The intriguing giant deer from the Bate cave (Crete): could paleohistological evidence question its taxonomy and nomenclature?

The research describes for the first time a possible case of pituitary gigantism in fossil mammals, precisely in deer. The pathology was detected in 2 long bones (tibia and metatarsus) belonging to an individual of an unusual large size found at the Bate cave (Rethymnon, Northern Crete). It formed the basis of Candiacervus major, the largest among the endemic deer species recorded in the Pleistocene-Early Holocene of Crete. Radiological and histomorphological examinations highlighted a reduction in cortical bone thickness and the presence of wide lacunae inside of the bone tissue. The pathological conditions suggest a pituitary gigantism diagnosis also supported by some morphological evidence, such as the extremely elongated distal part of the metatarsal diaphysis, the proportionally small proximal epiphysis, and some bone gracility. The diagnosis of a case of pituitary gigantism as presumed responsible for the extraordinary elongation of the tibia and the metatarsal bone is intriguing as they are, respectively, the paratype and the holotype of the C. major. The species represents a case of a deviation from the "island rule" in Pleistocene large mammals. The new evidence recommends a taxonomic and nomenclatural revision of this species. The main outcomes of this research are as follows: (i) a case of pituitary gigantism is described for the first time in an extinct mammal; (ii) it is underlined that paleohistology may provide interesting clues for disentangling taxonomic and nomenclatural issues; (iii) one of the very few cases of gigantism in insular mammals is being questioned.

Intra-skeletal vascular density in a bipedal hopping macropod with implications for analyses of rib histology

Human ribs are thought to be less affected by mechanical strain at the microscopic level than limb bones, implying that rib remodelling better reflects bone physiological homeostasis. Here, we test the hypothesis that rib tissue will be well vascularized and thus enhance susceptibility to metabolic influence. An intra-skeletal comparison of bone vascular canal density was conducted using a macropod animal model adapted to bipedal habitual hopping. The right humerus, ulna, radius, femur, tibia, fibula, a mid-thoracic and upper-thoracic rib of an eastern grey kangaroo (Macropus giganteus) were sectioned at the midshaft, from which histological sections were prepared. Bone vascularity from a maximum of 12 mm² of sub-periosteal parallel-fibred and lamellar bone was recorded, resulting in a total of 2047 counted vessels. Vascular canal density data were corrected by cortical width, maximum length, and midshaft circumference robusticity indices computed for each bone. The fibula consistently had the highest vascular canal density, even when corrected for maximum length, cortical width and midshaft circumference robusticities. This was followed by the mid- and upper-thoracic ribs. Vascularity differences between bones were relatively consistent whether vascular canal density was controlled for by cortical width or midshaft circumference robusticities. Vascular canal density and robusticity indices were also positively and negatively correlated (p < 0.05). Results confirm that the ribs are well vascularized, which facilitates bone metabolic processes such as remodelling, but the fibula also appears to be a well vascularized bone. Future research investigating human bone metabolism will benefit from examining thoracic rib or fibula samples.

Humerus midshaft histology in a modern and fossil wombat

The common wombat (Vombatus ursinus) is equipped with a set of physiological and morphological adaptations suited to a fossorial lifestyle. These allow wombats to engage in efficient scratch-digging and maintaining a low basal metabolic rate while living underground. While bone microstructure has been described for several subterranean animals, wombat bone histology has received very little attention to date. Here, we present preliminary insights into bone histology in modern adult V. ursinus (Mt Fairy, New South Wales) and Pleistocene fossil Vombatus sp. (Bakers Swamp, New South Wales) midshaft humeri. The modern sample was well preserved, allowing us to identify varying bone tissue types (woven, parallel-fibred, lamellar). The sample showed vascularity composed of primary and secondary osteons, and simple longitudinal and radial vessels. We also observed evidence for Haversian remodelling (i.e. localised replacement of pre-existing bone) and coarse compact cancellous bone within the inner cortex of the diaphysis. The fossil histology was poorly preserved, but likely showed bone matrix organisation similar to the modern specimen. We use these preliminary data to discuss hypotheses for wombat forelimb biomechanical and physiological microscopic adaptation to a burrow environment. We encourage future intraskeletal examination of microstructure in wombat populations to better inform their ecological adaptations and behaviour in palaeontological contexts.