An official website of the United States government
The fossil record of mammaliaforms (mammals and their closest relatives) of the Mesozoic era from the southern supercontinent Gondwana is far less extensive than that from its northern counterpart, Laurasia. Among Mesozoic mammaliaforms, Gondwanatheria is one of the most poorly known clades, previously represented by only a single cranium and isolated jaws and teeth. As a result, the anatomy, palaeobiology and phylogenetic relationships of gondwanatherians remain unclear. Here we report the discovery of an articulated and very well-preserved skeleton of a gondwanatherian of the latest age (72.1–66 million years ago) of the Cretaceous period from Madagascar that we assign to a new genus and species, Adalatherium hui. To our knowledge, the specimen is the most complete skeleton of a Gondwanan Mesozoic mammaliaform that has been found, and includes the only postcranial material and ascending ramus of the dentary known for any gondwanatherian. A phylogenetic analysis including the new taxon recovers Gondwanatheria as the sister group to Multituberculata. The skeleton, which represents one of the largest of the Gondwanan Mesozoic mammaliaforms, is particularly notable for exhibiting many unique features in combination with features that are convergent on those of therian mammals. This uniqueness is consistent with a lineage history for A. hui of isolation on Madagascar for more than 20 million years.
more »
« less
Craniofacial morphology of Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar
The cranium of Adalatherium hui, as represented in the holotype and only specimen (UA 9030), is only the second known for any gondwanatherian mammal, the other being that of the sudamericid Vintana sertichi. Both Adalatherium and Vintana were recovered from the Upper Cretaceous (Maastrichtian) Maevarano Formation of northwestern Madagascar. UA 9030 is the most complete specimen of a gondwanatherian yet known and includes, in addition to the cranium, both lower jaws and a complete postcranial skeleton. Aside from Adalatherium and Vintana, gondwanatherians are otherwise represented only by isolated teeth and lower jaw fragments, belonging to eight monotypic genera from Late Cretaceous and Paleogene horizons of Madagascar, the Indian subcontinent, Africa, South America, and the Antarctic Peninsula. Although the anterior part of the cranium is very well preserved in UA 9030, the posterior part is not. Nonetheless, comparable parts of the crania of Adalatherium and Vintana indicate some level of common ancestry through possession of several synapomorphies, primarily related to the bony composition, articular relationships, and features of the snout region. Overprinted on this shared morphology are a host of autapomorphic features in each genus, some unique among mammaliaforms and some convergent upon therian mammals. The cranium of Adalatherium is compared with the crania of other mammaliamorphs, particularly those of allotherians or purported allotherians (i.e., haramiyidans, euharamiyidans, multituberculates, Cifelliodon, and Megaconus). Particular emphasis is placed on several recently described forms: the enigmatic Cifelliodon from the Early Cretaceous of Utah and several new taxa of euharamiyidans from the Late Jurassic of China.
more »
« less
- Award ID(s):
- 1654949
- PAR ID:
- 10248820
- Date Published:
- Journal Name:
- Journal of vertebrate paleontology
- Volume:
- 40
- Issue:
- sup1
- ISSN:
- 0272-4634
- Page Range / eLocation ID:
- 19-66
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The living diversity of lemurs includes over 100 species spread across the diverse ecoregions of Madagascar. The late Pleistocene and Holocene subfossil record from Madagascar expands this diversity to include 17 extinct species, all larger than any extant lemur species. Numerous studies have explored this diversity by focusing on variation in life-history strategies in lemurs and other strepsirrhines, comparing them to haplorhine primates. In general, strepsirrhines gestate, wean, and reach sexual maturity more rapidly than haplorhines, but differences in relative brain size, body size, and ecology complicate these comparisons. Megaladapis madagascariensis is an extinct, large bodied (~46 kg) folivorous lemur that can provide an important point of reference in these studies, but early phases of M. madagascariensis ontogeny are necessary to develop these comparisons. Here, we describe a complete juvenile cranium of M. madagascariensis from Anjohibe cave in northern Madagascar. The specimen preserves the complete deciduous premolar row. MicroCT scans reveal the developing paracones of the canine, P2, and P3 are present in the crypts between the roots of the deciduous dentition. The crypt of M1 is preserved, though the crown is absent and the M1 alveoli are not fully developed. Using growth rate data collected from M. edwardsi dentition, the state of dental development in this specimen of M. madagascariensis suggests that it was less than one year-old at time of death. The entire cranium is about 55% the total length of an adult cranium from Anjohibe cave. As expected in such an immature individual, the rostrum is relatively short, post-orbital constriction is limited, and the nuchal crest is relatively small compared to the adult. This specimen also preserves an intact braincase, facilitating comparisons between the juvenile and adult endocasts from Megaladapis and extant lemurs at comparable developmental stages. Overall, the juvenile cranium supports previous observations that – adjusted for its large body mass – Megaladapis life history was consistent with the relatively accelerated life-history of other strepsirrhines. These observations provide important context and model parameters for exploring the impact of the very recent extinction of Megaladapis and other large bodied lemurs in Madagascar.more » « less
-
null (Ed.)The lower jaw of the holotype of Adalatherium hui, from the Late Cretaceous of Madagascar, is the most complete yet known for a gondwanatherian mammal. It reveals for the first time the morphology of the character-rich ascending ramus of the dentary in a gondwanatherian. Each half of the lower jaw is composed of only one bone, the dentary, which is short and deep and houses only five teeth: an enlarged, procumbent incisor and four postcanine teeth. In comparable parts of its anatomy, the dentary of Adalatherium is strikingly similar to that of Sudamerica but differs slightly from that of Galulatherium (conformation anterior to first postcanine, mental foramen position), the only two other gondwanatherians represented by complete horizontal rami. Among other Mesozoic mammaliaform taxa, the dentary of Adalatherium is most similar to those of the largely Laurasian group Multituberculata, most notably in absence of postdentary trough and Meckelian sulcus; presence of short, deep dentary with sizable diastema and articulating with squamosal via mediolaterally narrow condyle that continues onto posterior surface (i.e., no distinct peduncle); possession of much reduced dentition; absence of angular process; possession of large pterygoid fossa and pterygoid shelf, ventral surface of which is flat; absence of coronoid bone; and possession of unfused mandibular symphysis. Most of these features are clearly derived and stand in stark contrast to the much more plesiomorphic morphology exhibited by the lower jaw of the haramiyaviid Haramiyavia. The lower jaws of euharamiyidans, although derived in their own right, are also relatively plesiomorphic.more » « less
-
Abstract Although the Cretaceous is widely regarded as a time of great evolutionary transition for the freshwater fish fauna of North America, the fossil record of this period is notoriously poor, consisting mostly of fragments and isolated skeletal elements. Exceptions include the acipenseriforms, discussed in this paper, and some exceedingly rare teleosts. Here we describe two new species of well-preserved sturgeons (Acipenseridae) from the Tanis site in the Late Cretaceous Hell Creek Formation of North Dakota. The type and referred materials were preserved in a loosely consolidated matrix. † Acipenser praeparatorum n. sp. is represented by multiple body fossils (including the head and relatively complete postcranial remains) and a specimen of an intact, three dimensionally preserved skull and pectoral girdle. This taxon can be diagnosed based on features of the opercular elements (exceptionally tall and narrow branchiostegal). The second species, † Acipenser anisinferos n. sp., is represented by a partially preserved skull, and can be diagnosed by a relatively elongate preorbital region (i.e., snout) and the absence of thorn-like spines on the skull roofing bones. Most known sturgeon fossils from the Cretaceous are represented only by undiagnosable fragmentary remains (i.e., scutes and pectoral-fin spines) or poorly preserved partial skeletons (e.g., † Protoscaphirhynchus ), with † Priscosturion and † Anchiacipenser (both monotypic) being rare exceptions. Therefore, the newly discovered Tanis fossils give a rare glimpse into the evolution of Acipenseridae at a critical time in the phylogenetic history of acipenseriforms, and suggest significant morphological and taxonomic diversity early in the evolution of this group. UUID: http://zoobank.org/375b586a-2dd8-4a31-b6c4-42151e6e8fc8more » « less
-
Ricinulei Thorell, 1876 is an order of Arachnida currently represented in the New and Old Worlds by 103 living species. The order is also represented in the fossil record from the Carboniferous (ca. 305–319 Ma) and the Cretaceous (ca. 99 Ma) periods. In the present contribution, Hirsutisoma grimaldii sp. nov., a new extinct species of the suborder Primoricinulei Wunderlich, 2015, is described from a specimen preserved in Cretaceous Burmese amber. The specimen is a well-preserved adult male in which several taxonomically informative structures are visible, allowing the new species to be differentiated from Hirsutisoma bruckschi Wunderlich, 2017, the only other congener for which a male is known. This description raises the number of Cretaceous Ricinulei species to six. A comparative table documents morphological differences among the various species of this lineage. Hypotheses concerning the paleoecology and functional morphology of this species and, by extrapolation, other primoricinuleids, are presented. The evidence suggests that Primoricinulei were corticolous, scansorial predators.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/https://doi.org/10.1080/02724634.2020.1808665
