Mortality in a predator-free insular environment: the dwarf deer of Crete

Age-graded fossils of Pleistocene endemic Cretan deer (Candiacervus spp.) reveal unexpectedly high juvenile mortality similar to that reported for extant mainland ruminants, despite the fact that these deer lived in a predator-free environment and became extinct before any plausible date for human arrival. Age profiles show that deer surviving past the fawn stage were relatively long-lived for ruminants, indicating that high juvenile mortality was not an expression of their living a “fast” life. Although the effects on survivorship of such variables as fatal accidents, starvation, and disease are difficult to gauge in extinct taxa, the presence of extreme morphological variability within nominal species/ecomorphs of Candiacervus is consistent with the view that high juvenile mortality can function as a key innovation permitting rapid adaptation in insular contexts

The postcranial of the deer Hoplitorneryx (Pliocene; Italy): another example of adaptive radiation on Eastern Mediterranean islands

Durant el Pliocè, a l'illa de Gargano (costa sudest d'Itàlia) va evolucionar una fauna vertebrada altament endèmica. Aquesta fauna comprenia, entre d'altres, el eriçó gegant Deinogalerix, l'òliba gegant Tyto gigantea; el hàmster gegant Hattomys, i el cèrvol Hoplitomeryx amb cinc banyes i canins superiors en forma de sabre (tipus mòsquid). Els materials esquelètics d'HoplitomelYx formen un grup heterogeni, amb quatre classes de talla; dintre de les classes de talla poden estar presents diferents morfotipus. Totes les classes de talla comparteixen els mateixos trets típics d' Hoplitomeryx. Aquests són: una banya nasal central i un parell de banyes orbitals en punxa, canines sortints, fusió completa del navicocuboide amb el metatarsià, acanaladura metatarsiana distalment tancada, astràgal sense costats paral-lels, i una ròtula allargada. Les dife-rents classes de talla es troben repartides de forma igual a les fissures excavades, i a llavors no es poden considerar cronotipus. La hipòtesi d'un arxipèlag consistent en diferents illes on a cada una d'elles hi hagués un morfotipus no s'ha pogut confirmar, La situació de diferents morfotipus coexistint a una illa té un paral-lel amb Candiaceruus (Pleistocè, Creta, Gràcia). Les opinions sobre la seva taxonomia són diverses, i actualment prevaleixen dos models: un gènere per a vuit morfotipus o, alternativament, dos gèneres per a cinc espècies. El segon model només es basa en les proporcions dels membres, però aquestes són característiques taxonòmiques invàlides per als endemismes insulars, ja que canvien sota la influència de factors ambientals diferents dels continentals. També a Hoplitomeryx els morfotipus difereixen en les proporcions dels membres, però en aquest cas resulta improbable que provinguin de diferents ancestres, ja que en aquest cas els ancestres haurien d'haver compartit els trets hoplitomeríciids tipics. La morfoesfera d'Hoplitomeryx és massa coherent com per suposar dos a més ancestres, i indica un origen monofilètic de tots els morfotipus. En lloc d'això, la gran variació s'explica com a un exemple de radiació adaptativa, que va començar quan l'ancestre miocènic va colonitzar l'illa. Lespectre de ninxols buits degué promoure la seva radiació en diferents tipus tròfics, conduint a una diferenciació d' Hoplitomeryx. La manca compartida de mamifers depredadors grans i l'oferta limitada d'aliment a tots els ninxols degué promoure el desenvolupament de trets derivats secundaris a totes les classes de talla.During the Pliocene a highly endemic vertebrate fauna evolved on Gargano Island (south-east coast of Italy), comprising amongst others the giant hedgehog Deinogalerix, the giant barn owl Tyto gigantea, the giant hamster Hattomys, and the prongdeer Hoplitomeryx with five horns and sabrelike ('moschid' type) upper canines. The Hoplitomeryx skeletal material forms a he-terogenous group, containing four size groups; within the size groups different morphotypes may be present. All size groups share the same typical Hoplitomeryx features. These me: one central nasal horn and a pair of pronged orbital horns, protruding canines, complete fusion of the navicocuboid with the metatarsal, distally closed metatarsal gully, a nonparallel- sided astragalus, and an elongated patella. The different size groups are equally distributed over the excavated fissures, and are therefore not to be considered chronotypes. The hypothesis of an archipelago consisting of different islands each with its own morphotype cannot be confirmed. The situation with several co-existing morpho types on an island is paralleled by Candiacervus (Pleistocene, Crete, Greece). Opinions about its taxonomy differ, and at present two models prevail: one genus for eight morphotypes, or alternatively, two genera for five species. The second model is based upon limb proportions only, but these are invalid taxonomic features for island endemics, as they change under influence of environmental factors that differ from the mainland. Also in Hoplitomeryx the morphotypes differ in limb proportions, but here different ancestors are unlikely, because in that case they all ancestors must have shared the typical hoplitornerycid features. The morphosphere of Hoplitorneryx is too coherent to assume two or more different ancestors, and indicates a monophyletic origin of all morphotypes. The large variation is instead explained as an example of adaptive radiation, starting when the Miocene ancestor colonized the island. The range of empty niches promoted its radiation into several trophic types, yielding a differentiation in Hoplitomeryx. The shared lack of large mammalian predators and the limited amount of food in all niches promoted the development of secondary features in all size groups (apomorphies)

Parallel patterns and trends in functional structures in extinct island mammals

Endemic mammalian species on islands are generally known to have followed a different evolutionary pathway than their mainland relatives. General patterns, such as body size trends, have been described regularly. However, most island mammal species are unique and each of them is adapted to a specific local niche as part of an equally specific ecological assemblage. Therefore, comparing island species across taxa, islands and time is inherently dangerous without understanding the adaptational value of the studied feature in the compared taxa and without taking the ecological setting of the taxa into account. In this contribution, general and recurring patterns are described per taxon. Some features, like body mass change and sturdy limbs, are relatively general, whereas most features, like bone fusions and change of orbital axis, occur only in a very few taxa. Some features are even contradictory, such as brain size and degree of hypsodonty, with each taxon having its own particular design. In conclusion, general patterns are more often than not just trends and need to be applied with caution

Niche overlap and competition potential among tigers (Panthera tigris), sabertoothed cats (Homotherium ultimum, Hemimachairodus zwierzyckii) and Merriam's Dog (Megacyon merriami) in the Pleistocene of Java

On Java during the Pleistocene, tigers of more than 300 kg occurred, but these are restricted to a single Late Pleistocene faunal unit, while Early and Middle Pleistocene tigers possessed body masses comparable to those of historic Javanese and extant Sumatran tigers. The aim of this study is to test if competition for prey with other hypercarnivorous taxa such as sabertoothed cats and the large Merriam's Dog was the driver for the increase in body mass of tigers. We calculated body masses and prey mass spectrum for tigers and potential competitors using linear regressions. Niche overlap was then estimated based on the prey mass spectrum after which niche overlaps were used as indicators for competition potentials. Reconstructed body mass for Homotherium ultimum, Hemimachairodus zwierzyckii, Megacyon merriami are 154 kg (comparable to Homotherium from Untermassfeld), 130 kg and 52 kg, respectively. The niche overlap between tigers and Merriam's Dog is highest (100%) while it is comparatively low (60 %) between tigers and Homotherium ultimum. In order to reduce competition, tigers seem to have increased body mass to avoid competition especially with Merriam's Dog whereas Merriam's Dog on its turn seems to have decreased body mass to avoid competition with tigers. The sabertoothed cats on the other hand seem to have been unable to adapt and went extinct

The mounting of a skeleton of the fossil species Candiaceruus sp. II from Liko Cave, Crete, Greece

S'ha muntat un esquelet del cérvol pleistocènic endèmic de Creta per a la nova exhibició del Museu de Geologia de la Universitat d'Atenes. Aquest cérvol difereix de tots els cérvols continentals vivents i extingits, principalment en les seves proporcions. Les mesures i comparacions confirmen aquesta observació, però això no és prou com per a que el públic general se n'adoni del seu impacte. Per contra, un esquelet muntat deixa clar que aquest cérvol tertia uns membres considerablement escurçats, especialment els metàpodes, mentre que la llargària del cos, a la llargària de la columna vertebral, eren més aviat normals. La impressió global és més propera a la d'un bòvid nan insular, com ara Myotragus, que a la d'un cérvol petit, tal com Axis axis. El primer problema a resoldre fou la selecció de material. Ja que mai s'ha trobat un esquelet articulat complet, se n'ha de fer un de compost. Amb aquest motiu, només es varen seleccionar ossos de la classe de talla II (de Vos, 1979 ; Dermitzakis & de Vos, 1987) provinents d'un nivell d'una cova (cova de Liko, estrat B). D'aquesta manera es garanteix un interval geològic estret. Tot seguit, es varen mesurar tots els espècimens disponibles, i es va calcular el promig per a tots els elements. D'acord amb això, es va triar l'exemplar de cada element que més s'apropava a la mitjana calculada. Les peces dretes i esquerres havien de ser de la mateixa mida i robustesa, i els elements contigus havien de casar anatòmicament. Només en alguns casos s'ha hagut de recórrer a triar algun element que faltava a partir d'un llivell diferent, però mai a partir d'una cova diferent i mai a partir d'una classe de talla diferent. S'ha prioritzat la mida, la robustesa i l'ajustament anatòmic, i després que els ossos fossin complets i el color. Hi havia alguns peus articulats disponibles, encara que de mida i robustesa diferents, que s'han emprat per determinar les proporcions correctes i la posició correcta entre les falanges individuals, i els ossos carpians i tarsians. La mateixa cosa fou vàlida per a la columna vertebral. Per a l'establiment de la postura es van fer servir cérvols vivents com a comparació; per a l'extrapolació dels teixits tous (discos intervertebrals, cartílags de les articulacions) també es va recórrer al model dels cérvols vivents. De cara a amagar els bastiments de suport, es va inserir dins els ossos una armadura metàl-lica interna fent forats i fitxant-la amb goma de poliuretà. S'ha fabricat l'esquelet complet en parts modulars bones d'ajuntar pel seu transport fàcil a la mostra. Parts absents petites (principalment processos vertebrals, parts costals i les ales pèlviques) s'han reconstruït amb apoxy, en base a altres elements disponibles de Candiacervus de la cova de Liko a per interpolació del millor ajustament entre dues parts absents. Les traces de la matriu original han estat estretes, per a una impressió millor del material fòssil. Per completar l'esquelet s'ha fet una rèplica del crani de l'espècimen tipus de la classe de talla II de de Vos (1979) i una rèplica de l'espècimen tipus del banyam tipus I de de Vos (1984).For the new exhibition in the Museum of Palaeontology and Geology of the University of Athens a skeleton of the endemic Pleistocene Cretan deer was mounted. This deer differs from all known recent and extinct mainland deer, mainly in its proportions. Measurements and comparisons confirm this observation, but are not enough to make the public realize its impact. A mounted skeleton on the contrary makes it at once clear that this deer had considerably shortened limbs, especially the metapodals, whereas the body length and the vertebral column length are rather normal. The overall impression is closer to that of an insular dwarf bovid like Myotragus than to that of a small deer such as the spotted deer (Axis axis). The first problem to be tackled was the selection of the material. Since a complete articulated skeleton has never been found, a composite had to be made. For this purpose, only bones of size class II (de Vas, 1979; Dermitzakis & de Vas, 1987) coming from one layer of one cave (Liko Cave, layer El were selected. In this way a narrow geological range was assured. Subsequently, tile available specimens were measured, and of all elements the average size was calculated. Accordingly, of each element tile specimen that came tile most close to tile calculated average was selected. Left and right had to be of exactly the same size and robustness, and adjoining elements had to fit anatornically. Only in some cases a missing element had to be chosen from a different layer (layers C and Dl. but never from a different cave, and never from a different size class. Priority was first given to size, robustness and anatomical fitting, and next to completeness and colour. Several articulated feet were available, although of tile wrong size or robustness, which were used in determining the right proportions and right stance between individual phalanges, tarsal and carpal bones. The same was valid for tile vertebral column. For postural aspects, living deer were used as comparison; for extrapolation of soft tissue (intervertebral disks, articulation cartilage) also living deer stood model. In order to keep the supporting fabrication as hidden as possible, an internal metal armature was inserted in tile bones through drilled holes and fixed with polyurethane glue. The complete skeleton is fabricated in ready-to-assemble modular parts for easy transportation and reassembly on the spot. Minor missing parts (mainly vertebral processes, costal parts and tile pelvic wings) have been reconst: ructed in epoxy putty, based on other Candiaceruus elements from Liko or by interpolating the best fit between two existing parts. For a better impression of the fossil material, traces of tile original matrix were left on the bones. A cast of the skull of the type specimen of size II of de Vas (1979) and a cast of tile type specimen of antler type 1 of de Vas (1984) were made to complete the skeleton