Über die Funktionsweise prätribosphenischer und tribosphenischer Gebisse

In der mesozoischen Evolution der Säugetiere gilt die Entwicklung des tribosphenischen Molaren als ein Schlüssel zur Erschließung pflanzlicher Nahrungsressourcen. Während sich die Funktion des prätribosphenischen Molaren auf interdentales Scherschneiden beschränkt, erhält der tribosphenische Molar durch den neomorphen Protocon im oberen Molaren und das beckenartig geformte Talonid im unteren zusätzlich eine quetschende, komprimierende Funktion. Daher wird dem tribosphenischen Molaren allgemein eine höhere Effizienz zugesprochen als dem prätribosphenischen. In der Rezentfauna ist der prätribosphenische Molar nicht mehr vorhanden. Nach funktionalen Kriterien kommen ihm die zalambdodonten Molaren der Tenrecidae am nächsten. Die Molaren der untersuchten Arten der Tenrecidae werden in drei Gruppen unterteilt: Sie ähneln entweder dem tribosphenischen oder dem prätribosphenischen Zustand, oder weisen eine Vereinfachung auf, die über den prätribosphenischen Zustand hinausgeht. Bis auf die erste Gruppe, zu der nur Potamogale gerechnet wird, funktionieren diese Molarengebisse durch interdentales Ineinandergreifen von oberen und unteren Molaren. Dies gilt auch für die prätribosphenischen Molaren. Unterschiede bestehen dabei teilweise in der Führung des Kauschlages. Bei Nanolestes drescherae handelt es sich um einen prätribosphenisch bezahnten Vertreter der Stammlinie der Zatheria aus dem Oberjura. Das Abkaumuster offenbart deutliche Usuren, die auf Zahn-Zahn-Kontakte zurückzuführen sind. Es handelt sich dabei jedoch hauptsächlich um Dentinfreilegungen, während Schmelzfacetten kaum ausgeprägt sind. In Letzterem besteht ein Unterschied zur früheren Analyse von Dryolestidenmolaren und zu Amphibetulimus krasnolutskii, einem weiteren untersuchten Vertreter der Stammlinie der Zatheria aus dem Mitteljura. Für N. drescherae belegen die Usuren und die Form der Parastylarrinne und des Hypoflexids eine transversale und aufwärts gerichtete Bewegung des Unterkiefers. Es besteht dabei eine Führung durch zwei Höcker-Rinnen-Systeme: das Protoconid fährt durch die Parastylarrinne, das Hypoflexid wird entlang des Paracons geführt. Der erste Zahn-Zahn-Kontakt erfolgt dabei zwischen der Spitze des Protoconids und der Parastylarrinne. Der Schluss der potentiellen scherschneidenden Kanten, den Außenkanten des primären Trigons im oberen Molaren und des Trigonids im unteren Molaren, erfolgt danach. In gleichbleibender Bewegung wird der Unterkiefer weiter nach aufwärts und lingual bewegt. Für N. drescherae ergibt sich das Bild eines Insektenfressers, bei dem das attritive Scherschneiden eine untergeordnete Rolle bei der Nahrungsaufbereitung gespielt hat. Es wird eine Nahrungspräferenz von zähen, weichen Arthropoden angenommen. Diese werden während des Kieferschlusses durch die spitzen Höcker fixiert und im weiteren Kieferschluss zwischen den oberen und unteren Molaren gedehnt. Mit der Entwicklung der Zatheria und schließlich der Tribosphenida ändert sich die Führung des Kauschlages. Er wird nicht mehr durch das Ineinandergreifen von Protoconid und Parastylarrinne, bzw. Paracon und Hypoflexid bestimmt, sondern durch die Interaktion von Protocon und Talonid. Die Bedeutung des einspitzigen Talonids, genauer des Hypoflexids, als Führungsstruktur wird damit deutlich verringert. Mit der Entwicklung des tribosphenischen Molaren wird das Talonid dreihöckerig und bildet eine beckenartig geformte Struktur. In diese greift der neomorphe Protocon ein und kann so eine quetschende, komprimierende Funktion ausüben. Die hier zusammengefasste Differenzierung der Molarenfunktion von einem rein scherschneidenden zu einem scherschneidenden und quetschenden, komprimierenden Potential ist bereits mehrfach diskutiert worden. Nanolestes wird nach funktionalen Kriterien zu den wenig abgeleiteten Stammlinienvertretern der Zatheria gestellt, die sich durch ihr einspitziges Talonid und die einfache, dreieckige Grundform des oberen Molaren auszeichnen. Das Potential des tribosphenischen Molaren zur Erschließung unterschiedlicher Nahrungsquellen wird hier an drei Opossumarten gezeigt. Obwohl die Molaren sich nur wenig unterscheiden, hat Didelphis eine omnivore Lebensweise, ist Monodelphis insektivor-carnivor und Caluromys frugivor. Es zeigt sich, dass bei breiterem Nahrungsspektrum diversere Zahnusuren auftreten. Je nach Differenzierung der Schmelzdicke der Zahnkrone und Einsatz der Molaren können sich, wie bei Monodelphis, durch Abnutzung potentiell scherschneidende Schmelzkanten herausbilden. Abrasiv ausgekolkte Dentinareale belegen regelmäßige Kompression von Nahrung, wie sie beispielsweise bei Caluromys auftritt. Mit leichter Variation der tribosphenischen Molarenform können also unterschiedliche Nahrungspräferenzen entstehen. Unter der Hypothese, dass tribosphenische Molaren effizienter sind als prätribosphenische, wurden vergleichende Fütterungsversuche durchgeführt. Als tribosphenisch bezahnte Vertreter wurden Monodelphis und Tupaia verwendet. Als Analogon zum prätribosphenischen Molaren wurde Setifer genutzt. Obwohl Setifer zu der Gruppe der Tenrecidae gehört, deren Molaren stärker vereinfacht sind als die prätribosphenischen, wurde diese Art aufgrund der Verfügbarkeit herangezogen. Die Versuche haben gezeigt, dass die tribosphenisch bezahnten Taxa die verfütterten Mehlwürmer im Schnitt stärker zerkleinert haben als Setifer. Dies wird in der Regel mit einer besseren Nahrungsaufnahme gleichgesetzt. Die beobachteten Ergebnisse zeigen jedoch auch, dass bei ähnlichem Molarengebiss interspezifische, altersbedingte und sogar individuell unterschiedlich starke Zerkleinerung der Nahrung erfolgen kann. Im Vergleich hat der tribosphenische Molar ein höheres Anwendungspotential und kann eine wirkungsvollere Zerkleinerung der Nahrung bewirken als prätribosphenische, bzw. zalambdodonte Molaren.The origin of the tribosphenic molar is treated as an evolutionary key innovation of mammals in the Mesozoic, allowing the exploitation of vegetation as a food resource. While the function of the praetribosphenic molar is limited to an interdental shear-cutting, the tribosphenic molar develops an additional crushing and compressing function through the evolution of the neomorphic protocone and a basin-like talonid. This led to the assumption that the tribosphenic molar is generally more efficient than the praetribosphenic one. The praetribosphenic molar is no longer present in modern mammals. From a functional perspective, the zalambdodont molars of the Tenrecidae are the most similar Recent teeth. The level of zalambdodonty and praetribospheny in the molars of the investigated Tenrecidae was specified by defining three functional groups: one is similar to the tribosphenic habit, one to the praetribosphenic and the third is simpler than the praetribospenic molar. Except for the first group, which includes only Potamogale, the Tenrecidae molar dentition functions through an interdental locking of the upper and lower molars. This is also the case in praetribosphenic molars. Differences are partially caused by the guiding of jaw movement in the mastication cycle. Nanolestes drescherae is an Upper Jurassic representative of the stem-linage of Zatheria with a praetribosphenic dentition. The wear pattern includes definitive evidence of tooth-tooth-contact. It is dominated by areas of exposed dentine, whereas facets in the enamel are weakly developed. This wear pattern differs from previous analyses of dryolestid molars, and from the upper molar of Amphibetulimus krasnolutskii, another Middle Jurassic representative of stem-Zatheria, by missing of facets in the enamel. For N. dreascherae, the wear pattern and form of both the hypoflexid and the parastylar groove indicate a transverse and upward direction of lower jaw movement. This movement is guided by two cusp-groove systems: the protoconid slides through the parastylar groove, the hypoflexid is guided along the paracone. The first tooth-tooth-contact takes place at the tip of the protoconid and the parastylar groove. Subsequently the potential shear-cutting edges, the outer edges of the primary trigon and the trigonid, close. The lower jaw is moved further upwards and lingually in a continuous motion. N. drescherae is reconstructed as an insectivorous species with limited attritive shear-cutting during the processing of food. A preference for tough and weak arthropods is expected, which were fixed by acute cusps and stretched between the upper and lower molars by the subsequent jaw motion. The manner in which the upper molar cusps guide the motion of the lower molars changes within the Zatheria and Tribosphenida. It is no longer dominated by the guiding function of the parastylar groove on the protoconid and the hypoflexid on the paracone. Instead the interaction of the protocone and the talonid is crucial. The importance of the one-cusped talonid, respectvely of the hypoflexid, which acts as a guiding structure, thus decreases. During the course of its evolution, the talonid of the tribosphenic molar develops a three-cusped and a basin-like form. The neomorphic protocone performs a crushing and compressing action in an interaction with the talonid basin. This differentiation of the molars from a pure shear-cutting to a shear-cutting, crushing and compressing function has been discussed many times. Based on functional characters, Nanolestes appears to be a less derived representative of the stem-Zatheria, possessing upper molars with a simple, triangular outline. The capacity of the tribosphenic molar to make different food resources accessible is demonstrated by three opossum species. Although their molars differ only slightly, Didelphis has an omnivorous lifestyle, Monodelphis an insectivorous-carnivorous and Caluromys a frugivorous one. The wear pattern offers, that an omnivorous lifestyle is connected with a wide range of wear. Depending on the differentiation of enamel thickness and usage of the molars, wear can produce potential shear-cutting edges, as seen in Monodelphis. Abrasive washed out areas of exposed dentine were observed in Caluromys, indicating a regular amount of compression. This shows that slight variations in the tribosphenic molar enable different dietary preferences. Comparative feeding experiments were performed to test the hypotheses that tribosphenic molars are more efficient than praetribosphenic ones. Monodelphis and Tupaia were chosen to represent animals with tribosphenic molars. Setifer was used as an analogue to the praetribosphenic molar; although it belongs to the group of Tenrecidae with very simplified molars it was used for this experiment due to its availability. The experiments have shown that taxa with tribosphenic molars breakup mealworms in smaller pieces than Setifer. Normally this is connected with a better ingestion. Furthermore the experiments uncovered interspecific and age-dependent differences in the breakup of mealworms, as well as other individual differences, despite very similar molar dentitions. The tribosphenic molar has a higher potential range of use and can perform a better breakup of food particles in comparison to praetribosphenic, respectively zalambdodont molars

Unique bone microanatomy reveals ancestry of subterranean specializations in mammals

Acquiring a subterranean lifestyle entails a substantial shift for many aspects of terrestrial vertebrates’ biology. Although this lifestyle is associated with multiple instances of convergent evolution, the relative success of some subterranean lineages largely remains unexplained. Here, we focus on the mammalian transitions to life underground, quantifying bone microanatomy through high-resolution X-ray tomography. The true moles stand out in this dataset. Examination of this family's bone histology reveals that the highly fossorial moles acquired a unique phenotype involving large amounts of compacted coarse cancellous bone. This phenotype exceeds the adaptive optimum seemingly shared by several other subterranean mammals and can be traced back to some of the first known members of the family. This remarkable microanatomy was acquired early in the history of the group and evolved faster than the gross morphology innovations of true moles’ forelimb. This echoes the pattern described for other lifestyle transitions, such as the acquisition of bone mass specializations in secondarily aquatic tetrapods. Highly plastic traits—such as those pertaining to bone structure—are hence involved in the early stages of different types of lifestyle transitions

The helochelydrid turtle Helochelydra nopcsai from the Early Cretaceous (late Barremian – early Aptian) fissure fills of Balve, North Rhine-Westphalia, Germany, including a large sample of granicones

Early Cretaceous (late Barremian – early Aptian) fissure fill deposits near Balve, North Rhine Westphalia, Germany, have yielded a rich continental vertebrate fauna over the course of the last two decades. More than 250 fragmentary specimens, including more than 150 osteoderms (i.e., granicones), represent the late Early Cretaceous helochelydrid Helochelydra nopcsai, which had previously been reported from the UK, France, and Spain. The new material mostly differs from that from the type section by exhibiting a reduced to absent entoplastral scute and by displaying distinct cranial scute sulci, both of which are interpreted as intraspecific variation. Although morphological insights are limited, the new material reveals that the visceral cavity extends anteriorly and posteriorly to the bridge, a relatively novel feature previously reported for an eclectic mix of compsemydids, pleurosternids, and other helochelydrids. The available sample of granicones reveals great shape diversity, but a morphometric analysis concludes that no distinct morphotypes exist

Preservation of three-dimensional anatomy in phosphatized fossil arthropods enriches evolutionary inference

External and internal morphological characters of extant and fossil organisms are crucial to establishing their systematic position, ecological role and evolutionary trends. The lack of internal characters and soft-tissue preservation in many arthropod fossils, however, impedes comprehensive phylogenetic analyses and species descriptions according to taxonomic standards for Recent organisms. We found well-preserved three-dimensional anatomy in mineralized arthropods from Paleogene fissure fillings and demonstrate the value of these fossils by utilizing digitally reconstructed anatomical structure of a hister beetle. The new anatomical data facilitate a refinement of the species diagnosis and allowed us to reject a previous hypothesis of close phylogenetic relationship to an extant congeneric species. Our findings suggest that mineralized fossils, even those of macroscopically poor preservation, constitute a rich but yet largely unexploited source of anatomical data for fossil arthropods

Preservation of three-dimensional anatomy in phosphatized fossil arthropods enriches evolutionary inference

External and internal morphological characters of extant and fossil organisms are crucial to establishing their systematic position, ecological role and evolutionary trends. The lack of internal characters and soft-tissue preservation in many arthropod fossils, however, impedes comprehensive phylogenetic analyses and species descriptions according to taxonomic standards for Recent organisms. We found well-preserved three-dimensional anatomy in mineralized arthropods from Paleogene fissure fillings and demonstrate the value of these fossils by utilizing digitally reconstructed anatomical structure of a hister beetle. The new anatomical data facilitate a refinement of the species diagnosis and allowed us to reject a previous hypothesis of close phylogenetic relationship to an extant congeneric species. Our findings suggest that mineralized fossils, even those of macroscopically poor preservation, constitute a rich but yet largely unexploited source of anatomical data for fossil arthropods

Schwermann_He_et_al_2018_Systematis_and_macroevolution_of_extant_and_fossil_scalopine_moles_suppl

S1: Dental Formular f Yunoscaptor scalprum and Scapanulus oweni; S2: Matrix and characters for phylogenetic Analysis; S3: List of species used in this study, and their sample sizes; S4: Published North American Mioscalops-findings; S5: Notes on Mioscalops-findings from the Hemphillia

First spalacotheriid and dryolestid mammals from the Cretaceous of Germany

The new spalacotheriid “symmetrodontan” Cifellitherium suderlandicum gen. et sp. nov. from the Barremian–Aptian of the Balve locality in northwestern Germany is the first record of spalacotheriids in Central Europe. The new taxon is based on one lower and two upper molars. Cifellitherium is similar to Spalacotherium, but differs by smaller stylocone and larger paraststyle on the upper molars, and a labially interrupted cingulid on the lower molar. The new dryolestid Minutolestes submersus gen. et sp. nov. is based on one lower and two upper molars of small size. Phylogenetic analysis revealed it as sister taxon of the clade comprising Laolestes, Krebsotherium, Dryolestes, and Guimarotodus. A dryolestid mandible with unevenly rooted molars and extremely worn down teeth cannot be attributed to Minutolestes submersus gen. et sp. nov. due to possessing molars twice as large in size. The mandible is assigned to a new dryolestid taxon, Beckumia sinemeckelia gen. et sp. nov., and has the dental formula 3i, 1c, 4p, 8m and a fully reduced Meckel’s groove. The mandible lacks any trace of a coronoid or splenial. In the phylogenetic analysis, it appears as sister taxon of a clade comprising Achyrodon, Phascolestes, Crusafontia, and Hercynodon. The new mammals are the stratigraphically youngest European representatives of their clades. The late survival of Beckumia sinemeckelia gen. et sp. nov. and Minutolestes submersus gen. et sp. nov. is possibly the result of isolated evolution in an Early Cretaceous island environment. This finding of new spalacotheriid and dryolestid mammals from Central Europe adds to an emerging paleobiogeographic pattern that Europe was distinct from Asia in the constituents of mammalian faunas during the Barremian–Aptian

The first articulated skeletons of enigmatic Late Cretaceous billfish-like actinopterygians

Only few candidates of Mesozoic fishes with a similar body plan and ecological niche to the modern billfishes are suggested as their analogues. Several specimens were recovered from Cenomanian deposits in Germany and Lebanon and display a billfish-like fusiform body with elongated premaxillae. They are found close to the plethodids and show a unique combination of characters (rostrum pointed and extremely elongated, double articular head of the quadrate, anteroposteriorly elongated abdominal centra indicating a slender body and different types of scales on the body) allowing their inclusion in a new genus. Two ‘ Protosphyraena ’ species are also assigned to this new genus. This fish can be considered as an ecological analogue to the extant xiphioids sharing their feeding habits. This fish was abundant and roamed, as an apex predator, the Central Tethys and the Boreal realms during the Cenomanian. </p