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Discover the fascinating world of Xenarthra, a diverse group of mammals including armadillos, sloths, and ant-eaters. Learn about their unique characteristics, habitat, and evolution.
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Edentates, Pholidotes, and Tubulidentates. An hodge-podge of ant eaters
Xenarthra • The edentates (without teeth) include 4 families: armadillos, sloths, and vermilinguas (ant-eaters). • Verm – worm, lingua – tongue. • All are new world. • Only the 9-banded armadillo gets into the north.
Xenathra • Have relatively low body temperatures (34°C) compared to other eutherians. • In spite of this, 9-bandeds have been extending their range northward.
Xenarthra • Old name edentata is inappropriate because only the anteaters are without teeth. • New name, xenarthra, refers to accessory zygapophyses on the lumbar vertebrae. • These ‘extra’ articulations increase the rigidity of the axial skeleton.
Xenarthra • Incisors and canines are lost. • Molars and premolars lack enamel and are single-rooted. • In anteaters and armadillos, the acromion and coracoid are unfused and substantial, aiding powerful digging. • Anterior caudal vertebrae have transverse processes fused to Ischium.
Xenarthrans • Group was once much more diverse than today, with some extinctions occuring within recorded history. • Glyptodon was huge: 2m total length. Note what happens to the vertebral column.
Megalonychidae • 2 species of arboreal 2-toed sloths and ground sloths†. • Choloepus hoffmani occurs from Nicaragua to Peru and Brazil, while C. didactylus occurs only in S. America, east of the Andes. • Lack incisors and canines. • First upper premolar is caniniform, and separated from other cheek teeth by a diastema.
2-toed sloth utr: note diastema and caniniform premolar, and articular surface.
2 and 3 toed sloths. Both have incomplete zygomatic arches, and the jugal forms a flat plate.
Our extinct ground sloth: • Nothrotheriops: survived in N. America until about 11,000 years ago.
Right pes of Nothrotheriops, and the right manus of Paramylodon.
Megalonychidae • 2-toed sloths have “SURPRISE” 2 claws on fore-feet, and 3 on the rear, while 3-toed sloths have 3 claws on the fore-feet. • 2-toed sloths hang upside down almost all the time, except to defecate. • Exclusive arboreal folivores. • Symbiotic algae in the pelage. • Body temp varies from 24-33C. • Number of cervical vert. Varies from 5-8!
Collared anteater claw: corresponds to ‘D’ on previous slide.
Bradypodidae • 3-toed sloths. • Bradypus tridactylus is distributed from Honduras to Brazil. B. variegatus? • Less active than 2-toed sloths, using only a single tree each day. • Segmented stomach w/ microflora. Active day and night: Arboreal folivory is tough. • 8-9 cervical vert: 270 degree rotation.
Myrmecophagidae • 4 species, with no teeth. • Distributed from S. Mexico to Paraguay. • Giant anteaters tongue is 13mm wide, but extendable to 600mm! It is anchored to the base of the sternum, is covered by submaxillary secretion, and has posteriorly directed barbs to trap ants.
Dasypodidae • 8 genera and 20 species. • 9-banded is only xenarthran in N. America. • They have extended their range dramatically since the early 1800’s. • Northern limit is probably defined by temperature. High thermal conductance, and an inability to enter torpor.
Dadypodidae • Excellent diggers … it is almost impossible to fence them in. • Opportunistic feeders: invertebrates, plant material, and carion. • Defensive behaviors: roll into a ball or jump.
Dasypodidae • Vertebrae modified for attachment of carapace to lumbar vertebrae via ‘metapophyses.’ • Size varies from ‘pink fairy armadillo’ at 100g to giant armadillo at 60kg. • Open rooter, homodont molariform teeth w/o enamel.
Dasypodidae • Dasypus has delayed implantation. • Monozygotic polyembryony in some. • In Dasypus novemcinctus there are 4 young of same sex, all from a single fertilized egg. • They are used as models for medical models for leprosy research.
