Alexandra van der Geer, independent researcher

Evolution of Island Mammals

2010-09-14T01:12:00.000-07:00

Our book on the Evolution of Island Mammals, Adaptation and Extinction of Placental Mammals on Islands is out! Wiley-Blackwell published it this August. For a quick overview of contents and artwork, visit the online library of Wiley (move mouse over book cover shown to the right of this post). A second option is simply to order it.

If you are interested in the evolution of insular mammals, from the Eocene walking sirenian (Pezosiren portelli) of Jamaica to the recently extinct Falkland Wolf or Fox (Dusicyon australis) of the Falkland Islands and the still living island fox (Urocyon littoralis) of the Californian Channel Islands, this book is a must. It offers a complete overview of all fossil and most recently extinct mammals that once upon a time lived on islands somewhere on our planet. They were fully adapted to their environment, and often evolved bizarre features, like elongated, club-like antlers with hardly any tines (the deer Candiacervus of Crete), ever-growing front teeth (the bovid Myotragus of Majorca), enormous size (the cavia-like Amblyrhiza of the West Indies) or pygmy size (the hominid Homo floresiensis of Flores).

Unfortunately, the majority of them went extinct, often after spectacular long periods of gradual evolution in situ, when mainland colonisers discovered the islands and their fauna. Today, just a few islanders survived, in comparison with the number of islanders of the remote past. Their special features are unique, but in most cases less spectacular than seen in the fossil record, when elephants could shrink till a mere one or two percent of the body mass of their ancestral size (as in the case of Elephas falconeri).

To have an idea of how extreme evolution can be, you have to see the fossil islanders!

Dental eruption sequence of a fossil 'baboon' (Paradolichopithecus arvernensis)

2009-11-04T23:50:00.000-08:00

The fossil remains of this large-sized 'baboon' found at Vatera, Lesvos, Greece (Plio-Pleistocene boundary, or Late Pleistocene now that the boundary has been moved up again) includes a mandible of a young male with unerupted wisdom molar. We X-rayed the specimen to reveal the unerupted elements and the mineralization of their crowns. The chronological, or individual age of our Paradolichopithecus at the time of its untimely death is estimated at between 5.0 and 5.3 years of age, based on eruption patterns and root formation times of similar-sized living papionins. Mandrills, yellow baboons and Japanese monkeys are in their puberty at this age and stage of dental development, from which we conclude that our male was in his puberty as well. During this period, young males disperse from their natal groups and live at the periphery of their troupes. Risks of predation, disease, and injury are higher than before; a quarter of male mandrills dies before reaching adulthood. Among known Paradolichopithecus specimens, nearly half have died before the third molars erupted. This may be explained either by some taphonomic factor or due to higher mortality levels during puberty.
We further found that the eruption sequence of the permanent mandibular dentition of this male is {m1 i1–2 m2} p4, p3, c, m3. The order of the already fully erupted elements (between curly brackets) is based on data from the living baboons, mandrills, macaques and geladas. The p4 p3 sequence as seen in our Paradolichopithecus occurs at high frequency is other papionins as well: Macaca nemestrina, M. mulatta, Mandrillus sphinx, Papio cynocephalus, but not in Papio anubis, Macaca fuscata and M. fascicularis. Theearlier root formation of p4 seems thus not to be related with body size or phylogeny. There is a considerable delay in the canine development relative to the premolars, as in other papioninmales; the m3 is delayed in formation relative to the premolars and the canine. In total, the dental eruption sequence of Paradolichopithecus is very similar to that of the living papionins.

Read more in Van der Geer, A.A.E., Dermitzakis, M. 2008. Dental eruption sequence in the Pliocene Papionini Paradolichopithecus arvernensis (Mammalia: Primates) from Greece. Journal of Vertebrate Paleontology 28 (4): 1238-1244. (Ask a pfd, geeraae@geol.uoa.gr)

'Hobbit' skull found in Indonesia is not human indeed

2008-08-06T23:09:00.000-07:00

Since its first description in 2004, Homo floresiensis, or the Hobbit of Flores, has been attributed to a species of its own, a descendant of Homo erectus, Homo ergaster or another early hominid, such as Australopithecus. Non-believers however hold the new species for a pathological form of modern humans, Homo sapiens, or just a dwarf human like the Neolithic inhabitants of the very same island. Karen Baab and colleagues applied landmarks on the skull, and concluded Homo floresiensis is a species on its own, and related to hominins of 1.5 million years ago. We did the same, half a year earlier, and reached similar conclusion but dare to put one step further. We applied geometric morphometric analysis to the type skull of Homo floresiensis (LB1) and compared it with skulls of normal Homo sapiens, insular Homo sapiens (Minatogawa Man and Neolithic skulls from Flores), pathological Homo sapiens (microcephalics), Asian Homo erectus (Sangiran 17), African Homo habilis (KNM ER 1813), and Australopithecus africanus (Sts 5). Our analysis includes specimens that were highlighted by other authors to prove their conclusions. The geometric morphometric analysis separates the 'hobbit' from all modern humans, thus including both the pathological and the insular forms. It is further impossible to separate the 'hobbit' skull from Homo erectus. The very early hominin Australopithecus falls separately from all skulls.

Visual inspection of the skulls learned that the cranial shape of Homo floresiensis is most close to that of Homo erectus and not to that of any modern human. Apart from cranial shape, some features of Homo floresiensis are not unique but are shared with other insular taxa, such as the relatively large teeth (shared with Early Neolithic humans of Sardinia), and changed limb proportions (shared with Minatogawa Man).

We thus conclude that Homo floresiensis is a direct descendant of Asian Homo erectus and has no relation neither to primitive australopithecines nor to modern Neolithic pygmy people of Flores.

By G.A. LYRAS, M.D. DERMITZAKIS, A.A.E. Van der GEER, S.B. Van der GEER, J. De VOS. 2008. The origin of Homo floresiensis and its relation to evolutionary processes under isolation.© 2008 The Anthropological Society of Nippon

For free pdf, click here http://users.uoa.gr/~glyras/projects/Homo-floresiensis.pdf

Or go to the publisher http://www.jstage.jst.go.jp/browse/ase

The effect of insularity on the five-horned deer Hoplitomeryx (Late Miocene, Italy)

2008-08-06T23:05:00.000-07:00

Island studies increase our understanding of the effects of habitat fragmentation. The study of the Tertiary paleo-island Gargano is an important contribution, because of the long-term isolation under less fluctuating climatic conditions, free from anthropogenic influences; such a situation does not exist in the Quaternary period nor in the Holocene period. This makes the Gargano a unique case to study the effects of insularity in isolation. Here, a highly endemic, unbalanced vertebrate fauna evolved including the five-horned deer Hoplitomeryx. Its post-cranial material contains four size groups, based on the metapodals. In this study, the humerus and radius are described. The question whether the morphotypes are chronomorphs or ecomorphs is addressed. Sexual dimorphism is ruled out as the underlying principle of size separation in this case, based upon body mass estimations and data from living deer. Chronomorphs is the best explanation for the Megaloceros cazioti lineage (Pleistocene, Sardinia) and the Myotragus balearicus lineage (Pliocene–Holocene, Mallorca). Ecomorphs are a better explanation for the size groups of Candiacervus (Late Pleistocene, Crete) and Cervus astylodon (Late Pleistocene, Ryukyu Islands, Japan). An adaptive radiation into several trophic types took place, promoted by the ecological meltdown of the ancestral niche. The drive behind this speciation is increased interspecific competition. For Hoplitomeryx, although the hypothesis of chronomorphs cannot be discarded, that of ecomorphs seems most likely, based upon the coexistence of two or more size groups per fissure, and upon the presence of a huge morphotype, larger than mainland species, in the younger fissures.

Read more in VAN DER GEER A.A.E. (2008). The effect of insularity on the Eastern Mediterranean early cervoid Hoplitomeryx: the study of the forelimb. Quaternary International 182, 1: 145-159. See http://dx.doi.org/10.1016/j.quaint.2007.09.021 or ask me a pdf (geeraae@geol.uoa.gr).

For more general information of this enigmatic Late Miocene 'deer', see my Wikipedia page at http://en.wikipedia.org/wiki/Hoplitomeryx

Locomotor behavior of Paradolichopithecus arvernensis as inferred from the functional morphology of its ankle and elbow

2007-05-30T01:13:00.000-07:00

Taking all ankle and elbow elements of Paradolichopithecus into account, the picture emerges of a highly terrestrial monkey. This is not surprising as many fossil cercopithecines are found in open country habitats and show terrestrial adaptations, such as Dinopithecus (Late Pliocene, Africa), Procynocephalus (Late Pliocene, China and India), Paradolichopithecus (Pliocene, Spain and Asia), Theropithecus (Middle Pleistocene - Holocene, Africa) and, among the colobines, Paracolobus (Pliocene, East Africa) and Dolichopithecus (Pliocene, Europa) (Szalay & Delson, 1979). In addition, the larger species tend to be terrestrial, possibly as a response to predator pressure. This, too, makes a terrestrial adaptation of our large Paradolichopithecus very probable.
Body weight was carried more posterior, as the architecture of the olecranon and the trochlear notch are less apted for sustaining heavy load than is the case in the extant baboons. The morphology of the arm indicates an increased mobility in the elbow joint, with a departure from the sagittal plane during flexion. Paradolichopithecus could very well have used his strong arms for carrying food while walking or standing. Another option is the use of the arms in fights and defense.
The massive medial malleolus of the tibia also shows that a larger (part of the) body weight was carried on the hindlimbs. The suspensory facet for the fibular malleolus indicates an increased importance of the lateral malleolus in transferring body weight, and an increased fixation of the talus in the malleolar fork, formed by both the malleoli together.
As to the ankle joint, a remarkable parallel is seen with Australopithecus. Unique features that distinguish Paradolichopithecus, and probably also Procynocephalus, from the other papionins are seen also in Australopithecus, though the overall architecture of the Paradolichopithecus talus is typically cercopithecoid (pronounced lateral trochlear ridge, hardly developed groove for large toe flexor), whereas it is typically hominoid for Australopithecus (symmetrical trochlea, pronounced large toe flexor).The terrestrial traits in the postcranial elements show that this large monkey was clearly adapted to the habitat: an open savanna/bushland environment with seasonal availability of food, and large distances between the food sources.

Read more in SONDAAR P.Y., VAN DER GEER A.A.E., DERMITZAKIS M. (2006). The unique postcranial of the Old World monkey Paradolichopithecus: more similar to Australopithecus than to baboons. Hellenic Journal of Geosciences 41, 1: 19-28. Special volume in the memory of P.Y. Sondaar

and in VAN DER GEER A.A.E., SONDAAR P.Y. (2002). The postcranial elements of Paradolichopithecus arvernensis (Primates, Cercopithecidae, Papionini) from Lesvos, Greece. Annales Géologiques des Pays Helléniques 1e Série 39, A: 71-86. Free pdf at http://users.uoa.gr/~geeraae/publications/2002-agph-Paradolichopithecus.pdf .

and in SONDAAR P.Y., VAN DER GEER A.A.E. (2002). Arboreal and terrestrial traits as revealed by the primate ankle joint. Annales Géologiques des Pays Helléniques 1e Série 39, A: 87-98. Free pdf at http://users.uoa.gr/~geeraae/publications/2002-agph-terrestriality.pdf .

The postcranial of the deer Hoplitomeryx (Mio-Pliocene; Italy): another example of adaptive radiation on Eastern Mediterranean Islands.

2007-05-24T02:06:00.000-07:00

During the Late Miocene a highly endemic vertebrate fauna evolved on Gargano Island (south-east coast of Italy), comprising others the giant soricid 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 heterogenous group, containing four size groups; within the size groups different morphotypes may be present. All size groups share the same typical Hoplitomeryx features. These are: 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 non-parallel-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 morphotypes on an island is paralleled by Candiacervus (Late 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 hoplitomerycid features. The morphosphere of Hoplitomeryx 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 derived features in all size groups (apomorphies).

For full text, see VAN DER GEER, A.A.E. (2005). The postcranial of the deer Hoplitomeryx (Mio-Pliocene; Italy): another example of adaptive radiation on Eastern Mediterranean Islands.van der Geer. Monografies de la Societat d'Història Natural de les Balears 12: 325-336. Palma de Mallorca. For a free pdf [1,018 kb]: http://users.uoa.gr/~geeraae/publications/2005-IMEDEA-Hoplitomeryx.pdf. See my website http://users.uoa.gr/~geeraae for three more publications on this bizarre and enigmatic insular 'deer' of the Late Miocene.

For more general information of this enigmatic Late Miocene 'deer', see my Wikipedia page at http://en.wikipedia.org/wiki/Hoplitomeryx

New data on the Late Pleistocene Cretan deer Candiacervus sp. II

2007-05-24T02:00:00.000-07:00

For our museum, we mounted a skeleton of the endemic Late Pleistocene Cretan deer Candiacervus sp. II (Liko Cave), using bones of different individuals. This composite skeleton contributes to the study of taxonomy of insular ungulates as it reveals some additional features that were not detected in the isolated elements. Candiacervus sp. II differs from all known recent and extinct mainland deer, mainly in its proportions. Although its considerably shortened distal limbs were already noted in the past, Candiacervus sp. II now appears at the same time to have had a more or less normal vertebral column length relative to continental large deer, and moderately upwards curved lumbar section, both features reminding us more of the insular dwarf bovid Myotragus than of the mainland small deer Axis axis. Combined with an increased massivity of all bones and pronounced muscle scars, this change in body proportions appears to indicate that Candiacervus sp. II evolved towards the niche of goat-like bovids in rocky environments. Other additional diagnostic features are the horizontally directed transversal processus of the vertebras, fusion of the lateral metacarpal to the main metacarpal, a tail length of ten vertebras, a more pronounced difference between anterior and posterior hooves, and the presence of lateral toes upto the third phalanx, anterior as well as posterior.

Read more in VAN DER GEER A.A.E., DE VOS J., LYRAS G.A., DERMITZAKIS M.D. (2006). New data on the Pleistocene Cretan deer Candiacervus sp. II (Mammalia, Cervinae). Courier Forschungsinstitut Senckenberg 256: 131-137. For a pdf, send an e-mail to geeraae@geol.uoa.gr. For more Candiacervus publications, visit our websites at http://users.uoa.gr/~geeraae and http://users.uoa.gr/~glyras

For more general info on the extinct Cretan deer, see http://en.wikipedia.org/wiki/Candiacervus

The unique postcranial of the extinct Old World monkey Paradolichopithecus

2007-05-24T01:40:00.000-07:00

The talus (astragalus), distal tibia and the humerus of Paradolichopithecus arvernensis show some unique features, not seen in other monkeys.
The humerus has an increased articulation area on the head compared to Papio, a wide and deep groove for the biceps tendon, a gradually descending capitulum, and an oblique axis for flexion-extension through the elbow joint. During flexion, the ulna deviates from the parasagittal plane, and ends in a position medially to the humerus instead of parallel above it, due to the trochlear shape and axis. This unique feature yields a significant increased mobility.
The distal tibia bears a more massive, square and blunt malleolus that lacks the typically pronounced ball-shaped area, a wider groove (sulcus malleolaris) for the tendon of the M. tibialis posterior, a more square cross-section, clear scars for the fibula, and a double tendon groove on the dorsal surface (either for a bifurcated tendon for the M. flexorum tibialis posterior or a pronounced groove for the long toe flexor), which follows the parasagittal plane. None of these features is unique, and they make Paradolichopithecus resemble Australopithecus, a trained Japanese macaque and to a lesser extent some other macaques. The combination indicates a maintainance of the close-packed situation from dorsiflexion to plantar flexion, an increased importance of the fibula in weight transfer, a stronger plantar flexion, and possibly a slightly abducted foot. The flat tibial malleolus in Paradolichopithecus and Australopithecus, compared to baboons (Papio) and chimps (Pan) respectively, in combination with the corresponding facet on the talus acts as a blocking mechanism, preventing further dorsiflexion rotation during maximal dorsiflexion. This makes this ankle unsuitable for climbing.
The talus has an almost parallel trochlea, a large flap-like, protruding fibular suspensory facet, and a slightly deeper facet for the spring ligament on the talar head. These features are suggestive for a baboon-like ankle joint with the body weight more evenly distributed over the talar trochlea, a greater proportion of the weight transfer through the lateral (fibular) side, and with approximate the same stability in maximal dorsiflexion as in maximal plantar flexion. In these aspects Paradolichopithecus resembles Australopithecus.
Considering the unique features of the ankle and elbow of Paradolichopithecus, it may be expected that its locomotion differed from that of baboons. Main differences are the increased fibular component, the increased stability in plantar flexion, a more evenly distribution of stability during locomotion, and an equal medio-lateral stability in maximal plantiflexion and in maximal dorsiflexion. In our view, such a type of locomotion finds a parallel in Australopithecus and in trained Japanese macaques. The latter appear to develop significant modifications during training, especially in the hind limb, to satisfy the functional requirements for increased habitual bipedalism. Amongst others, the malleolus of the tibia has been remodeled under the influence of the greater stress and became less cusp-shaped, and the talar malleolar facet correspondingly more planar. The varus knee in the trained macaque further requires an increased fibular compound. This may have its parallel in Paradolichopithecus and Australopithecus, in whom we also find an increased fibular component. It should be stressed, however, that the kind of bipedalism of the trained macaque differs essentially from the striding gait bipedalism with erect trunk and straight knees of the genus Homo. The macaque bipedalism is characterised by high energy cost and bent knees. Considering the similar biomechanical features in Paradolichopithecus, Australopithecus and the trained macaque, it is tempting to conclude that also the two former genera had an all-round, energetically expensive bipedal mode with bent knees. This development then was not restricted to the hominoid clade, but appeared also in the papionins, as evidenced by the difference between Australopithecus and Pan on one hand and Paradolichopithecus and Papio on the other hand. The pattern shared indicates similar mechanical stresses, and reflects a shared increased frequency of bipedalism in the daily locomotor behavior, possibly but not necessarily, accompagnied by an increased mobility of the arm.

Read more in SONDAAR P.Y., VAN DER GEER A.A.E., DERMITZAKIS M.D. (2006). The unique postcranial of the Old World monkey Paradolichopithecus: more similar to Australopithecus than to baboons. Hellenic Journal of Geosciences 41, 1: 19-28. Special volume in the memory of Paul Yves Sondaar. Free pdf [868 kb] at http://users.uoa.gr/~geeraae/publications/2006-HJG-Paradolichopithecus.

Origin and adaptation of Cynotherium sardous (Mammalia: Carnivora) by Lyras, Van der Geer, Dermitzakis, De Vos in JVP 26 (3): 735-745

2007-05-24T01:32:00.000-07:00

The endemic insular canid Cynotherium sardous is known for one and a half century, yet its phylogenetic position remained unsolved. This was because inherited ancestral characters and acquired adaptations to different ecological pressures could not be separated. Morphological and biometrical data alone are therefore insufficient. In this study the problem is approached again, with the use of morphological features that were either overlooked or could not be explained properly, in combination with results from recent major revisions of canid phylogeny. It appears that Xenocyon is the most parsimonious ancestor of Cynotherium, and that this large hypercarnivorous canid, once on the island, faced a rather different menu consisting of small prey only. The subsequent necessary adaptation resulted in a small-sized dog which carried its head much in the way foxes do and was able to hold its body low to the ground and move its head laterally better than any living canid. Its dentition and brain morphology remained much the same, whereas its skull lost the typical fortifications seen in the other hypercarnivorous canids; these are considered superfluous for Cynotherium who had to exchange big and strong prey for small and fast prey.

Read the full text in LYRAS G.A., VAN DER GEER A.A.E., DERMITZAKIS M.D., DE VOS J. (2006). Cynotherium sardous, an insular canid (Mammalia: Carnivora) from the Pleistocene of Sardinia, and its origin. Journal of Vertebrate Paleontology 26(3): 735-745,

and in LYRAS G.A., VAN DER GEER A.A.E. (2006). Adaptations of the Pleistocene island canid Cynotherium sardous (Sardinia, Italy) for hunting small prey. Cranium 23 (1): 51-60 (for pdf, click http://users.uoa.gr/~geeraae/publications/2006-Cranium-Cynotherium.pdf )

For pdf's, ask me at geeraae@geol.uoa.gr or ask glyras@geol.uoa.gr, or visit our pages: http://users.uoa.gr/~geeraae and http://users.uoa.gr/~glyras and select Publications

Crete before the Cretans: the reign of dwarfs

2007-05-24T01:29:00.000-07:00

Crete was completely submerged during the Pliocene, and gradually emerged in the Early Pleistocene. New and empty islands like these are normally colonized overseas by sweepstake dispersal, which means that only a limited number of taxa is able to reach the island. This results in an unbalanced mammal fauna, as a rule consisting of only elephants, hippopotamus, deer, cattle, rodents, insectivores and sometimes otters. After successful colonization, as a rule a fast evolutionary change takes place, which can be explained as an adaptation to the restricted island environment. As a result, island faunas are very different from mainland faunas, but similar to each other. Crete is no exception to this general pattern, and during the Pleistocene there were two successive endemic mammalian faunas. The first (the Kritimys-biozone) is characterised by a dwarf mammoth, a dwarf hippopotamus and a giant mouse. The second (the Mus-biozone) is characterised by a dwarf elephant, a dwarf deer (next to medium and large-sized deer) and a large mouse. The reason for the dramatic faunal turnover between the two biozones is unknown, but may very well have been related to a significant sea-level drop. This decreases the distance between the now larger island and another firm ground. The second fauna got extinct just before or after the arrival of the first humans. Problems of dating and the lack of paleolithic artefacts or human remains obscures this point. In any case the fauna of the second biozone was already completely extinct at Aceramic Neolithic and Minoan times, and replaced by newcomers who came together or along with the humans.

Read more in VAN DER GEER A.A.E., DERMITZAKIS M., DE VOS J. (2006). Crete before the Cretans: the reign of dwarfs. Pharos 13: 121-132. Netherlands Institute at Athens, Greece. Free pdf [ 2,197 kb] at http://users.uoa.gr/~geeraae/publications/2006-pharos-crete.pdf .

Visit my homepage

2007-05-24T00:44:00.000-07:00

Hello everybody, I have a homepage, at last. Visit it at http://users.uoa.gr/~geeraae. If you are interested in paleontology, evolutionary biology, paleopathology, Sanskrit or Sardinian, then you are at the right address. If you're more interested in particle tracing, electron beams and accelerators, visit http://www.pulsar.nl.

Alexandra