Cretaceous Dipnoi fossil records discovered in Mahajanga Basin, Madagascar
Location
Philadelphia, PA
Start Date
3-5-2023 1:00 PM
End Date
5-2023 4:00 PM
Description
Introduction: Extant lungfish (Dipnoi), Lepidoserenidids, Protoperids and Neoceratodids are endemic to South America, Africa and Australia respectively. These landmasses combined and formed a prior supercontinent known as Gondwana. Extinct dipnoan organisms were much more cosmopolitan and may account for constantly changing land masses. Volcanic and marine events changed the topography of Gondwana, which in turn caused bodies of water to fluctuate between marine, brackish and freshwater. Among the changes was the isolation of Madagascar from Africa during the Cretaceous. In 1993 and 1998, the Mahajanga Basin Project led by researchers in the Department of Anatomy at Stony Brook University, recovered a plethora of fossil specimens in their expeditions to understand the faunal turnover occurring in the Cretaceous. In particular, they sampled from the Ankazomihaboka beds of the Mahajanga Basin, which is located on the northwest Madagascan coast. The Ankazomihaboka beds are representative of the Coniacian to Santonian age (~90 mya – ~84 mya) of the Upper Cretaceous epoch (~100 mya – ~66 mya). Several hundred specimens were discovered in Madagascan Upper Cretaceous deposits, consisting of skull case elements and tooth plates proposed to be of dipnoan origin.
Objective: The objective of this research was to present and describe the dipnoan tooth plates recovered from the Mahajanga basin, including the clay and sandstone Ankazomihaboka beds.
Methods: For the purpose of identification, the tooth plates were analyzed morphologically and compared to other extinct and extant species of lungfishes. Toothplates characters we examined included number of ridges, location of ridges, shape and size of ridges, ridge 1 (R1) length and curvature, internal angle value (ẟ), and when possible, pterygoid or prearticular morphology. All tooth plates recovered had 4 or 5 ridges, which we interpret to mean lower (prearticular) and upper (pterygoid) dentitions respectively. Specimens in general had an elongate and posteriorly reflecting R1, obtuse inner angle value, and distinct symphyseal process. In addition, there was evidence of an ascending pterygopalatine process or Mecklian groove.
Results: Based on these characters, these tooth plates have been assigned to †Ferganoceratodus madagascariensis. What was ultimately named †Ferganoceratodus madagascariensis, after failure to remain as Ceratodus or Ptychoceratodus, is believed to be related to a special group of Ptychoceratodontids called †Ptychoceratodus hislopianus, P. cf. hislopianus and †P. acutus; some of which were present in India and others in Madagascar. This is evidence that confirms suspected cosmopolitan behavior, the presence of strong terrestrial connections between India and Madagascar during Gondwanan rifting events. Although a connection is evident, the route for the Madagascan migration is unclear. The abundance of fossils however does provide evidence that at least for a time in the Early Upper Cretaceous, the Mahajanga, Madagascan environment supported a lungfish population.
Embargo Period
5-31-2023
Cretaceous Dipnoi fossil records discovered in Mahajanga Basin, Madagascar
Philadelphia, PA
Introduction: Extant lungfish (Dipnoi), Lepidoserenidids, Protoperids and Neoceratodids are endemic to South America, Africa and Australia respectively. These landmasses combined and formed a prior supercontinent known as Gondwana. Extinct dipnoan organisms were much more cosmopolitan and may account for constantly changing land masses. Volcanic and marine events changed the topography of Gondwana, which in turn caused bodies of water to fluctuate between marine, brackish and freshwater. Among the changes was the isolation of Madagascar from Africa during the Cretaceous. In 1993 and 1998, the Mahajanga Basin Project led by researchers in the Department of Anatomy at Stony Brook University, recovered a plethora of fossil specimens in their expeditions to understand the faunal turnover occurring in the Cretaceous. In particular, they sampled from the Ankazomihaboka beds of the Mahajanga Basin, which is located on the northwest Madagascan coast. The Ankazomihaboka beds are representative of the Coniacian to Santonian age (~90 mya – ~84 mya) of the Upper Cretaceous epoch (~100 mya – ~66 mya). Several hundred specimens were discovered in Madagascan Upper Cretaceous deposits, consisting of skull case elements and tooth plates proposed to be of dipnoan origin.
Objective: The objective of this research was to present and describe the dipnoan tooth plates recovered from the Mahajanga basin, including the clay and sandstone Ankazomihaboka beds.
Methods: For the purpose of identification, the tooth plates were analyzed morphologically and compared to other extinct and extant species of lungfishes. Toothplates characters we examined included number of ridges, location of ridges, shape and size of ridges, ridge 1 (R1) length and curvature, internal angle value (ẟ), and when possible, pterygoid or prearticular morphology. All tooth plates recovered had 4 or 5 ridges, which we interpret to mean lower (prearticular) and upper (pterygoid) dentitions respectively. Specimens in general had an elongate and posteriorly reflecting R1, obtuse inner angle value, and distinct symphyseal process. In addition, there was evidence of an ascending pterygopalatine process or Mecklian groove.
Results: Based on these characters, these tooth plates have been assigned to †Ferganoceratodus madagascariensis. What was ultimately named †Ferganoceratodus madagascariensis, after failure to remain as Ceratodus or Ptychoceratodus, is believed to be related to a special group of Ptychoceratodontids called †Ptychoceratodus hislopianus, P. cf. hislopianus and †P. acutus; some of which were present in India and others in Madagascar. This is evidence that confirms suspected cosmopolitan behavior, the presence of strong terrestrial connections between India and Madagascar during Gondwanan rifting events. Although a connection is evident, the route for the Madagascan migration is unclear. The abundance of fossils however does provide evidence that at least for a time in the Early Upper Cretaceous, the Mahajanga, Madagascan environment supported a lungfish population.