Conference Agenda

The origins of the regenerative nature of antlers, branched and deciduous apophyseal appendages of frontal bones, have long been associated with permanent evolutionary precursors. In this study, we provide novel insight into growth modes of evolutionary early antlers. We analysed a total of 34 early antlers affiliated to ten species, including the oldest known, dating from the early and middle Miocene (appr. 19 to 12 million years old) of Europe. Our findings provide empirical data from the fossil record to demonstrate that growth patterns and a regular cycle of necrosis, abscission and regeneration are consistent with data from modern antlers. The diverse histological analyses indicate that primary processes and mechanisms of the modern antler cycle were not gradually acquired during evolution, but were fundamental from the earliest record of antler evolution and, hence, explanations why deer shed antlers have to be rooted in basic histogenetic mechanisms. The previous interpretation that proximal circular protuberances, burrs, are the categorical traits for ephemerality is refuted based on our novel data.

Chevrotains or mouse-deer (Tragulidae, Mammalia) are non-pecoran ruminant artiodactyls that are considered to have branched off the Ruminantia stem lineage during the late Eocene or Oligocene to Early Miocene. Extant tragulids live in central Africa (Hyemoschus) and South to Southeast Asia (Moschiola, Tragulus).The fossil record is reported to have been more diverse in phenotypes with a wider Afro-Eurasian distribution in paleoenvironments. However, palaeobiogeography of tragulids is still far from being revealed. The debatable taxonomy of tragulids hampers the reconstruction of the big picture.

This study provides a revision of the taxonomy of tragulids from the early Miocene sites of Napak (ca. 20.5-19 million years old) in Uganda which have yielded one of the oldest records of ruminants on the African continent. Ongoing field work has helped to enlarge the size of the tragulid samples. On that basis, a morphometric re-examination and extensive comparison with Miocene Afro-Eurasian species is being conducted in order to assess the taxonomy of Napak tragulids.

So far, we can identify six species, two being new to science. The bunoselenodont Dorcatherium iririensis is the largest species of Napak. The selenodont Siamotragulus songhorensis is a small-sized species and the selenodont Afrotragulus parvus is the smallest species found in Napak. The latter three were recorded previously from Napak (S. songhorensis under the name Dorcatherium songhorensis and A. parvum under the name Dorcatherium parvum). In addition, we are able to document the bunoselendont Dorcatherium pigotti and the existence of a further, possibly new medium-sized Dorcatherium sp. nov.as well as Tragulidae genus and species indet.

The four formerly established species have been recorded so far only on the African continent, D. iririensis is even known only from Napak. D. pigotti from Napak predates all other occurrences known of that species. Notably, Afrotragulus parvus is reported to be endemic to Africa, however, there is Afrotragulus cf. parvum reported from Bugti Hills (Pakistan, Asia), what hints to a potential transcontinental distribution.

The fossil record of Platanistidae (Indian river dolphins and extinct partially marine relatives, Early Miocene to today) is suggestive of an early radiation of the group reflected in the diversification of the skull morphology, and a wide distribution in the Old World and New World during the Miocene that dropped coincidentally with the appearance of delphinoids (pelagic dolphins and closest relatives) in the Late Miocene. River dolphin radiation is correlated with the rise of shallow epicontinental seas, as a result of high sea levels during the Middle Miocene. Their stem group is interpreted to have remained in marine areas, serving as ancestor to species entering and adapting to freshwater environments. Here, a new Platanistidae skull is described from deep-marine sediments from the lower Miocene of Austria with an age of ca. 22 Ma. Morphological comparison with other dolphins provides insights into ecology and evolution through dentition, and cranial asymmetry related to hunting and navigating in aquatic environments. The skull belongs to a single-rooted homodont dolphin, known as a characteristic of the Platanistidae, in contrast to heterodont dentition in their platanistoid ancestors. According to our preliminary phylogenetic analysis, the skull represents the most ancient member known to date of the Platanistidae, predating all previous early records by 2 to 5 million years, and documenting a pelagic habitat adaptation.

Evolution of giant body size (>10 t) is a pervasive trend in the history of both marine and terrestrial amniote clades. The largest marine amniotes are today’s cetaceans, followed by giant ichthyosaurs of the Triassic. Here we describe a new giant ichthyosaur (skull length close to 2 m, est. total length 18 m, est. body mass ~ 27 t) from the early Middle Triassic Fossil Hill Member of Nevada, USA. The giant ichthyosaur is the largest member of a diverse fauna including several other large ichthyosaur species. This fauna existed only 6 million years after the appearance of marine reptiles in the fossil record and in the absence of the highly productive marine ecosystems of today. Cetaceans, which are the closest living analog to ichthyosaurs, appear to have evolved much more gradually, both in their late appearance after a mass extinction event and their slower size increase.
Using phylogenetic comparative methods and a newly compiled consensus phylogeny of all cetaceans, we quantitatively compared size evolution in the two clades. We chose skull length as size proxy in ichthyosaurs and bizygomatic skull width in cetaceans. Our analysis documents an amazingly rapid size increase from Chaohusaurus in the Olenekian at 248.5 ma (skull length 117 mm) to the new giant (skull length 1890 mm) a mere 2.5 ma later. This rate of evolutionary size increase fits an early burst model and far surpasses that seen in the origin and early evolution of whales. In this clade, size evolution was much more gradual. It took whales 15 ma to reach a comparable body size (Basilosaurus) to the new giant and to reach their first size peak. Both groups dominate the pelagic ecosystems and diversified into different niches and a wide morphospace in the first 50 ma of their evolution.
The early burst model for ichthyosaurs underscores the notion of explosive evolutionary body size increase in ichthyosaurs. This is consistent with the early burst previously detected in diversity and morphological disparity in ichthyosaurs. Why was whale size evolution slower than ichthyosaur size evolution, and why is there a delayed return to the sea in whales, 15 ma after the end of the Cretaceous? Possibly, eutherian mammals were more constrained in aquatic adaptation despite having one precondition, life birth, that most reptiles lack.