The ability to determine the sex of extinct dinosaurs by examining the bones they leave behind would revolutionize our understanding of their paleobiology; however, to date, definitive sex‐specific skeletal traits remain elusive or controversial. Although living dinosaurs (i.e., extant birds) exhibit a sex‐specific tissue called medullary bone that is unique to females, the confident identification of this tissue in non‐avian archosaurs has proven a challenge. Tracing the evolution of medullary bone is complicated by existing variation of medullary bone tissues in living species; hypotheses that medullary bone structure or chemistry varied during its evolution; and a lack of studies aimed at distinguishing medullary bone from other types of endosteal tissues with which it shares microstructural and developmental characteristics, such as pathological tissues. A recent study attempted to capitalize on the molecular signature of medullary bone, which, in living birds, contains specific markers such as the sulfated glycosaminoglycan keratan sulfate, to support the proposed identification of medullary bone of a non‐avian dinosaur specimen (
In 2001, a nearly complete sub-adult
- NSF-PAR ID:
- 10154216
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 9
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Tyrannosaurus rex MOR 1125). Purported medullary bone samples of MOR 1125 reacted positively to histochemical analyses and the single pathological control tested (avian osteopetrosis) did not, suggesting the presence of keratan sulfate might serve to definitively discriminate these tissues for future studies. To further test these results, we sampled 20 avian bone pathologies of various etiologies (18 species), and several MB samples. Our new data universally support keratan sulfate as a reliable marker of medullary bone in birds. However, we also find that reactivity varies among pathological bone tissues, with reactivity in some pathologies indistinguishable from MB. In the current sample, some pathologies comprised of chondroid bone (often a major constituent of skeletal pathologies and developing fracture calluses in vertebrates) contain keratan sulfate. We note that beyond chemistry, chondroid bone shares many characteristics with medullary bone (fibrous matrix, numerous and large cell lacunae, potential endosteal origin, trabecular architecture) and medullary bone has even been considered by some to be a type of chondroid bone. Our results suggest that the presence of keratan sulfate is not exclusive evidence for MB, but rather must be used as one in a suite of criteria available for identifying medullary bone (and thus gravid females) in non‐avian dinosaur specimens. Future studies should investigate whether there are definite chemical or microstructural differences between medullary bone and reactive chondroid bone that can discriminate these tissues. -
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Key points The functional neuroanatomy of the mammalian respiratory network is far from being understood since experimental tools that measure neural activity across this brainstem‐wide circuit are lacking.
Here, we use silicon multi‐electrode arrays to record respiratory local field potentials (rLFPs) from 196–364 electrode sites within 8–10 mm3of brainstem tissue in single arterially perfused brainstem preparations with respect to the ongoing respiratory motor pattern of inspiration (I), post‐inspiration (PI) and late‐expiration (E2).
rLFPs peaked specifically at the three respiratory phase transitions, E2–I, I–PI and PI–E2.
We show, for the first time, that only the I–PI transition engages a brainstem‐wide network, and that rLFPs during the PI–E2 transition identify a hitherto unknown role for the dorsal respiratory group.
Volumetric mapping of pontomedullary rLFPs in single preparations could become a reliable tool for assessing the functional neuroanatomy of the respiratory network in health and disease.
Abstract While it is widely accepted that inspiratory rhythm generation depends on the pre‐Bötzinger complex, the functional neuroanatomy of the neural circuits that generate expiration is debated. We hypothesized that the compartmental organization of the brainstem respiratory network is sufficient to generate macroscopic local field potentials (LFPs), and if so, respiratory (r) LFPs could be used to map the functional neuroanatomy of the respiratory network. We developed an approach using silicon multi‐electrode arrays to record spontaneous LFPs from hundreds of electrode sites in a volume of brainstem tissue while monitoring the respiratory motor pattern on phrenic and vagal nerves in the perfused brainstem preparation. Our results revealed the expression of rLFPs across the pontomedullary brainstem. rLFPs occurred specifically at the three transitions between respiratory phases: (1) from late expiration (E2) to inspiration (I), (2) from I to post‐inspiration (PI), and (3) from PI to E2. Thus, respiratory network activity was maximal at respiratory phase transitions. Spatially, the E2–I, and PI–E2 transitions were anatomically localized to the ventral and dorsal respiratory groups, respectively. In contrast, our data show, for the first time, that the generation of controlled expiration during the post‐inspiratory phase engages a distributed neuronal population within ventral, dorsal and pontine network compartments. A group‐wise independent component analysis demonstrated that all preparations exhibited rLFPs with a similar temporal structure and thus share a similar functional neuroanatomy. Thus, volumetric mapping of rLFPs could allow for the physiological assessment of global respiratory network organization in health and disease.
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Abstract The end‐Cretaceous mass extinction allowed placental mammals to diversify ecologically and taxonomically as they filled ecological niches once occupied by non‐avian 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 high‐resolution computed tomography (
CT ) scanning to describe the endocranial and inner ear endocasts of two species,Chriacus pelvidens andChriacus baldwini , which belong to a cluster of ‘archaic’ placental mammals called ‘arctocyonid condylarths’ that thrived during theca . 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 long‐mysterious ‘arctocyonids’, and suggest thatChriacus was an animal with anencephalization quotient (EQ) range of 0.12–0.41, 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 thatChriacus 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 ofChriacus 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 betweenChriacus 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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Abstract Paleopathological diagnoses provide key information on the macroevolutionary origin of disease as well as behavioral and physiological inferences that are inaccessible via direct observation of extinct organisms. Here we describe the external gross morphology and internal architecture of a pathologic right second metatarsal (MMNS VP‐6332) of a large‐bodied ornithomimid (~432 kg) from the Santonian (Upper Cretaceous) Eutaw Formation in Mississippi, using a combination of X‐ray computed microtomography (microCT) and petrographic histological analyses. X‐ray microCT imaging and histopathologic features are consistent with multiple complete, oblique to comminuted, minimally displaced mid‐diaphyseal cortical fractures that produce a “butterfly” fragment fracture pattern, and secondary osteomyelitis with a bone fistula formation. We interpret this as evidence of blunt force trauma to the foot that could have resulted from intra‐ or interspecific competition or predator–prey interaction, and probably impaired the function of the metatarsal as a weight‐bearing element until the animal's death. Of particular interest is the apparent decoupling of endosteal and periosteal pathological bone deposition in MMNS VP‐6332, which produces transverse sections exhibiting homogenously thick endosteal pathological bone in the absence of localized periosteal reactive bone. These distribution and depositional patterns are used as criteria for ruling out a pathological origin in favor of a reproductive one for unusual endosteal bone in fossil specimens. On the basis of MMNS VP‐6332, we suggest caution in their use to substantiate a medullary bone identification in extinct archosaurians.
