was subject to strong
stabilizing selection that placed a ceiling on increases in metabolic rate
and body temperature. Heat-dissipating capacity during the daytime during
the Triassic, Jurassic, and Cretaceous was thereby compromised. The release
from the constraint of the optimum temperature of spermatogenesis occurred
in placental mammals only with the advent of the externalization of testes
in the scrotum in Boreotheria in the Cenozoic or, with the recent claim
that the scrotum is plesiomorphic in mammals, as early as the Jurassic with
the origin of the marsupials.

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News:

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