Ben Creisler
Some new non-dino papers in Journal of Anatomy that may be of interest
Edina Prondvai, ÂP. Eckhard Witten, ÂAnick Abourachid, ÂAnn Huysseune Â& Dominique Adriaens (2019)
Extensive chondroid bone in juvenile duck limbs hints at accelerated growth mechanism in avian skeletogenesis.
Journal of Anatomy (advance online publication)
doi:
https://doi.org/10.1111/joa.13109https://onlinelibrary.wiley.com/doi/pdf/10.1111/joa.13109Modern altricial birds are the fastest growing vertebrates, whereas various degrees of precocity (functional maturity) result in slower growth. Diaphyseal osteohistology, the best proxy for inferring relative growth rates in fossils, suggests that in the earliest birds, posthatching growth rates were more variable than in modern representatives, with some showing considerably slow growth that was attributed to their assumed precocial flight abilities. For finding clues how precocial or altricial skeletogenesis and related growth acceleration could be traced in avian evolution, as a case study we investigated the growing limb diaphyseal histology in an ontogenetic series of ducks which, among several other avian taxa, show a combination of altricial wing and precocial leg development. Here we report the unexpected discovery that chondroid bone, a skeletal tissue family intermediate between cartilage and bone, extensively contributes to the development of limb bone shaft in ducks up to at least 30 days posthatching age. To our knowledge, chondroid bone has never been reported in such quantities and with an ontogenetically extended deposition period in postâembryonic, nonâpathological periosteal bone formation of any tetrapod limb. It shows transitional cellular/lacunar morphologies and matrix staining properties between cartilage and woven bone and takes a significant part in the diametric growth of the limb bone shaft. Its amount and distribution through duckling ontogeny seems to be associated with the disparate functional and growth trajectories of the altricial wings vs. precocial legs characteristic of duck limb development. The presence of isogenous cell groups in the periosteal chondroid bone implies that cartilageâlike interstitial growth took place before matrix mineralization complementing appositional bone growth. Based on these characteristics and on its fast formation rate in all previously reported normal as well as pathological cases, we suggest that chondroid bone in ducks significantly accelerates diametric limb bone growth. Related to this growth acceleration, we hypothesize that chondroid bone may be generally present in the growing limb bones of modern birds and hence may have key skeletogenic importance in achieving extreme avian growth rates and placing birds among the fastest growing vertebrates. Thus, we encourage future studies to test this hypothesis by investigating the occurrence of chondroid bone in a variety of precocial and altricial bird species, and to explore the presence of similar tissues in the growing limbs of other extant and extinct tetrapods in order to understand the evolutionary significance of chondroid bone in accelerated appendicular skeletogenesis.
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Of interest based on the recent "archaic ungulate" question...
Ornella C. Bertrand, Sarah L. Shelley, John R. Wible, Thomas E. Williamson, Luke T. Holbrook, Stephen G.B. Chester, Ian B. Butler & ÂStephen L. Brusatte (2019)
Virtual endocranial and inner ear endocasts of the Paleocene 'condylarth' Chriacus: new insight into the neurosensory system and evolution of early placental mammals.
Journal of Anatomy (advance online publication)
doi:
https://doi.org/10.1111/joa.13084https://onlinelibrary.wiley.com/doi/10.1111/joa.13084The endâCretaceous mass extinction allowed placental mammals to diversify ecologically and taxonomically as they filled ecological niches once occupied by nonâavian dinosaurs and more basal mammals. Little is known, however, about how the neurosensory systems of mammals changed after the extinction, and what role these systems played in mammalian diversification. We here use highâresolution computed tomography (CT) scanning to describe the endocranial and inner ear endocasts of two species, Chriacus pelvidens and Chriacus baldwini, which belong to a cluster of 'archaic' placental mammals called âarctocyonid condylarthsâ that thrived during the ca. 10 million years after the extinction (the Paleocene Epoch), but whose relationships to extant placentals are poorly understood. The endocasts provide new insight into the paleobiology of the longâmysterious 'arctocyonids', and suggest that Chriacus was an animal with an encephalization quotient (EQ) range of 0.12â0.41, which probably relied more on its sense of smell than vision, because the olfactory bulbs are proportionally large but the neocortex and petrosal lobules are less developed. Agility scores, estimated from the dimensions of the semicircular canals of the inner ear, indicate that Chriacus was slow to moderately agile, and its hearing capabilities, estimated from cochlear dimensions, suggest similarities with the extant aardvark. Chriacus shares many brain features with other Paleocene mammals, such as a small lissencephalic brain, large olfactory bulbs and small petrosal lobules, which are likely plesiomorphic for Placentalia. The inner ear of Chriacus also shares derived characteristics of the elliptical and spherical recesses with extinct species that belong to Euungulata, the extant placental group that includes artiodactyls and perissodactyls. This lends key evidence to the hypothesized close relationship between Chriacus and the extant ungulate groups, and demonstrates that neurosensory features can provide important insight into both the paleobiology and relationships of early placental mammals.
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We examined the morphological diversity of the quadrate bone in squamate reptiles (i.e. lizards, snakes, amphisbaenians). The quadrate is the principal splanchnocranial element involved in suspending the lower jaw from the skull, and its shape is of particular interest because it is potentially affected by several factors, such as phylogenetic history, allometry, ecology, skull kinesis and hearing capabilities (e.g. presence or absence of a tympanic ear). Due to its complexity, the quadrate bone is also considered one of the most diagnostic elements in fragmentary fossil taxa. We describe quadrates from 38 species spread across all major squamate clades, using qualitative and quantitative (e.g. geometric morphometrics) methods. We test for possible correlations between shape variation and factors such as phylogeny, size, ecology and presence/absence of a tympanum. Our results show that the shape of the quadrate is highly evolutionarily plastic, with very little of the diversity explained by phylogenetic history. Size variation (allometric scaling) is similarly unable to explain much shape diversity in the squamate quadrate. Ecology (terrestrial/fossorial/aquatic) and presence of a tympanic ear are more significant, but together explain only about 20% of the diversity observed. Other unexplored and more analytically complex factors, such as skull biomechanics, likely play additional major roles in shaping the quadrates of lizards and snakes.