Ben Creisler
Some recent (mainly) non-dino papers:
Bhart-Anjan S. Bhullar, Armita R. Manafzadeh, Juri A. Miyamae, Eva A. Hoffman, Elizabeth L. Brainerd, Catherine Musinsky & Alfred W. Crompton (2019)
Rolling of the jaw is essential for mammalian chewing and tribosphenic molar function.
Nature (advance online publication)
Over the past two centuries, mammalian chewing and related anatomical features have been among the most discussed of all vertebrate evolutionary innovations. Chief among these features are two characters: the dentary-only mandible, and the tribosphenic molar with its triangulated upper cusps and lower talonid basin. The flexible mandibular joint and the unfused symphysis of ancestral mammals--in combination with transformations of the adductor musculature and palate--are thought to have permitted greater mobility of each lower jaw, or hemimandible. Following the appearance of precise dental occlusion near the origin of the mammalian crown, therians evolved a tribosphenic molar with a craggy topography that is presumed to have been used to catch, cut and crush food. Here we describe the ancestral tribosphenic therian chewing stroke, as conserved in the short-tailed opossum Monodelphis domestica: it is a simple symmetrical sequence of lower tooth-row eversion and inversion during jaw opening and closing, respectively, enacted by hemimandibular long-axis rotation. This sequence is coupled with an eversion-inversion rotational grinding stroke. We infer that the ancestral therian chewing stroke relied heavily on long-axis rotation, including symmetrical eversion and inversion (inherited from the first mammaliaforms) as well as a mortar-and-pestle rotational grinding stroke that was inherited from stem therians along with the tribosphenic molar. The yaw-dominated masticatory cycle of primates, ungulates and other bunodont therians is derived; it is necessitated by a secondarily fused jaw symphysis, and permitted by the reduction of high, interlocking cusps. The development of an efficient masticatory system--culminating in the tribosphenic apparatus--allowed early mammals to begin the process of digestion by shearing and crushing food into small boli instead of swallowing larger pieces in the reptilian manner, which necessitates a long, slow and wholly chemical breakdown. The vast diversity of mammalian teeth has emerged from the basic tribosphenic groundplan.
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Free pdf:
Danielle L. Eastick, Glenn J. Tattersall, Simon J. Watson, John A. Lesku & Kylie A. Robert (2019)
Cassowary casques act as thermal windows.
Scientific Reports 9, Article number: 1966Â
Free pdf:
Many ideas have been put forward for the adaptive value of the cassowary casque; and yet, its purpose remains speculative. Homeothermic animals elevate body temperature through metabolic heat production. Heat gain must be offset by heat loss to maintain internal temperatures within a range for optimal performance. Living in a tropical climate, cassowaries, being large bodied, dark feathered birds, are under thermal pressure to offload heat. We tested the original hypothesis that the casque acts as a thermal window. With infrared thermographic analyses of living cassowaries over an expansive range of ambient temperatures, we provide evidence that the casque acts as a thermal radiator, offloading heat at high temperatures and restricting heat loss at low temperatures. Interestingly, at intermediate temperatures, the casque appears thermally heterogeneous, with the posterior of the casque heating up before the front half. These findings might have implications for the function of similar structures in avian and non-avian dinosaurs.
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Free pdf:
Mariela Soledad FernÃndez, Xia Wang, MÃtyÃs Vremir, Chris Laurent, Darren Naish, Gary Kaiser & Gareth Dyke (2019)
A mixed vertebrate eggshell assemblage from the Transylvanian Late Cretaceous
Scientific Reports 9, Article number: 1944Â
Free pdf:
A Late Cretaceous-aged multi-taxon nesting site from Romania preserved in three dimensions reveals the earliest example of nest site sharing yet known from the vertebrate fossil record. Eggshell and osteological evidence combined in this single accumulation demonstrate that at least four vertebrate taxa including enantiornithine birds and another avian of indeterminate affinities as well as crocodylomorphs and gekkotan squamates nested together in the same place. Colonial nesting in enantiornithines was previously described from this site; here, we present the first fossil evidence that other vertebrates also nested in the same place, perhaps exploiting the presence of the large bird colony. We describe four distinct eggshell morphotypes that have been collected from this site and draw palaeoecological inferences based on this unique multi-taxon nesting association.
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Ana M. BÃez & RaÃl O. GÃmez (2019)
Redescription of the overlooked basal frog Wealdenbatrachus reveals increased diversity among Early Cretaceous anurans.
Cretaceous Research (advance online publication)
Highlights
Redescription of the late Barremian Wealdenbatrachus jucarensis from Spain.
Exhaustive comparisons strengthen its distinctiveness and taxonomic validity.
Comments on its locomotor capabilities and basal position outside costatans.
Abstract
The anuran Wealdenbatrachus jucarensis Fey, 1988 is represented by several specimens, each consisting of an association of disarticulated bones preserved on slabs from a lignite mine near the village of UÃa, Cuenca Province, Spain, from which remains of plants and other vertebrates also have been recovered. The bearing unit, La HuÃrguina Formation, is estimated to be late Barremian in age. Originally these anuran specimens were considered to represent a crown-group costatan closer to the living Discoglossus than to Alytes or Bombina. Herein we redescribe this material, including some hitherto unknown skeletal elements, such as nasal and atlas, and reinterpreting other elements, such as pterygoid and squamosal. Our observations and comparisons led us to validate this taxon and to present an updated restoration. It is noteworthy that several characters that have been used to ally Wealdenbatrachus with the early Barremian Eodiscoglossus santonjae occur widely in basal frogs, thus probably being plesiomorphic at this phylogenetic level, and contrast sharply with the conditions in living costatans. Available information points to a position of W. jucarensis outside the node that unites crown-group costatans, as a relatively basal taxon within Anura.