Analía M. Forasiepi

New Jurassic Mammals from Patagonia, Argentina: A Reappraisal of Australosphenidan Morphology and Interrelationships

Abstract A new mammal, Henosferus molus, n.gen. and n.sp., from the Callovian–Oxfordian (latest Middle to earliest Late Jurassic) Cañadón Asfalto Formation from Chubut Province (Argentina) is described. This taxon corresponds to a new species clearly different from Asfaltomylos patagonicus from the same locality and stratigraphic level. This new species is based on three lower jaws with relatively well-preserved dentition. The lower jaw shows a primitive morphology having a Meckelian groove, a prominent medial flange associated with a lateral ridge of the dentary, and a deep dentary trough, which possibly indicates the presence, even though reduced, of postdentary bones still attached to the dentary. The lower dental formula is i4, c1, p5, m3. The premolars are simple, bearing a main cusp, while the molars appear to be tribosphenic, with an obtuse to right-angled trigonid and a basined talonid with three cusps. This association of plesiomorphic features in the jaw and derived features in the molars is documented in several taxa of the recently proposed Australosphenida. A phylogenetic analysis of mammaliaforms nests the new species with Asfaltomylos from the same locality and stratigraphic level; Henosferidae, new family, is recognized for Asfaltomylos and Henosferus, representing the basal radiation of Australosphenida. Henosferidae is the sister group to Ambondro from the Middle Jurassic of Madagascar, which, in agreement with previous phylogenies, is the sister taxon to the remaining australosphenidans. Additionally, our phylogenetic analysis does not support the inclusion of australosphenidans within eutherians. Henosferids likely retained some connection of the postdentary elements with the dentary; therefore, if the inclusion of Monotremata within Australosphenida is confirmed, final freeing of the postdentary elements and development of a tri-ossicular middle ear would be convergent events in Monotremata and Theria. Finally, the distinctiveness of the yet sparse South American record of Jurassic mammals when compared with the slightly better documented Cretaceous data is emphasized. The clear faunistic break between the Middle Jurassic and Early/Late Cretaceous underlies our rudimentary understanding of the evolution of Mesozoic mammals in Gondwana.

Mammalian skull heterochrony reveals modular evolution and a link between cranial development and brain size

The multiple skeletal components of the skull originate asynchronously and their developmental schedule varies across amniotes. Here we present the embryonic ossification sequence of 134 species, covering all major groups of mammals and their close relatives. This comprehensive data set allows reconstruction of the heterochronic and modular evolution of the skull and the condition of the last common ancestor of mammals. We show that the mode of ossification (dermal or endochondral) unites bones into integrated evolutionary modules of heterochronic changes and imposes evolutionary constraints on cranial heterochrony. However, some skull-roof bones, such as the supraoccipital, exhibit evolutionary degrees of freedom in these constraints. Ossification timing of the neurocranium was considerably accelerated during the origin of mammals. Furthermore, association between developmental timing of the supraoccipital and brain size was identified among amniotes. We argue that cranial heterochrony in mammals has occurred in concert with encephalization but within a conserved modular organization.

Neotropical mammal diversity and the Great American Biotic Interchange: spatial and temporal variation in South America's fossil record.

The vast mammal diversity of the Neotropics is the result of a long evolutionary history. During most of the Cenozoic, South America was an island continent with an endemic mammalian fauna. This isolation ceased during the late Neogene after the formation of the Isthmus of Panama, resulting in an event known as the Great American Biotic Interchange (GABI). In this study, we investigate biogeographic patterns in South America, just before or when the first immigrants are recorded and we review the temporal and geographical distribution of fossil mammals during the GABI. We performed a dissimilarity analysis which grouped the faunal assemblages according to their age and their geographic distribution. Our data support the differentiation between tropical and temperate assemblages in South America during the middle and late Miocene. The GABI begins during the late Miocene (~10–7 Ma) and the putative oldest migrations are recorded in the temperate region, where the number of GABI participants rapidly increases after ~5 Ma and this trend continues during the Pleistocene. A sampling bias toward higher latitudes and younger records challenges the study of the temporal and geographic patterns of the GABI.

Evolutionary Patterns of Bone Histology and Bone Compactness in Xenarthran Mammal Long Bones

Bone microstructure reflects physiological characteristics and has been shown to contain phylogenetic and ecological signals. Although mammalian long bone histology is receiving increasing attention, systematic examination of the main clades has not yet been performed. Here we describe the long bone microstructure of Xenarthra based on thin sections representing twenty-two species. Additionally, patterns in bone compactness of humeri and femora are investigated. The primary bone tissue of xenarthran long bones is composed of a mixture of woven, parallel-fibered and lamellar bone. The vascular canals have a longitudinal, reticular or radial orientation and are mostly arranged in an irregular manner. Concentric rows of vascular canals and laminar organization of the tissue are only found in anteater bones. The long bones of adult specimens are marked by dense Haversian bone, a feature that has been noted for most groups of mammals. In the long bones of armadillos, secondary osteons have an oblique orientation within the three-dimensional bone tissue, thus resulting in their irregular shape when the bones are sectioned transversely. Secondary remodeling is generally more extensive in large taxa than in small taxa, and this could be caused by increased loading. Lines of arrested growth are assumed to be present in all specimens, but they are restricted to the outermost layer in bones of armadillos and are often masked by secondary remodeling in large taxa. Parameters of bone compactness show a pattern in the femur that separates Cingulata and Pilosa (Folivora and Vermilingua), with cingulates having a lower compactness than pilosans. In addition, cingulates show an allometric relationship between humeral and femoral bone compactness.

New mammalian remains from the Late Cretaceous La Colonia Formation, Patagonia, Argentina

Knowledge of the latest Late Cretaceous mammalian fauna in the South America was, until now, mostly based on dentally known taxa recovered at Los Alamitos (Río Negro, Argentina). Here we describe new mammalian remains collected in outcrops of the La Colonia Formation (Campanian—Maastrichtian) exposed in Chubut Province, Argentina, warranting the recognition of a new mesungulatid: Coloniatherium cilinskii gen. et sp. nov. The mammalian high-level taxonomic compositions of the localities in the La Colonia Formation and at Los Alamitos are roughly similar (Reigitheriidae, Mesungulatidae, and Ferugliotheridae are represented in both localities), but gondwanatheriids and the more plesiomorphic dryolestoids from Los Alamitos are missing from La Colonia. The most abundant mammalian remains collected at La Colonia correspond to large-sized mesungulatids. Coloniatherium cilinskii is recognized by the dentition and lower jaw, and we assign five isolated petrosal bones, focusing our study primarily on the analysis of the ear regions. The morphology of the petrosals suggests a phylogenetic position similar to Vincelestes, but sharing some derived features, possibly convergent, with therians. Attribution of the petrosals to the mesungulatid Coloniatherium cilinskii is supported by overall morphology, size, and relative abundance among the mammalian remains from La Colonia.

Timing of cranial suture closure in placental mammals: Phylogenetic patterns, intraspecific variation, and comparison with marsupials

Used as markers of postnatal growth closure sequences of 22 ectocranial sutures and synchondroses were recorded in a sample of 1161 skulls belonging to 38 species from all major placental clades: Afrotheria, Xenarthra, Laurasiatheria and Euarchontoglires (Boreoeutheria). The maximum closure level, which is not significantly correlated to body mass, is higher in Afrotheria and Xenarthra than in Boreoeutheria. Only the basioccipito‐basisphenoid and the basioccipito‐exoccipital synchondroses close in all species sampled, the supraoccipito‐exoccipital and the inter‐parietal sutures do in most species. Parsimov retrieved more heterochronic shifts for Afrotheria and Xenarthra than for Boreoeutheria. The amount of intraspecific variation differs among the species sampled being high among xenarthran species and low among afrotherians. Specimens (162) representing 12 marsupial genera were also analysed. Placentals exhibit a larger number of suture closures than marsupials and in both groups the sutures at the base of the skull are the first to fuse starting with the basioccipito‐exoccipital. J. Morphol. 275:125–140, 2014.

Heterochrony and post‐natal growth in mammals – an examination of growth plates in limbs

Mammals display a broad spectrum of limb specializations coupled with different locomotor strategies and habitat occupation. This anatomical diversity reflects different patterns of development and growth, including the timing of epiphyseal growth plate closure in the long bones of the skeleton. We investigated the sequence of union in 15 growth plates in the limbs of about 400 specimens, representing 58 mammalian species: 34 placentals, 23 marsupials and one monotreme. We found a common general pattern of growth plate closure sequence, but one that is universal neither between species nor in higher‐order taxa. Locomotor habitat has no detectable correlation with the growth plate closure sequence, but observed patterns indicate that growth plate closure sequence is determined more strongly through phylogenetic factors. For example, the girdle elements (acetabulum and coracoid process) always ossify first in marsupials, whereas the distal humerus is fused before the girdle elements in some placentals. We also found that heterochronic shifts (changes in timing) in the growth plate closure sequence of marsupials occur with a higher rate than in placentals. This presents a contrast with the more limited variation in timing and morphospace occupation typical for marsupial development. Moreover, unlike placentals, marsupials maintain many epiphyses separated throughout life. However, as complete union of all epiphyseal growth plates is recorded in monotremes, the marsupial condition might represent the derived state.

Evolutionary Relationships among Extinct and Extant Sloths: The Evidence of Mitogenomes and Retroviruses

Macroevolutionary trends exhibited by retroviruses are complex and not entirely understood. The sloth endogenized foamy-like retrovirus (SloEFV), which demonstrates incongruence in virus–host evolution among extant sloths (Order Folivora), has not been investigated heretofore in any extinct sloth lineages and its premodern history within folivorans is therefore unknown. Determining retroviral coevolutionary trends requires a robust phylogeny of the viral host, but the highly reduced modern sloth fauna (6 species in 2 genera) does not adequately represent what was once a highly diversified clade (∼100 genera) of placental mammals. At present, the amount of molecular data available for extinct sloth taxa is limited, and analytical results based on these data tend to conflict with phylogenetic inferences made on the basis of morphological studies. To augment the molecular data set, we applied hybridization capture and next-generation Illumina sequencing to two extinct and three extant sloth species to retrieve full mitochondrial genomes (mitogenomes) from the hosts and the polymerase gene of SloEFV. The results produced a fully resolved and well-supported phylogeny that supports dividing crown families into two major clades: 1) The three-toed sloth, Bradypus, and Nothrotheriidae and 2) Megalonychidae, including the two-toed sloth, Choloepus, and Mylodontidae. Our calibrated time tree indicates that the Miocene epoch (23.5 Ma), particularly its earlier part, was an important interval for folivoran diversification. Both extant and extinct sloths demonstrate multiple complex invasions of SloEFV into the ancestral sloth germline followed by subsequent introgressions across different sloth lineages. Thus, sloth mitogenome and SloEFV evolution occurred separately and in parallel among sloths.

Australohyaena antiqua (Mammalia, Metatheria, Sparassodonta), a large predator from the Late Oligocene of Patagonia

An almost complete skull of Australohyaena antiqua (Ameghino), from the Late Oligocene (Deseadan SALMA) of Cabeza Blanca, Chubut Province, Argentina is described and analysed. For more than a century, this species was represented by isolated teeth. The genus Australohyaena gen. nov. is proposed based on a phylogenetic reconstruction that demonstrates that A. antiqua is a Borhyaenidae (Mammalia, Sparassodonta), grouped with Arctodictis and Borhyaena, but not with Pharsophorus lacerans, the genus to which antiqua was formerly assigned. A. antiqua is recognized by several features on the skull, dentary and dentition. In addition, a short snout, large canines, deep jaw, reduced protocone and talonid determine A. antiqua as hypercarnivorous. A vaulted skull, well-developed temporal fossa and little difference on the jaw depth at p3 and m4, are suggestive of bone-cracker specializations. A. antiqua is within the largest Deseadan sparassodonts with a body mass of about 70 kg. Homoplasies are detected within borhyaenoids on lower molar cusps. The metaconid is lost within Sparassodonta, although Pharsophorus and borhyaenids retained the metaconid on m2–m4 or m2–m3. http://zoobank.org/urn:lsid:zoobank.org:pub:EDB0575A-C1D9-4C17-B6EB-3D761D1D7DB3

Comment on "Independent origins of middle ear bones in monotremes and therians" (II).

The malleus, incus, and stapes are the middle ear bones spanning from the eardrum externally to the oval window in the inner ear (1). The malleus is formed in both groups of living mammals (monotremes and therians) from the embryonic prearticular and articular (2, 3), which early in development are attached to the lower jaw (dentary). The prearticular and articular are also so attached as postdentary bones in fossil members of the mammalian lineage that show a progressive reduction in size and attachment (4). Rich et al. (5) argue that the malleus has been independently freed from the dentary in monotremes and in therians and acknowledge that BEa^ssertions of fundamental differences in development and morphology between monotreme and therian ears are no longer supported.[ Therefore, fossils like Teinolophos, an extinct relative of Australia_s modern platypus, are the only potential sources of conflict. Our recent study of all available Teinolophos specimens suggests that the claim of Bindependent origins of middle ear bones in monotremes and therians[ is not supported. Rich et al. acknowledge that Teinolophos lacks facets indicating the presence or location of the prearticular-articular. Consequently, there is no direct evidence for the middle ear bones, making their report a discussion of indirect evidence. It is the position and relation of the angular/ectotympanic, which is not a middle ear bone per se, together with the Btrough on the posteromedial side of the dentary,[ that are the core of the Rich et al. argument. The identified Bfacet[ for the purported angular/ectotympanic is not a facet. It has no limits, no textural changes, and no indication of a conspicuous area for articulation. The flattened facet is exaggerated in its distinctiveness and medial orientation in figure 2C in (5), which is a hypothetical cross section, not an actual tracing or computed tomography (CT) image. The angular facet is merely the floor of the large mandibular canal, which in broken Teinolophos specimens continues anteriorly inside the dentary at least up to the level of the antepenultimate molar and would transmit the hypertrophied trigeminal system, as in the platypus (6). Teinolophos jaws NMV P216575, P212933, and P216680 indicate that the lingual edge of the mandibular foramen (the mandibular canal entrance) was posterior to the apex of the dentary_s posterointernal angle. Therefore, most of the supposed angular facet is inside the mandibular canal Ecompare figure 2, A and D, in (5)^. Rich et al. acknowledge that there is no model for the extension of the angular into the mandibular canal among mammaliaforms but note that the Early Triassic cynodont Thrinaxodon shows the angular so placed to the level of the last molar. This comparison is problematic because the condition argued to be present in Teinolophos should be corroborated among other Mammalia, immediate outgroups, or embryology. That the extension of the angular into the mandibular canal could be associated with the great enlargement of the mandibular foramen (5) is an ad hoc explanation of a hypothetical condition that has no support in any mammalian model. Additionally, supposed similarities between the Teinolophos angular facet and Thrinaxodon are superficial, because in Thrinaxodon all the postdentary bones are wholly medial to the dentary and there is no mandibular foramen at the level of the angular (7). Identification of a mandibular trough for support of postdentary bones in Teinolophos is also problematic. A deep, well-defined groove directed toward the condyle, with a prominent medial flange (8) characteristic of mammaliaforms with known postdentary bones is lacking in Teinolophos; individual facets and ridges inside the trough are also absent. Following the platypus model (6), the likely occupant of the groove in Teinolophos would be V3, the mandibular division of the trigeminal nerve. Rich et al. recognize, as do we (9), that other Mesozoic forms may question the monophyletic origin of the mammalian middle ear, but the uncertain phylogenetic position of these taxa renders the case inconclusive (9–11). Rich et al. (5) choose to interpret their findings under a particular tree topology, because Bit is in accord with the polyphyletic origin of the definitive mammalian middle ear but requires the least amount of homoplasy in comparison with other proposed phylogenetic placements of monotremes.[ Given that no reference, matrix, or other data is provided in support of this claim, the reasoning seems circular. Finally, the topology of the tree selected by Rich et al. does not support their claim, because upon optimization, the character Bfree middle ear bones[ is equivocal at the base of Monotremata and present at the root of Mammalia.